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COMPUTER NETWORKS (CS610)
VU
COMPUTER NETWORKS
(CS610)
HANDOUTS
LECTURERS # 01 – 45
PREPARED BY:
HAMMAD KHALID KHAN
1
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
Table of contents
Lecture No
...
4
INTRODUCTION
...
2
...
9
Lecture No
...
13
Overview of Data Communication
...
4
...
14
PACKETS AND TDM:
...
2 illustration of TDM
...
5
...
17
Lecture No
...
22
SHIFT OPERATION
...
7
...
24
Lecture No
...
28
CARRIER SENSE MULTIPLE ACCESS (CSMA)
...
9
...
33
Lecture No
...
35
FRAME TYPE IDENTIFICATION
...
11
...
39
Lecture No
...
43
LAN WIRING AND PHYSICAL TOPOLOGY
...
13
...
48
Lecture No
...
51
BRIDGES
...
15
...
54
Lecture No
...
58
ROUTING
...
17
...
62
Lecture No
...
66
CONNECTION-ORIENTED NETWORKING AND ATM
...
19
...
68
Lecture No
...
72
ATM AND NETWORK OWNERSHIP
...
21
...
75
Lecture No
...
79
NETWORK PERFORMANCE
...
23
...
81
Lecture No
...
85
IP: INTERNET PROTOCOL ADDRESSES
...
25
...
87
Lecture No
...
90
IP SUBNETING
...
27
...
93
Lecture No
...
97
ARP MESSAGE FORMAT
...
29
...
101
Lecture No
...
105
IP ENCAPSULATION, FRAGMENTATION AND REASSEMBLY
...
31
...
110
Lecture No
...
113
IPv6 AND AN ERROR REPORTING MECHANISM
...
33
...
117
Lecture No
...
119
UDP: DATAGRAM TRANSPORT SERVICE
...
35
...
122
Lecture No
...
125
TCP: RELIABLE TRANSPORT SERVICE (Cont
...
37
...
128
Lecture No
...
131
NETWORK ADDRESS TRANSLATION
...
39
...
133
Lecture No
...
135
IP ROUTING (Part-2)
...
41
...
137
Lecture No
...
139
IP ROUTING (Part-4)
...
43
...
142
Lecture No
...
144
IP ROUTING (Part-6)
...
45
...
147
3
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
Lecture No
...
The computers can communicate with each other in a network
...
INTERNET:
The Internet is defined as the set of networks connected by routers that
are configured to pass traffic among any computers attached to any network in the set
...
CLASSIFICATION OF NETWORKS
Computer networks are classified by four factors which are as follow:
1)
2)
3)
4)
BY SIZE:
BY CONNECTIVITY:
BY MEDIUM:
BY MOBILITY:
1) BY SIZE:
According to their size there are two classifications of networks
...
Local Area Network
...
Wide Area Network (WAN)
In LAN network occupies the smaller area like a room a floor or a building
...
Internet is a Wide Area
Network
...
4
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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2) BY CONNECTIVITY:
Networks are also classified by connectivity in which two topologies are discussed
...
1) STAR topology
2) TREE topology
In star topology each computer is connected to a central hub
...
It is shown in the figure below
...
1: star and tree topologies
In Tree topology all computers are connected to each other in such a way that they
make a tree as shown in the figure above
...
5
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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Ring
Satellite/Radio
Figure: 1
...
3) BY MEDIUM:
The classification of networks is also based on the Medium of transmission
...
These
parameters are speed of transmission, range of the receiver and transmitter computer,
sharing of information, topology, installation & maintenance costs and reliability
...
Similarly other mediums differ from each other and appropriate medium is selected
for the sake of transmission
...
In this respect there are two types of networks
...
Mobile networks have been emerged
in the last decade
...
6
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COMPUTER NETWORKS (CS610)
VU
NETWORKS IN DAILY LIFE:
The major use of networks is in business side
...
In fact now there is
an entire industry that develops networking equipment
...
Networks are very much useful at government level as federal government, local
government and military organization use networks for communication purposes
...
This is
all just due to the networks
...
This is because many companies have developed networking standards, which
are not compatible with each other
...
• NO SINGLE UNDERLYING THEORY OR MODEL:
The second reason for the complexity of networks is that there is no single underlying
theory or model, which specifies or defines different aspects of networking
...
• MODELS ARE EITHER SO SIMPLISTIC OR SO COMPLEX:
Another reason for the complexity of networks is that the conceptual models
made by organization are either so simplistic that they do not distinguish between
details, or they are so complex that they do not simplify the subject
...
Different technologies use
different terminologies
...
7
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
MASTERING THE COMPLEXITY
To master the complexity one must follow the following points
...
For example:
Instead of how a specific protocol handles congestion, we should concentrate on
what congestion is and why it must be handled
...
In addition to this one must concentrate the concepts and not details,
concentrate on breath and not the depth of technologies, also one should understand the
analogies and illustrations
Network terminology is introduced with new concepts so it is much helpful to learn the
terminology to overcome the complexity of networks
...
2
Motivation and Tools
One of the reasons of motivation towards networking was resource sharing which is
discussed as follows
...
In an office as it is very expensive to give a separate printer to each worker
...
This leads to the motivation of resource sharing
...
For example: the sharing of a printer among the workers in an office and also the
sharing of information is a goal of resource sharing
...
By resource sharing a researcher could use
whichever computer was best suited to perform a given task
...
For this purpose ARPA started investing in ways to do data networking
ARPA use a new approach consisting of packet switching and internetworking to
fulfill the purpose of resource sharing
...
In this way the internet was emerged in 1970’s and it has grown drastically since then
as shown in the figure below
...
2
...
In log scale the position on y-axis is proportional
to the log of the number being represented
...
Fig
...
2 Growth of the internet on Log Scale
10
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COMPUTER NETWORKS (CS610)
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We see that on log scale the growth appears almost linear it means that internet experienced an
exponential growth
...
PROBING THE INTERNET:
Let us see how are the figures in above graphs obtained?
In the early days when there were some dozen computers on the network, it was done manually
but now as we have seen that there are millions of computers on the internet so how can we
calculate the number of computers connected to the internet
...
Now an automated tool is required that tests to see whether the given computer is online or not
...
Figure 2
...
com and 5 packets are received
...
com, the sequence
of packets and the times of transmission known as the round-trip time, as there is no packet loss
so it means that sears
...
PROBLEM WITH ‘PING’:
Ping, as a tool seems to be simplistic
...
If ping does not review any responses from host computer it can not tell the reason of problem
...
•
•
•
Remote computer might have a problem
...
Ping sometimes fails because of congestion
...
They do this to avoid denial of service of
flooding attack
...
Network administrators use ping as soon as they learn about the failure
...
To get more detail it is used
...
4
As shown in the figure about the route to DANDELION-PATCH
...
EDU was traced out and
the program showed all eight computers that were in the way
...
Thus we see that tracing a route is more interesting tool than Ping as it tells about each computer
that falls in the way of source and destination computers
...
3
Overview of Data Communication
NOTE: Chapter 4, 5, 6 deals with the course of DATA COMMUNICATION, which has
been studied as a separate, course earlier
...
It should also be noted that these chapters will contain no assignment, or quizzes
and these chapters will also be out of the examination
...
4
PACKETS, FRAMES AND ERROR DETECTION
INTRODUCTION:
The previous chapters of data communication described how bits are transmitted
across a physical network using a transmission medium
...
CONCEPT OF ‘PACKET’:
Network systems divide data in small blocks or junks called packets, which they
send individually
...
Also the
individual connection between each pair of computers is not possible
...
PROBLEMS WITH SHARING:
The demand of sharing is very high because many computers need to use the shared
networks
...
In this way they
hold the network for long time
...
So we need a mechanism for fairness
...
Computers take turns to send one packet at a time over the shared
connection
...
14
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
Example:
In the figure one reason for using the packets is illustrated
...
To understand
the use of packet here, let’s suppose a transmission with packets in the figure
...
This means that all that computers will be forced to wait for 12 minutes before initiating
other transfers
...
9 minutes
60 secs / minute * 56x103 bits / second
WITH PACKETS:
Now if the file is broken into packets, other computers must only wait until packet (not
entire file) has been sent
...
Now each packet takes less than 0
...
Here other computers must only
1000 bytes * 8 bits / byte
=
...
14 sec before beginning to transmit
...
But if the
second file is 10MB long it sill be transmitted in only 2
...
PACKETS AND TDM:
Dividing data into small packets allow time division multiplexing
...
At the destination the packet is switched through a demultiplexer to the
destination
...
15
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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Figure 4
...
Packet have different
format
...
FRAME:
A frame or hardware frame denotes a packet of a specific format on a specific
hardware technology
...
Header and tail are used to frame the data as shown in the figure below
...
3 illustration of a Frame
We see that in the figure soh and eot are used to denote the start of header and end of tail
...
To avoid the no delay between
two frames each frame sends an extra character between block of data
...
• Missing soh indicates receiving computer missed beginning of message
...
16
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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Lecture No
...
The solution to this problem is Byte stuffing
...
There are two types of data stuffing:
• Byte Stuffing
• Bit Stuffing
Byte stuffing refers stuffing with character oriented hardware and bit stuffing
refers to bit oriented hardware
...
For
example: it can use esc as prefix followed by x for soh, y for eot and z for eco
...
This is shown in figure below:
Figure 5
...
17
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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TRANSMISSION ERRORS:
Transmission errors may occur due to different causes for example interference or
power surges may destroy data during transmission
...
ERROR DETECTION AND CORRECTION:
To detect and correct errors, frames include additional information, which is
inserted by the sender and checked by the receiver
...
Also the incorrect data can be corrected and accepted
...
