2. Go-Back-N protocol Concept Introduce a window of size n Can inject n packets on net before hearing an ACK Each packet is labeled with a sequence number.
3. ADVANTAGES OF GO-BACK N The sender can send many frames at a time. Timer can be set for a group of frames. One ACK can acknowledge more than one frames. Efficiency is more.
4. DISADVANTAGES Buffer requirement. Transmitter needs to store the last N packets. Scheme is inefficient when delay is large and data transmission rate is high. Unnecessary Retransmission of many error-free packets.
5. Selective Repeat Protocol Go-Back-N inefficient because multiple frames are resent when errors or losses occur. SR protocol retransmits only an individual frame containing the error. Buffer is provided in this case.