Re: AS/400 IP COMMUNICATION WAIT TIME

[Jim Langston <jlangston@xxxxxxxxxxxxxxxx>]

Bob,

Actually, HTTP does use connection based, but in short
spurts.  The way HTTP works is the client requests a
file from the server, the client connects and establishes
a connection, then the client requests the file, the server
sends the file and closes the connection.  Every graphic
you see on a web page was actually downloaded using
a separate connection.  TCP is connection based, it's
just that HTTP is not.  Although it uses TCP to get the
files.  If you were receiving a web page file from a
HTTP sever and disconnected your ether net and plugged
it back in in the middle of the transfer, you would not
receive the rest of the file.  Unless you hit "refresh" and
then it would download the whole thing again.

UDP is used for broadcasting because it is not permanent
connection based.

Regards,

Jim Langston

Bob Crothers wrote:

> Jim,
>
> You've got it mostly right.  Except the part about TCP being "Connection
> Based".  It does not have to be that way.  Look at HTTP.  The connection is
> not maintained for the duration of the session.  Only while data is being
> exchanged.  Other protocols/applications are different.  Telnet is
> connection based.  FTP is actually both.  The control part of the
> conversation is connection based, but data is exchanged over a
> connectionless conversation.  And custom applications can be how ever you
> want them.
>
> The main difference between TCP & UDP is that when you send data via TCP, it
> is guaranteed to not only arrive at the destination (or cause an error) but
> also in the same order you send it.
>
> When you send with UDP, not only is the data NOT guaranteed to arrive at the
> destination, but the data MIGHT be out of order.  As a result, UDP tends to
> be used for "trivial" things (like ping) or broadcast where each byte of
> data is not that important (streaming sound/video).
>
> Bob

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