In parity checking, parity refers to the number of bits set to 1 in the data
item
...
of 1’s in data should be an even number
...
of bits should be an odd number
...
18
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
For example an even parity data 10010001 has parity bit 1 as it has odd number of 1’s
...
Let us consider another example, if noise or other interference introduces an error
one of the bits in the data will be changed from a 1 to a 0 or from a 0 to a 1
...
Suppose original data and parity is 10010001+1 (even parity)
...
LIMITATIONS OF PARITY CHECKING:
Parity can only detect errors that change in odd number of bits for example the original
data and parity is 10010001+1 (even parity) and the incorrect data is 10110011+1 (even
parity)
...
of bits have been changed due to noise so parity checking
can not detect this error
...
ALTERNATIVE ERROR DETECTION SCHEMES:
In addition to parity checking alternative error detection mechanisms have been
introduced
...
•
•
•
The size of the additional information (transmission overhead)
Computational complexity of the algorithm (computational overhead)
The number of bits errors that can be detected (how well errors are detected )
CHECKSUM
The second procedure used to detect errors is checksum
...
Then checksum is calculated by transmission then it is sent
along the data and the receiver and the same calculation is performed and then compared
with the original checksum transmitted
...
The figure illustrates the example
...
3
The integers can be 8, 16 or 32 bits
...
It uses only addition but it
has also limitations and can not detect all errors
...
19
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
Figure 5
...
To understand the concepts of CRC consider data in a message as co-efficient of a
polynomial
...
The remainder of this division is then transmitted as CRC and checked at the
receiver to detect errors
...
It is easy to implement in hardware
...
Figure 5
...
It performs two operations
...
20
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
VU
Figure 5
...
6
SHIFT OPERATION
This operation shifts all bits to the left one position
...
Figure 6
...
Also in the figure, we see that the
registers are initialized to zero and the bits of message are shifted through the input
...
In another figure, we see that input data is all 1s and CRC shown after 15, 16, 17
bits are shifted and feedback introduces 0s in CRC
...
a) Vertical errors
b) Burst errors
a) VERTICAL ERRORS:
This type of error occurs due to a hardware failure
...
g
...
b) BURST ERRORS:
When a small set of bits changes near a specific location due to lighting or electric motor
starting nearby etc
...
FRAME FORMAT AND ERROR DETECTION:
The modified frame format also includes CRC
...
The frame including CRC is
shown in the figure
...
2
22
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COMPUTER NETWORKS (CS610)
VU
LAN TECHNOLOGY AND NETWORK TOPOLOGY
Most networks are local and are designed to share resources among multiple
computers
...
In this shared medium the computers must take turns
using the shared medium
...
In such a mode of
communication each communication channel connects exactly two computers
...
Figure 6
...
Individual connections can choose a different frame format and error detection
mechanism etc
...
DISADVANTAGES:
Direct point-to-point communication has the following disadvantages:
•
•
•
•
•
The no
...
of computers
For ‘n’ computers connections = (n^2 – n)/2
...
Direct point-to-point communication is expensive due to a no
...
Another disadvantage is that adding a new computer to the network requires N-1 new
connections as shown in the above figure
...
7
GROWTH OF LAN TECHNOLOGY
The development of shared communication channels (LANs) started in 1960s and
early 1970
...
The computers take turns using
the medium
...
But sharing a single medium over long distances is efficient, due to
the long delays
...
of connections
...
The local communication consists of
LAN exclusively
...
SIGNIFICATION OF LANs AND LOCALITY OF REFERENCE:
LANs are most popular form of computer networks
...
The demand of LANs is related to a principle known
as “Locality of Reference Principle”
...
There are two patterns given as follows:
A) SPATIAL LOCALITY OF REFERENCE
B) TEMPORAL LOCALITY OF REFERENCE
a) SPATIAL LOCALITY OF REFERENCE:
In this pattern computers are likely to communicate with other computers that are located
nearby
...
Thus LANs are effective because of spatial locality of reference
...
24
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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LAN TOPOLOGIES:
Network can be classified by shape
...
FIGURE 7
...
It means that their shape does not look like a star but their
connections are just like a star
...
Here is shown a star
network in practice in the figure below:
FIGURE 7
...
In this network first computer passes data to the second and then second passes data
to third and so on, as shown in the figure
...
3
Like star topology the ring network are also logically ring and not physically
...
For this purpose, coordination is required to decide which computer has to use the
line at what time
...
4 BUS TOPOLOGY
REASON FOR MULTIPLE TOPOLOGIES:
Each topology has advantages and disadvantages, which are discussed below:
IN A RING:
It is easy to coordinate access to other computers however entire network is
disabled if a cable cut occurs
...
IN A BUS:
The network needs fewer wires than a star, however entire network is disabled
when a cable cut occurs
...
It was invented at EXROX PARC
(Palo Alto Research Center) in 1970s
...
The
standard is now managed by IEEE in which 802
...
The Ethernet uses bus topology
...
To which multiple
computers connect
...
This segment is limited to 500
meters in length
...
ETHERNET SPEEDS:
The Ethernet speed was originally 3Mbps, and the current standard is 10Mbps
the fast Ethernet operates at 100Mbps
...
ENCODING USED IN ETHERNET:
The encoding used in Ethernet is Manchester encoding
...
e
...
A change from positive voltage to 0 encodes as shown in the figure below:
FIGURE 7
...
8
CARRIER SENSE MULTIPLE ACCESS (CSMA)
There is no central control management when computers transmit on Ethernet
...
CSMA is a coordination scheme that defines how to take turns using a shared
cable
...
e
...
If the cable is idle it starts
transmitting and if the cable is in use then it waits
...
COLLISION DETECTION:
As explained above, the signals from two computers will interfere with each other
and the overlapping of frames is called a collision
...
ETHERNET CD:
To detect the collision, Ethernet interfaces include hardware to detect
transmission
...
Grabbled signal is interpreted as a collision
...
So Ethernet uses CSMA/CD to
coordinate transmission
...
Computer then waits for other to be idle before transmission
...
So the standard
specifies maximum delay and both computers choose random delay, which is lesser
...
The computer with shorter delay will go first and other computer may transmit later
...
Computers double delay with each subsequent collision
...
802
...
11 is standard wireless LAN that uses radio signals at 2
...
Its data
rate is 11Mbps
...
Bluetooth specifies a wireless LAN for short distances
...
LIMITED CONNECTIVITY WITH WIRELESS:
In contrast with wired LANs, not all participants may be able to reach each other
...
•
In wireless LANs the propagation is blocked by walls etc
...
This is shown in the figure below:
FIGURE 8
...
Transmitting
computer sends very short message to receiver
...
The response from receiver is broadcast, so all potential
transmitters receive reservation
...
The receiver may receive closely spaced requests
...
LOCAL TALK:
Apple invented the LAN technology that uses bus topology
...
It has relatively low speed i
...
230
...
Also it is of low cost and we can get a free
with a Macintosh, which is easy to install and connect
...
TOKEN RING:
Many LAN technologies that are ring topology use token passing for
synchronized access to the ring
...
Both pass from transmitter passed by other computers and are
copied by destination
...
This is shown in figure below
...
2
USING THE TOKEN:
When a computer waits to transmit it waits a token
...
Next computer is then ready to transmit, receive and then
transmits
...
Token is a short reserved frame that can not appear in data
...
Token gives computer permission to send
one frame
...
But if
now computer is ready to transmit, token circulates around ring
...
It was originally 4Mbps and now it is upto 16Mbps
...
FDDI: Fiber distributed data interconnect (FDDI) is another ring technology
...
It uses pair of fibers to form two concentric rings
...
In case of fiber a station failure, remaining stations loop back and reroute data through
spare ring
...
It is shown in figure below
FIGURE 8
...
ATM switches form a hub into which computers can connect in a star topology
...
Data from transmitters is routed directly
through hub switches to destination
...
4 ATM SWITCH
31
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ATM DETAILS:
•
•
•
•
It transmits data at over 100Mbps
...
Each connection includes two fibers
...
FIGURE 8
...
9
HARDWARE ADDRESSING
We need to devise technique for delivering message through LAN medium to
single, specific destination computer
...
The sending computer also identifies type of
data carried in the frame
...
Interface hardware detects delivery of frame and extracts frame from
medium
...
HARDWARE ADDRESSING:
Most network technologies have a hardware-addressing scheme that identifies stations on
the network
...
Sender also includes hardware address in each transmitted frame
...
Most LAN technologies include sender's
hardware address in frame too
...
1
LAN INTERFACE:
LAN interface handles all details of frame transmission and reception which are
given as follows:
33
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
•
•
•
•
•
•
•
VU
It adds hardware addresses, error detection codes, etc
...
It may use DMA to copy frame data directly from main memory
...
g
...
It checks error detection codes on incoming frames
...
It checks destination address on incoming frames
...
FORMAT OF HARDWARE ADDRESS:
It consists of a numeric value and its size is selected for specific network
technology
...
ASSINGING HARDWARE ADDRESS:
The hardware address must be unique on a LAN
...
There are three categories of address
forms:
•
•
•
Static
Configurable
Dynamic
STATIC:
In this category the hardware manufacturer assigns permanent physical address to
each network interface and manufacturer must ensure that every interface has a unique
address
...
g
...
g
...
The system administrators must coordinate to avoid the conflict
...
This automatic scheme must be reliable to prevent conflicts
...
For this
purpose shared communication channel can make broadcast efficient in such a way that
message is delivered to all stations
...
34
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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Lecture No
...
For every broadcast frame on the
network each computer uses computational resources and places the contents into
memory, which interrupt the CPU
...
Another problem is that if a pair of computer use broadcasting instead of sending
them directly all other computers waste CPU time while discarding the frames
...
