[Network] Transport Layer 2

Transport Layer 2

Pipelined protocols

• Sender allows multiple “in-flight”, yet-to-be-acknowledged packets

• Go-back-N (sliding window protocol)
  • Sender can have up to N unacked packets in pipeline (if problem happen, then send N packets)
  • Receiver only sends cumulative ACK (Doesn’t ack packet if there’s a gap)
  • When Receiver receive Out-of-order packet, then discard(don’t buffer)
  • Sender has timer for oldest unacked packet (When timer expires, retransmit all unacked packets)
• Selective Repeat
  • Sender can have up to N unacked packets in pipeline
  • Receiver sends individual ack for each packet
  • Sender maintains timer for each unacked packet (When timer expires, retransmit only that unacked packet)

Go-back-N

• Scenario

• Window size problem

Selective repeat

Scenario

• No problem

• Problem (Sequence number size < sender’s window size + receiver’s window size)

• Solution (Sequence number size >= sender’s window size + receiver’s window size)