G711 Payload size query....

[fazza]

Hi,

I am encountering an something I wasn't expecting when setting up G711 calls for SIPML5.

Although the rtp map clearly shows that MULAW codec is to have a 8Khz sampling time, I would expect to see a 160byte payload in the RTP stream. I am observing a 170 byte payload. 

Can anyone shed any light what I am overlooking. Is there a way to force the SIPML5 phone to send the standard 160 byte payload for G711 ?

a=rtpmap:0 PCMU/8000

a=rtpmap:126 telephone-event/8000

a=rtpmap:106 CN/8000

a=ptime:20

Thanks

[Mamadou]

Perhaps 10 bytes added for SRTP authentication

You should attach logs when reporting an issue.

[fazza]

Hi,

Thanks for your reply. I dont believe SRTP is being invoked. Also SRTP adds 4 bytes to a 20ms payload.  I have verified that the phone has not security enabled whatsoever. Can you confirm that G711 calls being created by SIPML phones have 160 byte (20ms ) payload as I have never observed this

Thanks

George

[Mamadou DIOP]

SIPML5 cannot send/recv something not SRTP. If SIPML5 is the sender or receiver then, for sure it’s SRTP.

I’ve done a test and confirm that the 10bytes are added for SRTP.

Don’t know why you’re focusing on this “160 bytes”.

“Also SRTP adds 4 bytes to a 20ms payload.” -> check again and you’ll see that you’ve missed something

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