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SIP Multiple m-line Support

 

Overview:

Feature 1393 multiple m-line supports RFC 3264 (Offer/Answer Model with SDP) and allows the IMG to select an acceptable media stream from a valid SIP offer containing multiple media streams (m-lines). The answer or response will contain the media streams that are accepted and will also contain the media streams that are rejected. The rejected media streams in the answer will have the media port number set to zero in the m-line. The IMG accepts a minimum of 1 m-line and a maximum of 4 m-lines and by default, accepts the first matching media stream with at least one media format. The feature is enabled by default and no configuration is required for the feature to function. See below for more information on F-1393.

Related Topics:

 IMG 1010 - SIP Profile - 10.5.3

Diagram:

 

 

Examples:

Below are examples of how IMG would react to SIP offers with different types of Media Descriptors. (Ex: Audio, Video, Fax). See Additional Information below explaining how the IMG selects which Media Descriptor. 

Info

...

The IMG will NOT select the best matching media stream, it will match on the first media stream (m-line) from a valid Offer which has multiple media streams. Matching the first Media Stream assumes the media streams are sorted by preference and the first being the highest preference.

 Note:

Info
In both examples below, the Codec Priority setting will have no effect on the IMG behavior to accept the first matching media stream in the offer. Codec Priority setting will only affect the IMG method used to select media formats for answer after having selected a media stream.

 

Audio:

  • A SIP INVITE comes into IMG with an Offer indicating that there are two audio streams. The IMG parses the message and sends back an answer with both the accepted and rejected audio stream. In this example, the m-line with payload type of 0 is accepted and m-line with the payload type 8 is rejected. Note that the rejected m-line has a port value of 0. The rejected m-line is sent back in a response to the Offer even though it was rejected.  

    VoIP Configuration in IMG

    Offer to IMG

    Answer from IMG

    Profile

...

  • 5

    Default Codec = G.711

...

  • ulaw

    Codec Priority = Local

    m=audio 38400 RTP/AVP

...

  • 0

    a=rtpmap:0 PCMU/

...

  • 8000

    m=audio 49500 RTP/AVP

...

  • 8

    a=rtpmap:8 PCMA/8000

    m=audio 6000 RTP/AVP

...

  • 0

    a=..(a-line present as applicable)

    m=audio 0 RTP/AVP 8

     

  • A SIP INVITE comes into IMG with an Offer indicating that there are three audio streams. The IMG parses the message and rejects the first m-line because of the Codec. It accepts the second m-line even though the second and third m-line are acceptable. The IMG accepts the FIRST ACCEPTABLE m-line.  

    VoIP Configuration in IMG

    Offer to IMG

    Answer from IMG

    Profile

...

  • 5

    Default Codec = G.711

...

  • ulaw

    Codec Priority = Local

    m=audio 10000 RTP/AVP

...

  • 98

    a=rtpmap:98 ilbc/

...

  • 8000

    m=audio 18000 RTP/AVP

...

  • 18

    m=audio 38400 RTP/AVP 0

...

  • 8

    a=rtpmap:0 PCMU/

...

  • 8000

    a=rtpmap:8 PCMU/8000

    m=audio 0 RTP/AVP

...

  • 98

    m=audio 0 RTP/AVP

...

  • 18

    m=audio 6000 RTP/AVP

...

  • 0

    a=..(a-line present as applicable) 

     

  • The IMG will select the CODEC depending on the Codec Priority field (Local/Remote) setting in the SIP SGP Profile.  

    VoIP Configuration in IMG

    Offer to IMG

    Answer from IMG

    Profile

...

  • 5

    Default Codec = G.711 alaw (default), G.711

...

  • ulaw

    Codec Priority = Local

    m=audio 10000 RTP/AVP

...

  • 98

    a=rtpmap:98 ilbc/

...

  • 8000

    m=audio 38400 RTP/AVP 0

...

  • 8

    a=rtpmap:0 PCMU/

...

  • 8000

    a=rtpmap:8 PCMA/

...

  • 8000

    m=audio 18000 RTP/AVP 18

    m=audio 0 RTP/AVP

...

  • 98

    m=audio 6000 RTP/AVP

...

