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Introduction to Networking Technologies
Document Number GG24-4338-00
April 1994
International Technical Support Organization
Raleigh Center
Take Note!
Before using this information and the products it supports, be sure to read the general information under
“Special Notices” on page ix
...
Order publications through your IBM representative or the IBM branch office serving your locality
...
An ITSO Technical Bulletin Evaluation Form for reader's feedback appears facing Chapter 1
...
985, Building 657
P
...
Box 12195
Research Triangle Park, NC 27709-2195
When you send information to IBM, you grant IBM a non-exclusive right to use or distribute the information in any
way it believes appropriate without incurring any obligation to you
...
All rights reserved
...
S
...
Abstract
There are many different computing and networking technologies — some
available today, some just now emerging, some well-proven, some quite
experimental
...
This document describes a sampling of technologies of various types, by using a
tutorial approach
...
In addition, the applicability of these technologies within a particular situation is
illustrated using a set of typical customer situations
...
(202 pages)
© Copyright IBM Corp
...
Special Notices
...
xi
How This Book is Organized
...
xi
International Technical Support Organization Publications
...
xii
Chapter 1
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1
1
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1
1
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2
1
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9
1
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1 Stacks of Software
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3
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13
1
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3 Application Definition
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3
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1 Non-Distributed Application
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3
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2 Distributed Application
...
3
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3 Information Flow Patterns
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3
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4 Basic Information Flow Patterns
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3
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5 Composite Information Flow Patterns
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3
...
6 Client-Server Information Flow Patterns
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3
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22
1
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4
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23
1
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4
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24
1
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4
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25
1
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4
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26
1
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5 Networking Definition
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3
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1 Basic Networking Componentry
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3
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2 Repeaters and Multiplexors
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3
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3 Bridges, Routers, and Gateways
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4 Importance of Technologies
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4
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42
1
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2 Simple Networking
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4
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44
1
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4 Combined (Shared) Networking
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Positioning and Usage of Technologies
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1 Introduction
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2 Subnetworking Technologies
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2
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51
2
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2 Shared WAN (Multiplexor) Technique
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2
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55
2
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4 Shared LAN (Local Bridge) Technique
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2
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59
2
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6 Encapsulation Techniques
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2
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1 End-to-End Encapsulation Technique
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2
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2 Single-Gateway Encapsulation Technique
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2
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3 Double-Gateway Encapsulation Technique
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2
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67
© Copyright IBM Corp
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2
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69
2
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71
2
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1 Multi-Protocol Router Technique
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3
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74
2
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3 Multi-Protocol Transport Network (MPTN) Technique
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3
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1 Single MPTN Gateway Technique
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3
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2 Multiple MPTN Gateways Technique
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4 Application Support Technologies
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4
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82
2
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2 X/Open Transport Interface (XTI) Technique
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4
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86
2
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4 Application Gateway Technique
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4
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90
2
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5
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2
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5
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2
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Chapter 3
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95
3
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3
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1 Situation 1 - Adding A New Application
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2
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104
3
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3 Situation 3 - Network Interconnection
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2
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3
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121
Appendix A
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2
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8
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50
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© Copyright IBM Corp
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2
OSE, OSI, and Our Terminologies
...
5
Some Computing Equations
...
10
Network Access Mechanism
...
13
Application Definition
...
16
Distributed Application
...
18
Composite Information Flow Patterns
...
22
Some Types of Application Support
...
24
Standard-Applications Support
...
26
Networking Definition
...
28
Networking Componentry Choices
...
30
Subnetworking Definition
...
32
Physical Media and "Short" Stacks
...
34
Bridges, Routers, and Gateways
...
36
Routers
...
39
Technologies by Layers (SNETG, TPORT, SUPP)
...
42
Simple Networking
...
44
Combined Networking
...
49
Separate Wide Area Networks (WANs) Technique
...
53
Shared LAN (Multi-Protocols) Technique
...
57
Shared LAN (Remote/Split Bridge) Technique
...
61
End-To-End Encapsulation Technique
...
65
Double-Gateway Encapsulation Technique
...
67
Packet Interface Technique
...
71
Multi-Protocol Router Technique
...
74
MPTN Technique
...
79
vii
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56
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58
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60
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62
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64
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72
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viii
Multiple MPTN Gateways Technique
...
81
The Middleware Technique
...
84
Remote API Technique
...
88
Multi-Protocol Server Technique, Server-Only
...
93
Situations and Range of Consideration
...
98
Situation 1A: Technology Choices
...
101
Situation 1B: Technology Choices
...
105
Situation 2A: Technology Choices
...
108
Situation 2B: Technology Choices
...
111
Situation 3A: Technology Choices
...
114
Situation 3B: Technology Choices
...
117
Situation 4: Technology Choices
...
121
Introduction to Networking Technologies
Special Notices
This publication is intended to provide consultants, systems designers, and
system architects information about the alternatives that are available in
developing an open networking infrastructure so that they can help customers
make network protocol decisions to meet their existing and growing business
requirements
...
See the PUBLICATIONS section of the IBM Programming Announcement for the
products in this document for more information about what publications are
considered to be product documentation
...
Any reference to an IBM product, program, or service is not intended
to state or imply that only IBM's product, program, or service may be used
...
Information in this book was developed in conjunction with use of the equipment
specified, and is limited in application to those specific hardware and software
products and levels
...
The furnishing of this document does not give you any license to
these patents
...
The information contained in this document has not been submitted to any
formal IBM test and is distributed AS IS
...
The use of this
information or the implementation of any of these techniques is a customer
responsibility and depends on the customer's ability to evaluate and integrate
them into the customer's operational environment
...
Customers
attempting to adapt these techniques to their own environments do so at their
own risk
...
The copyright notice must appear on each page being
reproduced
...
1994
AnyNet
CICS
OfficeVision/VM
ix
The following terms, which are denoted by a double asterisk (**) in this
publication, are trademarks of other companies:
AppleTalk
Banyan Vines
cisco
cc:Mail
DECnet, All-in-One
EDA/SQL
Ethernet
IDNX
IPX, NetWare
UNIX
X/Open
x
Introduction to Networking Technologies
Apple Corporation
Banyan Systems, Incorporated
CISCO Systems, Incorporated
cc:Mail, Incorporated
Digital Equipment Corporation
Information Builder, Incorporated
Xerox Corporation
Network Equipment Technologies,
Incorporated
Novell Corporation
UNIX Systems Laboratories, Incorporated
X/Open Company, Ltd
...
Since there are many considerations that must be kept in mind as as one
evaluates alternative solutions to complex connectivity and interoperability
problems (and since there are many technologies), this book:
•
First identifies the technologies by categories
•
Then describes the operating characteristics of each technology
•
Finally compares the technologies in a representative set of typical customer
situations, including the advantages and disadvantages of each of the
technologies in a particular situation
The extensive index makes this a handy reference book, as well as a general
information book
...
It also identifies networking technologies, by groups and model
layers
...
•
Chapter 3, “Typical Customer Situations”
This chapter evaluates, through typical customer situations, the use of
various existing and emerging technologies
...
Related Publications
The following publications offer more information about the topics discussed in
this book:
IBM publications:
•
•
The Networking Blueprint, (a fanfold card), IBM order no
...
•
© Copyright IBM Corp
...
GC31-7057
...
xi
Other publications:
•
Cypser, Rudy, Communications for Cooperating Systems: OSI, SNA, and
TCP/IP, The Systems Programmer Series, Addison-Wesley Publishing
Company, 1991, ISBN #0-201-50775-7
...
•
IEEE, Guide to POSIX Open Systems Environment, 1992
...
, Computer Networks
...
, 1981, ISBN
#0-13-165183-8
...
To get listings of ITSO technical bulletins (redbooks) online, VNET users may
type:
TOOLS SENDTO WTSCPOK TOOLS REDBOOKS GET REDBOOKS CATALOG
How to Order ITSO Technical Bulletins (Redbooks)
IBM employees in the USA may order ITSO books and CD-ROMs using
PUBORDER
...
Visa and Master Cards are accepted
...
You may order individual books, CD-ROM collections, or customized sets,
called GBOFs, which relate to specific functions of interest to you
...
Boyd
IBM U
...
Federal
Steve Smith
IBM Networking Systems
This publication is the result of a residency conducted at the International
Technical Support Organization, Raleigh Center
...
Thanks to the following people for reviewing the document and providing
invaluable feedback:
Robert Louden
Marketing and Services, RTP
John Maas
TCP/IP Strategy, RTP
Kathleen Riordan
AnyNet Planning, Strategy and Marketing Support, RTP
Thanks also to the following people for their invaluable assistance in editorial
and graphics support:
Peter Andrews
Gray Heffner
Shawn Walsh
Gail Wojton
Janet Yoho
International Technical Support Organization, Raleigh Center
Preface
xiii
xiv
Introduction to Networking Technologies
THIS PAGE INTENTIONALLY LEFT BLANK
SPONSORSHIP PROMOTION
transforming communitites
it’s where the concept of community is reborn
...
THIS PAGE INTENTIONALLY LEFT BLANK
© 2011 Cisco and/or it’s affiliates
...
THE ABOVE IS A PAID PROMOTION
...
NOR DOES IT REFLECT THE OPINION OF IBM, IBM MANAGEMENT, SHAREHOLDERS OR OFFICERS
...
Chapter 1
...
1 Introduction
There are many different computing and networking technologies — some
available today, some just now emerging; some well-proven, some quite
experimental
...
Some technologies are being obsoleted, some are maturing,
some are adequate, and some are vital
...
The various technologies share
many fundamental concepts
...
It
establishes a very generalized reference model, and then classifies technologies
into categories relative to this model
...
If you are already familiar with reference models and wish to skip our
discussion of them, we suggest you quickly examine Figure 6 on page 12 to
discover our layer labeling conventions and then continue reading with
Chapter 2, “Positioning and Usage of Technologies” on page 47
...
1994
1
1
...
Many different groups in the computing industry have been involved during the
last decade in developing computing reference models — some models for
operating systems, some for data bases, some for application systems, and
some for communications networking — but only recently have efforts begun in
earnest to combine these various models into a single, more complete, but yet
simpler reference model
...
There are, indeed, many different technologies available in today's marketplace
that provide solutions for a variety of networking problems; but, to comprehend
how these technologies function, one must start with a reference model
...
We will utilize this reference model for all discussion throughout this
book in a slightly simplified format
...
Figure 1
...
Introduction to Networking Technologies
Referring to the right side of the above diagram, the application programs (the
APPL box in the diagram) conditionally depend upon the application support
programs (the SUPP box in the diagram), which in turn conditionally depend
upon the networking programs (the NETG box in the diagram)
...
Likewise, sometime during
their execution, application support programs may require networking programs
(or in some cases they may not)
...
