Re: Address allocation

[Marshall Eubanks <tme@21rst-century.com>]

Ali Boudani wrote:

> Hello,
> If all sources use the same G , there is no meaning of multicast group.
> because S1 ....Sn can use the same address G and in that case all the
> multicast world is using the same address G. So we can maybe just assign or
> allocate a single multicast address to all the multicast recievers in the
> internet and use the S just to differciate between them.
> Isnt true??
> Ali

What you say is true in principle.

This would cause problems in practice on Ethernet links, because of the mapping between
group addresses and MAC addresses is not unique -
see the discussion at the end of
http://www.multicasttech.com/faq/multicast_faq.html

Also, remember, for any given S, the sources must be unique. We
(for example) source 3 to 6 G for each S.

But SSM basically does remove any need to assign or allocate group addresses.

Note that not all multicast applications will migrate to SSM.

>
>
> Marshall Eubanks wrote:
>
> > Hello Ali;
> >
> > Ali Boudani wrote:
> > >
> > > I didnt understand the issue aof address allocation in ssm.?
> > > we have a source S and a receiver say R want to recieve informations
> > > from S.
> > > So in that case R should inform its DR by using IGMPv3.
> > > How R knows that he is a member of a group G and how is G is allocated?
> >
> > R knows he is a member of the group because he joined it ? If you
> > are asking "how does R know that a group exists to be joined ?",
> > this is done "out of band" - that is, you will know about SSM groups
> > because you have been informed about them in some other fashion, such
> > as by clicking on a button on a web page, or in an e-mail, etc., etc.
> >
> > The address G is allocated by the source. There are basically no
> > restrictions on G, except that it has to be kept in the 232/8
> > address range (for multicasts to the general Internet) and,
> > if you are sourcing more than one group from the same IP address, S,
> > you have to give them unique group  addresses, G.
> >
> > Also, from
> > http://www.ietf.org/internet-drafts/draft-holbrook-ssm-arch-02.txt
> >
> > The network service
> > identified by (S,G), for SSM address G and source host address S, is
> > referred to as a "channel."
> >
> > So the use of "Group" is considered obsolete !
> >
> > Again, from the above draft :
> >
> > The following table summarizes the terminology:
> >
> >   Service Model:        Any-Source          Source-Specific
> >   Network Abstraction:  group               channel
> >   Identifier:           G                   S,G
> >   Receiver Operations:  join, leave         subscribe, unsubscribe
> >
> > (Personally, I regard unnecessary changes in widely used terminology to be
> > unwise, but the rough consensus seems to have gone otherwise.)
> >
> > > is the address g is allocated by the application ??
> > >
> > > I just want to know the complete process because it is not clear in the
> > > drafts.
> > > thanx
> >
> >                                    Regards
> >                                    Marshall Eubanks
> >
> >
> >    Multicast Technologies, Inc.
> >    10301 Democracy Lane, Suite 410
> >    Fairfax, Virginia 22030
> >    Phone : 703-293-9624          Fax     : 703-293-9609
> >    e-mail : tme@on-the-i.com    http://www.on-the-i.com
> >
> >  Test your network for multicast : http://www.multicasttech.com/mt/




--
                                 Regards
                                 Marshall Eubanks


T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624
Fax     : 703-293-9609
e-mail : tme@multicasttech.com
http://www.on-the-i.com

Test your network for multicast : http://www.multicasttech.com/mt/