Re: Multicast Query

["Marshall Eubanks" <tme@multicasttech.com>]

On Fri, 03 Dec 2004 09:22:02 +0000
 Gorry Fairhurst <gorry@erg.abdn.ac.uk> wrote:
> Krishna Vora wrote:
> > Hi,
> > 
> > I would like to have some information regarding use of Multicast IP for
> > a DVB-S Set Top Box scenario. Is the STB user required to first contact
> > some network centre to be a part of a multicast group. 
> > Similarly how is the multicast MAC addressing done?
> > 

Multicast group address allocations are described by rfc3171 (and its references)

http://www.ietf.org/rfc/rfc3171.txt

The 239/8 address range is analgous to 10/8 for unicast (i.e., these are internal addresses that can
be used freely as long as they don't leak out).


> > 
> 
> In ULE the rules for multicast MAC addressing are described in section 4.5,
> 
> " 4.5 SNDU Destination Address Field
> 
>     The SNDU Destination Address Field is optional (see section 4.1).
>     This field MUST be carried (i.e. D=0) for IP unicast packets
>     destined to routers that are sent using shared links (i.e., where
>     the same link connects multiple Receivers). A sender MAY omit this
>     field (D=1) for an IP unicast packet and/or multicast packets
>     delivered to Receivers that are able to utilise a discriminator
>     field (e.g. the IPv4/IPv6 destination address), which in combination
>     with the PID value, could be interpreted as a Link-Level address.
> 
>     When the SNDU header indicates the presence of a SNDU Destination
>     Address field (i.e. D=0), a Network Point of Attachment, NPA, field
>     directly follows the SNDU Type Field.  NPA destination addresses are
>     6 Byte numbers, normally expressed in hexadecimal, used to identify
>     the Receiver(s) in a MPEG-2 transmission network that should process
>     a received SNDU. The value 0x00:00:00:00:00:00, MUST NOT be used as
>     a destination address in a SNDU. The least significant bit of the
>     first byte of the address is set to 1 for multicast frames, and th


In IP multicast, there is a mapping  between the IP Group address
of the multicast, and the MAC address. For example, in IPv4,
multicast MAC addresses start with 01:00:5E, followed by a zero bit, followed
by the low order 23 bits of the multicast group address. Was there a 
specific reason why not to follow this ?

Regards
Marshall Eubanks


>     remaining bytes specify the link layer multicast address. The
>     specific value 0xFF:FF:FF:FF:FF:FF is the link broadcast address,
>     indicating this SNDU is to be delivered to all Receivers. "
> 
> The draft is available from:
> 
> http://www.ietf.org/internet-drafts/draft-ietf-ipdvb-ule-03.txt
> 
> Gorry
>