But how long must the sender wait to be certain that something has been lost?
The sender must clearly wait at least as long as a round-trip delay between the
sender and receiver (which may include buffering at intermediate routers) plus
whatever amount of time is needed to process a packet at the receiver. In many networks, this worst-case maximum delay is very difficult even to estimate, much less
know with certainty. Moreover, the protocol should ideally recover from packet
loss as soon as possible; waiting for a worst-case delay could mean a long wait
until error recovery is initiated. The approach thus adopted in practice is for the
sender to judiciously choose a time value such that packet loss is likely, although
not guaranteed, to have happened. If an ACK is not received within this time, the
packet is retransmitted. Note that if a packet experiences a particularly large delay,
the sender may retransmit the packet even though neither the data packet nor its
ACK have been lost. This introduces the possibility of duplicate data packets in
But how long must the sender wait to be certain that something has been lost?The sender must clearly wait at least as long as a round-trip delay between thesender and receiver (which may include buffering at intermediate routers) pluswhatever amount of time is needed to process a packet at the receiver. In many networks, this worst-case maximum delay is very difficult even to estimate, much lessknow with certainty. Moreover, the protocol should ideally recover from packetloss as soon as possible; waiting for a worst-case delay could mean a long waituntil error recovery is initiated. The approach thus adopted in practice is for thesender to judiciously choose a time value such that packet loss is likely, althoughnot guaranteed, to have happened. If an ACK is not received within this time, thepacket is retransmitted. Note that if a packet experiences a particularly large delay,the sender may retransmit the packet even though neither the data packet nor itsACK have been lost. This introduces the possibility of duplicate data packets in
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