In a Go-Back-N (GBN) protocol, the sender is allowed to transmit multiple packets
(when available) without waiting for an acknowledgment, but is constrained to have no
more than some maximum allowable number, N, of unacknowledged packets in the
pipeline. We describe the GBN protocol in some detail in this section. But before reading
on, you are encouraged to play with the GBN applet (an awesome applet!) at the
companion Web site.
Figure 3.19 shows the sender’s view of the range of sequence numbers in a GBN
protocol. If we define base to be the sequence number of the oldest unacknowledged
packet and nextseqnum to be the smallest unused sequence number (that is, the
sequence number of the next packet to be sent), then four intervals in the range of
sequence numbers can be identified. Sequence numbers in the interval [0,base-1]
correspond to packets that have already been transmitted and acknowledged. The interval
[base,nextseqnum-1] corresponds to packets that have been sent but not yet
acknowledged. Sequence numbers in the interval [nextseqnum,base+N-1] can
In a Go-Back-N (GBN) protocol, the sender is allowed to transmit multiple packets(when available) without waiting for an acknowledgment, but is constrained to have nomore than some maximum allowable number, N, of unacknowledged packets in thepipeline. We describe the GBN protocol in some detail in this section. But before readingon, you are encouraged to play with the GBN applet (an awesome applet!) at thecompanion Web site.Figure 3.19 shows the sender’s view of the range of sequence numbers in a GBNprotocol. If we define base to be the sequence number of the oldest unacknowledgedpacket and nextseqnum to be the smallest unused sequence number (that is, thesequence number of the next packet to be sent), then four intervals in the range ofsequence numbers can be identified. Sequence numbers in the interval [0,base-1]correspond to packets that have already been transmitted and acknowledged. The interval[base,nextseqnum-1] corresponds to packets that have been sent but not yetacknowledged. Sequence numbers in the interval [nextseqnum,base+N-1] can
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