- Frame number:
- Frame number = a
number used to
identify:
- a specific frame or
- a range of frames
- Frame number = a
number used to
identify:
- Example: 5 can mean:
- the frame #5
- All frames upto frame #5
- Recall:
- The supervisory frame of HDLC contains positive/negative acknowlegement for frames
- There are 4 types of
S-frames:
- Receive Ready N (RR) S-frame:
- Acknowledge the
correct receiption of
frames with the given
send sequence number N
- And: indicate that the station can receive more data
- Acknowledge the
correct receiption of
frames with the given
send sequence number N
- Receive Not Ready N (RNR)
S-frame:
- Acknowledge the
correct receiption of
frames with the given
send sequence number N
- And:
indicate that the
station is
not ready
to receive
more data
- For example, the station is low on buffer space !!!!
- Acknowledge the
correct receiption of
frames with the given
send sequence number N
- Reject N (REJ) S-frame:
- Request the
retransmission of
all frames
starting at
the
send sequence number N
- REJ is a negative acknowledgement !!!
- Request the
retransmission of
all frames
starting at
the
send sequence number N
- Selective Reject (SREJ) S-frame:
- Request the retransmission of the frame with the send sequence number N
- Receive Ready N (RR) S-frame:
- How to recognize the
4 different types of
S-frames:
Note:
- The
sss field
contains the
send sequence number N
(We will discuss the use of this field next)
- The
sss field
contains the
send sequence number N