Subject: Re: Socket Programming
From: (Rob Warnock)
Date: Wed, 02 Jun 2004 05:02:47 -0500
Newsgroups: comp.lang.lisp
Message-ID: <>
Antony Sequeira  <> wrote:
| Antony Sequeira wrote:
| > The serialized print of the socket obtained by 'ss.accept()'
| > looks something like
| >    Socket[addr=/,port=2126,localport=9876]
| >    Socket[addr=/,port=2128,localport=9876]
| > 
| > I guess this is the socket port versus TCP port confusion that
| > Harald Hanche-Olsen was referring to.
| > 
| Bad guess :(, the 'port' refers to the port number on the remote host to 
| which the socket is connected.

Correct: A TCP[1] connection is defined by a quadruple: {Local address,
Local port, Remote address, Remote port}. If *any* element of that
quadruple is different, you have a different connection. Therefore
*many* TCP connections may have the same Local address/Local port


[1] More generally, many (most?) IP/TCP/UDP/xxx-over-IP protocol stacks
    (at least the connection-oriented ones and others that use "ports")
    have some notion of a Protocol Control Block (PCB), which is identified
    when receiving a packet by a quintuple: {Local address, Local port,
    Remote port, Remote address, IP-protocol-type} [where IP-protocol-type
    is TCP (6), UDP (17), or any of the other protocol numbers found in
    "/etc/protocols" (at least on Unix systems). To a rough approximation,
    PCBs are one-to-one with sockets.

Rob Warnock			<>
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