CST 311 - Module 7

 Week 7

This week covered the link layer of the internet. The last two weeks involved the network layer which centered around routing algorithms using IP addresses to send and receive data. The link layer is what takes the IP address and determines how to get from interface to interface in each router/host link using a MAC address. Each host and router have a LAN table including IP/MAC address mappings. However, they don't know each other's MAC addresses initially, which is where the address resolution protocol (ARP) comes to play. Using ARP, a host or router can send a broadcast looking for a specific MAC address using a known IP address. This broadcast floods other switches and routers until the host with the IP address sees the broadcast and replies with it's MAC address, which then is cached in the initial host's ARP table. There is much more to this, but I must keep this brief.

The link layer offers other services besides delivery between adjacent nodes, though one that stood out is error detection/correction. We have previously looked at how we can detect errors using checksums in the transport layer, where if detected, have the sender retransmit the packet. However, that is not the only way and has the potential to be inaccurate. The link layer can use parity checking, which can detect single bit errors using a parity bit but using two-dimensional parity bits allow for detecting single bit errors and corrects them. Though if we care more about detecting errors, we can also use a cyclic redundancy check which can detect more burst errors.

There is much more to this than what is stated here, such as switches and multiple access protocols, but I will leave that for you to read from "Computer Networking" by Jim Kurose and Keith Ross.

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