Question

For Networks in Computer Science, please tell me about:

a.)   The responsibilities of the data link layer?

b.)   What is a frame?

c.)   How does the byte count method for framing work?

d.)   What is byte stuffing?

e.)   How do the FLAG and ESC bytes work?

Answer 1

a)Responsibilities of DLL

1) Framing of data

2) Adding physical address to data packet

3) Detection and correction of lost or corrupted frames

4) Encoding at sender, Decoding at receiver

5) Responsible for media access control

c) Byte count determines the number of bytes presented in the packet which can be useful in finding end of the data in the data packet at the receiver.

d) Data packet generally contains start and end delimiters to represent starting and ending of the data in the packet. If data in the message matches with those delimiters, Byte will be stuffed in the message to differentiate message from delimiters. This is called Byte stuffing.

e)If data pattern matches with the flag ESC will be added. This indicates that next byte is not flag it is data.So receiver remove that ESC and consider the next byte as data.

b)Frame:

At datalink layer packet is called as "Frame". Frame contains sender, receiver address and some error correction methods, both header and data at data link layer is called frame.