In
the pure OSI networking model, application services are defined to be entirely
within layer 7 (at the bottom of the application layer)
...
Relative to networking, the simple model shown in Figure 1 on page 2 is
extremely similar to the more detailed IEEE POSIX Open System Environment
(OSE) model3 , as shown on the extreme left side of Figure 2 on page 4, using
just the 'communication entities' (our networking), 'application platform entities'
(our application support), and 'application entities' (our application) parts of the
OSE model
...
We have coined these terms for our own convenience
in comparing terminologies
...
0/D16
...
Many other computing models are also similar to the POSIX
OSE model, but, when simplified, most models reduce to our simple model with respect to networking and ignoring the people
and information exchange entities represented in the complete OSE model
...
Fundamental Concepts of Technologies
3
Figure 2
...
We have labeled this separator software as simply
application support (SUPP) in our simple reference model
...
4
Introduction to Networking Technologies
Figure 3
...
These four layers (or software program groups) provide the basis
for the discussions in the remainder of this book
...
The “top” two layers can always be
regarded as the application environment
...
4
The sub-equation 'NETG = TPORT + SNETG' causes the original three layers (boxes) to be expanded into four layers
(boxes) in our simple model
...
Fundamental Concepts of Technologies
5
Figure 4
...
The diagrams throughout this book use the short labels APPL, SUPP, TPORT,
and SNETG for the four layers of our computing model
...
In our diagrams, the top
two layers are closely associated with one another, as are the bottom two
layers
...
Briefly, the four major
groupings identified above are as follows:
•
Application is abbreviated APPL-A for a particular application 'A' under
consideration
...
That is, computing involves, at various times, just applications (APPL) , or applications and
application support (APPL and SUPP), or applications and application support and networking (APPL, SUPP, TPORT and
SNETG)
...
400 mail application or an
X
...
•
Application Support has two divisions, called the Application Programming
Interface (abbreviated API-A for a particular application 'A'), and Application
Support (abbreviated SUPP-A)
...
Examples of application programming interfaces include CPI-C (Common
Programming Interface for Communications), RPC (Remote Procedure Call),
and MQI (Message Queue Interface)
...
For instance, CPI-C utilizes
Advanced Program-to-Program Communication (APPC) and SNA logical unit
6
...
2) services, which includes the protocol flows between two
applications for establishing a conversation, exchanging data, ensuring
commitment of resources, and terminating a conversation
...
RPC usually operates over TCP/IP
protocols
...
MQI operates over LU 6
...
•
Transport Network, which corresponds to the critical Transport and Network
OSI layers, is abbreviated TPORT-A for a particular application 'A
...
Depending upon the specific protocol chosen, these layers provide such
functions as optimal route determination, error detection and recovery, and
congestion control
...
Each of these protocols utilizes
unique addressing structures, protocol flows between peer transport layers
in end nodes, and routing protocols between intermediate nodes
...
Also note that, historically, the Application Support and Transport Network
have been very closely tied together, and the selection of a particular API
forced the selection of a particular network protocol, or, conversely, a
programmer was forced to select an API based on the currently supported
transport protocol in the network
...
•
Subnetworking, abbreviated SNETG, corresponds to the OSI Data Link
Control and Physical layers
...
Chapter 1
...
25, and Frame Relay)
...
These groups are discussed in much more detail throughout the
remainder of the book
...
3 Fundamental Concepts
The fundamental concepts necessary for an easy discussion of available and
emerging techniques are:
•
Stacks of software
•
Switching points
•
Model layers (or software program groups)
Application (APPL)
Application Support (SUPP)
Networking (NETG)
Transport Network (TPORT)
Subnetworking (SNETG)
You will recognize these concepts as being related to the computing equation
introduced earlier (that is, Computing = APPL + SUPP + TPORT + SNETG)
...
These concepts are discussed in the following
sections
...
Fundamental Concepts of Technologies
9
1
...
1 Stacks of Software
As evidenced by both the POSIX-OSE computing model and the OSI networking
model6, it is often convenient to think of groups of computer programs as being
stacked7 , one group on top of another, and that one on top of yet another
...
Stacks of Software
Figure 5 illustrates this stacks of software concept for the software program
groups or layers:
•
Application
•
Application Support
•
Transport Network
•
Subnetworking
An application program interface (API) is a mechanism that defines
interoperation between the application (APPL) and application support (SUPP)
program groups
...
7
Each group of programs has its own set (or sets) of formats (information bit patterns) and protocols (information exchange
rules); hence, part of or all of this stack is often referred to as a protocol stack, whereby a format stack is also implied
...
10
Introduction to Networking Technologies
The API is a “contract of sorts” whereby the application software (above the API)
requests particular functions and the application support software (beneath the
API) supports the interface by interpreting the requests (program calls),
executing them, and returning the results across the API to the application
software
...
The application support (SUPP) group of programs is often
divided into several general types of application support, according to what the
support does for the application
...
The network access operates in much the same way as the API but, instead,
operates between a networking user (for example, an application support
program) and a networking provider (for example, a transport network program)
...
The various subgroups of the above main groups (layers) of programs are
discussed in more detail later in this chapter
...
This chapter identifies many of
these technologies, particularly those in the networking groups (that is, in the
transport network and in the subnetworking program groups)
...
Fundamental Concepts of Technologies
11
Figure 6
...
Access to networking is almost always through the transport network so that the
transport network access and the network access, as shown in the middle of
Figure 6, are usually synonymous
...
In most of the diagrams within this book, you will see the networking group of
programs replaced by two groups of programs, the transport network group and
the subnetworking group, so that the stack of software will appear as in Figure 6
(that is, with the NETG box expanded into the TPORT and SNETG boxes)
...
3
...
In the best
case, these group-separating dividers allow for a selection of software beneath
each in such a way that each divider serves as a switching point
...
The
transport network access mechanism is the switching point between application
support and transport network layers and, as such, is a system programming
interface, often referred to as an SPI, as contrasted with an application
programming interface in that it is most often used by those programmers
responsible for systems programming
...
The programs
within each group can interact, directly and indirectly, with programs in other
groups above and below it
...
This might, for example, represent an invoice
printing application program using the OSI FTAM program to transmit an invoice
batch over a TCP/IP transport network using a LAN between the invoice printing
application program and the invoice printing device
...
Switching Points
...
For example, a particular type of
application support might be available only with a particular type of transport
network, which is available with only two types of subnetworking
...
Fundamental Concepts of Technologies
13
rare case that all layers are found within a single software package; usually the
layers are distributed across many software packages where each package may
span layers or exist entirely within a layer
...
Transport
network (TPORT) and subnetworking (SNETG) are sometimes discussed
collectively under networking (NETG)
...
3
...
”
For example, a credit inquiry application and a highway traffic control application
are both serving a particular useful purpose (that is, getting information about
credit worthiness, and controlling automobiles and trucks on a highway system,
respectively)
...
A collection of
computer programs does the information processing while interacting with one
or more humans and devices (input devices, data storage devices, printing
devices, display devices, communications devices, and such)
...
Figure 8
...
Chapter 1
...
3
...
1 Non-Distributed Application
A Non-Distributed Application is best described as “an application existing
entirely within one location
...
Non-Distributed Application
As shown in Figure 9, all of the programs of a non-distributed application are at
the same location (for example, within one computer processor at location '1')
...
No networking is required
...
Of course, much of the application processing can be executed within
each program
...
3
...
2 Distributed Application
A Distributed Application is best described as “an application existing within two
or more locations
...
Distributed Application
As shown in Figure 10, some of the programs of a distributed application are at
one location (for example, within one computer processor at location 1) while
others are at another location (for example, within one computer processor at
location 2)
...
In this example, program 'A1' (within application 'A') is communicating
with program 'A6' (also within application 'A' but at a different location)
...
In the remainder of this book, the label 'APPL-Ax' is often used in diagrams and
in text as a short label for 'Application Program Ax'
...
Similarly, 'APPL-A (without
the number)' is usually meant to denote the entire application collection of
programs
...
1
...
3
...
Fundamental Concepts of Technologies
17
designs8
...
Networking technologies support information flow patterns of all sorts among
application programs (and, indeed, among all kinds of programs) in different
application and system environments
...
Information can take the form
of a request, a response, a one-way signal, a one-way tidbit of data, a sequence
of messages, and many other forms
...
Figure 11
...
In the above diagram, the five basic flows (unstaged transfer, staged transfer,
relay, split, and join) are in the left column and the four composite flows
(extended dialog, tree, chain, and lattice) are in the right column
...
In the more
general case, two-way (returning) flows occur in a nested fashion
...
Blakeley, et al
...
18
Introduction to Networking Technologies
1
...
3
...
Composite
flow patterns involve two or many more programs
...
Transfer Flow: A transfer of information involves exactly two programs and is
accomplished either in an unstaged manner or in a staged manner
...
)
Unstaged Transfer: The simplest flow pattern is an unstaged transfer of
information whereby all of the information is transferred with a single operation
(request from a program)
...
A one-way message is an example of an unstaged transfer
...
Staged means multi-staged
...
Relay Flow: A serial, unstaged transfer among three programs is a relay
whenever one program transfers to a second, which transfers to a third
...
)
Split Flow: A split of information involves exactly three programs whereby
information is simultaneously sent from one program to two others
...
)
Join Flow: A join of information involves exactly three programs whereby
information is simultaneously received by one program from two others
...
)
1
...
3
...
The three most interesting composite information flow patterns are the tree,
chain, and lattice, as shown in Figure 12 on page 20
...
Fundamental Concepts of Technologies
19
Figure 12
...
The above diagram shows a returning (2-way) closed flow for the tree structure
(flow pattern), a non-returning (1-way) closed flow for the chain structure, and a
non-returning (1-way) open flow for the lattice
...
Open flows do not return to the origin
...
Composite flows quite often involve unlike application and communication
environments and depend heavily upon networking technologies to support
interoperating applications
...
Tree Flow: A tree structure consists of a series of split basic flows (and
constitutes the classical “nested” programming structure)
...
A chain
structure is much like a degenerate tree where every split has only one branch
...
20
Introduction to Networking Technologies
1
...
3
...
There are lots of implications associated with this flow pattern —— for
example, configurations of small client machine and a larger server machine and
configurations of multiple clients and a single server
...
Superimposed over a client-server configuration can be many 2-element, closed
chains consisting of the client and the server where the server is a single server
...
In one direction the server is a server; in the other direction
the server is a client
...
One or more networking technologies are often vital in accomplishing
client-server information flow patterns, especially whenever either the client or
the server or both are well-established programs but in different computing
environments
...
Fundamental Concepts of Technologies
21
1
...
4 Application Support Definition
Application Support is best described as “a set of software services useful to an
application
...
Application Support Definition
As shown in Figure 13, application support is generally composed of multiple
software packages, each offering a particular set of helpful functions
...