It is the restricted form of
broadcasting
...
The interface hardware is programmed in advance to accept certain frames that have
multicast address as the destination address
...
The interface hardware frame then begins accepting three types of frames:
• Multicast frames
• Broadcast frames
• The frames that are distend to the station itself
...
We see that they
can receive audio frames if the interface are programmed to received them and the other
computers that are not running that audio application will not waste resources
...
For this
purpose it can use two types which are given as follows
...
35
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IMPLICIT FRAME TYPE:
In implicit frame the receiver must infer from frame data
...
All
contemporary standards use the following general format
...
Information typically in fields has fixed size and location
...
The Ethernet frame format is shown in the figure
...
1 the Ethernet frame format
The different friends of ether frame format and their purposes is explained below:
FIELD
PURPOSE
Preamble
Receiver synchronization
Destination Address
Identifies intended receiver
Source Address
Hardware address of sender
Frame Type
Type of data carried in frame
Data
Frame payload
CRC
32-bit CRC code
ETHERNET FIELDS:
In Ethernet fields the preamble and CRC is often not shown in frame
...
There is special value reserved for
frame type field
...
Sender and receiver can agree on interpretation, which is as follows:
They agree on single data format and use only that format this limits to one type of data
...
Also they agree to encode the
data format into first few bytes of the data field
...
Figure 10
...
Encoding the data type
To ensure interoperability format of encoding area must be universally agreed upon it
typically set by standards only
...
2 LLC:
IEEE 802
...
SNAP/LLC format is widely used for example by Ethernet
...
3
...
Also the type field is interpreted as in Ethernet (in this case, IP ) as shown in
figure above
...
g
...
The receiving computer examines the field and discards any frame with unknown type
...
It can report statistics such as capacity utilization, distribution of frame size,
collision rate or token circulation time
...
Many desktop computers have interface that can be configured for promiscuous mode
...
In this way the
communication across LAN is guaranteed to be private
...
Network analyzer can be configured to filter and process frames
...
It displays only frames from or to specific computers
...
`
38
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Lecture No
...
LANs
speeds are defined independent of any specific processor speeds, which allows for mix of
any attached systems
...
NETWORK INTERFACE HARDWARE:
CPU can’t process data at network speeds
...
The connector on NIC at the back of computer then accepts cable to physical
network
...
Figure 11
...
39
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COMPUTER NETWORKS (CS610)
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Figure 11
...
For example Ethernet interface can
not be used with token ring and similarly ATM interface cannot be used with FDDI
...
NIC AND CPU PRCESSING:
NIC contains sufficient hardware to process data independent of system CPU
...
In addition to this it also include
analog circuitry interface to system bus, buffering and processing
...
The system CPU forms
message request and sends instructions to NIC to transmit data
...
CONNECTION BETWEEN NIC AND PHYSICAL
NETWORK:
TWO ALTERNATIVES:
NIC contains all circuitry and connects directly to network medium
...
THIN ETHERNET VERSUS 10BASE-T:
Thin Ethernet and 10Base-T are both Ethernet
...
40
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THICK ETHERNET WIRING:
It uses thick coax cable
...
AUI cable carries digital signal from NIC to transceiver
...
The wires in AUI carry digital signals
power and other control signals
...
This is shown in the figure below:
Figure 11
...
g
...
Connection multiplexer connects multiple computers to a single transceiver
...
One AUI from multiplexer to
Ethernet coax
...
Figure 11
...
In this case transceiver electronics are built into NIC and NIC connects
directly to network medium
...
Coax runs directly to back of each
connected computer by T-connector
...
This is
shown in the figure below
...
5
Thin Ethernet is useful when many computers are located close to each other
...
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Lecture No
...
It is commonly called 10Base-T,
Twisted Pair or TP Ethernet
...
This makes it cheaper and that ‘s why it is most useful technology of today
...
1
HUBS:
They are used for extension of connection with multiplexing concept
...
It is effectively a very short Ethernet with very long
AUI cables
...
PROTOCOL SOFTWARE AND ETHERNET WIRING:
All wiring technologies use identical Ethernet specifications
...
g
...
They use same CSMA/CD algorithms
...
NICs can provide all three-connection technologies
...
The NIC is shown in the figure below with three
connectors
...
2
COMPARISON OF WIRING SCHEME:
The wiring schemes are compared as follows:
Separate transceiver allows computers to be powered off or disconnected from
network without disrupting other communication
...
In other case, thin coax cable takes minimum of cable
...
Hub wiring centralizes electronics and connections
...
Bottom line 10Base-T is most popular because of lowest cost
...
The token ring
network topology is a ring but wiring topology is a star
...
A
topology is logically a star or it is physically a star
...
It can count frames of
a specific type or size
...
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In general, it can be configured to match value of any field and capture only those
frames making the filter specification
...
A cable cut occurring in hub wiring only
affects one computer
...
Thicknet is
the most costly wiring, which is no longer used
...
3
As shown in the figure eight offices are wired with
a) Thick Ethernet
b) Thin Ethernet
c) Twisted pair Ethernet
We can see that the length of wired varies in three schemes so cost varies in three
schemes
...
10Base-T Ethernet is often called a star shaped bus
...
PHYSICL TOPOLOGY:
It depends on the wiring scheme
...
4
To allow changing the wiring without changing the interface hardware, NICs support
multiple wiring schemes
...
10/100 NETWORK INTERFACES AND AUTONEGATIATION:
10Base-T version of twisted pair Ethernet operated at 10Mbps
...
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100Base-T technology is backward compatible and allows the participants to negotiate a
speed when connection is established
...
CATEGORIES OF WIRES:
Cable used for wiring should match the following:
• The intended data rate
• The distance between devices
• The amount of em-noise
• Anticipated future needs
• Cost
Some categories and their typical uses are shown in the figure below
...
5
WIRING SCHEMES AND OTHER NETWORK TECHNOLOGIES:
Multiple wiring schemes are not limited to Ethernet technology
...
e
...
, local talk uses hubs
(physical star) to simulate a bus topology
...
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Lecture No
...
However
most companies or institutions have offices located far apart from each other
...
The delays must be short to allow access mechanisms
(CSMA/CD, token passing) work properly
...
For example: extending a company LAN to another building
...
In this purpose most
techniques use additional hardware
...
Resulting mixed technology stays within original engineering constraints while
spanning greater distance
...
1
The fiber-modem coverts digital data into pulses of light then transmits over the optical
fiber
...
This mechanism will successfully extend the optical fiber across several
kilometers because delays on optical fiber are very low and bandwidth is very high
...
According to
the fact that electrical signal gets weaker while traveling over copper wires
...
It amplifies the weakening signal received from one
segment and then retransmits onto another segment
...
2
One repeater doubles, two repeaters triple the maximum cable length limitation
...
It is to be noted that we cannot increase the maximum cable length as many times
as we wish by just adding repeaters
...
Ethernet standard specifies that any two stations cannot be separated by more than
four repeaters
...
3
The figure shows repeaters using the vertical segment
...
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DISADVANTAGES OF REPEATERS:
Repeaters do not recognize frame formats, they just amplify and retransmit the
electrical signal
...
BRIDGES:
A bridge is a hardware device also used to connect two LAN segments to extend a
LAN
...
It listens to all
traffic and recognizes frame format
...
A typical bridge has two NICs, a CPU a memory and a ROM
...
FRAME FILTERING:
The most important task a bridge performs is frame filtering
...
A frame is forwarded to the other segment, if it id destined to that segment
...
A bridge keeps a list for each segment that consists of physical addresses of the
computer attached to that segment
...
Most bridges are self learning bridges
...
In this way a bridge builds up address lists
...
4
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Lecture No
...
The bridge
forwards frames to the other segment if it can not find its destination address in its lists
...
PLANNING A BRIDGE NETWORK:
In a steady state, a bridge allows simultaneous use of each segment
...
For example:
Frequently contacting computers can be attached to the same segment
...
BRDGING BETWEEN BUILDINGS:
If two buildings are located far from each other, a bridge, a pair of fiber modems
and an optical fiber can be used to connect two LANs as shown in the figure below
...
1
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BRIDGING BETWEEN BUILDINGS:
ADVANTAGES:
COST:
An optical fiber modem pair is sufficient to connect many computers located on
separate buildings
...
PERFORMANCE:
The traffic on each building does not affect the other
...
It is usually not allowed to lay an optical fiber if the land does
not belong to you
...
LEASED SERIAL LINE CONNECTION: Which is less distant
...
It is shown in the figure below
...
2
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Unlike optical fibers, satellite connections are low bandwidth to save cost
...
The bridge must use buffering (saving a copy of frame into memory until it can be
sent)
...
The communication software usually waits for a
response after sending a few frames
...
One bridge is needed to connect
each segment to the rest of the bridge network
...
3
If the bridges on the longer network form a cycle, then broadcasting frames introduce a
problem i
...
the copies of broadcast frame continuously flows around the cycle (each
computer receiving an infinite number of copies)
...
Figure14
...
The bridges configure themselves automatically to decide which bridge will
forward broadcast frames and which bridge will not
...
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Lecture No
...
A hub with multiple ports simulates a single shared medium
...
A switch is shown in the figure below
...
1
If a hub is used to connect among computers on a LAN, then only two computers can
communicate at a given time
...
They can communicate at the
same time
...
Hubs simulate single shared LAN
segments and a switch simulates a bridged LAN connecting segments
...
They are available also for other networking technologies such as token ring, FDDI etc
...
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WAN TECHNOLOGIES AND ROUTING;
INTRODUCTION:
LANs can be extended using techniques in previous chapter
...
Because there are distance
limitations even with extensions so we need other technologies for larger networks
...
LOCAL AREA NETWORK (LAN):
It is used for a single building
...
