Re: [splices] Using Two Separate Devices to Start a Conversation proposal

[Peter Musgrave <[e-mail]>]

HI Rifaat,

I have concerns about this approach. Fundamentally the RTP stream is not
symmetric (in the sense of RFC4961). This has consequences for NAT
traversal, general interoperability and media path security schemes like
ZRTP.

I think an approach in which one of the loosely coupled endpoints acts as a
media relay would eliminate all these issues. It can then source and sink
audio on the same port to the external device and provide the appearance of
symmetric RTP. (This approach would also have merit in the case where one LC
endpoint does audio and the other does video since there is now an RTP/RTCP
path between the endpoints for exchanging data for the purposes of
lipsync).

I recognize this imposes an additional role of relaying media in the
implementation of a LC device - but if the objective is to be interoperable
with non LC devices "in the wild" - I see no other alternative.

Regards,

Peter

On Thu, May 26, 2011 at 8:37 PM, Shekh-Yusef, Rifaat (Rifaat) <
[e-mail]> wrote:

> Hi,
>
> The following proposal is to cover the first use case in the disaggregated
> media draft.
>
> Regards,
>  Rifaat
>
>
>   Alice                 Alice                Proxy                  Bob
>    PC                 Desk Phone
>    |                     |                     |                     |
>    |                     |                     |                     |
> Both Alice's devices subscribe to the reg event package, which allows each
> device to
> discover the capabilities of the other device based on the feature tags
> provided by each device.
> The Desk Phone knows that the PC supports Video, while the PC knows that
> the Desk Phone only supports audio.
>    |                     |                     |                     |
>    |                     | SUBSCRIBE reg       |                     |
>    |                     |-------------------->|                     |
>    |                     | 200 OK              |                     |
>    |                     |<--------------------|                     |
>    |                     |                     |                     |
>    | SUBSCRIBE reg       |                     |                     |
>    |------------------------------------------>|                     |
>    | 200 OK              |                     |                     |
>    |<------------------------------------------|                     |
>    |                     |                     |                     |
>    |                     |                     |                     |
> The two devices also subscribe to the dialog of each other.
>    |                     |                     |                     |
>    |                     |                     |                     |
>    | SUBSCRIBE dialog    |                     |                     |
>    |-------------------->|                     |                     |
>    | 200 OK              |                     |                     |
>    |<--------------------|                     |                     |
>    |                     |                     |                     |
>    | SUBSCRIBE dialog    |                     |                     |
>    |<--------------------|                     |                     |
>    | 200 OK              |                     |                     |
>    |-------------------->|                     |                     |
>    |                     |                     |                     |
>    |                     |                     |                     |
>
>
>
> Alice wants to initiate a call to Bob, but wants to use her Desk Phone to
> receive the audio from Bob and use her PC to send audio to Bob.
> The PC instructs the Desk Phone to initiate a call to Bob in a receive only
> mode.
>
>    |                     |                     |                     |
>    | INVOKE Action:
> urn:invoke:call:initiate;media=audio;direction=recvonly;target=bob@whatever
>    |-------------------->|                     |                     |
>    | OK                  |                     |                     |
>    |<--------------------|                     |                     |
>    |                     | INVITE [recvonly]   |                     |
>    |                     |-------------------->|                     |
>    |                     |                     | INVITE [recvonly]   |
>    |                     |                     |-------------------->|
>    |                     |                     | 180                 |
>    |                     | 180                 |<--------------------|
>    |                     |<--------------------|                     |
>    |                     |                     | 200 OK              |
>    |                     | 200 OK              |<--------------------|
>    |                     |<--------------------|                     |
>    |                     |                     |                     |
> As soon as Bob answers the call, a NOTIFY is sent to Alice's PC (dialog
> event package)
>    |                     |                     |                     |
>    | NOTIFY              |                     |                     |
>    |<--------------------|                     |                     |
>    | OK                  |                     |                     |
>    |-------------------->|                     |                     |
>    |                     |                     |                     |
> PC sends a new INVITE with Join with a sendonly SDP offer
>    |                     |                     |                     |
>    | INVITE Join [sendonly]                    |                     |
>    |-------------------->|                     |                     |
>    | 100 Trying          |                     |                     |
>    |<--------------------|                     |                     |
>    |                     |                     |                     |
>    |                     | re-INVITE [sendrecv]|                     |
>    |                     |-------------------->|                     |
>    |                     |                     | re-INVITE [sendrecv]|
>    |                     |                     |-------------------->|
>    |                     |                     | 200 OK              |
>    |                     | 200 OK              |<--------------------|
>    |                     |<--------------------|                     |
>    | 200 OK              |                     |                     |
>    |<--------------------|                     |                     |
>    |                     |                     |                     |
>    |                     |                     |                     |
>    |<----dialog2-------->|<---dialog1------------------------------->|
>    |                     |                     |                     |
>    |                     |<======audio===============================|
>    |=============================audio==============================>|
>    |                     |                     |                     |
>    |                     |                     |                     |
>
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