Application support is simultaneously available to multiple application programs
and saves each program from having to support itself
...
9 Application support is usually packaged so
that multiple APIs, one or more for each package, are required to access all of
the functions available within the total aggregate of application support
...
22
Introduction to Networking Technologies
1
...
4
...
Figure 14
...
The following
sections describe the more-global (more network-oriented) application support
identified above
...
Chapter 1
...
3
...
2 Communications Support
Communications support programs support communication within and between
applications11
...
Communications Support
The communications support programs provide application-to-application
(commonly called “program-to-program” or “queue-to-queue”) communication
...
The example above shows queue-based
application support, which differs from connection-based application support
...
11
Any program of any type can use the communications support programs to provide its services in a distributed fashion
...
24
Introduction to Networking Technologies
1
...
4
...
400
or SMTP) or file transfer (FTAM or FTP) between systems
...
Standard-Applications Support
These are applications that have become “standardized” through constant and
heavy usage over a long period of time by large numbers of organizations
...
Chapter 1
...
3
...
4 Distributed Services Support
Distributed services programs provide ancillary support for communication
within and between applications
...
Figure 17
...
There are no uniform sets of distributed services available
yet, except for such consortium offerings as OSF-DCE
...
3
...
”
Figure 18
...
A
particular program 'S' from within the application support group selects a
particular program 'T' from within the networking group
...
Chapter 1
...
3
...
1 Basic Networking Componentry
As shown in Figure 19, Networking (NETG) is composed of two parts:
•
Transport Network (TPORT)
•
Subnetworking (SNETG)
Figure 19
...
The TPORT box is composed of several selectable transport network types with
the implication that only one is used at a time
...
28
Introduction to Networking Technologies
Figure 20
...
In this example, TCP/IP was chosen for the transport
network and LAN was chosen for the subnetworking
...
Similarly, the
TPORT can choose exactly one of the SNETG choices
...
The number of mix-and-match combinations between SUPP, TPORT, and SNETG
available today is limited but this number is destined to grow with more choices
becoming available
...
Fundamental Concepts of Technologies
29
Transport Network Definition: A Transport Network is best described as “a
collection of networking programs that exchange information between and
among adjacent and non-adjacent computer systems using a variety of available
communications media
...
Transport Network Definition
The transport network (TPORT in Figure 21) is composed of selectable transport
network types, including:
•
SNA transport
•
APPN transport
•
TCP/IP transport
•
NetBIOS transport
•
IPX** transport
•
others
In this example diagram, a NetBIOS transport network is being used to support
conversational communication between applications
...
In the
above diagram, both application support programs have selected a NetBIOS
transport network
...
In a similar manner, many of today's networking diagrams purposely
exclude subnetworking for simplicity
...
”
Figure 22
...
Networking Cloud: A “network cloud” is often substituted for subnetworking
across a particular communications medium, as shown in Figure 23 on page 32
...
Fundamental Concepts of Technologies
31
Figure 23
...
Network “clouds” are used in a quite universal manner in the computer industry
to reduce the complexity of networking diagrams
...
Physical Media and "Short" Stacks: Adjacent subnetworking (SNETG) layers are
interconnected across a physical medium of some sort (for example, a twisted
pair of wires), as is shown in Figure 24 on page 33
...
Physical Media and "Short" Stacks
In the middle of a communications network, the application (APPL) and
application support (SUPP) layers are often absent, as is shown in the middle
column of Figure 24, since there is usually no demand for application
programming in the middle of a communications network
...
Chapter 1
...
3
...
2 Repeaters and Multiplexors
Repeaters and multiplexors span subnetworking (SNETG) stacks “on the bottom
side,” as shown in Figure 25
...
Repeaters and Multiplexors
In this way, subnetworking stacks are connected to one another through a
physical medium, which is most often not discussed in subnetworking
descriptions
...
Please be aware that actual product implementations may
not match these definitions
...
•
Repeaters
Repeaters operate at the physical layer (OSI layer one), simply extending the
physical characteristics of the network by regenerating signals so that the
optimum performance in terms of signal quality and distance can be
achieved
...
•
Multiplexors
Multiplexors operate at the physical layer (OSI layer one), taking data bits
from several devices, and interleaving this data onto a single physical link
...
Multiplexors “manage the bandwidth” available on the
serial link, and, hence, are often called bandwidth managers
...
3
...
3 Bridges, Routers, and Gateways
Aside from the reference model, some basic concepts and terminology must be
defined so that particular technologies can be better understood
...
Figure 26 illustrates the “formal” definition of these terms with
regard to the OSI model
...
However, these terms are not always used in this strict manner (for example,
routers are described as existing at layer 3 and gateways are described as
existing at layer 4 and above)
...
Bridges, Routers, and Gateways
Bridges, routers, and gateways all serve the same general purpose of
interconnection of software
...
Fundamental Concepts of Technologies
35
Bridges: Bridges effectively “melt” two LANs of like12 types together
...
They connect two LAN segments, and forward
frames from one LAN segment to the other
...
Since all the processing
takes place at OSI layer 2, and does not involve the higher layers, bridges are
often referred to as being “protocol-independent
...
Figure 27
...
In the first case, the single bridge is called
a local bridge
...
The two bridges (one local and one remote) are
sometimes collectively called a split bridge (one part in one LAN and another in
different, non-adjacent LAN)
...
Some level of lower-layer protocol conversion is often a feature of
a bridge, router, or gateway without the product being so advertised
...
36
Introduction to Networking Technologies
token-ring and Ethernet LANs there exist many special types of bridges that
involve hidden (or at least proprietary) protocol conversion
...
Fundamental Concepts of Technologies
37
Routers: Routers interconnect different networks, and determine the optimal
path for a packet of data to traverse, through an interconnected series of
networks, to reach its destination
...
At the network
layer, the network address varies according to the choice of protocol
...
Routers enable the
connection of different subnetwork types to perform this routing function, for
instance, connecting a LAN to a Frame Relay wide area network for a specific
OSI layer 3 protocol
...
Routers
A Brouter is a combination of a remote bridge and a router, performing the
functions of both
...
38
Introduction to Networking Technologies
Gateways: The most basic (and earliest) concept of a gateway is that entity
(software and hardware, combined) which “funnels” traffic from one place to
another
...
Gateways exist at that point where LANs,
networks, or applications touch one another
...
In the case of network gateways, the networks are
usually of different types; for example, a collection of devices (that is, a device
network) attached to a communications network
...
Gateways usually operate above the network layer, layer three, and may involve
all layers
...
A gateway will convert all layers
up through the layer at which it operates
...
An electronic mail gateway, which takes office mail
from one type of electronic mail system (such as, IBM PROFS) and converts it to
another mail format (such as, DEC All-In-One**), is an example of this type of
gateway
...
These gateways usually
operate at the higher OSI layers
...
Gateways
Although not shown in the above diagram, another special type of a gateway is a
transport gateway spanning transport network (TPORT) layers, where different
transport facilities are matched to each other
...
Fundamental Concepts of Technologies
39
application run over an SNA network
...
There is usually extra code provided at the
transport level to compensate for the change in transport protocol, and to permit
the relaying of the application information through the network, without
impacting the application program itself
...
4 Importance of Technologies
As shown in Figure 30, technologies can be grouped by layers, from the lowest
to the highest:
•
Subnetworking
•
Transport network
•
Application support
The remaining sections of this chapter discuss technologies, by layers
...
Figure 30
...
Similarly, programs
within the application program group are labeled program 'S', indicating a
support program
...
In the subnetworking
program group, programs are labeled program 'W', indicating the “wire” (or
equivalent physical communication medium)
...
Fundamental Concepts of Technologies
41
1
...
1 Direct and Indirect Networking
Ideally, only application support programs, and not ordinary application
programs, are involved in networking, as shown in Figure 18 on page 27
...
These cases are often to effect extremely high efficiency and
performance at the expense of application program simplicity, portability, and
maintainability
...
Direct and Indirect Networking
Indirect networking saves enormous amounts of application development time
and complexity
...
42
Introduction to Networking Technologies
1
...
2 Simple Networking
Simple networking involves just a single network interconnecting two systems,
within each of which are application programs
...
Simple Networking
With simple networking, program 'A1' and program 'A2' within the same
application intercommunicate (indirectly through the SUPP layer) with great
simplicity and efficiency across a single network of some particular type
...
The application support is used by the APPL software and provided by the SUPP
software
...
Fundamental Concepts of Technologies
43
1
...
3 Separated (Private) Networking
Separated networking involves two or more disjoint networks each
interconnecting two (or more) systems
...
Nothing is shared,
logically or physically
...
Separated Networking
...
44
Introduction to Networking Technologies
1
...
4 Combined (Shared) Networking
Combined networking involves two (or more) separate networks operating as
one combined network
...
Combined Networking
...
Chapter 1
...
Positioning and Usage of Technologies
The objective of this chapter is to describe today's technologies and point out
some of their inherent advantages and disadvantages13
...
1 Introduction
There are a variety of considerations that must be kept in mind as one evaluates
alternative solutions to complex connectivity and interoperability problems
...
Each solution is described, and its inherent
advantages and disadvantages are listed
...
In
Chapter 3, “Typical Customer Situations” on page 95, the applicability of these
technologies within a particular situation is illustrated using a set of typical
customer situations
...
For instance, consider bridges that
originally connected two adjacent local LAN segments
...
This “remote bridge” is no longer a bridge in the
formal definition sense of operating strictly at OSI layer 2, yet lacking a better set
of definitions, we still call it a “bridge
...
We will examine these
technologies in a sequential fashion, starting with techniques that are concerned
with the lowest levels of connectivity at the subnetworking OSI layers 1 and 2
(physical and data link control layers), and then evaluate techniques which
gradually increase the scope of connectivity and interoperability
...
Techniques that operate primarily at the subnetworking (SNETG) level:
• Separate Wide Area Networks
• Bandwidth Management
• Shared Subnetworks - LANs
• Local Bridges
• Encapsulation
• Extended Subnetworking Approaches
- Remote/Split Bridges
- Data Link Switching (DLSW)
- Packet Interfaces - Frame Relay, X
...
Techniques that operate primarily at the transport network (TPORT) level
• Native Multi-Protocol Routers
13
Because circumstances where these technologies apply will differ and because more than one technology may be applicable,
and because implementation and packaging of these technologies varies widely, there can be no simple and definitive choices
...
1994
47
•
•
Mixed-Protocol Standards (RFCs, etc)
...
Techniques that operate primarily at the application support (SUPP) level,
including applications services and application programming interface
• XTI
• Middleware
• Remote APIs
• Application Gateways
• Multi-Protocol Servers
For each of these possible connectivity and interoperability solutions, the
technology is described in general terms
...
Assume that
each node14 represented in the diagrams is separate and distinct from other
nodes indicated, and that these nodes are not currently physically connected or
in any way currently communicating
...
