none
Lync: Offer/Answer Exchange for multi-channel main-video modality - documentation missing RRS feed

  • Question

  • Hello,

    I have a question about the documentation for "Extensions for multi-channel main-video modality negotiation", specifically the "The client has discovered through some other means that the MCU conference supports a multi-channel main-video modality supporting up to six main-video streams (2)." on http://msdn.microsoft.com/en-us/library/hh656931(v=office.12).aspx .

    Please can a member of the docs / engineering team supply more information about how the client discovers this information?  When joining the MCU conference, how does the client know that up to six main-video streams are supported in the offer?

    Many thanks,

    Simon


    Sunday, October 12, 2014 3:31 PM

Answers

  • Hi Simon,

    In your original question you refer to [MS-SDPEXT] section “4.8 Offer/Answer Exchange for multi-channel main-video modality” asking how the client discovers the maximum number of main-video streams.

    The same document in sections 3.1.5.34 and 3.1.5.35 describes it. Section “3.1.5.34.2 User agent behavior for negotiating multiplexed media channels” states that the SDP offer contains the multiplexed “main-video” media descriptors. The number of the descriptors in the SDP offer is the maximum number of the “main-video” streams supported.

    The client creates an audio/video conference with INVITE, the server successful (200) answer contains the maximum number of the supported streams. In the capture below, please count the “a=label:main-video” attributes, there are six.

    m=video 62482 RTP/SAVP 122 121 123
    ……………………………………………………….
    a=candidate:5 2 tcp-act 1684796926 10.32.191.83 64584 typ srflx raddr 10.32.191.83 rport 64584
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    a=rtpmap:122 x-h264uc/90000
    ……………………………………………………….
    a=x-sourceid:MainCamera
    a=rtcp:62483
    a=ice-ufrag:gT+G
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    a=sendonly
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=rtpmap:123 x-ulpfecuc/90000

    I hope this answered your question.

    Thanks, Vilmos
    Tuesday, November 4, 2014 8:18 PM

All replies

  • Hi Simon,
    Thank you for this inquiry. One of our engineers will follow-up with you soon.

    Regards,

    Edgar

    Sunday, October 12, 2014 7:33 PM
    Moderator
  • Hi Simon,

    Thank you for your question. I am the engineer who will be working with you on this issue. I am currently researching the question and will provide you with an update soon.

    Regards,
    Vilmos Foltenyi - MSFT

    Tuesday, October 14, 2014 8:51 PM
  • Hi Vilmos,

    Any updates on this? It's been over a week. 

    Many thanks,

    Simon

    Tuesday, October 21, 2014 8:33 PM
  • Hi Simon,

    Thank you for your patience. I‘m still researching your question, I asked other groups, too. Soon I’ll provide you with the finding.

    Thanks, Vilmos

    Wednesday, October 22, 2014 5:20 PM
  • Hi Simon,

    Thank you for your patience. The SDP is using SIP as the transport protocol. SIP is defined by
    RFC 3261 SIP: Session Initiation Protocol

    Chapter “11 Querying for Capabilities” states:

    “The SIP method OPTIONS allows a UA to query another UA or a proxy server as to its capabilities. This allows a client to discover information about the supported methods, content types, extensions, codecs, etc.”

    This would provide the user agent one means to discover the video capabilities mentioned in the section 4.8 text you cited. Does this help? If not, please clarify your question.

    Thanks, Vilmos
    Monday, October 27, 2014 11:13 PM
  • Hi Vilmos,

    Hmmm, this wasn't exactly what I was after.  Phrasing this another way, what is the maximum number of m=video lines someone calling a Lync conference can add to their session description?

    As this is only useful/relevant for Lync conferences, is there any data in the RFC4575 XML that says either what the maximum number of streams someone calling the Lync conference can put in their session description, or even if multiple m=video lines are supported by the AVMCU (to tell the difference between Lync 2010 and 2013 setups)?

    Thanks,

    Simon

    Wednesday, October 29, 2014 10:03 AM
  • Hi Simon,

    I’m sorry for not answering your question, I continue my research how the client discovers the maximum number of main-video streams. Please, tell what kind of problem you are trying to solve, knowing it I might be more useful.

    Thanks, Vilmos

    Thursday, October 30, 2014 8:57 PM
  • Hi Simon,

    In your original question you refer to [MS-SDPEXT] section “4.8 Offer/Answer Exchange for multi-channel main-video modality” asking how the client discovers the maximum number of main-video streams.

    The same document in sections 3.1.5.34 and 3.1.5.35 describes it. Section “3.1.5.34.2 User agent behavior for negotiating multiplexed media channels” states that the SDP offer contains the multiplexed “main-video” media descriptors. The number of the descriptors in the SDP offer is the maximum number of the “main-video” streams supported.

    The client creates an audio/video conference with INVITE, the server successful (200) answer contains the maximum number of the supported streams. In the capture below, please count the “a=label:main-video” attributes, there are six.

    m=video 62482 RTP/SAVP 122 121 123
    ……………………………………………………….
    a=candidate:5 2 tcp-act 1684796926 10.32.191.83 64584 typ srflx raddr 10.32.191.83 rport 64584
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    a=rtpmap:122 x-h264uc/90000
    ……………………………………………………….
    a=x-sourceid:MainCamera
    a=rtcp:62483
    a=ice-ufrag:gT+G
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    a=sendonly
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=ice-pwd:Nyt/6ffBWye0nzyNDGEH9MMT
    a=label:main-video
    a=cryptoscale:1 server AES_CM_128_HMAC_SHA1_80 inline:NVz5tAEpUvRT7b3rMm88scki+JzS+AWsg5vhhBwF|2^31|1:1
    ……………………………………………………….
    a=rtpmap:123 x-ulpfecuc/90000

    I hope this answered your question.

    Thanks, Vilmos
    Tuesday, November 4, 2014 8:18 PM
  • Hi Simon,

    Because there is no response to this issue, I assume my explanation was adequate, your problem is solved, you no longer require my assistance and I’ll close the case; if in the future you will have any problem regarding the Open Specifications documentation, please contact us through dochelp or on the forums and we’ll be glad to assist you.

    Thanks, Vilmos

    Monday, November 10, 2014 6:56 PM