Notes

Question 3
1. Consider the parity-check code with 4-bit dataword

- What is the length of the codeword?

K = n + 1 = 4 + 1 = 5

- How many codewords the code has?

16

- What is the minimum Hamming distance?

The minimum Hamming distance for the 4-bit dataword is 2.

- How many errors can be corrected?

A single bit error can be corrected with the parity-check code.

2. Alice and Bob
At the application layer, the data is to be exchanged is referred to as a message. This message does not contain any header or trailer. The transport layer takes the message as the payload, the load that the transport should take care of. It adds a transport layer header to the message. The network layer takes the transport-layer packet as data or payload and adds its own header to the payload. The header now contains the addresses of the source and destination hosts and some more information used for error checking of the header. The result of all this is the datagram. The data-link layer takes the network-layer packet as data or payload and adds its own header, which now contains the link-layer addresses of the host or the next hop (the router). This is the frame, which is passed to the physical-layer for transmission.

How Alice gets R1’s link layer address is using Address Resolution Protocol (ARP). ARP handles resolving link layer addresses. ARP broadcasts to devices on the network asking if they have a certain IP, and then the device which matches will reply back.

How the routers get the next destination and link-layer addresses is performed in 3 major steps. First, de-encapsulation of the layer 2 frame header and footer to expose the Layer 3 packet. The second step is that the destination IP address of the IP packet is examined, to find the best path in the routing table. The third step is if the router find a path to the destination, it encapsulates the Layer 3 packet into a new Layer 2 frame, and then forwards the frame out to the located destination.

The Link layer addresses in the network between Alice and Bob are L2L6 during framing link 1, L4L3 during framing link 2 and L5L1 during framing link 3.