” Sometimes the solutions will
impact the end nodes in terms of changing the application or adding additional
equipment (such as adapter cards) to the end node; other times the end node
will be untouched, but additional hardware and software must be procured for
one or more intermediate nodes
...
The network “clouds” shown in these diagrams represent transport
networks and not physical networks (that is, they are running a single transport
protocol)
...
Nor does the “cloud” indicate anything about the configuration of the
physical network itself, which may have many intermediate nodes
...
For instance, the IBM 6611
routers implement native multi-protocol routing, local bridging, remote bridging,
and data link switching
...
However, once these technologies are understood,
it is much easier to evaluate particular product implementations
...
48
Introduction to Networking Technologies
2
...
Figure 35
...
These
technologies provide a shared subnetwork environment for a variety of transport
protocols
...
In fact, with
these extended subnetworking approaches, the end nodes believe that they are
Chapter 2
...
“Extended subnetworking” technologies include:
•
The Remote (Split) Bridge technique
See 2
...
5, “Shared LAN (Remote/Split Bridge) Technique” on page 59
•
The Data Link Switching (DLSW) technique
See 2
...
7, “Data Link Switching (DLSW) Technique” on page 67
•
The Packet Interface technique
See 2
...
8, “Packet Interface (Using Frame Relay) Technique” on page 69
...
50
Introduction to Networking Technologies
2
...
1 Separate WANs Technique
Figure 36
...
Assume that the two nodes on the right side of the
diagram are in the same physical location, which is remote from the node on the
left
...
A common approach is to use separate serial links to connect the
three nodes (one on the left and two on the right of the diagram)
...
Thus, Appl-A would use only the network that utilized transport
protocol A, and Appl-B could communicate only over the second network
...
Separate networks have no impact on the applications, but require that multiple
copies of all hardware, software, and facilities necessary for communications be
purchased
...
Each transport
protocol requires its own network
...
For example,
Network A might be using HDLC, while Network B might be using X
...
Chapter 2
...
Depending upon throughput
requirements and traffic volume, different line speeds might be chosen
...
People can specialize
in the administration, configuration, and problem resolution for this single
protocol
...
Agreements must be reached as how to handle shared servers,
such as in the left-hand node
...
Disadvantages of Separate Wide Area Networks
•
•
52
Physical network costs might be prohibitive, such as separate lines, wiring,
network interface cards, modems, etc
...
Personnel costs can get very high, if each network has its own staff to
support administration, configuration, and problem resolution
...
2
...
Shared WAN (Multiplexor, Bandwidth Management) Technique
If leased circuit costs are prohibitive for separate wide area networks, then a
possible solution is to use a multiplexor or bandwidth manager which allows the
sharing of leased facilities
...
As shown in Figure 37, the end
nodes in each location will interface to their individual bandwidth manager
through a subnetwork interface
...
The bandwidth manager will take data from multiple local
links/subnetworks and multiplex this traffic over a single line to the recipient
bandwidth manager
...
Based on these algorithms, the recipient bandwidth manager will know which
local subnetwork should receive the data
...
Since the multiplexing function is taking place at the lowest OSI layer, bandwidth
managers are insensitive to the transport network, and are thus
protocol-independent
...
To “terminate” the DLC means to
handle these timed messages by emulating the responses at the originating
Chapter 2
...
Actual products may also include remote
bridges and routers to be more efficient and provide some transport layer
sensitivity
...
Each geographical location that wishes to participate in using this shared
bandwidth must have a bandwidth manager
...
There will be no impact to the applications
...
•
Statistical multiplexing techniques allow for some “over-committing” of WAN
bandwidth, yielding extra savings for bandwidth managers
...
•
Depending upon the number of leased circuits between sites, the topology of
the bandwidth manager network, and the capabilities of the bandwidth
manager product, redundancy and automatic re-routing of traffic may be
possible
...
For instance, if
End Node A in Location #1 wishes to communicate with End Node B in
Location #2 and End Node C in Location #3, then End Node A must have two
serial interfaces into two separate ports for the bandwidth manager in
Location #1, one for each of the other locations
...
Adding more End Nodes or
locations can be very difficult, and obtaining a “mesh” topology where any
node can communicate with any other node might be prohibitively expensive
...
Introduction to Networking Technologies
2
...
3 Shared LAN (Multi-Protocols) Technique
Figure 38
...
5), Ethernet V2, IEEE 802
...
All participants on a LAN share the LAN's high
bandwidth by following the access protocol for that particular LAN type
...
3, a collision-detection scheme
called CSMA/CD is used to permit access to the LAN
...
As the term local area network implies, the
nodes must be in close physical proximity to each other, usually within the same
building or campus not requiring the crossing of a right-of-way
...
Note that Appl-A does not interoperate
with Appl-B
...
Usually these LANs are created along
departmental lines, in the belief that people within a single department need
primiarly to communicate with one another
...
”
Although the applications will probably not be directly affected by adding a LAN,
additional hardware and facilities must be purchased to set up the LAN
...
Positioning and Usage of Technologies
55
may need to be purchased (such as multistation access units for token ring or
transceivers for Ethernet), and software might also need to be purchased to
enable particular transport protocol(s) to utilize the adapter card
...
•
Can utilize shared personnel resources, since a single group of people can
handle the administration and network management for all applications on
the network
...
The MAC-level
protocol determines how to locate particular nodes, and how to transmit the
data to that node and this MAC protocol is built into each adapter card
...
•
The use of a shared medium sometimes has an impact on application
throughput
...
•
56
LANs are restricted to limited distances
...
Introduction to Networking Technologies
2
...
4 Shared LAN (Local Bridge) Technique
Figure 39
...
Two LANs, with One Bridge
As mentioned in the previous LAN description, all LANs operate at OSI layer 2,
the Data Link Control layer
...
If two local LANs need to be connected to enable communication
between similar applications, then a local bridge can be used
...
In Figure 39, if the two nodes shown are located on two separate LAN segments
(perhaps these LANs belong to two different departments of a company within a
building), and Appl-A on the left node needs to communicate with Appl-A on the
right node, physical connectivity must be arranged
...
The MAC bridge will
be able to detect that frames need to be forwarded from the left-hand segment to
the right-hand segment
...
If the two LAN segments are of the same type, such
as two token rings, then this forwarding can be extremely fast since the frame
formats and the bridging protocol are identical on both sides
...
In this case, the frame formats are different and conversion needs
to take place
...
As long as the
conversion takes place strictly at OSI layer 2, one can consider this function to
Chapter 2
...
The IBM 8209 bridge performs
this function for token ring and Ethernet LANs
...
The bridge will need to attach to each LAN
segment as a regular device on the LAN segment, and thus there needs to be
planning to ensure that it can be attached to both LAN segments
...
Advantages of Local Bridge
•
Since bridges operate at OSI layer 2, they are not sensitive to the choice of
transport protocols
...
•
Bridges can forward frames very fast since little, if any, conversion needs to
take place
...
Disadvantages of Local Bridge
•
•
Inherent limitations of the bridging protocol might prohibit extensive
connectivity
...
These limitations will affect the design and
extensibility of any large LANs
...
For instance, with TCP/IP networks, it is quite possible to get
“broadcast storms” where a single user might flood the network with
extraneous messages
...
Since all traffic can flow over the bridge, there is no organizational
separation by addresses or subnets
...
2
...
Shared LAN (Remote/Split Bridge) Technique
...
These bridges are referred to as remote or split bridges
...
An encapsulation approach is typically used by the bridges to send these
frames across the wide area network
...
In fact, a single remote bridge may connect multiple LANs, and can
multiplex for all these LANs over a single connection to a partner bridge; this is
referred to as multi-port bridging
...
As shown in Figure 40, these bridges are
shown to be true MAC bridges for taking traffic off of the attached LAN; then an
extra protocol stack is involved to provide the encapsulation function across the
wide area network utilizing transport protocol C
...
This type of filtering
is performed only at the Data Link Control layer (OSI layer 2), and rarely do
these remote bridges filter at the upper layers (layer 3 and above); thus they are
transport protocol-independent
...
Chapter 2
...
Point-to-point connections are required
between the bridges
...
The IBM Remote Token-Ring Bridge/DOS is an example of such a split
bridge
...
Additional
hardware and software will be needed to provide the remote bridge function;
also, these devices must be able to attach to their respective local LANs
...
Advantages of Remote (Split) Bridge
•
Transport protocol is independent
...
•
These remote bridges are usually inexpensive, and show good performance
for the given link speed between the remote bridges
...
This may change, however, as new standards such as PPP become
more popular
...
•
There may be limited, if any, flow control over the lower-speed link between
partner bridges
...
This extraneous traffic may impact critical
session timers for certain sensitive transport protocols (such as SNA and
NetBIOS), causing sessions to be dropped
...
Introduction to Networking Technologies
2
...
6 Encapsulation Techniques
The general principle of encapsulation is to “mis-use” a program-to-program
logical connection as a physical link, as shown in Figure 41
...
General Encapsulation Technique
In the above diagram, the facilities of B are used as an emulation of link-A; the
3-group stack, SUPP-TPORT-SNETG, has been used twice, once in its normal
manner at the top of the diagram and once as a substitute for a physical link at
the bottom of the diagram
...
We have merely collapsed
each diagram (vertically) to conserve space and line up the layers
...
The networking control headers for the packet-A are encapsulated within the
networking control headers for packet-B
...
Chapter 2
...
2
...
1 End-to-End Encapsulation Technique
Figure 42
...
That is, service of type A is found in the application
support program group (that is, communication support)
...
In other words, the entire protocol stack is labeled
with 'A' (APPL-A, SUPP-A, TPORT-A, and SNETG-A)
...
This technique encompasses a whole range of possibilities, as it can be used to
describe many aspects or methods of mixed-protocol networking
...
From the viewpoint of the application and its protocol
stack, the second transport network is being used as subnetwork
...
From the viewpoint of the intermediate network, the
originating network's “link” is just another user session
...
Appl-A in the left node would generate its data as
normal, and it would proceed through the usual protocol stack for Appl-A
...
62
Introduction to Networking Technologies
transport protocol information, and emulated link information) is sent to the
application programming interface (api-B) of the second protocol stack in the
same node
...
Sometimes the Appl-A packet is treated simply as data, and no
attention is paid to the particular needs of the Appl-A transport or subnetwork
levels
...
In either case, the Appl-A packet will be “enveloped” or
“encapsulated” with the appropriate transport and subnetwork headers and
trailers necessary to traverse Network B
...
Once this packet reaches the destination in the node on the right side of the
diagram, these headers and trailers are removed, thereby de-enveloping or
de-encapsulating the original Appl-A packet
...
The partner Appl-A applications believe that they have just communicated
over their “native” transport network
...
