Question

While sending packets across a network, how can one determine where one packet ends and where another starts?

Is sending/receiving acknowledgment one of the ways of doing so?

Answer 1

I assume here that you mean application-level ‘packets’.

If you use UDP, you don’t need to since it’s a message protocol. TCP is a byte streaming protocol, so it cannot send packets, just bytes. If you need to send anything more complex than a byte-stream across TCP, you have to add another protocol on top – HTTP is one such protocol. Text is fairly easy since lines have terminating characters, usually CR/LF/CRLF. Sending non-text messages will require a different protocol.

One approach that is often used with TCP is to connect, stream a protocol-unit, disconnect. This works OK, but slowly because of the huge latency of continually opening and closing TCP connections. HTTP usually works like this in order to serve up web pages to large numbers of users who, if left permanently connected while they viewed pages, would needlessly use up all the server sockets.

Waiting for an application-level ACK from the peer is sometimes necessary if it absolutely essential that peer receipt is known before the next message is sent, but again, this is slow because of the connection latency. TCP was not designed with this approach in mind.

If the commonly available IP protocols cannot directly provide what you need, you will have to resort to implementing your own.

What sort of ‘packet’ are you sending?

Rgds,
Martin