Question

Give one example where buffering out-of-order segments would significantly improve the throughput of a GBN protocol.

Answer 1

Go-Back-N Protocol to improve throughput for out of order segments:

• Following figure illustrates Go-Back-N protocol out of order example.
• In this two host are communicate with each other, host A and host B.
• First host A sent sequence number 120 with string "xyz" to host B then host B gives acknowledgment number 123 to host A.
• In second sequence host A sent sequence number 123 with string "abcd" to host B but due to communication error string not received by host B.
• In third sequence host A sent sequence number 127 with string "ef" to host B but host B provides acknowledgement out of sequence to host A.
• In fourth sequence host A sent sequence number 129 with string "gh" to host B but again host B provides acknowledgement out of sequence to host A, this condition is called as out-of-order segment in Go-Back-N protocol.
• To avoid this condition the sender host must follows sequence number with pipeline concept. It means it process the sequence string in the given pipeline sequence only.
• Following figure illustrates the improved performance of Go-Back-N:
• In above figure it shows in case of data 2 the receiver gives negative acknowledgement to sender then sender resend the given segment again.
• This process is in given pipeline only and it avoids the out-of-order sequence in Go-Back-N protocol.