WIDE AREA NETWORK (WAN):
It is used for a country level networking and even for continents
...
But it still can’t accommodate arbitrarily many computers
...
PACKET SWITCHES:
To span long distances or many computers, networks must replace shared
medium with packet switches
...
That’s why they are called packet switches
...
A packet switch is shown in the figure below
...
2
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CONNECTION TO PACKET SWITCHES:
A packet switch many connect to computers and to other packet switches
...
There are typically high-speed connections to other
packet switches but lower speed connections to the computers
...
PACKET SWITCHES AS A BUILDING BLOCKS:
Packet switches can be linked together to form WAN
...
Each switch may connect to one or more other
switches and one or more other computers as shown in the figure below
...
2
STORE AND FORWARD:
Data delivery from one computer to another is accomplished through store and
forward technology
...
For this purpose packet switch has
internal memory into which it can hold packet if outgoing connection is busy
...
PHYSICAL ADDRESSING IN A WAN:
The physical addressing in a WAN is similar as in LAN in the following way:
• The data is transmitted in packets equivalent to frames
...
• The packet header includes destination and source addresses
...
One part of address
identifies destination switch
...
This is
shown in the figure below
...
4
NEXT HOP FORWARDING:
Packet switch must choose outgoing connection for forwarding the packet
...
•
•
•
If the destination is local computer, packet switch delivers computer port
...
The choice of another switch is based on destination address in packet
...
16
ROUTING
SOURCE INDEPENDENCE:
Next hop to destination does not depend on source of packet
...
It has several benefits
...
Packet switch need not hove complete information about all destinations in spite it just
has next hop so reduces total information and increases dynamic robustness
...
HIERARCHICAL ADDRESSING AND ROUTING:
The process of forwarding the packets of information is called routing
...
Note that many entries have same
next hop
...
Figure 16
...
These routing
tables can be collapsed
...
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Figure 16
...
We can
add capacity to WAN by adding more links and packet switches
...
There are two types of switch according to the attached
computers
...
EXTERIOR SWITCH:
The switch that has computers attached with it is called exterior switch
...
The
routing table must have two things
...
OPTIMAL ROUTES:
The next hop in table must be on shortest path to destination
...
The modeling captures essence of
network and it ignores attached computers as shown in the figure below
...
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Figure 16
...
4
The graph algorithms can be applied to find routes
...
We see that switch has only outgoing connection, all traffic must traverse that
connection
...
If the destination does
not have in explicit routing table entry, then it use a default route
...
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Figure 16
...
17
ROUTING ALGORITHMS
BUILDING ROUTING TABLES:
There are basically two methods for building routing tables, which are as follows:
•
•
Manual entry
Software
Further there are two methods for computing routing table information
...
It is simple and has low network overhead
...
DYNAMIC ROUTING:
It allows automatic updates by a programmer
...
COMPUTING SHORTEST PATH IN A GRAPH:
While computing shortest path, first we assume graph representation of network
at each node then we use Djikstra’s algorithm to compute shortest path from each node to
every other node
...
WEIGHTED GRAPH:
Djikstra’s algorithm can accommodate weights on edges in graph
...
It should
be noted that the shortest path is not necessarily with fewest edges (or hops)
...
1
The shortest path in the figure from node 2 to node 6 is 2 to 3 and 3 to 6 as this
path has the smallest weight so it is the shortest path
...
This cost may be in time,
dollars or hop counting (weight == 1)
...
DISTRIBUTED ROUTE COMPUTATION:
Each packet switch computes its routing table locally and sends messages to the
neighbors
...
If a link or a packet switch fails then
the network adapts its failure
...
DISTANCE-VECTOR ROUTING:
Local information is next hop routing table and distance from each switch
...
e
...
Other switches update routing table based on received information
...
If entry has shortest path to destination, insert source as next hop to destination
and record distance as distance from next hop to destination plus distance from this
switch to next hop
...
Switches send link-state information about local connections
...
It uses link-state information to update global topology and runs Djikstra’s
algorithm
...
Packet switch updates its own routing table first
...
LINK-STATE ALGORITHM:
•
•
•
It is much more complex
...
It is used in OSPF
...
ARPANET:
It began in 1960’s
...
It was incubator for many of current ideas,
algorithms and Internet technologies
...
25:
It was early standard for connection-oriented networking
...
It predates computer connections, which are used for
terminal/time sharing connection
...
It is connection based
service and must contract with Telco for circuit between two endpoints
...
5Mbps and can run to 100Mbps
...
It is a
connection less service
...
It is typically ranges from 1
...
ATM (ASYNCHRONOUS TRANSFER MODE):
It was designed as a single technology for voice, video and data and has low jitter
(variance in delivery time) and high capacity
...
It can also
connect multiple ATM switches into a network
...
18
CONNECTION-ORIENTED NETWORKING AND
ATM
LANs and WANs can both connect multiple computers, but they have different
base technologies and meet different goals
...
ATM uses the concept of connection-oriented networking
...
It
provides universal service for all subscribers and support for all users for voice, video
and data
...
It gives
guaranteed service when it is appropriate and support for low cost devices
...
Jitter is significance for voice, video and data
...
PACKET SIZES:
Large packets result in fewer overheads because a smaller fraction of the packet is
used for header information
...
Large packets can’t easily be used for voice for example 8-bit samples (at
125usec per sample) would require half a second to fill a 4kB packet
...
ATM CELLS:
To meet its goals, ATM uses small, fixed sized packets called cells
...
VPI/VCI fields identify the cells destination
...
ATM header
is about the 10% of the cell
...
Engineers
sometimes call the ATM overhead the cell tax
...
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Figure
...
1
CONNECTION-ORIENTED SERVICE:
The connection-oriented service paradigm for networking is similar to the
manner in which telephones are used
...
The telephone at the destination signals
the arrival of a connection request
...
If the called person does answer, then the connection is
established
...
VIRTUAL CHANNEL (OR CIRCUITS):
Connections in ATM are called virtual channels (VC) or virtual circuits (a term
preferred by some)
...
The VC is identified by a 24-bit value formed from the VPI or Virtual Path Indicator (8bit), which identifies a particular path through the network and the VCI or Virtual
Channel Indicator (16-bits), which identifies the channel in the virtual path being used by
the connection
...
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...
The attachment
points or ports can be connected to computers or other ATM switches
...
The forwarding table is essentially indexed by the incoming cell’s VPI/VCI and
the contents yield the new VPI/VCI
...
ATM is thus called a label rewriting or label switching system
...
Figure 19
...
2
EXAMPLE:
As an example, in the figure we see that the sending computer S uses a VPI/VCI
of 3 and sends a cell
...
Switch B receives the cell and looks up 4 then rewrites the VPI/VCI as 1 and
sends the cell at its port 2
...
The receiving computer R receives the cell with a VPI/VCI of 6, which is the
value it is using for the connection
...
PERMANENT VIRTUAL CIRCUITS:
ATM can provide customers with virtual circuits that look like traditional leased
digital circuits
...
The forwarding tables are automatically restored after power
of equipment failure
...
Provisioning requires two steps:
1
...
2
...
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SWITCHED VIRTUAL CIRCUITS:
Most networks offer dynamic connections, which last for a relatively short time
...
The terminology comes from the Telco’s where switching system normally refers
to all switching
...
Software in the switch finds a network path to the destination and sends along the
connection request
...
Once the connection is established by the destination, a message is sent back to
the originating computer to indicate the SVC is ready
...
SIGNALING:
The term signaling is used to describe communication about the network, as
opposed to communication that just uses the network
...
These
connection requests and network control messages are also sent in cells and since the
VPI/VCI use in these cells are reserved there is no confusion between data and control
cells
...
For example: - a typical voice telephone call might give a QoS parameter for throughput
of 64kbps and delay less than 500msec
...
PROVIDING DESIRED QoS:
QoS desires are specified at connection setup time and one never altered for the
connection duration
...
If a switch cannot provide the resources, it rejects the connection requests and an
appropriate error message is returned
...
VARIABLE BIT RATE (VBR):
It is used for compressed audio and video where the data rate depends on the level
of compression that can be achieved
...
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...
Handling variable length packets leads to memory fragmentation
...
With cells bits can just be counted
as they arrive
...
QoS
can’t be guaranteed with variable length packets as easily as it can with fixed
length cells
...
Since it was designed
to handle arbitrarily large numbers of users, each of which could be willing to pay for
high throughput
...
A typical
port on an ATM switch operates at OC-3 speed (155Mbps) or higher
...
Connection setup time
may be excessive for short communications
...
Broadcast is inefficient and has to be simulated by sending the same message to
each computer separately
...
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NETWORK OWNERSHIP:
There are two categories in this case:
PRIVATE NETWOK:
Single organization or company owns this
...
There can be multiple LANs in a building or campus linked together
...
PRIVATE NETWORK ARCHITECTURE:
It operates autonomously from other networks (e
...
internet)
...
They may restrict
access at connections
...
It is responsible for all network management
...
They can only
install cables on their own property
...
PUBLIC NETWORK:
This is owned by common carrier e
...
Phone Company
...
It may be a telephone company
or another organization that builds network out of leases lines
...
Data transits public network to other organizations
...
PRIVATE
DISADVANTAGES
There are no decisionmaking
equipment
or
policies
...
technical
decision
and
policies
...
21
NETWORK SERVICE PARADIGM
VIRTUAL PRIVATE NETWORK:
Virtual Private Network (VPN) combines the features of both private and public
networks
...
These connections are sometimes called tunnels and connect sites
...
There is no access for other users of public networks
...
Even if an outside does manage to obtain a copy of the packet the
outside will be unable to interpret the contents
...
