Datagrams Under UNIX IPC Domain in 4.2BSD

[gwyn%brl-vld at sri-unix.UUCP]

From:      Doug Gwyn (VLD/VMB) <gwyn at brl-vld>

User datagrams indeed are not useful for reliable communication, unless
you layer around them a reliable transport protocol.  The intention of
datagrams is to provide a cheap service for applications where delivery
of messages need NOT be guaranteed.  Most applications require a more
reliable message-passing mechanism.

Some possible datagram applications are:
	Net information servers, such as the "rwho" daemon.  It may not
	be too important to get EVERY update for such information so
	long as nobody trusts the absolute accuracy of the net status.

	Sampling data acquisition.  It may not be necessary to collect
	EVERY datum if you are randomly sampling something.

	System clock rate adjustments in a network.  Generally some
	slop in the relative clock rates must be permitted; it is okay
	to miss a few packets from the master time server so long as
	the rate is eventually tweaked on each host.

	Junk mail.  It is more important to have the transport done
	cheaply than it is to ensure delivery.