The following items are independent of each other unless stated otherwise. (a) C
ID: 658553 • Letter: T
Question
The following items are independent of each other unless stated otherwise.
(a) Consider a TCP source whose destination is 10 hops away, the round-trip propagation
delay is 100 ms, the transmission time is negligible, and the bandwidth of the slowest link
in the path is 10 Mbits/sec. Assume no other connection shares the path with this source.
What should be the optimum window size for TCP? (i.e., a window size that maximizes
throughout but minimizes congestion).
(b) Assume the slow-start-threshold is 5000 bytes, the congestion-window size is 10,000 bytes,
the maximum-segment size is 500 bytes, let the round-trip time be 100 ms, and the number
of hops to the destination be 7. Assume the application continuously has data to send.
What is the congestion window size after 500 ms has ellapsed?
(c) Same as (b) above, except that the congestion-window-size is 500 bytes.
(d) Assume a packet with sequence number X is lost and a fast retransmission for X is
performed. About how much time will elapse from the moment X is transmitted the first
time until the X is retransmitted? Briefly explain why.
Explanation / Answer
a)
Bandwidth per second * round trip latency = TCP window size/8 = TCP window size in bytes
10240 * 100 =TCP window size
1024000 bits/8=1,28,000 bytes
d)
In TCP Retransmission, new connection requests, the retransmission timer is 3 seconds, and the resent request (SYN) is up to TcpMaxConnectRetransmissions times. The default for Windows 2000 & XP is 2 times, Windows NT 4.0 is 3 times.
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