There are two types of service paradigms:
CONNECTION-ORIENTED:
It is similar to the telephone system: endpoints establish and maintain a
connection as long as they have data to exchange
...
CONNECTION-ORIENTED SERVICE:
One endpoint requests connection from network
...
Computers exchange data through connection
...
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CONTINUOUS AND BURST TRAFFIC:
Networks handling voice or video are engineered to accept and deliver continuous
data at fixed rate
...
Connection does not disappear when no data is sent
...
To communicate using a simplex design a pair of computers must
establish two connections one from computer A to computer B and another from
computer B to A
...
There are two types:
•
•
Switched Connection or Switched Virtual Circuit (SVC)
...
Permanent connections are originally hardwired and now configured at system unit time
...
Internal components are switched networks is a
switched data network
...
They may guarantee a throughput rate maximum packet loss rate
...
STREAM OR MESSAGE INTERFACE:
Some connection-oriented networks provide stream interfaces
...
Others provide a message interface that delivers data in the same size chunks that
the sender transmitted
...
The source of data
adds destination information in data and delivers to the network
...
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INTERIOR AND EXTERIOR SERVICE PARADIGM:
A network providing one service paradigm to the attached computers can use an
entirely different service paradigm internally
...
COMPARISON:
CONNECTION-ORIENTED:
•
•
Accounting is easier
...
CONNECTIONLESS:
•
•
It has fewer overheads
...
An example of service paradigm is shown in the figure below
...
1
ADDRESSES AND CONNECTION IDENTIFIERS:
Address is a complete unique identifier
...
Connection-oriented delivery can use a short hand that identifies the connection
rather than the destination
...
-8-bit Virtual Path Identifier (VPI)
-16-bit Virtual Circuit Identifier (VCI)
The connection identifier is local to each computer and it may be different at
different parts of the ATM switch
...
22
NETWORK PERFORMANCE
There are two types of characteristics in case of network performance
...
Delay is a measure how long
it takes for a bit of data to travel across the network from one compute to the other
...
TYPES OF DELAY:
There are following types of delay:
PROPAGATION DELAY:
It defined as the time to travel across medium
...
ACCESS DELAY:
It is the time required to get control of medium (CSMA/CD, token)
...
THROUGHPUT:
Throughput is a measure of the rate at which data can be sent through the
network
...
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Because each frame contains headers, the effective throughput is less than the hardware
bandwidth
...
RELATIONSHIP BETWEEN DELAY AND THROUGHPUT:
If a packet switch has a queue of packets waiting when a new packet arrives
...
Throughput and delay are not completely independent
...
DELAY THROUPUT PRODUCT:
It is computed as delay time multiplied by effective throughput
...
In fast network with long delay times,
sending computer can generate large amounts of data before destination receives first bit
...
A network with
zero jitter takes exactly the same amount of time to transfer each packet
...
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Lecture No
...
A large
organization with diverse networking requirements needs multiple physical networks
...
The interconnection of two or more networks, usually local area networks so that
data can pass between hosts on the different networks as though they were one network,
this requires some kind of Router or Gateway, which led to the motivation for
internetworking
...
In the 1970s large organizations began to acquire multiple networks
...
Employees needed to choose a
computer appropriate for each task
...
UNIVERSAL SERVICES:
A communication system that supplies universal services allows arbitrary pairs of
computers to communicate
...
UNIVERSAL SERVICES IN A HETEROGENEOUS WORLD:
Although universal service is highly desirable incompatibilities among network
hardware and physical addressing prevent an organization from building a bridged
network that includes arbitrary technologies
...
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INTERNETWORKING:
Despite the incompatibilities among networks, researchers have devised a scheme
that provides universal service among heterogeneous networks called ‘internetworking’
...
PHYSICAL NETWORK CONNECTION WITH ROUTERS:
A router is a special purpose system dedicated to the task of interconnecting
networks
...
A router connecting two
physical networks is shown in the figure below
...
1
INTERNET ARCHITECTURE:
Organization seldom uses a single router to connect its entire network for two reasons
...
Redundancy improved Internet reliability
...
The Internet scheme allows each organization to choose the number and type of network,
the number of routers to use to interconnect them, and the exact interconnection
topology
...
Figure 23
...
To provide this service all computers and routers must agree to forward information from
a source on one network to a specified destination
...
The key of achieving universal service is
universal protocol software (TCP/IP)
...
Figure 23
...
Although some layers of the TCP/IP reference model correspond to layers of the ISO
reference model, the ISO layers scheme does not have a layer that corresponds to TCP/IP
Internet Layer
...
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Figure 23
...
LAYER 2:
Specifies how to organize data in frames
...
LAYER 4:
Specifies how to ensure reliable transfer
...
HOST COMPUTERS, ROUTERS AND PROTOCOL LAYERS:
TCP/IP defines the term host computer to refer to any computer system that
connects to an Internet and runs applications
...
Both host and routers need TCP/IP protocol software but routers do not need layer
5 protocols for applications, as they do not run applications
...
24
IP: INTERNET PROTOCOL ADDRESSES
ADDRESSES FOR THE VIRTUAL INTERNET:
To provide uniform addressing in Internet, protocol software defines an abstract
addressing scheme that assigns each host a unique protocol address
...
THE IP ADDRESSING SCHEME:
An Internet address (IP address) is a unique 32-bit binary number assigned to a
host and used for all communication with the host
...
THE IP ADDRESS HIERARCHY:
Each 32-bit IP address is divided into two parts:
PREFIX:
It identifies the physical network to which the computers are attached
...
The physical network in an Internet is assigned a unique value known as a
network number
...
A suffix value can be
used on more than one network
...
Each computer is assigned a unique address
...
Although network number assignment must be coordinated globally, suffixes can
be assigned locally
...
The class of an address determines the boundary between the network prefix and suffix
...
Figure: 24
...
25
INTERNET PROTOCOL ADDRESS NOTATIONS
COMPUTING THE CLASS OF AN ADDRESS:
Whenever it handles a packet, IP software needs to separate the destination
address into a prefix and suffix
...
The table shows in the
figure below how the class of address can be computed
...
1
DOTTED DECIMAL NOTATION:
Dotted decimal notation is a syntactic form the IP software uses to express 32-bit
binary values when interacting with humans
...
This is shown in the figure below
...
2
CLASSES AND DOTTED DECIMAL NOTATION:
The relationship between classes and dotted decimal notation is given as follows
...
In class B the last two octets are the host octets
...
The range of decimal values found in the first octet of each address class is given below
in the figure
...
3
DIVISION OF THE ADDRESS SPACE:
The IP class scheme does not divide the 32-bit address space into equal size class
and the classes do not contain the same number of networks
...
This is shown in the table
below
...
4
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AUTHORITY FOR ADDRESSES:
Throughout the Internet, each network prefix is unique
...
The Internet service
providers coordinate with the Internet assigned number authority to obtain their network
numbers
...
The first step is to assign IP addresses in which usually class C addresses are
assigned
...
Figure: 25
...
26
IP SUBNETING
SUBNETS AND CLASSLESS ADDRESSING:
As the Internet grew, the original Classful addressing scheme became a limitation
...
Many addresses were unused
...
The classless addressing scheme solves the
problem by allowing an ISP to assign a prefix that is, 28 bits long (allowing the host to
have up to 14 hosts)
...
Suppose
D = Destination Address
(A, M)= (32-bit IP Address, 32-bit Address Mask)
A = = (D & M)
Now as an example consider a 32-bit mask:
11111111 11111111 00000000 00000000
Which can be denoted in dotted decimal as 255
...
0
...
Consider a network prefix:
10000000 00001010 00000000 00000000
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Which can be denoted in dotted decimal value as 128
...
0
...
Consider a destination address: 128
...
2
...
10
...
0
...
When we enter a
prefix and an address mask they use a modified form of dotted decimal addressing called
CIDR addressing, which is known as CIDR Notation
...
g
...
211
...
0) i
...
216 host addresses 16-bit CIDR mask denoted as:
128
...
0
...
It will be fine if 216 hosts are attached
...
•
Two of them each big enough for one of two customers
...
For example one customer can be assigned 128
...
0
...
211
...
32/28
...
e
...
CIDR HOST ADDRESSES:
The example below in the figure shows the CIDR host addresses:
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Figure: 26
...
Figure 26
...
27
ADDRESS REOLUTION PROTOCOL (ARP)
PROTOCOL ADDRESSES AND PACKET DELIVERY:
Protocol addresses are abstractions provided by software
...
The protocol
address of the next hop must be translated to an equivalent hardware address before a
packet can be sent
...
A host or router uses address resolution when it needs to send a packet to
another computer on the same physical network
...
In the figure below a simple Internet with routers R1 & R2 connecting three
physical networks is shown each network has two host computers attached
...
1
In the figure, A resolves protocol address for B for protocol messages from an
application on A sent to an application on B
...
Through the Internet layer, A delivers to F by routing through R1 and R2
...
Network layer on A passes packet containing destination protocol address F for
delivery to R1
...
TABLE LOOKUP:
In Table Lookup, binding or mapping is stored in a table in memory, which the software
searches when it needs to resolve an address
...
CLOSED-FORM COMPUTATION:
In Closed-form computation, the protocol address assigned to a computer is chosen
carefully so that computer’s hardware address can be computed from the protocol address
using basic Boolean and arithmetic operations
...
MESSAGE EXCHANGE:
In Message Exchange, Computers exchange messages across a network to resolve an
address
...
Now we discuss in some detail these three categories
...
A
separate address-binding table is used for each physical network
...
For less than a dozen hosts, a sequential search can suffice
...
In the table below the hardware addresses
for their corresponding IP addresses are given
...
2
There are two standard implementations to improve computational efficiency:
•
•
Hashing
Direct indexing
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HASHING:
Hashing is the transformation of a string of characters into a usually
shorter fixed-length value or a key that represents the original string
...