Encapsulation always requires a pair of nodes to cooperatively perform the
enveloping and de-enveloping steps
...
Figure 42 on page 62 shows a
scenario where the encapsulation and de-encapsulation are performed in end
nodes over a single transport network
...
Appl-A in the left node is a TCP/IP-based application, which must traverse
Network B, which is SNA, to reach its partner application in the right node, which
resides in Network A
...
If Appl-A in the left node sent data to Appl-A in the right node, the
encapsulation would take place in the left node, and de-encapsulation would
take place in the gateway
...
The IBM SNALINK function utilizes this approach, where the left
node and the gateway are hosts in Figure 43 on page 65
...
This type of
approach is very common with routers that are attached to LANs, where the
router is acting as the gateway
...
The
applications use their native transport protocol on their local network, and the
router detects that the traffic is destined for a remote location
...
This “tunneling” approach has been used for transmitting SNA
traffic between IBM 6611 or cisco** routers
...
25
traffic over the SNA backbone network using this technique
...
This private protocol is
often proprietary to a given vendor
...
Positioning and Usage of Technologies
63
configurations is utilized, additional software may need to be added to the end
nodes, or gateways may need to be purchased, but the applications should not
need to be changed
...
•
Only one network protocol will be in use
...
•
Encapsulation is usually a software-based solution, so the cost may be kept
low
...
If encapsulation takes
place in the end nodes, as in Figure 42 on page 62, then two protocol stacks
are present in this end node: the stack for the application, and the stack for
encapsulation/de-encapsulation
...
For example, this may not even be feasible on a PC DOS
machine, where there is a 640KB memory limitation
...
If a gateway is involved, then additional hardware or software may
be required to provide this encapsulation function
...
This can cause problems if neither the application's subnetwork
nor transport network requirements are met
...
•
There is increased overhead in each transmission in terms of headers and
trailers
...
This extra overhead can increase network
load requirements, and potentially affect the performance of the traversed
network
...
•
64
Encapsulation techniques are often proprietary, limiting the user to a single
vendor for equipment or software
...
For example, encapsulating
SNA traffic on a TCP/IP network may result in degrading or defeating the
SNA priority scheme (class of service)
...
2
...
2 Single-Gateway Encapsulation Technique
Encapsulation can be accomplished through a single gateway, one side only, as
shown in Figure 43
...
Single-Gateway Encapsulation Technique
In the above diagram, Application-A at the upper left-hand corner is connected to
the gateway in the middle by an emulation of a type-A (IP) link over a type-B
(SNA) transport network
...
Chapter 2
...
2
...
3 Double-Gateway Encapsulation Technique
Encapsulation can be accomplished through two (or even more) gateways, in a
series, as shown in Figure 44
...
Double-Gateway Encapsulation Technique
In the above diagram, Application-A and Application-B at the upper left-hand
corner are both connected through the two gateways in the middle to their
partners at the upper right-hand corner
...
An example of this is the
encapsulation of SNA and NetBIOS over a TCP/IP network
...
2
...
Data Link Switching (DLSW) Technique
Data Link Switching (DLSW) is an example of filtered encapsulation at the
transport level
...
In fact,
many packets are suppressed over the wide area network, and compensations
are made locally to provide necessary functions
...
At
the transport level, NetBIOS broadcasts to locate session partners are
intercepted and suppressed
...
At the Data Link
Control level, there is some traffic which is timing-dependent
...
Examples of this DLC
termination are the handling of polling-type messages or “keep-alive” messages
...
As shown in Figure 45, the routers that implement Data Link Switching utilize an
application to provide the encapsulation plus the specific transport and data link
control functions
...
Chapter 2
...
Currently the IBM 6611 router
provides this capability, and many other router vendors have indicated that they
will be providing Data Link Switching in the future
...
Routers that implement this data link switching technique must be purchased
...
•
It compensates for transport- and data link control-level timing
dependencies, thus keeping SNA and NetBIOS sessions up in these timeout
situations
...
•
DLSW has techniques to accomplish congestion control at both the local and
global levels, thereby easing the load on the backbone network
...
Disadvantages of Data Link Switching
•
•
The DLSW specification does not define some advanced functions, such as
priorities, adaptive pacing, and expedited flows
...
Current implementations exist for NetBIOS and SNA over token ring,
Ethernet, and SDLC connections, using TCP/IP as the backbone transport
...
Introduction to Networking Technologies
2
...
8 Packet Interface (Using Frame Relay) Technique
Figure 46
...
Using Frame Relay
Many of these technologies operate at OSI layer 2
...
Although it operates through OSI layer 3, X
...
For all of
these technologies, there is always a device that will take the traffic from the
local subnetworks, such as LANs or serial lines, and convert it to a format
understood by the wide area network (an interface protocol)
...
The size of these packets may be variable (as with
Frame Relay or X
...
The wide
area network, such as the Frame Relay network illustrated in Figure 46, consists
of a set of switches that understand this interface protocol, and routes the data
to the appropriate final location
...
At the final location, there must also be a device that
understands the same interface protocol, which will take the data from the wide
area network and deliver it to the end node
...
Both
transport protocol A and transport protocol B can share the same Frame Relay
network, but Appl-A can still only communicate with Appl-A, and Appl-B can only
communicate with Appl-B
...
Positioning and Usage of Technologies
69
The equipment at the customer locations that understand the interface protocol
are often routers
...
The customer must decide on whether to utilize a public network service for the
wide area network, or to build a private network by procuring switches and using
leased lines
...
•
It can also provide a “mesh” network, permitting any location to
communicate to any other location
...
Traditional packet switching, using the X
...
Fast packet switching, which includes
Frame Relay and cell relay (ATM), has much better performance, but at the
cost of error checking and recovery in the network
...
How much error recovery is actually performed in these nodes can vary
greatly depending on implementation
...
3 Transport Network Technologies
Transport network technologies are implemented at the higher layers (OSI layers
3 and 4) of a network
...
Transport Network (TPORT) Technologies
Some of the technologies implemented within the transport network layer
(program group) are:
•
Multi-Protocol Router
•
Mixed-Protocol RFCs
•
Multi-Protocol Transport Network (MPTN)
Chapter 2
...
3
...
Multi-Protocol Router Technique
...
Each router in the network must utilize the transport levels for each protocol for
which it has support
...
Appl-A in the left node uses Tport-A to
communicate with its partner nodes indicated by the A network on the left side
...
The same transport protocol is used
throughout the data transmission
...
This is often referred to as “ships-in-the-night” routing
...
There are some approaches that are
standards-based, such as the PPP protocol, but many routers also use a
proprietary algorithm
...
These routing protocols may be standardsbased, such as RIP and OSPF, or proprietary, such as cisco's IGRP
...
Using this approach, if there are 10 transport protocols to be
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Introduction to Networking Technologies
transmitted over the intermediate router network, then 10 transport protocols will
exist natively in that network
...
Encapsulation techniques were discussed earlier in 2
...
6,
“Encapsulation Techniques” on page 61
...
For SNA networks, the IBM 3745 and NCR
Comten products provide this routing capability
...
Note: 3745/NCP now also “natively” routes IP
...
There is usually
no impact to the end nodes or to the applications
...
Advantages of Native Multi-Protocol Routers
•
Each transport protocol is treated natively
...
Disadvantages of Native Multi-Procotol Routers
•
Many transport protocols will exist on the intermediate router network
...
There are also implications in terms of configuration and change
management, and address and directory access
...
•
Multiple transport protocols complicate network design and planning
...
Chapter 2
...
3
...
'Mixed-Protocol Standards for TCP/IP' Technique
As described earlier in Chapter 1, “Fundamental Concepts of Technologies” on
page 1, application programming interfaces and application services have
historically been tied to a particular transport protocol
...
There are some techniques, often referred to as a
“hybrid stack” or “mixed-protocol stack” approaches, where the protocol stack
to support a particular application is built from parts of two different protocol
stacks
...
There are a variety of mixed-stack approaches that exist, but only a few are
standards-based
...
There is also a
more generic approach to this mixed-stack situation, which the forthcoming
MPTN standard addresses
...
The particular RFCs discussed in this
section describe methods to allow certain non-native applications to utilize a
TCP/IP transport network
...
400 to run over TCP/IP networks
...
Hybrid stacks exist to support this function; for instance, for RFC
1006, there exists the upper part of the OSI stack and the lower part of the
TCP/IP stack in the end nodes
...
This extra code is defined by the RFCs for this situation
...
The RFCs allow Appl-A
to be coded as usual using the standard application programming interface and
application services required for that application type; the same application
coding takes place as if it were an application running on a native OSI network
...
Address mapping is
provided by the RFCs, so Appl-A is unaware that a different transport is being
used
...
Similarly, a NetBIOS application can be handled over
TCP/IP using RFCs 1001 and 1002
...
There should not be any impact to the
TCP/IP network to support this functionality
...
These applications are unaware that they are
running on a different transport network
...
Using a single transport protocol reduces the complexity and cost of the
network, since a single network management, configuration management,
and change management approach can be selected
...
Only OSI over TCP/IP,
and NetBIOS over TCP/IP compensations exist currently
...
A
new RFC will need to be defined for each mixed-protocol stack combination
that is desired
...
Positioning and Usage of Technologies
75
2
...
3 Multi-Protocol Transport Network (MPTN) Technique
Multi-Protocol Transport Networking (MPTN) is a relatively new technology that
permits an application to utilize different transport protocols
...
Whereas the RFCs are currently specific for particular
mixed-protocol stacks, namely for OSI over TCP/IP or NetBIOS over TCP/IP,
MPTN provides a methodology to make this approach general for any application
service over any transport protocol
...
These compensations also
include address mapping
...
Figure 50
...
MPTN Access Nodes at End Points
The code required to perform this function must be available in a paired
arrangement
...
The data from Appl-B in the left node is intercepted by MPTN code in that node
after passing through Appl-B's application services layer
...
MPTN then provides compensations for
Tport-A, so that this data can be sent over a normal Tport-A session
...
There is one
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Introduction to Networking Technologies
surrogate session per Appl-B to Appl-B session, therefore maintaining a unique
end-to-end session identity and providing all necessary session management
functions for Appl-B
...
Although Appl-B's data is being encapsulated in a Tport-A packet, MPTN
provides more of a conversion function than a traditional encapsulation
technique; that is, Tport-A is actually being substituted for Tport-B, instead of the
standard encapsulation procedure of Tport-A headers and trailers being wrapped
around a Tport-B packet
...
Figure 50 on page 76 illustrates the situation when the MPTN partners exist in
end nodes
...
A single gateway is
illustrated in Figure 51 on page 79
...
A gateway that contains the MPTN
code is referred to as a transport gateway, to emphasis the fact that this function
(shown as MPTN Relay) is taking place at OSI layer 4, the transport layer
...
