Subject: RE: [bmwg] measuring TCP connection setup on proxy firewalls

From: "Hickman, Brooks" <[email-masked]>
Date: Mon, 2 Apr 2001 15:25:19 -0700

Problem I see is actually performing the connection establishment time
measurement when a proxy is between the client and the server. Since the
proxy is going to terminate the TCP connection from the client and create
another connection from itself to the actual server, you are going to be
dealing with two separate connections. Question is how are you going to be
able to correlate the two connections in order to measure the connection
establishment time? Basically, the time from the client sending the first
SYN to the proxy to the actual server receiving the final ACK from the
proxy.

Since the methodology requires some data be sent across each connection in
order for the given connection to be considered valid, what about the data
including some signature field identifying the connection. This way, as soon
as data is received across a given connection, the timestamp of the
originating SYN from the client can be correlated with the final
ACK(Connection Setup handshaking) received on the server from the proxy. 

-----Original Message-----
From: Michael Richardson [mailto:[email-masked]]
Sent: Sunday, April 01, 2001 8:07 PM
To: [email-masked]
Subject: Re: [bmwg] measuring TCP connection setup on proxy firewalls 

>>>>> "David" == David Newman <[email-masked]> writes:
    >> I'm not sure which draft you are dealing with right now, but will you
    >> also include a statement that directly connected client<->server
setup
    >> time should be measured?

    David> Hi Michael,

    David> It's the firewall performance measurement methodology ID. And,
    David> yes, client-to-server setup time is DEFINITELY included.

    David> In a private email, someone else suggested another even simpler
    David> method than the one I proposed for proxy setup time: Measure
    David> client-to-server setup time with and without a proxy, and call
the
    David> delta proxy setup time. I like the simplicity of that approach --
    David> any reason we *shouldn't* use it instead of what I proposed?

  I was suggesting the same thing really.

  Except, that as you pointed out, with a three way handshake, it is hard to
know where the mark points are.

  I prefer your t4-t0 measurement myself.

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From: "David Newman" <[email-masked]>
Date: Mon, 2 Apr 2001 19:33:12 -0400

Brooks and I just discussed this. One problem with the foregoing is that it
relies on both client and server behavior. Embedding a signature in a data
packet might not isolate proxy behavior (or, as mcr puts it, to know where
the mark points are).

Take an extreme example where the proxy is 1 meter from the client and the
server is on Mars. Yes, a signature in a data packet would allow correlation
of client and server times, but it wouldn't be terribly useful in isolating
how much of client connection setup was attributable to the server, and how
much was attributable to the proxy.

Brooks also made an excellent point in saying why he prefers the t4-minus-t0
method over subtracting with-a-proxy time from without-a-proxy. The
t4-minus-t0 method has the advantage of being observable solely from the
client's perspective, which is probably a good thing.

dn

 -----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Hickman,
Brooks
Sent: Monday, April 02, 2001 6:25 PM
To: 'Michael Richardson'; [email-masked]
Subject: RE: [bmwg] measuring TCP connection setup on proxy firewalls

-----Original Message-----
From: Michael Richardson [mailto:[email-masked]]
Sent: Sunday, April 01, 2001 8:07 PM
To: [email-masked]
Subject: Re: [bmwg] measuring TCP connection setup on proxy firewalls

setup
    David> Hi Michael,