tcp dummy's question;
udp has "message length" in it's header but tcp doesn't.
how tcp knows length?
thanks,

This is because there is no concept of a message in a TCP connection.
TCP is a stream oriented protocol, so if you need to correlate
input/output streams into a data structure, for instance, you will need
to develop a protocol to exchange your structures over the TCP stream.
UDP, on the other hand, relies on discrete datagrams to pass data back
and forth, so you are able to nicely encapsulate one 'message' per
recv.


jim wrote:
> tcp dummy's question;
> udp has "message length" in it's header but tcp doesn't.
> how tcp knows length?
> thanks,

In article <1161301279.190162.54570@h48g2000cwc.googlegroups. com>,
"baringforge@gmail.com" <baringforge@gmail.com> wrote:
> jim wrote:
> > tcp dummy's question;
> > udp has "message length" in it's header but tcp doesn't.
> > how tcp knows length?
> > thanks,

> This is because there is no concept of a message in a TCP connection.
> TCP is a stream oriented protocol, so if you need to correlate
> input/output streams into a data structure, for instance, you will need
> to develop a protocol to exchange your structures over the TCP stream.
> UDP, on the other hand, relies on discrete datagrams to pass data back
> and forth, so you are able to nicely encapsulate one 'message' per
> recv.

I don't think you're answering the question he asked. I think he wants
to know how TCP knows the *segment* length, since there's no length
field in the header.

It does this by knowing the length of the IP payload that the segment is
contained in, and the length of the TCP header. It subtracts the header
length from the payload length, and that's the length of the TCP
segment's payload.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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