A client sends a 200 byte request message to a service, which produces a response containing 5000 bytes. Estimate the total time to complete the request in each of the following cases, with the performance assumptions listed below:
i) Using connectionless (datagram) communication (for example, UDP);
ii) Using connection-oriented communication (for example, TCP);
iii) The server process is in the same machine as the client.
[Latency per packet (local or remote,
incurred on both send and receive):5 milliseconds
Connection setup time (TCP only):5 milliseconds Data transfer rate:10 megabits per second MTU:1000 bytes
Server request processing time:2 milliseconds
Assume that the network is lightly loaded.]
The send and receive latencies include (operating system) software overheads as well as network delays.
Assuming that the former dominate, then the estimates are as below. If network overheads dominate, then the times may be reduced because the multiple response packets can be transmitted and received right after each other.
i) UDP: 5 + 2000/10000 + 2 + 5(5 + 10000/10000) = 37.2 milliseconds
ii) TCP: 5 + 5 + 2000/10000 + 2 + 5(5 + 10000/10000) = 42.2 milliseconds
iii)same machine: the messages can be sent by a single in memory copy; estimate interprocess data transfer rate at 40 megabits/second. Latency/message ~5 milliseconds. Time for server call:
5 + 2000/40000 + 5 + 50000/40000 = 11.3 milliseconds
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