Subject: What on earth is the difference in broadcast and Multicast?

From: Jian Bo Huang <[email-masked]>
Date: Wed, 14 Aug 2002 00:52:16 +0100

Hello, All,
 
I am doing something in Multicast service in UMTS. Found something
confusing.
 
If a service broadcast (?) / multicast (?) data  to a Routeing Area, it
does not stop even if there is no any member in the RA, but it do have
explicit join / query / response / leave procedures.
 
What Can I call it? Broadcast or Multicast?
 
From the definition of Multicast, we can say it is a multicast for the
data to send to a group of users. But it is more like broadcast because
there isn't distribution tree truncate when no member in a RA.
 
Thank you!
 
Truly yours,
 
Jian Bo Huang
MSc Student
 
Department of Electronic Engineering,
University of Surrey
Guildford, Surrey
GU2 7XH, UK
Email: [email-masked]

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From: Fred Baker <[email-masked]>
Date: Tue, 13 Aug 2002 18:11:21 -0700

Multicast is the case where one or more messages sent in a network is 
routed to a generalized subset of the systems in the network, including the 
null set, all of them, or any level in between.

Unicast is the special case of that in which it is sent to exactly one of 
the systems, at least on the ultimate hop.

Broadcast is the special case in which it is sent to all of them.

Clearly there are algorithmic differences here. When I send to all the 
devices in a network, it is possible to use (as Novell Netware did at one 
time) an algorithm in which a router only accepts transmissions that 
succeed in an URPF test (we only accept messages from the interface[s] that 
we would use to forward a message to the source address of the message), 
and forwards them to all of its other interfaces. In unicast routing, there 
is a pretty specific network map generated. But in multicast routing, where 
one might send to any possible subset of the systems, one has to have some 
variation on joining and leaving the group and figuring out what subset of 
the links a message should be repeated on at each router.