It is also used in many encryption
algorithms
...
It is possible only is cases where protocols
address are assigned from a compact range
...
Figure 27
...
A re-solver is used to compute a mathematical function that maps an IP address to a
hardware address
...
The two
values can be chosen to make address resolution trivial
...
EXAMPLE:
Suppose a configurable network number:
220
...
5
...
123
...
1
Hardware Address = 1
The IP address of second host = 220
...
5
...
123
...
101
Hardware Address = 101
A simple Boolean ‘and’ operation can compute the computer’s hardware address
...
A computer that
needs to resolve an address sends a message across a network and receives a reply
...
In this category there are two possible designs:
•
•
Centralized
Distributed
CENTRALIZED:
A network includes one or more servers that are assigned the task of answering
address resolution requests
...
DISTRIBUTED:
Each computer on the network participates in address resolution by agreeing to
answer resolution request for its address
...
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Figure 28
...
To guarantee that all computers
agree on the exact format and meaning of message used to resolve addresses
...
The ARP standard defines two basic message types:
•
•
Request
Response
REQUEST:
This contains and IP address and requests the corresponding hardware address
...
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ARP MESSAGE DELIVERY:
ARP message delivery is shown in the figure below
...
2
ARP MESSAGE FORMAT:
Although the ARP message format is sufficiently general to allow arbitrary
protocol and hardware addresses
...
ARP format is shown in the figure below:
Figure 28
...
Technically, placing a message inside a frame for transport is called
encapsulation as shown in the figure below
...
4
IDENTIFYING ARP RESPONSES:
Let’s find out how a computer knows whether an incoming frame contains an
ARP message
...
The Ethernet standard species that the type field in an Ethernet frame carrying
an ARP message must contain the hexadecimal value 0 x 806, as shown in the figure
below
...
5
CASHING ARP RESPONSES:
Although message exchange can be used to bind addresses, sending a request for
each binding is hopelessly inefficient
...
ARP manages the Table as a cache short-term storage
...
First the receiver extracts the sender’s addresses binding and checks to see if
It is present in the cache
...
The receiver examines the operation field of the message to determine whether
the message is a request or a response
...
If the two are identical, the
computer is the target of the request and must send an ARP response
...
Protocol
addresses are used in all higher layers
...
This is shown in the figure below
...
6
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The main features of
connectionless service are as follows:
It includes extension of LAN abstraction
...
It combines collection of physical
networks into a single virtual network
...
Each packet has
a header
...
These packets have a uniform hardware-independent format
...
They are encapsulated in
hardware frames from delivery across each physical network
...
It includes header area
and data area as shown in the figure below
...
1
IP DATAGRAM SIZE:
Datagrams can have different sizes i
...
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Header area is usually fixed (20 octets) but can have options
...
535 octets (216-1)
...
FORWARDING DATAGRAMS:
Header contains all information needed to deliver datagram to the destination
computer
...
ROUTING TABLE:
For efficiency, information about forwarding is stored in a routing table, which is
initialized at system initialization and must be updated as network topology changes
...
An example routing table is shown in the figure below
...
2
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ROUTING TABLES AND ADDRESS MASKS:
In practice, additional information is kept in routing table
...
Next hop is stored as IP address of router
...
Prefix defines how much of address used to identify
network
...
0
...
0 which is used for subnetting
...
3
ADDRESS MASKS:
To identify destination, network apply address mask to destination address and
compare to network address in routing table
...
i
...
if ((Mask[i] & D) == Dest[i] ) forward to NextHop[i]
FORWARDING, DESTINATION ADDRESS AND NEXT-HOP:
Destination address in IP datagram is always ultimate destination
...
Network interface layer takes two parameters:
•
•
IP datagram
Next-hop address
Next-hop address never appears in IP datagram
...
It does not guarantee to prevent duplicate
datagrams, delayed or out-of-order delivery, corruption of data and datagram loss
...
Network layer – IP – can detect and
report errors without actually fixing them
...
Application
layer is not interested in differentiating among delivery problems at intermediate routers
...
30
IP ENCAPSULATION, FRAGMENTATION AND
REASSEMBLY
It is shown in the figure below:
Figure 30
...
H
...
SERVICE TYPE shows sender’s preference for low latency, high reliability that is
rarely used
...
IDENT, FLAGS, FRAGMENT OFFSET show the values used with fragmentation
...
TYPE shows type of protocol carried in datagram e
...
, TCP, UDP
...
SOURCE DIST IP ADDRESS shows IP addresses of original source and ultimate
destination
...
g
...
Header with no options has H
...
Options are added between DESTINATION IP
ADDRESS and data in multiples of 32 bits
...
LEN
field value 8
...
Network interface layer has following tasks:
•
It binds next hop address to hardware address and prepares datagram for
transmission
...
Hardware ignores IP datagram format
...
Standard defines data type for IP datagram, as well as others (e
...
, ARP)
...
The encapsulation process is
shown in the figure below
...
2
ENCAPSULATION ACROSS MULTIPLE HOPS:
Each router in the path from the source to the destination un-encapsulates
incoming datagram from frame, processes datagram and determines next hop and
encapsulates datagram in outgoing frame
...
Datagram itself is (almost) unchanged as shown in the
figure below
...
3
MTU:
Every hardware technology specification includes the definition of the maximum
size of the frame data area, which is called the Maximum Transmission Unit (MTU)
...
MTU AND HETEROGENEOUS NETWORKS:
An Internet may have networks with different MTUs as shown in the figure
below
...
Figure 30
...
IP uses
fragmentation i
...
datagrams can be split into pieces to fit in network with small MTU
...
Each fragment is an independent datagram
...
Bit in
header indicates that the datagram is a fragment
...
Fragment offset gives original location of fragment
...
It puts part of data from
original datagram in each fragment and puts other information into header
...
Figure 30
...
Ultimate destination
performs reassembly as shown below
...
6
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Fragments may arrive out of order
...
In the figure 30
...
FRAGMENT IDENTIFICATION:
Let’s see how fragments are associated with original datagram
...
Fragments from different
datagrams can arrive out of order and still be sorted out
...
Destination sets timer with each fragment to identify lost fragment
...
Source
(application layer protocol) is assumed to retransmit
...
Router
fragments the fragment to fit
...
There is no need to reassemble hierarchically as sub-fragments include
position in original datagram
...
31
THE FUTURE IP (IPV6)
INTRODUCTION:
The current version of IP- Version 4 (IPV4) is 20 years old
...
IEFT has proposed entirely new version
to address some specific problems
...
But basic principles
are still appropriate today
...
SCALING:
Scale is also dramatically changed
...
Speed has increased from 56Kbps to 1Gbps
...
MOTIVATION FOR CHANGE:
One of the parameters, which motivated IP for change is address space
...
But most networks are class C and too small for many organizations
...
The second parameter is type of service, the IP provides
...
Current IP has type of service that is not often implemented
...
NAME AND VERSION NUMBER:
A preliminary version of IP was called IP- Next Generation (IPng)
...
One name was selected and it used next available
version number i
...
6
...
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NEW FEATURES:
The new features of IPV6 are as follows:
•
•
•
•
•
IPV6 addresses are 128 bits
...
Additional information is stored in optional extension headers, followed by data
...
New features can be added more easily
...
IPV6 DATAGRAM FORMAT:
It is shown in the figure below:
Figure: 31
...
Next header points to first
extension header
...
Routers use flow label to forward datagrams along prearranged path
...
2
IPV6 NEXT HEADER:
It is shown in the figure below:
Figure 31
...
e
...
NEXT HEADER field in the base header
defines type of header and it appears at end of fixed-size base header
...
NEXT HEADER field in extension header defines type
...
4
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Each fragment
has base header and (inserted) fragmentation header
...
This process is shown in the figure below
...
1
FRAGMENTATION AND PATH MTU:
IPv6 source (not intermediate routers) is responsible for fragmentation
...
So
source must fragment datagram to reach destination
...
The smallest MTU on any network between source
and destination and it fragments datagram to fit within that MTU
...
Path
MTU discovery is used
...
It must be dynamic i
...
path may change during transmission of datagrams
...
Flexibility: it can add new headers for new features
...
IPv6 ADDRESSING:
IPv6 uses 128-bit addresses
...
An advantage of IPv6 addressing is that it has no address classes i
...
prefix/suffix boundary can fall anywhere
...
It is used for multiple destinations; possibly not at same site
...
IPv6 ADDRESS NOTATION:
128-bit addresses unwidely in dotted decimal; requires 16 numbers:
105
...
136
...
255
...
255
...
0
...
18
...
140
...
255
...
69DC: 8864:FFFF: FFFF: 0:1280:8C0A:FFFF
Zero-compression – series of zeroes indicated by two colons
FF0C: 0:0:0:0:0:0:B1
FF0C::B1
IPv6 address with 96 leading zeros is interpreted to hold an IPv4 address
...
Delivery problems can be ignored; datagrams can
be ‘dropped on the floor’
...
BEST-EFFORT SEMANTICS AND ERROR DETECTION:
Internet layer can detect a variety of errors: e
...
•
•
•
•
Checksum (header only)
TTL expires
No route to destination network
...
g
...
Internet layer discards datagrams with problems
...
INTERNET CONTROL MESSAGE PROTOCOL:
Some errors can be reported
...
Message contains information about problem
...
TYPES OF MESSAGES:
Internet control Message Protocol (ICMP) defines error and informational
messages
...
ERROR MESSAGES:
These are as follows:
•
•
•
•
•
Source quench
Time exceeded
Destination unreachable
Redirect
Fragmentation required
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2
...
