[SR-Users] [Sems] directed media problem when video is included in sdp

Stefan Sayer stefan.sayer at frafos.com
Mon Sep 19 21:47:12 CEST 2011


o Juha Heinanen on 09/19/2011 08:39 PM:
> when sems receives voice call invite from ua behind nat that has
> direction:active in its sdp, like this:
>
>          Session Description Protocol
>              Session Description Protocol Version (v): 0
>              Owner/Creator, Session Id (o): foo.bar 0 0 IN IP4 192.168.1.
> 68
>              Session Name (s): -
>              Connection Information (c): IN IP4 192.168.1.68
>              Time Description, active time (t): 0 0
>              Media Description, name and address (m): audio 8500 RTP/AVP 18 4 112 100 101 0 8 106
>              Media Attribute (a): sendrecv
>              Media Attribute (a): rtpmap:18 G729/8000
>              Media Attribute (a): rtpmap:4 G723/8000
>              Media Attribute (a): rtpmap:112 AMR/8000
>              Media Attribute (a): rtpmap:100 EG711U/8000
>              Media Attribute (a): rtpmap:101 EG711A/8000
>              Media Attribute (a): rtpmap:0 PCMU/8000
>              Media Attribute (a): rtpmap:8 PCMA/8000
>              Media Attribute (a): rtpmap:106 telephone-event/8000
>              Media Attribute (a): direction:active
>
> sems includes direction:passive in 200 OK and starts to correctly send
> rtp packets to the ip address/port of received rtp packets.
>
> however, then sems receives a voice+video call invite like this:
>
>          Session Description Protocol
>              Session Description Protocol Version (v): 0
>              Owner/Creator, Session Id (o): foo.bar 0 0 IN IP4 192.168.1.68
>              Session Name (s): -
>              Connection Information (c): IN IP4 192.168.1.68
>              Time Description, active time (t): 0 0
>              Media Description, name and address (m): audio 8500 RTP/AVP 18 4 112 100 101 0 8 106
>              Media Attribute (a): sendrecv
>              Media Attribute (a): rtpmap:18 G729/8000
>              Media Attribute (a): rtpmap:4 G723/8000
>              Media Attribute (a): rtpmap:112 AMR/8000
>              Media Attribute (a): rtpmap:100 EG711U/8000
>              Media Attribute (a): rtpmap:101 EG711A/8000
>              Media Attribute (a): rtpmap:0 PCMU/8000
>              Media Attribute (a): rtpmap:8 PCMA/8000
>              Media Attribute (a): rtpmap:106 telephone-event/8000
>              Media Description, name and address (m): video 8600 RTP/AVP 34
>              Bandwidth Information (b): AS:300
>              Media Attribute (a): sendrecv
>              Media Attribute (a): rtpmap:34 H263/90000
>              Media Attribute (a): direction:active
>
> it does not include direction:passive in 200 OK and keeps on sending rtp
> packets to 192.168.1.68 even after receiving first voice rtp packet from
> public ip of the ua.
>
> is this a bug in sems or is it a bug in sr nathelper_k
> fix_nated_sdp("1") implementation, i.e., does that function place
> direction:actvive line to only one place, when it should place it in two
> places (in both voice and video media descriptions)?
The latter. The direction attribute from comedia draft is a media 
level attribute. If it is set in the video stream only, it applies 
only to the video stream. fix_nated_sdp should put it in the audio m 
section as well.

Note that the 'setup' attribute from rfc 4145 - which is not honored 
by sems - can be media or session level; if it is added to session 
level, it applies to all media lines.

Stefan


>
> -- juha
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