Solution:

What is framing?

The data link layer must use the service provided to it by the physical layer. This bit stream is not guaranteed to be error-free.

Data link layer to break the bit stream into discrete frames and compute the checksum for each frame.

When a frame is at the destination the checksum is recomputed.

If the newly computed checksum is different from the one continued in the Frame, the data link the layer is known that an error has occurred and takes steps to deal with it.

Character count method of framing:

The first framing method uses a field in the header to specify the number of characters in the frame.

When the data link layer at the destination sees the character count, it knows how many characters follow and hence where the end of the frame is.

Make the first field in the frame’s header the length of the frame. That way the receiver knows how big the current frame is and can determine where the frame ends.

The receiver loses synchronization when the bit becomes garbled.

If the bits in the count become corrupted during transmission, the receiver will think that the frame contains fewer (or more) bits than it does.

Although the checksum will detect the frames are incorrect, the receiver will have difficult resynchronizing to the start of a new frame. This technique is not used anymore, since better techniques are available.