Another configuration is illustrated in Figure 52 on page 80, where two transport
gateways are present, and there is no MPTN code in the end nodes
...
MPTN access node specifications have been submitted to X/Open** to be
considered as a standard for mixed-protocol processing; X/Open has published
an initial Guide to MPTN
...
Thus, networking protocol software
may need to be changed in end nodes to provide MPTN access node
functionality, or in gateway node to provide the transport gateway functionality
...
Current examples of MPTN implementations are the IBM AnyNet* products,
available for MVS/ESA and OS/2
...
Support has also been
announced for NetBIOS applications over SNA networks
...
Once X/Open adopts MPTN, it is anticipated
that many more vendors will use this technology
...
Positioning and Usage of Technologies
77
Advantages of MPTN Access Nodes
•
MPTN permits applications to use non-native transport protocols, therefore
enhancing connectivity
...
•
Existing applications, written to a standard API and utilizing supported
application services for which compensations exist, will be supported without
modification
...
•
A single transport protocol can be selected for a given network, therefore
reducing the complexity and cost of multiple transport networks
...
Disadvantages of MPTN Access Nodes
•
•
78
At least two nodes in the network must have MPTN software
...
Introduction to Networking Technologies
2
...
3
...
Figure 51
...
Two Adjacent Networks (of unlike types)
In the above diagram, all traffic from Application-B (upper left-hand corner,
second column from left) flows first through a “foreign transport network” of
type-A, then through an MPTN relay point, and finally through a “native transport
network” of type-B to its partner Application-B (upper right-hand corner, second
column from right)
...
Chapter 2
...
3
...
2 Multiple MPTN Gateways Technique
Multiple MPTN gateways can interconnect two like networks by each performing
a “relay function,” as shown in Figure 51 on page 79
...
Multiple MPTN Gateways Technique
...
The application partners are connected
indirectly through two native transport networks and one non-native transport
network
...
4 Application Support Technologies
Application support technologies are implemented outside of a network
...
Application Support (SUPP) Technologies
Some of the technologies implemented within the application support layer
(program group) are:
•
Middleware
•
XTI (Transport Interface Selection)
•
Remote API
•
Application Gateway
•
Multi-Protocol Server/Gateway
Chapter 2
...
4
...
The Middleware Technique
Historically, middleware is any software that “sits in the middle between an
application and something more complex” — such as, between an application
program and an operating system function or between an application and a file
storage device or (especially for program-to-program communications) between
an application program and a communications network
...
Most affected are the application programming
interface and application support layers, OSI layers 5-7
...
Communications middleware products provide a variety of programming, data
management, and networking services
...
They provide support for their applications across more than one transport
protocol
...
Actually, this is product-wise true only for a
limited number of transport protocols that the middleware product has either
implemented within its own product or accessed through interfaces to full-stack
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Introduction to Networking Technologies
implementations
...
The details of the transport
protocols are often hidden from the application programmer
...
The remote system must have a
corresponding application, developed using the same middleware product
...
Thus,
separate transport networks may still be needed to support the various transport
protocol requirements
...
Some examples include Arthur Andersen's
Foundation, IBM's DAE, and IBM's CICS*
...
Each node must have a copy of the middleware product, and existing
applications must be recoded to utilize the middleware product's API
...
Advantages of Middleware Technique
•
Application programming may be easier with the middleware's simplified API
than an equivalent industry-standard API
...
•
Application portability usually exists across multiple hardware and operating
system platforms supported by the middleware product
...
Disadvantages of Middleware Technique
•
All nodes must implement the same middleware product in the appropriate
hardware or operating system platform version
...
•
Existing applications will need to be redeveloped on the middleware product,
which may be quite expensive
...
Chapter 2
...
4
...
X/Open Transport Interface (XTI) Technique
...
The 'SUPP-C' layer, based upon application-provided
parameters, selects the transport network to be used
...
There is also a forthcoming
specification for an application to run over an SNA network
...
However, it does not provide transparent access to these transport layers; the
application support programs must be aware of the protocol to be selected
...
If
Appl-A is a standard OSI application, it will proceed through its protocol stack as
normal to communicate with its partner application over an OSI network
...
However, if Appl-C wishes to be able to select which transport
protocol to utilize, it must be coded as a common subset of OSI and TCP/IP
transport services
...
This selection could be made either at compilation
time or runtime, depending upon the implementation
...
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Introduction to Networking Technologies
An application that uses this XTI interface can communicate to a partner
application which is coded natively, assuming that only the common subset of
application services is utilized
...
These are available for
OSI, for TCP and UDP over IP, and for NetBIOS
...
XTI code must exist in the end nodes
...
Advantages of Selectable Transport Standard -- XTI
•
New applications can be developed using XTI, permitting interoperability
over NetBIOS, OSI and TCP/IP networks
...
•
XTI is currently not widely implemented
...
•
Restricting application development to the least common denominator of
functions of the transport protocols can severely hinder a major development
effort
...
•
XTI does not specify a directory service, so application developers must
choose their own
...
•
Multiple transport networks exist, resulting in increased costs in terms of
network management, configuration management, and change management
...
Chapter 2
...
4
...
Remote API Technique
Remote APIs allow the use of a different API over a non-native network
...
As shown in Figure 56, Appl-A in the left node wishes to communicate
with its partner Appl-A in the right node, but must cross Network-B first
...
A special client stub is provided, which will take the information from the calls to
api-A, and envelop it within protocol B to reach the communications server
...
Appl-A in the left node
believes it is communicating directly with its partner, and is unaware of the extra
processing taking place over the first network
...
In fact, it is sometimes referred to as a “LAN-based middleware” or
“client-server” approach
...
Many products
implement this approach
...
2 applications on the end nodes to communicate with the
communication server using AppleTalk**, and only the communication server
has the full SNA protocol stack to interact with the host over the SNA network
...
2 session between the client and server
...
The communication server must provide dedicated
support for each desired application programming interface, and there may be
limitations imposed due to the number of supported protocols
...
Disadvantages of Remote API Technique
•
They are dependent on the communication server, which can be a single
point of failure
...
•
The same API cannot be easily or efficiently used to communicate with a
partner on the same network (program 'B' in the example)
...
Positioning and Usage of Technologies
87
2
...
4 Application Gateway Technique
Figure 57
...
A very common type of application gateway exists to
convert messages from dissimilar electronic mail applications
...
Application gateways are very protocol- and/or
product-dependent
...
The functionality of an application gateway is illustrated in Figure 57
...
Everything
about Appl-B is quite different from Appl-A: transport protocol, application
services, application programming interface, and data format
...
The application gateway in the middle node, which is
connected to both Network A and Network B, realizes that this packet is destined
for Appl-B in the remote node, and will receive the packet
...
The new packet, with
Appl-B's address indicated, will proceed through the Appl-B stack in the
gateway, cross Network B, and be received and processed by Appl-B in the
remote node
...
In reality, the gateway
may not be able to compensate for all difference between the applications, or
between the transport layers
...
Application gateways are often implemented in different nodes than the end
nodes; in fact, the application gateway node may serve to physically connect the
two different networks as well as convert the application data
...
The application code on the end
nodes is not impacted
...
•
For applications that were never built on a standard protocol stack, such as
many electronic mail packages, this approach may be the only choice to
provide interoperability
...
A combination of
gateways may be required to achieve the desired result
...
•
Functionality of the native applications may be limited depending upon how
fully the gateway can convert between the applications
...
Thus, unless the gateway
is duplicated, it becomes a single point-of-failure
...
Chapter 2
...
4
...
Such a server is
often designated a multi-protocol server, since it serves its clients across
multiple networking protocols
...
90
Introduction to Networking Technologies
2
...
5
...
Multi-Protocol Server Technique, Server-Only
In the above diagram, the application in the middle is playing the role of server,
communicating (with application support program help) through two different
network types
...
The server often
supports applications which run over different transport protocols
...
Note that in Figure 58,
Appl-A communicates with its partner Appl-A, which is part of the server code
...
However, Appl-A does not
communicate directly with Appl-B; they may share results maintained by the
server (for example, databases), and thus communicate indirectly
...
Appl-A and Appl-B
can make requests of the server; if the server does not have the desired
information locally, it will invoke a client Appl-C within itself to obtain the
information from Appl-C
...
This is much like a “subcontract operation” or “farmed-out operation,” and is
often so labeled
...
The remote server responds back to
the original server with the desired data, and the original server reponds back to
Chapter 2
...
An example of this combination is the EDA/SQL**
products from Information Builders, Inc
...
To achieve
this interoperability, the products employ multiple protocol stacks and
applications to translate between the different file structures and different
SQL-call syntax
...
A separate server is used, and this node will have multiple protocol
stacks and applications to provide this functionality
...
Advantages of Multi-Protocol Server
•
Only one protocol stack is required in the end stations
...
To the user, he receives data in
the usual format, even though this data may come from a different
application
...
Disadvantages of Multi-Protocol Server
•
•
The server is a single point-of-failure
...
•
Skills need to be developed to manage the server software and hardware
...
Network management is more complex, since it is difficult to see beyond the
server to the end stations
...
4
...
2 Multi-Protocol Server (Server and Gateway) Technique
Figure 59
...
There are three client-server pairs: A-(MP Server/GW), B-(MP Server/GW),
and (MP Server/GW)-C
...
2
...
Each particular technology
must be selected with regard to a specific customer situation In Chapter 3,
“Typical Customer Situations” on page 95, the applicability of these technologies
within a particular situation is illustrated using a set of typical customer
situations
...
Positioning and Usage of Technologies
93
94
Introduction to Networking Technologies
Chapter 3
...
3
...
There is an old joke among networking professionals that there are always three
additional layers or levels of complexity beyond whatever is shown in a protocol
stack (for OSI, SNA, TCP/IP, etc
...
Quite frankly, most networking decisions
are made on the basis of these three factors, and not on the basis of the “best”
technology
...
“Total cost” should be examined
carefully; it is more than the price quote given by a vendor for hardware and
software products, but includes the personnel costs of the people involved in
administering and managing the new network configuration
...
Also hidden are the costs to
train end users on using this new equipment, and impact of performance, and
availability/reliability differences on personnel productivity
...
No
matter how many facts are shown to certain individuals to argue for or against a
particular technology, there are people who are simply set in their opinion, and
nothing can dissuade them
...
We can identify some general
questions to assess when examining these technologies for a given situation
...
Something else to consider is that these techniques as described are NOT
specific to any particular protocols or products
...
1994
95
to obtain the desired solution
...
3
...
Many complex customer scenarios are often composed
of a mixture of the four fundamental situations listed below
...
•
Situation 1
...
Application Interoperability
•
Situation 3
...
Network Consolidation
The first two situations focus on application requirements, and must be
evaluated from the application's viewpoint, from the application layer down the
protocol stack (a “top-down” approach); whereas the last two situations focus on
the lower networking layers, and will be evaluated using a “bottom-up”
approach
...
