Network Models

TCP/IP Application layer

Includes the OSI session and presentation layer details

Handles issues of:

• Representation
• Encoding
• Dialog control

Network Models

TCP/IP Transport layer

Deals with the quality of service issues of

  - reliability

  - flow control

  - error correction

- It maintains a dialogue between source and destination while packaging application layer information into units called segments

Network Models

TCP/IP Internet layer

- Divide TCP segments into packets and send them from any network

- The packets arrive at the destination network independent of the path they took to get there

- Best path determination and packet switching occur at this layer

Network Models

TCP/IP Network Access layer

- Concerned with all of the components, both physical and logical, that are required to make a physical link

- Including all the details in the OSI physical and data link layers

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

- Build the data

- Package the data for end-to-end transport

- Add the network IP address to the header

- Add the data link layer header and trailer

- Convert to bits for transmission

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

Build the data

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

Package the data for end-to-end transport

• Transport layer obligation
• The data is packaged for internetwork transport
• By using segments, the transport function ensures that the message hosts at both ends of the e-mail system can reliably communicate

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

Add the network IP address to the header

• The data is put into a packet or datagram that contains a packet header with source and destination logical addresses
• These addresses help network devices send the packets across the network along a chosen path

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

Add the data link layer header and trailer

• Each network device must put the packet into a frame
• The frame allows connection to the next directly-connected network device on the link
• Each device in the chosen network path requires framing in order for it to connect to the next device

Network Models

Networks must perform the following five conversion steps in order to encapsulate data:

Convert to bits for transmission

• The frame must be converted into a pattern of 1s and 0s (bits) for transmission on the medium
• A clocking function enables the devices to distinguish these bits as they travel across the medium
• The medium on the physical internetwork can vary along the path used
• For example, the e-mail message can originate on a LAN, cross a campus backbone, and go out a WAN link until it reaches its destination on another remote LAN

Network Models

Which layer has the task of moving data through the internetwork?

How does int accomplish this?

Network Layer

• It accomplishes this task by encapsulating the data and attaching a header creating a packet (the Layer 3 PDU)
• The header contains information required to complete the transfer, such as source and destination logical addresses

The source sends SYN segment to initialize the data sequence

Once recieved, the destination responds with a SYN/ACK, letting the source know that it received the SYN segment and stating its sequence number

Once received, the source then sends an ACK based on the destinations sequence number