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Title: OSI LAYERS
Description: - 7 layers of the OSI

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Delwin Thermitus
03/27/2022
Cyber Security

The OSI Model
-

The Open System Interconnection model is a model for layered communications and
computer network protocol design
...


7 Layers of the OSI Model
1
...
(Physical Structure)
(Coax, Fiber, Wireless, Hubs, Repeaters)
2
...
(Frames) (Ethernet, PPP, Switch, Bridge
...
Network – Defines network addresses in a way that routes can be determined
systemically
...
Transport – transfers data between end users (This is where TCP & UDP live) (End-ToEnd connections)
5
...
It’s also referred to as ‘Port Layer’
...
) (API’s, Sockets,
WinSock
...
Presentation – Formats the data (e
...
, encryption
...
)
7
...
(Programs that fallout the scope of
the OSI Model
...
) (HTTP, FTP, IRC, SSH, DNS
...

- Guide to understand the flow of data across a network
...

o Reference for the location of protocols
...

- Upper Layer (Host)
o Application
o Presentation
o Sessions
- Lower Layers (Network)
o Transport

o Network
o Data Link
o Physical
-

Common Mnemonics
o (A)ll (P)eople (S)eem (T)o (N)eed (D)ata (P)rocessing
...


Physical – Layer 1
- Physical and Electric components
...

o 1’s & 0’s
...

- Not really about protocols
...

Data Link – Layer 2
- The ‘Switching’ layer
o Logical Link Controls (LLC)
...

o Media Access Control (MAC)
...

- PDU Frames
o Organizes bits into frames
- Protocols
o ARP, Spanning tree protocol token ring, Frame Relay, IEEE(The Institute of Electrical
& Electrical Engineers
...
)
Network – Layer 3
- The ‘routing’ layer
o Path determination
o IP Addresses
o IP Fragments
- PDU : Packets
o Packets can be fragmented for specific bandwidth constraints between routers
...

- Hardware
o Routers

Transport – Layer 4
- Protocols
o TCP (Transmission Control Protocol
...

o UDP (User Datagram Protocol
...

- The ‘post office’ layer
o Port numbers
...

o End-to-end service
...

o Flow control
...

- PDU: Segments/ Datagrams
o TCP Segments
...

o Syncs multiple transport layer connections and send them to ports
...

o Encodes/ translates data
...

o Compresses data
...

- Protocols:
o SSL, TLS, MIME
...

Application – Layer 7
- End – User layer
o Human – Computer Interaction
...

o Or create what will be sent
- Where apps access Network Services
- Protocols
o HTTP/S, DNS, SMTP, Email, FTP, Telnet, SSH
- Software

o Browsers, Email clients, User Apps
Title: OSI LAYERS
Description: - 7 layers of the OSI