Figure 60
...
A few considerations for the applicable technologies are listed for
each situation
...
”
Chapter 3
...
2
...
A new application
must be added to this single physical network, which utilizes a different transport
protocol (Tport-B)
...
There is no requirement for the new application to
interoperate with existing applications
...
In this situation, only the original transport protocol, Tport-A, is
allowed to run on the existing network
...
If a
separate physical network can be built for Tport-B, or a subnetwork can be
shared by both Tport-A and Tport-B, then Situation 1B (as depicted in Figure 63
on page 101) exists
...
Situation 1A: Adding a New Application B to an Existing Network
Figure 61 illustrates a situation where the current network utilizes Transport
Protocol A
...
The network is
probably a wide area network due to the assumption that the new transport
protocol cannot be accommodated on the same subnetwork (LANs do allow the
sharing of the subnetwork)
...
25), or else the wide area network would be multi-protocol-capable
...
All of these technologies permit the
utilization of a mixed-protocol stack approach, or some form of encapsulation
...
Situation 1A: Technology Choices
If this new application will be developed by the customer, it may be possible to
select an Application Support-level solution, such as middleware or XTI
...
For
instance, if the current network is TCP/IP-based, and X
...
If an off-the-shelf application is being purchased, it is more probable that a
solution operating at the transport or subnetworking levels will be selected
...
Most of these solutions function at the transport level, with the exception of
middleware, which operates at the application services and application
programming interface level
...
Application programmers are usually
aware of restrictions imposed by middleware and XTI; the other approaches are
usually transparent from an application programming viewpoint
...
Considerations to be kept in mind as these technologies are evaluated include
the following:
Chapter 3
...
Situation 1B: Adding a New Application B via a Separate Transport Network
Three possibilities exist in this case:
1
...
For instance, if the network is a LAN, then additional
protocols can use the same shared subnetwork
...
The customer is willing to modify the network to make it multi-protocol; for
instance, by adding routers
...
The customer is willing to procure a separate wide area network to handle
just the new transport protocol
...
All three of these possibilities are represented in the conceptual diagram in
Figure 63
...
If a new transport protocol is to be added, it requires that a new protocol stack
be installed in all end nodes which desire to use this new application
...
Since the network can handle
the new protocol, there is no need for mixed-protocol stacks or encapsulation
approaches
...
Chapter 3
...
Situation 1B: Technology Choices
Obviously, LANs are a solution only if the communicating nodes are local in the
same facility or campus
...
These wide area networks might be public or private, depending
upon the availability of services
...
25, SMDS) preferable to a private
network? What are the costs involved, and how much control over the
network is desired?
• Is this critical traffic? Does a prioritization scheme exist in this extended
subnetworking implementation to handle higher priority traffic?
• How do the end nodes interface to the extended subnetwork? What is
the cost of upgrading equipment or adding additional equipment?
Shared Subnetworks - LANs
• Are the nodes within the same physical location?
• Can the same adapter card be shared by multiple protocols?
• What is the performance impact of adding this new application to
current LAN traffic?
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Introduction to Networking Technologies
Bandwidth Management
• How many logical point-to-point connections are required for each node
to communicate with its partners? Are there adequate communications
ports on these nodes?
• How many locations are involved and thus how many bandwidth
managers are needed? Is a mesh network needed?
• How expandable is this network if more devices or more locations are
needed in the future?
Separate Wide Area Networks
• What are the costs involved with a separate network - additional
hardware and software in end nodes, modems, routing equipment,
leased line costs, and personnel costs to manage this network?
• Are there performance or security concerns to mandate that this protocol
be handled separately?
Chapter 3
...
2
...
The need for application interoperability might
arise due to a merger of two companies, establishment of a joint business
operation, or the provision of a service by an enterprise to other enterprises
...
For instance, if both Appl-A and
Appl-B used CPI-C over TCP/IP, then if Appl-A was on UNIX** system and Appl-B
was on a MVS system, the data formats might need to be converted between
ASCII and EBCDIC as well as any particular file formats
...
Electronic mail
packages written to the OSI X
...
More complicated scenarios arise when conversion is required, not only of the
application-level data, but also of the information from other protocol layers as
well
...
Database formats
and the inquiry tools used to interrogate the data have historically varied
considerably in format and access mechanisms
...
Thus, not only will data formats need to be
changed, but also the application service and transport protocols may need
conversion
...
If the customer
can rewrite the applications to use similar application programming interfaces,
application services, and/or the same transport protocol, fewer conversions will
be necessary
...
The more complex situation, when the application cannot be
recoded, is shown in Situation 2B (Figure 67 on page 108)
...
Situation 2A: Application Interoperability with Application-Level Translation
If the customer has the flexibility to recode part or all of the application, there
are many choices
...
The
first level of complexity involves the choice of a common API and Application
Services level, therefore minimizing the amount of conversion that must take
place at these levels
...
If one of the Application Support-level choices shown in Figure 66 on page 106
is selected, these technologies would provide the consistent API and
Applications Services-level required, as well as permitting the utilization of more
than one transport protocol, hopefully a transport protocol that is compatible with
the existing user network
...
A mixed-protocol stack
approach, such as with MPTN or mixed-protocol standards (RFCs or other
standards), might be appropriate to transmit the data across the network, and
then the user code would still need to convert any data format differences at the
highest layers
...
Chapter 3
...
Situation 2A: Technology Choices
As before, the marketplace will determined what is actually available for a
particular desired combination of application services, transport protocols and
operating systems
...
Typical Customer Situations
107
Figure 67
...
Usually multiple protocol layers must be converted, including
the transport protocol
...
108
Introduction to Networking Technologies
Figure 68
...
The
fundamental difference between the two approaches is whether end-to-end
connectivity is required between the applications
...
It might be critical for
a database access application to maintain end-to-end connectivity, but perhaps
not for an electronic mail “mailbox” application to do so
...
Considerations to be kept in mind as these technologies are evaluated include
the following:
Multi-Protocol Servers
• Is an end-to-end connection required? Or is it adequate for the server to
provide translation capabilities for various applications?
• Is this a mission-critical application which should be dependent on a
potential single point of failure?
• How much traffic can a particular server handle efficiently? How can
additional users be handled?
• Can additional transport protocols be supported? Can additional
applications be supported?
Application Gateway
•
Does full translation capability exist to communicate with the remote
application, or is just a subset of functions available?
Chapter 3
...
2
...
Interconnection always involves physically connecting two
separate networks, which might also be some distance apart
...
Thus, two steps are usually involved in network interconnection:
first, addition of the application to the networks (if needed), and second,
establishment of physical connectivity between these networks
...
In the first situation, a low-cost,
single gateway between the two networks is desired: this is Situation 3A
(Figure 69)
...
This intervening network may be owned by one of the
organizations, or in fact may be owned by a third organization
...
This scenario is discussed in Situation 3B (Figure 71 on page 114)
...
Situation 3A: Network Interconnection via Direct Connection
For Situation 3A, the interconnection involves the addition of an existing
application in one network to the second network (often referred to as extending
the “reach” of the application)
...
This forces Network #2
to handle the second protocol
...
Typical Customer Situations
111
Although this application addition to Network #2 might initially appear to be
similar to Situation 1, there are several significant differences
...
The issues become more
complex in this situation, when the two networks are physically separate,
perhaps quite a distance apart, and often under the control of different
organizations
...
For instance, Network A might be an SNA wide area network with 3745 front
end processors, and Network B might be a token ring network with Novell
Netware and IPX transport protocol - and now the Novell Netware users must
access an SNA application
...
Due to the condition that direct connection is required, with no intervening
network, the following solutions shown in Figure 70 are possible
...
Note that these
solutions span quite a range; from those that focus strictly on the subnetwork
level to solutions that operate at the upper layers
...
Situation 3A: Technology Choices
If the two networks are LANs that are physically located next to each other, then
a local bridge can be considered
...
112
Introduction to Networking Technologies
For wide area networks, particularly those networks which desire to restrict the
number of transport protocols, encapsulation can be used
...
MPTN can similarly be used in a single gateway
configuration, with one end node being the access node
...
One might also wish to consider where the data is physically located in the
network in deciding among these solutions
...
For
distributed data, remote APIs, encapsulation, and MPTN might be appropriate
...
Typical Customer Situations
113
Multi-Protocol Servers
• Is an end-to-end connection required? Or is it adequate for the server to
provide translation capabilities for various applications?
• Is this a mission-critical application which should be dependent on a
potential single point of failure?
• How much traffic can a particular server handle efficiently? How can
additional users be handled?
• Can additional transport protocols be supported? Can additional
applications be supported?
Figure 71
...
The intermediate network, Network
#3 in Figure 71, is often called a backbone network
...
The backbone network might be controlled by a
different organization than Network #1 and Network #2
...
For instance, Appl-A might use TCP/IP, but Network #3 might use SNA
...
Solutions which have double gateway implementations, such as those shown in
Figure 44 on page 66, will work quite well in this situation
...
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Introduction to Networking Technologies
Figure 72
...
25, SMDS) preferable to a private
network? What are the costs involved, and how much control over the
network is desired?
• Is this critical traffic? Does a prioritization scheme exist in this extended
subnetworking implementation to handle higher priority traffic?
• How do the end nodes interface to the extended subnetwork? What is
the cost of upgrading equipment or adding additional equipment?
Encapsulation
• Will this encapsulating software be placed in the end nodes - or in a
separate node, requiring additional hardware?
• How is the encapsulation actually performed? Are Data Link Control
protocols properly terminated and emulated? Are the transport-level
Chapter 3
...
2
...
Situation 4: Network Consolidation
The next progressive step from Situation 3, Network Interconnection, is Network
Consolidation
...
The first phase of
network consolidation involves sharing the subnetworks
...
A single transport protocol is much easier to administer and manage
than multiple protocols
...
Since application services are
often tied to the transport protocol, the choice of a single transport protocol
restricts the choices for application development
...
Since both Network #1 and Network #2 utilize transport protocol A
due to the presence of Appl-A in both networks, a decision might be made to use
just transport protocol A for both networks
...
It might seem quite reasonable to save line
costs by saving on subnetwork facilities, as well as administration and network
management personnel costs by reducing transport protocols and/or
Chapter 3
...
The impact to the users must be considered as well as the impact
to the company's profitability if applications are discontinued or modified to
accommodate a change in transport protocol
...
A variety of common solutions
are illustrated in Figure 74
...
Figure 74
...
25, SMDS) preferable to a private
network? What are the costs involved, and how much control over the
network is desired?
• Is this critical traffic? Does a prioritization scheme exist in this extended
subnetworking implementation to handle higher priority traffic?
