Sequence numbers are sent in numbered frames is a
binary synchronous data transmission.
The sequence number indicates how the frames that
are being sent are numbered. For example, if the frames are numbered from 0-7,
then it is a 3-bit sequence number. If the frames are numbered from 0-15 then
it is a 4-bit sequence number.
The send sequence number is the number (in the
specified modulus) of the current I-frame being sent by the local node. Each
transmitted I-frame is numbered in succession with a sequence number. This is
implemented by copying the send state variable, V(S), into the send sequence
number, N(S), in the frame. After a frame is transmitted the send state
variable is incremented. The N(S) in retransmitted frames are not changed (i.e.
the original N(S) value is sent in the retransmitted frame).
Binary Synchronous Communications. Binary
Synchronous Communication (BSC or Bisync) is an IBM character-oriented,
half-duplex link protocol, announced in 1967 after the introduction of
System/360. It replaced the synchronous transmit-receive (STR) protocol used
with second generation computers.
HDLC (High-level Data Link Control) is a group of
protocols or rules for transmitting data between network points (sometimes
called nodes). In HDLC, data is organized into a unit (called a frame) and sent
across a network to a destination that verifies its successful arrival.