Understanding TCP/IP Model Internals and Interfaces

1508 Understanding TCP/IP Model Internals and Interfaces
Lab 2: TCP Flavor Comparison
Background
TCP detects a packet loss when:
• Retransmission timer expires, or
• n-th duplicate acknowledgement is received for the connection.
TCP flavors differ in how they respond to packet loss. While all TCP implementations reset the
congestion window after retransmission timeout expiration to one maximum segment size (MSS),
they may proceed differently after duplicate ACKs are received. The missing segment is always
resent immediately, but transmission of new or unacknowledged data depends on the selected flavor.
We will compare the following flavors:
• Tahoe—Fast retransmit followed by slow start
• Reno—Fast retransmit followed by fast recovery
• New Reno—Similar to Reno, but does not halve congestion window multiple times during
recovery process
• Selective acknowledgement (SACK)—Selective retransmission based on received selective
acknowledgements
• Reno with Explicit Congestion Notification (ECN) – similar to Reno, but has ability to
process congestion notification from network upon which it performs fast recovery
Objective
We will study TCP behavior after three segments are dropped from the same window of data. The
following graph shows the sequence numbers of sent and dropped segments.
Dropped
segments
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