Delim a frame

One way to delim frames is to use special characters or bit patterns to indicate the start and end of a frame.
Such as 0111110 indicates start and end.

What if the frame data contain delim character/bit patterns

This is when we need stuffing. We will escape that character/bit pattern.
EG: when we see 011111 in our data, we will add a 1 to it so it won’t coincide with the delim bit pattern. When we are reading it from the other end of communication, we will remove that extra 1 appropriately.

Can’t have fixed size frame

Since we don’t know how many char/bit patterns that coincide with the escape sequence, we might need to escape an unknown amount of the data. So we can’t have fixed size frame.