Subject: RE: [ANCP] Multicast in ANCP

From: <[email-masked]>
Date: Wed, 7 Mar 2007 14:19:26 +0530

My view on use of ANCP for multicast is as follows:

As defined the ANCP framework draft, the Access Node could get the
subscribers configuration for Multicast from the NAS. This would
typically include the list of channels authorized to view by the
subscribers connected to user ports.

Having said that, whether the Access Node gets the subscribers
configuration list from the NAS using PUSH or PULL mechanism and whether
Access Node gets the list statically or dynamically (or every few time
intervals) should be left to implementation specific. I think we don't
need to mention about this in any of ANCP drafts. The objective is to
get the configuration information from the NAS.

Now, what Access Node can possibly do with the subscriber configuration
(specically channel entitlement list)? The main usage of this list I see
is, the Access Node (which is performing IGMP snoop or IGMP proxy) can
start replicating the channel to a suscriber based on the channel
entitlement list. 

Consider a case, if user post '5' is already subscribed to channel 'x',
if user port '10' issue a join message to receive channel 'x', the
Access Node could decide to replicate the channel 'x' to user port '10'
based on the authorization list. This way the channel zap time would be
faster.

Again an optimization could be that Access Node after exchancing channel
authorization list could subscribe to all/all the premium channels which
user ports are entitiled to join, and start replicating to user ports
(based on authorization list)as when the join requests come. This is
debatable and asolutely an implementation issue. We don't need to cover
this in any of ANCP drafts.

On the downside of ANCP use case for multicast, I see ANCP serves no
purpose, when two subscribers (two Set-Top-Boxes) are attached to a
single user port, where application based authorization (based on
encryption/decryption) would be a better choice.

My answer to Mtthew's point in below mail below would be,

1. I don't see a need to specify any use case in the framework draft,
since this draft already talks about exchanging the subscriber related
information between Access Node and NAS for multicast purposes at high
level. It should be left to implementation how this information is used
in Access Node or how this information is exchanced with NAS.

2. Never the less, the protocol draft could include message type, format
and associated TLVs for exchanging the multicast related subscriber
information between the Access Node and NAS.

Comments are welcome.

Rgds,
Sathiya

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]
Sent: Tuesday, March 06, 2007 7:19 PM
To: [email-masked]
Subject: [ANCP] Multicast in ANCP

I would like to start a discussion on what the working group would like
to do with Multicast in ANCP.

Currently the ANCP charter includes multicast as one of the use cases,
as
follows:

"When multicast replication for subscriber-bound traffic is performed at
the AN, it off-loads the network between the AN and NAS. However, a
subscriber's policy and configuration for multicast traffic may only be
known at the NAS. ANCP will provide a mechanism to communicate the
necessary information exchange between the AN and NAS so as to allow the
AN to perform subscriber bound multicast group replication in line with
the subscriber's policy and configuration, and also allow the NAS to
follow each subscriber's multicast group membership."

The framework draft (draft-ietf-ancp-framework-01.txt) says that the
access loop configuration mechanisms may be useful for setting the
per-Subscriber multicast channel entitlement information, used for IPTV
applications where the Access Node is performing IGMP snooping or IGMP
proxy function. It goes on to say that a Subscriber's policy and
configuration for multicast traffic might only be known at the NAS. The
Access Node Control Mechanism could be used to exchange the necessary
information between the Access Node and the NAS so as to allow the
Access Node to perform multicast replication in line with  the
Subscriber's policy and configuration, and also allow the NAS to follow
each Subscriber's multicast group membership.

None of these multicast mechanisms are defined in the ANCP protocol
draft, and I think there is insufficient detail in the framework draft
to fully specify this use case.

There has been very little work on this since the charter discussions,
but the ANCP working group needs to clarify what it wants to do (if
anything) with multicast for the framework can move forward. I think
there are two
choices: Either we should clarify the use case and specify the ANCP
protocol to support it, or we should remove the multicast use case from
the framework for now.

Please post your opinions to the list. We plan to have a discussion on
this in Prague, and to try to reach a consensus at around that time.

Best regards,

Matthew

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