From: Scott Morris (swm@emanon.com)
Date: Sat Feb 10 2007 - 01:53:38 ART
SSM is Source-Specific Multicast. Which is wholly a choice to be made by
the client joining. Typically a client joins a group. Doesn't care (or
possibly even know) where this source comes from, just joins it.
Think of it like television. You want to watch something on NBC. There are
MANY different cities that NBC feeds run in, and perhaps you don't know or
care what city you are in. You just turn on the TV to something that says
NBC and you get the TV shows you want.
In a larger city, perhaps you have multiple choices, two affiliates of the
NBC network. And you happen to like one better than the other. NOW you are
into source-specific where you know you want the group "NBC" but you really
prefer the stuff from source 1.1.1.1 instead of 2.2.2.2... Perhaps in the
networking world it's a latency thing, or political thing, or a "just
because" thing. But you make a choice.
SSM gives you that choice. Well ... Ok... IGMPv3, v3lite or URD actually
give you that choice as a client, but SSM makes the transport happen.
More generically, you may see (S,G) and (*,G) notations. This has to do
with the efficiency of multicast moving through your network and whether you
have a better efficient path through the RP (*,G) or directly from the
source (S,G). Two different concepts at a theorhetical level though.
SSM does make some changes in the details of the (S,G) operations, but those
details may be beyond the level of caring for what we need to do in a lab
environment to get this working. The * represents shared tree talking
through the RP though. Nothing directly to do with SSM.
So even in a small organization, whether (*,G) and (S,G) are the same has to
do with your network architecture, not with whether you're using SSM or not.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
johngibson1541@yahoo.com
Sent: Friday, February 09, 2007 11:42 PM
To: ccielab@groupstudy.com
Subject: don't understand how SSM can be superior than just SM
SSM is designed for one-to-many.
If there is only 1 source in our administration , (S,G) and (*,G) are the
same.
Because * implies our only source.
Maybe the only advantage is that we don't need to configure any RP ?
John
This archive was generated by hypermail 2.1.4 : Thu Mar 01 2007 - 07:38:46 ART