33
AN ERROR REPORTING MECHANISM (ICMP)
ICMP MESSAGE TRANSPORT:
ICMP message transport is acted upon by getting ICMP encapsulated in IP
...
2
ICMP message is sent in response to incoming datagrams with problems
...
USING ICMP TO TEST REACHABILITY:
ICMP can also be used to test different tools
...
Ping program tests
reachability
...
it uses ICMP echo
request and echo reply messages
...
USING ICMP TO TRACE A ROUTE:
List of all routers on path from A to B is called the route from A to B
...
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Tracert (Windows version) sends ICMP echo messages with increasing TTL
...
First, with TTL 1, gets to first router, which discards and sends
time exceeded message
...
It
continues until an ICMP echo reply message from destination is received
...
•
•
Send and ICMP echo request, destination host will generate an ICMP echo reply
...
USING ICMP FOR PATH MTU:
Fragmentation should be avoided
...
Source determines path MTU- smallest network MTU on path from
source to destination
...
Router responds with ICMP fragmentation required message
...
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Source and destination addresses are computers
...
TRANSPORT PROTOCOLS:
•
•
•
Provide application-to-application communication
...
Are called end-to-end communication
...
UDP protocol
allows applications on the computers to send and receive datagrams
...
It uses best-effort delivery service
...
Fields in the IP datagram header refer to computers, not applications
...
THE USER DATAGRAM PROTOCOL (UDP):
TCP/IP contains two transport protocols:
•
•
UDP
TCP
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UDP:
UDP is less complex and easier to understand
...
CHARACTERISTICS OF UDP:
UDP has the following characteristics
...
It provides application-to-application communication
...
It is a Message-Oriented protocol
...
It follows arbitrary interaction
...
THE CONNECTIONLESS PARADIGM:
UDP does not need to pre-establish communication and also there is no need to
terminate communication
...
There are no Control Messages; only Data Messages
...
MESSAGE-ORIENTED INTERFACE:
UDP offers application programs a Message-Oriented Interface
...
Let’s discuss its advantages and disadvantages
...
DISADVANTAGES:
•
•
•
Each UDP message must fit into a single IP datagram
...
UDP COMMUNICATION SEMANTICS:
UDP uses IP for all delivery, that is, same best effort delivery as IP
...
EXAMPLES:
•
•
Audio transmission
On-line shopping application
ARBITRARY INTERACTION:
UDP follows four types of interaction
•
•
•
•
1-to-1:
1-to-many:
Many-to-1:
application
...
One application can communicate with one application
...
Many applications can communication with one
Many
applications
can
communicate
with
many
SUPPORT FOR UNICAST, MULTICAST AND BROADCAST:
UDP allows multicast 1-to-many interaction using multicast or a broadcast
...
It is especially useful for Ethernet networks
...
Mechanism cannot be the same as of the operating system
...
There are multiple identifiers like protocol identifiers, job names and task
identifiers
...
’
It is independent of the underlying operating system
...
The address and protocol port specifications of an application define the type of
communication
...
35
DATAGRAM FORMAT AND TCP: RELIABLE
TRANSPORT SERVICE
UDP DATAGRAM FORMAT:
It is shown in the figure below:
Figure 35
...
Figure 35
...
It uses unreliable
datagram service offered by IP when sending data to another computer
...
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THE NEED FOR RELIABLE TRANSPORT:
Reliability is fundamental in a computer system
...
Software must guarantee
prompt and reliable communication without any loss, duplication, and change in the
order
...
In TCP/IP, TCP provides
reliable transport service
...
SERVICE PROVIDED BY TCP:
Following are the services provided by TCP:
• Connection-oriented service
• Point-to-point
• Complete reliability
• Full-duplex communication
• Stream interface
• Reliable connection startup
• Graceful connection shutdown
END-TO-END SERVICE AND DATAGRAMS:
Applications can request a connection
...
They are created by software only
...
TCP software modules on two computers create an
illusion of a connection
...
TCP message is encapsulated in IP datagram and
sent to the destination
...
It is shown
in the figure below
...
3
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ACHIEVING RELIABILITY:
The major problems in the reliable delivery are:
•
•
Unreliable delivery by the underlying communication system
...
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)
PACKET LOSS AND RETRANSMISSION:
TCP achieves reliability by retransmission
...
If acknowledgement does not arrive, the previous data
is retransmitted
...
1
HOW LONG SHOULD TCP WAIT BEFORE RETRANSMITTING:
The time for acknowledgement to arrive depends on:
•
•
Distance to destination
Current traffic conditions
Multiple connections can be opened simultaneously
...
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ADAPTIVE RETRANSMISSION:
Setting a timer sounds so easy but the question is “what time interval?” If the time
interval is too large, you are spending time waiting for something that is just not going to
happen
...
So keep estimate of round trip time on each connection, and use current estimate
to set transmission timer
...
This is a key to
TCP’s success
...
The network having short
intervals has a short timeout and the network having large interval has large timeout
...
2
BUFFER, FLOW CONTROL AND WINDOWS:
TCP uses window mechanism to control the flow of data
...
In the figure below a sequence of messages that illustrates TCP flow control when
the maximum segment size is 1000 octets
...
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Figure 36
...
Acknowledgements sent in each direction are used to guarantee that all data has arrived
before the connection is terminated
...
4
THREE-WAY HANDSHAKE TO BEGIN A CONNECTION:
Part of the 3-way handshake used to create a connection, requires each end to
generate a random 32-bit sequence number
...
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Reducing the window size quickly in response to the lost messages
does it
...
We have to resume carefully
...
TCP SEGMENT FORMAT:
It is shown in the figure below
...
TCP
uses the term segment to refer to a message
...
Figure 37
...
It allows multiple computers to share a single address
...
Its implementations are available e
...
,
•
•
Stand-alone hardware device
IP router with NAT functionality embedded
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NAT DETAILS:
Site that consists of more than one computer, obtains a single valid IP address
...
NAT translates address in IP datagrams
...
When a computer in the site
communicates to the internet, the NAT device, as shown in the figure below, translates its
private address in the site to the global IP address and vice versa
...
2
NAT EXAMPLE:
For example, a site uses private network 10
...
0
...
First computer is assigned 10
...
0
...
0
...
2 and so on…
Site obtains a valid IP address (e
...
128
...
24
...
Let’s assume that the
computer 10
...
0
...
211
...
4 (another global IP address)
...
NAT also translates
the destination address of incoming datagram to the private site address
...
Figure 37
...
e
...
IMPLEMENTATION OF NAT:
The figure below shows the implementation of NAT
...
Figure 37
...
The value is entered in the table
when NAT box receives outgoing datagram from new
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...
The basic NAT simply changes IP addresses
...
It is the most popular form of NAT
...
it is used with site that runs server
...
NETWORK ADDRESS AND PORT TRANSLATION (NAPT):
It is by far the most popular form of NAT that can change TCP or DP protocol
port numbers as well as IP addresses
...
EXAMPLE NAPT TRANSLATION TABLE:
An example NAPT translation table is shown in the figure below
...
Figure 38
...
The
port numbers are reassigned to avoid conflicts
...
It interconnects two independent TCP
connections and performs segment rewriting
...
It uses
extended translation table
...
Twice NAT allows a site to run servers
...
Twice NAT fails if an application uses the IP addresses instead of Domain Name
...
It includes NAPT plus additional functionality
...
NAT AT HOME:
NAT is useful at a residence with Cable Modem or DSL connectivity as it allows
the customer to have multiple computers at home without requiring an IP address for
each of them
...
NAT software
allows a PC to connect with the Internet and act as a NAT device at the same time
...
Figure 38
...
39
IP ROUTING (Part-1)
TERMINOLOGY:
The forwarding and Routing are two different concepts and explained as follows:
FORWARDING:
It refers to datagram transfer
...
It uses routing
table
...
It is performed by routers
...
TWO FORMS OF INTERNET ROUTING:
STATIC ROUTING:
It is one of the forms of Internet routing
...
DYNAMIC ROUTING:
In dynamic routing the table is initialized when system boots
...
In this way continuous changes are
possible due to routing software
...
The typical routing table has two entries as
shown in the figure
...
The example is
shown in the figure below where four hosts are attached to an Ethernet which connects to
the rest of the internet through router R1
...
It requires special software which continuously updates the
routing information
...
It passes routing
information and uses Route Propagation Protocol to exchange the information with other
routers
...
In such a situation, dynamic
routing can be used to propagate information about remote networks
...
40
IP ROUTING (Part-2)
ROUTING IN THE GLOBAL INTERNET
As the route information protocol allows one router to exchange routing
information with another, however this scheme cannot scale to the entire Internet
because, if all routers attempted to exchange information, the resulting traffic would
overwhelm the backbone networks
...
All routers within a group exchange routing information
...
AUTONOMOUS SYSTEM CONCEPT:
An autonomous system can be thought of as a set of networks and routers under one
administrative authority
...
It can be or correspond to an entire
intuition or a single corporation
...
Each Autonomous System chooses a routing protocol to exchange routing
information which is summarized before being passed to another group
...
The destinations lie within IGP
...
The destinations lie throughout Internet
ILLUSTRATION OF IGP/EGP USE:
The following figure illustrates the IGP/EGP use
...
Each autonomous system used to
communicate among autonomous systems chooses an IGP to use
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After an ISP advertises destination D,
datagram destined for D can begin to arrive
...
After a router in ISP advertises
routes to customers, data can arrive for these customers
...
"Border Gateway Protocol (BGP)
"Routing Information Protocol (RIP)
"Open Shortest Path First Protocol (OSPF)
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BORDER GATEWAY PROTOCOL:
It is most popular Exterior Gateway Protocol in Internet
...
"It provides policies to control routes advertised
...
"It gives path of autonomous systems for each destination
...