118
Introduction to Networking Technologies
How do the end nodes interface to the extended subnetwork? What is
the cost of upgrading equipment or adding additional equipment?
Encapsulation
• Will this encapsulating software be placed in the end nodes? Or qill it be
placed in a separate node, requiring additional hardware?
• How is the encapsulation actually performed? Are Data Link Control
protocols properly terminated and emulated? Are the transport-level
protocols properly emulated? Is filtering of unnecessary packets
performed?
• What are the performance characteristics of this encapsulation software?
Is this acceptable?
• How are the different network addresses handled? What directory
services exist?
• How expandable is this approach if the network grows and more nodes
are added?
Multi-Protocol Routers
• Are all needed protocols handled by the router?
• Are there any Data Link Control-level concerns? Does the router
properly handle these protocols?
• What happens in congestion situations? Are all protocols equal? Can
the traffic be prioritized?
• How much filtering is available for each protocol?
Mixed-Protocol Standards
• Is it a supported application/transport combination currently supported
by the RFCs or another standard, such as a NetBIOS or OSI application,
which needs to run over TCP/IP?
• Do the protocol stacks installed in the end nodes support the standards?
MPTN
• Do MPTN implementations exist for the necessary protocols?
• If MPTN implementations exist for these protocols, do they exist on the
required operating system platforms in the end nodes? If not, do they
exist for operating system platforms which could be used as a gateway?
XTI
• Is the new transport protocol a currently available XTI protocol, such as
TCP/IP, NetBIOS, or OSI?
• If this is a new customer-developed application, can communications
software and compilers be found that utilize this interface for the
currently installed hardware and operating system platforms?
• If flexibility is desired in this customer-developed application, can the
application be coded with just the necessary subset of the transport
functions?
• If this is an off-the-shelf purchased application, has it been coded to
utilize the XTI interface? If so, does it support the transport protocol you
want?
Middleware
• Does this middleware implementation exist on all required operating
systems in the end nodes?
• How much flexibility does the middleware application programming
interface give to the application developers?
• What are the extra facilities provided by the middleware implementation
in terms of directory, security, and recovery?
Remote APIs
• What APIs are supported over which protocols? Does the correct
combination exist?
•
Chapter 3
...
3 Summary of Technology Positioning
Figure 75
...
As we have seen, the range of techniques
available for designing open networking solutions is very large
...
In most situations, a combination of these
techniques will be required to deliver the level of service and 'openness'
desired
...
Like an architect designing
a building, network designers need to architect their own plan to ensure that it
can meet the ever changing business and technical environment
...
Typical Customer Situations
121
122
Introduction to Networking Technologies
Appendix A
...
1994
123
124
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
127
128
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
131
132
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
135
136
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
139
140
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
143
144
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
147
148
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
151
152
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
155
156
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
159
160
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
163
164
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
167
168
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
171
172
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
175
176
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
179
180
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
183
184
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
187
188
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
191
192
Introduction to Networking Technologies
Appendix A
...
Master Foil Set
195
196
Introduction to Networking Technologies
Appendix A
...
1994
74
computing equation 6
computing model 6
concepts of technologies
introduction 1
Consolidation
Network 117
CPI-C 7
Customer Situations 95
D
Data Link Switching (DLSW) 67—68
Data Link Switching Technique 67
Definition
application 15
application support 22
bridge 35
gateway 35
networking 27
router 35
subnetworking 31
transport network 30
dialog flow 20
direct networking 42
distributed application 17
distributed-services support 26
DLS
See Data Link Switching (DLSW)
DLSW Technique 67
Double-Gateway Encapsulation 66
E
Encapsulation 61—66, 100, 107, 113, 115, 119
Double-Gateway 66
End-to-End 62
Single-Gateway 65
Encapsulation Technique 61
End-to-End Encapsulation 62
equation
computing 6
Extended Subnetworking 50, 102, 115, 118
F
flow 17
chain 20
dialog 20
join 19
lattice 20
relay 19
split 19
staged transfer
transfer 19
tree 20
19
199
flow (continued)
unstaged transfer 19
flow patterns
basic 19
basic information 19
client 21
client-server 21
client-server information 21
composite 19
composite information 19
information 17
server 21
frame of reference 1
Frame Relay 69—70
Frame Relay Technique 69
fundamental concepts 1
G
Gateway 39, 76
application 39
MPTN 76, 79
Single MPTN 79
transport 39
gateway definition 35
Gateway Encapsulation 65
Gateways
Intermediate Network 80
MPTN 80
Multiple MPTN 80
group
program 5
H
Hybrid stack
74
I
IEEE 3
OSE model 3
indirect networking 42
information flow 17
information flow patterns
Interconnection
Network 111
Interoperability
Application 104
17
J
join flow
19
L
LAN 102
lattice flow 20
Layer
APPL 6
200
Introduction to Networking Technologies
Layer (continued)
NETG 6
SNETG 6
SUPP 6
TPORT 6
Local Area Networks 55— 56
Local Bridges 57—58, 113, 115, 118
M
MAC Bridge 57— 58
Media
physical 33
Medium
physical 32
subnetworking 32
Middleware 82—83, 100, 106, 119
Middleware Technique 82
Mixed-protocol stack 74
Mixed-Protocol Standards 74
Mixed-Protocol Standards for TCP/IP Technique 74
Model
computing 6
distributed 17
IEEE OSE 3
OSE 3
OSI 2
OSI reference 2
POSIX OSE 3
reference 2
model layer 5
MPTN 76—80, 100, 107, 113, 116, 119
MPTN Access Node 76
MPTN Gateway 79
MPTN Technique 76
MQI 7
Multi-Protocol Router 72
Multi-Protocol Router Technique 72
Multi-Protocol Server (Server and Gateway)
Technique 93
Multi-Protocol Server (Server-Only) Technique 91
Multi-Protocol Server Technique 90
Multi-Protocol Servers 91—93, 106, 109, 114, 120
Multi-Protocol Transport Network 76
Multi-Protocol Transport Network Technique 76
Multi-Protocol Transport Networking 80
Multiple MPTN Gateways Technique 80
Multiplexors 34, 53—54
N
NETG layer 6
Network
Transport 71
network access 11
network access mechanism 12
network cloud 32
Network Consolidation 117
Network Interconnection 111
Networking
combined 45
direct 42
indirect 42
separated 44
shared 45
simple 43
networking componentry 28
networking definition 27
networking layers 5
OSI 5
non-distributed application 16
O
OSE model 3
OSI 5
networking layers 5
OSI model 2
OSI reference model 2
P
Packet Interface 69
Packet Interface Technique 69
patterns 17
basic information flow 19
client-server information flow 21
composite information flow 19
information flow 17
physical media 33
Points
switching 13
Positioning of Technologies 47
POSIX 3
OSE model 3
program group 5
protocol converter 36
Protocol Router 72
protocol stacks 10
R
reference model 2
relay flow 19
relay function 39
Remote API Technique 86
Remote APIs 86—87, 106, 113, 119
Remote Bridge 59—60
repeater 34
RFCs 74
Router 38
Multi-Protocol 72
Protocol 72
router (WAN) 38, 72
Multi-Protocol 72
router definition 35
Routers 72— 73, 102, 113, 116, 119
RPC 7
S
Selectable Transport Standard 84
Selectable Transport Standard Technique 84
Separate WANs Technique 51
Separate Wide Area Networks 51— 52, 103
separated networking 44
Services
distributed 26
Shared LAN (Local Bridge) Technique 57
Shared LAN (Multi-protocols) Technique 55
Shared LAN (Remote Bridge) Technique 59
Shared LAN (Split Bridge) Technique 59
shared networking 45
Shared WAN (Bandwidth Management) Technique
Shared WAN (Multiplexor) Technique 53
short stacks 33
simple networking 43
Single MPTN Gateway Technique 79
Single-Gateway Encapsulation 65
Situations
Customer 95
SMDS 69—70
SNETG layer 6
software stacks 10
Split Bridge 59—60
split flow 19
stack
Hybrid 74
Mixed-protocol 74
protocol 10
short 33
software 10
staged transfer flow 19
standard applications support 25
structure 17
Subnetworking 7
Extended 50
subnetworking access 12
subnetworking definition 31
subnetworking medium 32
Subnetworking Technologies 49
SUPP layer 6
Support
communications 24
distributed-services 26
standard applications 25
switching points 13
53
T
Technique
'Mixed-Protocol Standards for TCP/IP'
Application Gateway 88
Bandwidth Management (WAN) 53
Bridge (LAN) 57, 59
Local 57
74
Index
201
Technique (continued)
Bridge (LAN) (continued)
Remote 59
Split 59
Data Link Switching 67
DLSW 67
Double-Gateway Encapsulation 66
Encapsulation 61, 62, 65, 66
Double-Gateway 66
End-to-End 62
General 61
Single-Gateway 65
End-to-End Encapsulation 62
Frame Relay 69
Gateway 76, 79, 88
Application 88
MPTN 76
Single MPTN 79
Gateway Encapsulation 65, 66
Double 66
Single 65
Gateways 80
Multiple MPTN 80
General Encapsulation 61
LAN 55, 57, 59
Shared 55, 57, 59
Local Bridge 57
Middleware 82
Mixed-Protocol Standards 74
MPTN 76
MPTN Gateway 79
Single 79
MPTN Gateways 80
Multiple 80
Multi-Protocol Router 72
Multi-Protocol Server 90
Multi-Protocol Server (Server and Gateway) 93
Multi-Protocol Server (Server-Only) 91
Multi-Protocol Transport Network 76
Multi-Protocols (LAN) 55
Multiple MPTN Gateways 80
Multiplexor (WAN) 53
Packet Interface 69
Remote API 86
Remote Bridge 59
RFCs for TCP/IP 74
Selectable Transport Standard 84
Separate WANs 51
Shared LAN (Local Bridge) 57
Shared LAN (Multi-Protocols) 55
Shared LAN (Remote Bridge) 59
Shared LAN (Split Bridge) 59
Shared WAN (Bandwidth Management) 53
Shared WAN (Multiplexor) 53
Single MPTN Gateway 79
Single-Gateway Encapsulation 65
Split Bridge 59
WAN 53
Shared 53
202
Introduction to Networking Technologies
Technique (continued)
WANs 51
Separate 51
X/Open Transport Interface 84
XTI 84
Technologies
Application Support (SUPP) 81
Subnetworking (SNETG) 49
Transport Network (TPORT) 71
technologies, concepts of
introduction 1
TPORT layer 6
transfer flow 19
staged 19
unstaged 19
transport gateway 39
transport network 7
transport network access 12
transport network cloud 32
transport network definition 30
Transport Network Technologies 71
Transport Standard
Selectable 84
tree flow 20
U
unstaged transfer flow 19
Usage of Technologies 47
W
WAN
36
X
X/Open Transport Interface Technique
X
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