TCP/IP

What is TCP/IP?

A stack of networking protocols

What is the order of the layers?

Application, transport, internet, link

Only goes through internet and link layer at intermediate routers.

Application layer

Adds the protocol (give example)

Encrypts/decrypts data

Transport layer

Splits data into packets

Adds packet number (total number of packets) to each packet

Adds the port number

Responsible for requesting resends if packets are lost

Internet layer

Adds the source and destination IP addresses

Directs the packets towards destination - the router operates on this layer

Link layer

Connects devices on the same network

Adds the MAC address identifying the Network Interface Cards of the source and destination computers.

New link layer header added at each router. Old one stripped.

Assigning MAC addresses

For devices on the same network, the destination MAC address is the address of the recipient computer, otherwise, it will be the MAC address of the router.

How to answer question that asks about specific layer

• 2+ tasks

• Reverse of the 2 tasks

• Where does it send data when data is being set

• Where does data come from when data is being received

Packets

Trailer - checksum (calculated at the start and end of journey - if not equal, data has been corrupted). Flags end of packet. Most protocols do not attach a trailer to a packet.

Payload - the data itself

Header - sender’s IP, receiver’s IP, packet number, TTL (time to live decreases by 1 every router it passes through), protocol