"The current version is four (BGP-4)
...
ROUTING INFORMATION PROTOCOL (RIP):
It has the following characteristics:
"It is used for routing within an autonomous system (IGP)
...
"It uses UDP for all message transmissions
...
Version 1 of RIP uses hardware broadcast and version 2 allows
delivery via multicast
...
An organization can use RIP to
install a default route in each router
...
"RIP allows hosts to listen passively and update its routing table
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The
message contains a list of destinations and a distance to each
...
THE OPEN SHORTEST PATH FIRST PROTOCOL (OSPF):
As the internet grew in size, so did organizations
...
To satisfy demand for a routing protocol that can scale to large organizations,
the IETF devised an IGP known as the Open Shortest Path First Protocol (OSPF)
...
"FULL CIDR AND SUBNET SUPPORT:
OSPF includes a 32-bit address mask with each address, which allows the address
to be classful, classless, or subnetted
...
"IMPORTED ROUTES:
OSPF allows a router to introduce routes learned from another means (e
...
, from
BGP)
...
"SUPPORT FOR MULTI-ACCESS NETWORKS:
Traditional link state routing is inefficient across a multi-access network, such as
an Ethernet, because all routers attached to the network broadcast link status
...
OSPF GRAPH:
Networks and Routers can be illustrated using OSPF graph
...
Networks correspond to edges
...
Each router
uses link-status messages to compute shortest paths
...
A corresponding OSPF
graph is also shown in figure b
...
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OSPF AREAS:
OSPF allows subdivision of Autonomous System into areas
...
The routes are summarized before being propagated to
another area
...
Because it allows a manager to
partition the routers and networks in an autonomous system into multiple areas, OSPF
can scale to handle a larger number of routers than other IGPs
...
43
IP ROUTING (Part-5)
INTERNET MULTICAST ROUTING:
Internet multicast routing is difficult because internet multicast allows arbitrary
computer to join multicast group at any time
...
It also allows arbitrary computer to send message to a group
(even if not a member)
...
Neither a sender nor a receiver knows the identity or the number of group
members
...
Routers and hosts do not know which applications will send a datagram to a
group
...
The computer uses IGMP to inform the local router about the
last application when it leaves
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The size and topology of groups may vary e
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Teleconferencing often
creates small groups and on the other side web casting can create a large group
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To avoid routing loops, flood-and-prune
protocols use a technique known as Reverse Path Broadcasting (RPB) that breaks cycles
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, has a few members at each site, with sites separated by
long distances)
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The router then consults
its configuration table to determine which other sites should receive a copy
...
CORE-BASED DISCOVERY:
To provide smooth growth, some multicast routing protocols designate a core
unicast address for each multicast group
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As the datagram travels through the
Internet, each router examines the contents
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If the message contains
a multicast datagram switch a destination address equal to the group_s address, R2
forwards the datagram to members of the group
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Thus the set of routers participating in a multicast
group grows from the core outward
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143
© Copyright Virtual University of Pakistan
COMPUTER NETWORKS (CS610)
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Lecture No
...
Some of the proposed protocols are:
DISTANCE VECTOR MULTICAST ROUTING PROTOCOL
(DVMRP):
This protocol is used by the Unix program mrouted and the Internet Multicast
backBONE (MBONE)
...
CORE BASED TREES (CBT):
A multicast routing scheme in which the protocol software builds a delivery tree
from a central point
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e
...
PROTOCOL INDEPENDENT MULTICAST_ SPARSE MODE
(PIM-SM):
This is a protocol that uses the same approach as CBT to form a multicast routing
tree
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PIM-SM does not depend on any particular unicast routing protocol
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Routers that use PIM-DM
broadcast (i
...
flood) multicast packets to all locations within the organization
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e
...
The scheme works well
for short-lived multicast sessions (e
...
, a few minutes) because it does not require setup
before transmission begins
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MOSPF builds on OSPF and
reuses many of the same basic concepts and facilities
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CLIENT-SERVER INTERACTION:
Although an internet system provides basic communication service, the protocol
software cannot initiate contact with, or accept contact from, a remote computer
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e
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HOW TWO APPLICATION PROGRAMS MAKE CONTACT?
The two application programs make contact in the following way:
One application actively begins execution first and another application waits
passively at prearranged location
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CLIENT-SERVER PARADIGM:
It is used by all network applications
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CHARACTERISTICS OF A CLIENT:
The characteristics of a client are explained below:
"Client is an arbitrary application program
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"It can also perform other computations
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"It runs locally on the user’s computer
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"It contacts one server at a time
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"It is dedicated to provide one service
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"It invoked automatically when system boots
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"It needs powerful computer and operating system
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"It accepts requests from arbitrary clients
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For example, the figure below illustrates a client and server using the
TCP/IP stack
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The client and server each interact with a protocol in the transport
layer
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45
COURSE REVISION
COURSE SUMMARY
(This lecture contains the summary of the topics that were covered during the course
...
The topics are also given below:
PACKETS, FRAMES AND ERROR DETECTION
•
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•
•
•
•
•
•
•
•
•
•
The Concepts of Packets
Packets and Time-Division Multiplexing
Packets and Hardware Frames
Byte Stuffing
Transmission Errors
Parity Bits and Parity Checking
Probability, Mathematics, and Error Detection
Detecting Errors with Checksums
Detecting Errors with Cyclic Redundancy Checks
Combining Building Blocks
Burst Errors
Frame Format and Error Detection Mechanisms
LAN TECHNOLOGY AND NETWORK TOPOLOGY
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Direct Point-to-Point Communication
Shared Communication Channels
Significance of LANs and Locality of Reference
LAN Topologies
o Star Topology
o Ring Topology
o Bus Topology
Example Bus Network: Ethernet
Carrier Sense on Multi-Access Networks (CSMA)
Collision Detection and Backoff with CSMA/CD
802
...
The topics are also given below:
INTERNETWORKING: CONCEPTS, ARCHITECTURE, AND
PROTOCOLS
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•
•
•
•
•
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•
•
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The Motivation for Internetworking
The Concept of Universal Service
Universal Service in a Heterogeneous World
Internetworking
Physical Network Connection with Routers
Internet Architecture
Achieving Universal Service
A Virtual Network
Protocols for Internetworking
Layering and TCP/IP Protocols
Host Computers, Routers and Protocol Layers
151
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COMPUTER NETWORKS (CS610)
VU
IP: INTERNET PROTOCOL ADDRESSES
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Addresses for the Virtual Internet
The IP Addressing Scheme
The IP Address Hierarchy
Original Classes of IP Addresses
Computing the Class of an Address
Dotted Decimal Notation
Classes and Dotted Decimal Notation
Division of the Address Space
Authority for Addresses
A Classful Addressing Example
Subnet and Classless Addressing
Address Masks
CIDR Notation
A CIDR Address Block Example
CIDR Host Addresses
Special IP Addresses
The Berkeley Broadcast Address Form
Routers and the IP Addressing Principle
Multi-Homed Hosts
BINDING PROTOCOL ADDRESSES (ARP)
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Protocol Addresses and Packet Delivery
Address Resolution
Address Resolution Techniques
Address Resolution with Table Lookup
Address Resolution with Closed-Form Computation
Address Resolution with Message Exchange
Address Resolution Protocol
ARP Message Delivery
ARP Message Format
Sending an ARP Message
Identifying ARP Frames
Caching ARP Responses
Processing an Incoming ARP Message
Layering, Address Resolution, Protocol Addresses
152
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COMPUTER NETWORKS (CS610)
VU
IP DATAGRAMS AND DATAGRAM FORWARDING
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Connectionless Service
Virtual Packets
The IP Datagram
Forwarding an IP Datagram
IP Addresses and Routing Table Entries
The Mask Field and Datagram Forwarding
Destination and Next-Hop Addresses
Best-Effort Delivery
The IP Datagram Header Format
IP ENCAPSULATION, FRAGMENTATION, AND
REASSEMBLY
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Datagram Transmission and Frames
Encapsulation
Transmission across an Internet
MTU, Datagram Size, and Encapsulation
Reassembly
Identifying a Datagram
Fragment Loss
Fragmenting a Fragment
THE FUTURE IP (IPv6)
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The Success of IP
The Motivation for change
A Name and a Version Number
IPv6 Datagram Format
IPv6 Base Header Format
How IP v6 handles Multiple Headers
Fragmentation, Reassembly, and Path MTU
The Purpose of Multiple Headers
IPv6 Addressing
IPv6 Colon Hexadecimal Notation
153
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UDP: DATAGRAM TRANSPORT SERVICE
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Need for End-to-End Transport Protocols
The User Datagram Protocol
Connection-less Paradigm
Message Oriented Interface
UDP Communication Semantics
Arbitrary Interaction
End Point Identification with Protocol Port Numbers
UDP Datagram Format
TCP: RELIABLE TRANSPORT SERVICE
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The Need for Reliable Transport
The Transmission Control Protocol
The Service TCP Provides to Applications
End-To-End Service and Datagrams
Achieving Reliability
Packet Loss and Retransmission Times
Adaptive Retransmission
Buffers, Flow Control, and Windows
Three-Way Handshake
Congestion Control
TCP Segment Format
INTERNET ROUTING
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Static Vs Dynamic Routing
Static Routing In Hosts and a Default Route
Dynamic Routing and Routers
Routing in the Global Internet
Autonomous System Concept
The Two Types of Internet Routing Protocols (IGP & EGP)
Routes and Data Traffic
Border Gateway Protocol (BGP)
The Routing Information Protocol (RIP)
RIP Packet Format
154
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COMPUTER NETWORKS (CS610)
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VU
The Open Shortest Path First Protocol (OSPF)
An Example OSPF Graph
OSPF Areas
Multicast Routing
155
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