Why Does Persistent HTTP Have an Extra RTT?

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SUMMARY

The discussion centers on the additional round-trip time (RTT) incurred in persistent HTTP connections. The user initially calculated the total time as RTT1 + ... + RTTn + (2 * RTT0), but realized an extra RTT0 is necessary due to the requirement of first requesting the base HTML file before the client can request additional objects. This results in two distinct RTTs for the initial handshake and the subsequent requests for embedded resources. The conclusion confirms that the extra RTT is indeed due to the sequential nature of HTTP requests in persistent connections.

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  • Understanding of HTTP/1.1 persistent connections
  • Knowledge of round-trip time (RTT) in network communications
  • Familiarity with DNS resolution processes
  • Basic concepts of client-server architecture
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perplexabot
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Hello all. I am trying to understand number 2c of this pdf:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDEQFjAA&url=http%3A%2F%2Fwww.nyu.edu%2Fclasses%2Fjcf%2FCSCI-GA.2262-001_fa12%2Fhandouts%2FHomework2Solutions.pdf&ei=DX1sUurmCeOYiQKnwYFg&usg=AFQjCNElBG4mGrEvpyPHCu4HeWcWQYGxSA&sig2=0D9G34-MeX0IDDOVNdZWhQ&bvm=bv.55123115,d.cGE.

I have tried solving it on my own but I got the wrong answer. I am starting to get irritated.

How I solved the problem:
Time for DNS to supply client with IP: RTT1 + ... + RTTn
Time for client to have initial handshake: RTT0
Time for client to receive all message: RTT0

Total time = RTT1 + ... + RTTn + RTT0 + RTT0 = RTT1 + ... + RTTn + (2 * RTT0)

According to the answer I am missing a RTT0. I have no idea where that extra RTT0 comes from. May someone please help me out?
 
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I think I realize why now. Is it because, first you have to request the base HTML file, and it is until this file is received at the client that the client can go on and ask about the objects contained in that HTML file? Hence, two different RTTs will occur.

Can someone confirm this?
 
perplexabot said:
I think I realize why now. Is it because, first you have to request the base HTML file, and it is until this file is received at the client that the client can go on and ask about the objects contained in that HTML file? Hence, two different RTTs will occur.

Can someone confirm this?

Seems right to me.
 

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