[Linphone-developers] Bad duration value in rfc2833 RTP payloads

[Dmitry Akindinov]

Hello,

While testing our server against Linphone 3.5.2 for Windows for SIP/SRTP 
compatibility we discovered that RTP packets generated for DTMF 
keypresses come with non-monotonic duration value:

19:40:56.230 5 MEDIA-000003 s-inp:(230,9240)1C1(229):(4) 01 0A 00 00
19:40:56.230 5 MEDIA-000003 s-inp:(231,9240)1C1(101):(4) 01 0A 00 A0
19:40:56.230 5 MEDIA-000003 s-inp:(232,9240)1C1(101):(4) 01 0A 00 50
19:40:56.230 5 MEDIA-000003 s-inp:(233,9240)1C1(101):(4) 01 0A 00 F0
19:40:56.271 5 MEDIA-000003 s-inp:(234,9240)1C1(101):(4) 01 0A 01 E0
19:40:56.271 5 MEDIA-000003 s-inp:(235,9240)1C1(101):(4) 01 0A 01 90
19:40:56.271 5 MEDIA-000003 s-inp:(236,9240)1C1(101):(4) 01 0A 02 30
19:40:56.312 5 MEDIA-000003 s-inp:(237,9240)1C1(101):(4) 01 8A 03 20

The packets come in the correct order, but the duration is not monotonic:

00 00
00 A0
00 50
00 F0
01 E0

Our code treats this as a possible packet loss between 00 A0 and 00 50 
and thus generates duplicate DTMF keypress. We noticed this in SRTP 
streams, but the bug may exist in the regular (not encrypted) streams too.

Is this the known bug?

--
Best regards,
Dmitry Akindinov