  • 8

    a=..(a-line present as applicable)

    m=audio 0 RTP/AVP 18

...


  • Info

...

  • The IMG selected the first matching media stream and the media format selected is based on codec priority setting (local)


  • The IMG will select the CODEC depending on the Codec Priority field (Local/Remote) setting in the SIP SGP Profile.  

    VoIP Configuration in IMG

    Offer to IMG

    Answer from IMG

    Profile

...

  • 5

    Codec = G.711 alaw (default)G.711

...

  • ulaw

    Codec Priority = Remote

    m=audio 10000 RTP/AVP

...

  • 98

    a=rtpmap:98 ilbc/

...

  • 8000

    m=audio 38400 RTP/AVP 0

...

  • 8

    a=rtpmap:0 PCMU/

...

  • 8000

    a=rtpmap:8 PCMA/

...

  • 8000

    m=audio 18000 RTP/AVP 18

    m=audio 0 RTP/AVP

...

  • 98

    m=audio 6000 RTP/AVP

...

  • 0

    a=..(a-line present as applicable)

    m=audio 0 RTP/AVP 18

...


  • Info

...

  • The IMG selected the first matching media stream and the media format selected is based in codec priority setting (Remote) as the preference.


  • The IMG will always accept fax (m=image line) if one of the Media streams offered in Re-INVITE is for fax.  

    VoIP Configuration in IMG

    Offer to IMG

    Answer from IMG

    Profile

...

  • 5

    Default Codec = G.711

...

  • Ulaw

    Codec Priority =

...

  • Local

    Fax T38 Enabled

    m=image 7228 udptl t38

...

  •                

    a=T38FaxVersion:

...

  • 0

    a=T38MaxBitRate:

...

  • 14400

    a=T38FaxRateManagement:

...

  • transferredTCF

    a=T38FaxUdpEC:

...

  • t38UDPRedundancy

    m=audio 7228 RTP/AVP 8

...

  • 0

    a=rtpmap:8 PCMA/

...

  • 8000

    a=rtpmap:0 PCMU/

...

  • 8000

    a=ptime:

...

  • 20

    a=silenceSupp:off - - - -

    a=ecan:fb on -

    a=X-fax

    m=image 8001 udptl t38

...

  • m=audio 0 RTP/AVP 8 0

    Profile

...

  • 5

    Default Codec = G.711

...

  • Ulaw

    Codec Priority =

...

  • Local

    Fax T38 Enabled

    m=audio 7228 RTP/AVP 8

...

  • 0

    a=rtpmap:8 PCMA/

...

  • 8000

    a=rtpmap:0 PCMU/

...

  • 8000

    a=ptime:

...

  • 20

    a=silenceSupp:off - - - -

    a=ecan:fb on -

    a=X-

...

  • fax

    m=image 7228 udptl t38

...

  • a=T38FaxVersion:

...

  • 0

    a=T38MaxBitRate:

...

  • 14400

    a=T38FaxRateManagement:

...

  • transferredTCF

    a=T38FaxUdpEC:t38UDPRedundancy

    m=audio 0 RTP/AVP 8

...

  • 0

    m=image 8001 udptl t38

...

  •    


Additional Information:

  • The IMG by default will accept all offers with multiple valid m-lines.
  • IMG supports a minimum of 1 m-line and a Maximum of 4 m-lines. A 488 Not Acceptable Here will be sent if less than 1 or more than 4 m-lines are sent. The only exception to this is in a PRACK scenario.
  • The answer will contain the same number of m-lines as was in the Offer.
  • The IMG will accept the first matching media stream from an offer with multiple m-lines except when offer has a media stream of fax.
  • IMG supports fax only in RE-INVITE scenarios. If Offer contains m=image, it will be rejected.
  • When IMG rejects a Media stream, it will set the port number to 0 in the answer and will include the media formats.
  • The IMG cannot generate an offer with multiple m-line.
  • IMG will reject the session with a 488 Not Acceptable Here if none of the media streams is accepted.
  • IMG Shall log all codec information and media types across all m-lines in the Radius VSA. Support for m=video is added but not supported as of Software release 10.5.2. The remote m-line parameters will be logged as follows:
    • dialogic-voip-remote-vocoders ="PCMU,PCMA,Video"