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[ANCP] RE: Multicast Admission Control issues.
Hi Peter,
Your comments regarding to the admission control for multiple flows
are absolutely correct, in fact the draft does not complete address the
scenarios that you mentioned. What we first had in mind for these cases
was to give the NAS the capability to specify how many multicast flows
belonging to the same flow group can be simultaneously accepted by AN,
but there were some additional comments on flow group concept raised by
Sanjay on the mailing list (see below) thus I think we may need more
discussion and inputs from the working group in order to finalize what
will be the admission control mechanism for multiple flow.
Thanks and best regards,
Roberta
The message flows indicate that the replication always starts for a
given flow on reception of an "Admission Response" for that flow. This
might not always be true. There are atleast two conditions here:
(a) A Join for a different flow in the same flow-group is received by
the AN due to a channel change, before the admission response is
received for the pending request. In this case one would assume the
admission response is still applicable (since it is for the flow-group)
and the replication for the new flow can commence.
(b) A new Join for a different flow in a different flow-group (e.g.
going from an SD to a HD flow) might be received while admission
response for the old join is still pending. In this case another
admission request is generated and no replication happens.
Message flows or text is needed to indicate these scenarios.
-------------------------------------------------------
Roberta Maglione - CCIE #18425
Telecom Italia
Broadband Network Services Innovation
-------------------------------------------------------
-----Original Message-----
From: peter.naveen at wipro.com [mailto:peter.naveen at wipro.com]
Sent: Monday, January 14, 2008 12:36 PM
To: ancp at ietf.org
Cc: Maglione Roberta; Garofalo Angelo
Subject: Multicast Admission Control issues.
Hi,
The protocol defined in draft-maglione-ancp-mcast-00.txt may not scale
well for multiple flows per Access Port.
There exists a scenario where the user (behind the Access Port) can
request for a new channel when the first channel is still being streamed
on his Access Port, that is, a join is sent by the user for the 2nd flow
without leave being sent for the 1st flow. As per the draft, AN will
honor the 2nd flow as that flow group was already
authorized/authenticated by the NAS, when Admission Request was sent for
the 1st flow (by AN to NAS) for the 1st flow of that flow group. This
will cause issues if sum of the bandwidth demanded by 1st and 2nd flow
exceeds the DSL synch up rate of the Access Port.
A similar issue might exist with White list configuration as well. As
per the draft, AN does not need to consult with NAS for channels listed
in white list. In this case,
* The bandwidth demanded by a channel in White list may be more than
the DSL sync up rate on the Access Port.
* The sum of the bandwidth demanded by the 1st and subsequent White
list channels on an Access Port may be more than the DSL sync up rate on
the Access Port.
In both the scenarios, explained above, NAS is not aware of the Access
Port bandwidth used by,
* White list channels Joined.
* 2nd and subsequent flows (of an already authenticated Flow group)
Joined.
NOTE: The protocol seems to address only the "Conditional Access"
requirement but not the "Admission control" for multiple flows. Also the
"Multicast Accounting" requirement for "Joins of White list channels"
and "Joins of 2nd and subsequent flows of a flow group" are not
addressed, as there is no NAS-AN communication for these cases.
Regards,
Peter
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