[Netalyzr] What is TCP Connection Setup Latency?

Nicholas Weaver nweaver at ICSI.Berkeley.EDU
Fri Mar 23 23:16:55 PDT 2012

On Mar 23, 2012, at 11:13 PM, Christian Kreibich wrote:
>> I was guessing the TCP connection setup latency should be roughly 3x the
>> network latency because it takes three packets (for ack, syn-ack, syn).
>> But today I'm getting 50ms for the network latency and 54 seconds for
>> the TCP connection setup latency, so my theory is obviously incorrect.

Although TCP setup latency should, in most systems, be equivalent to the estimated RTT, since we are recording the time it takes the Connect() call to complete, which usually returns when the host receives the SYN-ACK.

When it is substantially longer, it suggests something is slowing down TCP handshakes without slowing down the network (eg, a process which checks or prompts for new connections).

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