Re: [MMUSIC] IETF#89: First version of CLUE Data Channel slide set.

["Makaraju, Maridi Raju (Raju)" <[e-mail]>]

+ mmusic to cover some of the discussions.

Hi,
Please see comments inline.

Hi,

For the gateway use-case, do we really need to indicate the SCTP stream during Offer/Answer?

Or, would it be enough if we indicate that the data channel is going to be used for CLUE, and the gateway then figures out which stream is used when it receives DCEP OPEN?
[Raju] This approach has 2 implications:

1.       The gateway needs to look at bearer packets and notify the signaling layer about the streams. Though possible, this is computationally intensive and new mechanism needed for such notification between bearer and signaling layers.

Why does it need to inform the signalling layer about the streams? The controller needs to tell the media gateway: "please let CLUE go through"
[Raju] "Please let CLUE through" is a simple scenario without much interworking and other needs.
I want to point out couple of other interworking scenarios:

1.       Lawful intercept (LI): A CLUE channel may have to be reported to LI agents per regulatory requirements. For various reasons such reporting may have to be interworked with non-data channel SCTP/dTLS transport (e.g. TCP).

2.       For Non-LI reasons, a CLUE could be interworked to a TCP based transport in an end-to-access-edge kind of approach.
In either of these cases, the media gateway will not be aware of how to do such interworkings. Even if controller can ask gateway ahead of time what to do (in a yet to be defined complex way by protocols like H.248/Megaco) then still gateway have to report the TCP transport address back to controller so that it can inform LI agents about this address.
Essentially, not having external negotiation will complicate other protocols (like H.248/Megaco MG-MGC protocol) and still won't avoid per-data channel notification to the signaling entity (controller). Please note that such "media gateway centric/driven" complex procedures may not even be allowed by H.248/Megaco as controllers wants be the one making such decisions as they happen.


2.       There could be several streams using the same subprotocol. Then how does gateway know which maps to what? CLUE may have just one data channel stream; but we may also have to think about CLUE combined with other data channels under same SCTP association. Even for single CLUE stream case item (1) is still an issue though.

The gateway is going to get DCEP for each subprotocol, so it knows which one is CLUE.
[Raju] As noted, since in this specific case there is one single CLUE data channel a gateway unambigously can map. But still the above mentioned interworking requires controller involvement as the data channels are open.

Regards
Raju

Regards,

Christer