HDLC DataLink Layer
Chapter 6
69
Continuing with the example, consider a node receiving the following bit
stream from across the link:
0101
1111
0
1001
1011
111
0
1
1111
0
1011
111
0
0
The previously inserted zeros would be deleted as follows:
0101
1111
1001
1011
111
1 1111
1011
111 0
Zeros Deleted
0
0
0
0
The original bit stream would then be passed through as follows:
0101
1111
1001
1011
1111
1111
1011
1110
Invalid Frame
A node must ignore any invalid frames it receives. A frame is invalid if it
falls into either of the two following categories:
A frame is invalid if it is not properly bounded by two flags. An
aborted frame falls into this category.
A frame is invalid if it is too short. A valid frame requires a minimum
of 32 bits between flags.
Order of Bit Transmission
The order of transmission of bits within a frame depends on the field the
bits are in.
In the address field, the order of bit transmission is low bit first. An
address of 1 would be:
Time
1 0 0 0
0 0 0 0