Tcp/Ip vs a store & forward network


Phil Karn (karn@ka9q.bellcore.com)
Sun, 29 Mar 87 23:58:42 EST


Actually, I thought the Internet WAS a store-and-forward network. Gateways
store up packets as they are received and forward them after a queueing
delay. I think you really meant "message switching" as opposed to "packet
switching".

But even this distinction is rather artificial. One of the most popular
message switching networks is UUCP. Like the Internet, each UUCP node also
stores up a block of information, makes a routing decision (sometimes
specified in a source route) and sends it on its way. The only real
differences are quantitative, i.e., the maximum allowable message size and
the typical end-to-end delivery delay, although admittedly they heavily
influence the way end-user nodes make use of the service. You *could* run
TCP on top of UUCP (encapsulating one segment per message) as long as it is
prepared to deal with RTTs of several days. On the other hand UDP
query-response applications use the Internet as though it were a message
switching network, since messages fit neatly into Internet datagrams.

Perhaps the only real qualitative distinction is whether the network is
useful for "real time" communications, however you define them. Nobody runs
SMTP/TCP/IP on UUCP because few are willing to wait several days for a TCP



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