CM: RTP payload changes from G.711/G.729 to DynamicRTP-Type-125 mid stream

Doc ID    SOLN312417
Version:    4.0
Status:    Published
Published date:    15 Nov 2017
Created Date:    12 Jul 2017
Author:   
gtefft
 

Details

Saw strange RTP packet type 125 (instead of the normal g729 or g711)
RTP flow changes mid stream from G.729 to DynamicRTP-Type-125 with no SIP SDP update event

Problem Clarification

RTP flow changes mid stream from G.729 to DynamicRTP-Type-125 with no SDP events - this causes the customer voice recorder (Verint,Nice,etc) to stop recording or audio to become garbled

 

In this case, G.729 voice codec changed to a dynamic payload type 125. This payload type can become any number in the dynamic range. This is change is the indication in the sniffer capture of the transition from voice codec to the specialized fax codec.

 

 

 

Cause

IP-codec_set is set up as "pass-through"

Working as designed - FAX/ Modem as "pass-through" sets up the VOIP engine in the GW/Medpro to "listen" for FAX and/or Modem tones and adjust the RTP payload accordingly.

Fax mode t.38-standard is considered a "pass-through" mode as well

display ip-codec-set 1                                          Page   1 of   2

                          IP CODEC SET

    Codec Set: 1

    Audio        Silence      Frames   Packet
    Codec        Suppression  Per Pkt  Size(ms)
 1: G.729             n         2        20
 2: G.711MU           n         2        20
 3:
 4:
 5:
 6:
 7:

                             Allow Direct-IP Multimedia? n
                                                                        Packet
                          Mode                   Redundancy             Size(ms)
    FAX                   t.38-standard           0            ECM: y
    Modem                 pass-through            0
    TDD/TTY               pass-through            0
    H.323 Clear-channel   n                       0
    SIP 64K Data          n                       0                     20
 

Solution

Set IP stations to use IP-Network-Region that does not have fax or modem as "pass-through".

 


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