Subject: Clarification on MCAP message format

From: Ganesh S <[email-masked]>
Date: Thu, 9 Sep 1999 12:52:27 +0530

Hello,

I need a clarification on the MCAP message format described in the
IP1394-ipv4 draft 16.

If i have more than one multicast group addresses, then how should the
MCAP message be framed.

1. Should the MCAP message data contain a MCAP group address descriptor
    header for each of the multicast group address, such as

MCAP header ( length, reserved, opcode )
MCAP message data containing
       12 bytes of MCAP group address descriptor header
       A multicast group address
       12 bytes of MCAP group address descriptor header
       A multicast group address
       ........

--- OR ---            

2. Should the MCAP message data contain  one MCAP group address descriptor
    header for set of multicast group addresses, such as 

MCAP header ( length, reserved, opcode )
MCAP message data containing
       12 bytes of MCAP group address descriptor header
       multicast group address 1
       multicast group address 2
       ......

The ambiguity is because, it appears from Figure 11 of the draft, that
the format should be as in 2 above, which seems to be more logical.
But from the description in section 9.1 of the draft, it appears 1 above 
is meant.

Please clarify.

Thanks,

Ganesh.S

---

From: "Hattig, Myron" <[email-masked]>
Date: Mon, 13 Sep 1999 10:52:10 -0700

Ganesh,

The answer to your question is 1. Each mapping is 1:1 from 1394 channel
number to IP multicast group address.
Thus if there are two IP multicast group addresses there must be two
separate entries or mappings. I looked over the text and figure 11 to see if
this is confusing. It is not confusing to me, but of course with my previous
context it probably would not be confusing.

One slight point of confusion has been the variable length a single mapping.
The variableness is to allow for IPv6 addresses someday in the future. It is
not to allow for a list of IP addresses. Hence the name of the field in
figure 11 is "group_address" not "group_addresses".

-myron

-----Original Message-----
From: Ganesh S [mailto:[email-masked]]
Sent: Thursday, September 09, 1999 12:22 AM
To: [email-masked]
Subject: Clarification on MCAP message format

Hello,

--- OR ---

Please clarify.

Thanks,

Ganesh.S