Subject: Multicast Query

From: Krishna Vora <[email-masked]>
Date: 03 Dec 2004 11:14:23 +0530

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?

-- 
Regards,
Krishna Vora

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From: Gorry Fairhurst <[email-masked]>
Date: Fri, 03 Dec 2004 09:22:02 +0000

> Similarly how is the multicast MAC addressing done?

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 the
    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

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From: "Marshall Eubanks" <[email-masked]>
Date: Fri, 03 Dec 2004 10:03:16 -0500

On Fri, 03 Dec 2004 09:22:02 +0000
> > 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).

>     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

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From: Gorry Fairhurst <[email-masked]>
Date: Fri, 03 Dec 2004 15:40:22 +0000

> specific reason why not to follow this ?

The MAC address format in the spec above is consistent with what you say, (and 
also with the similar mapping used in IPv6). That is "01" in 01:00:5E sets bit 
zero of the first byte.

>>http://www.ietf.org/internet-drafts/draft-ietf-ipdvb-ule-03.txt

Gorry Fairhurst.