Answer to Question #231725 in Computer Networks for shayan

Question

What are the responsibilities of data link layer?

Why mac address is not sufficient to transport data on internet?

What are the steps performed by the switch when it receives a frame?

(5 marks)

Answer 1

The responsibilities of a data link layer:

• Acts as as an abstraction such that the upper layers i.e. Network and Transport layer do not have to be concerned what type of devices are being used on the layer 1 that could have caused incompatibility.
• Used to transmit Ethernet frames from one host to another host using the MAC addresses of hosts connected on the same local network, as the source and destination host for any packet to be delivered.

MAC addresses are not sufficient to transport data on the internet because MAC addresses are not routable and are only used to transmit Ethernet frames from a source to a destination host on the same local network.

Steps performed by a switch when it receives a frame:

1. It decodes the Ethernet frame and checks the source and destination MAC addresses.
2. If the destination MAC is not on the MAC address table the switch will send a broadcast ARP request to all the connected hosts on an internal network on the broadcast MAC address.
3. The host with a matching configured MAC address to the desdtination MAC will send an ARP reply to the switch which contains itsMAC address.
4. The switch receives the ARP reply and records the MAC address in its MAC address table. The switch can now send the frame to the destination host through the associated port. And finally creates a temporary connection called a circuit for further communication between the two now hosts.