[SIPForum-discussion] DTMF - rfc 2833

[Raghul Prasanna]

Hi All,
 
When DTMF is sent using RFC 2833, we see in wireshark one digit repeated several times.
 
Say for example if an user hits digit 6, in my wireshark trace i see the rfc2833 packet 8 times for digit 6 and 3 ENDS.
 
each digit has a duration 80 and the duration between 7th and 8th packet is less than 80 and its 48. On what basis is the DTMF chunked into duration of 80, i believe its in ms.
 
I think the entire tone lasted 608 ms and its divided into 80 ms rfc2833 pkt, so the last one had just 48 ms. Is that right?
 
The codec used for RTP in this case is G.729. The payload size for G.729 is 20 ms, but I think this is for Voice alone and does not apply for DTMF tones. Is that right?
 
If that's the case on what basis is the DTMF chunked into 80?
 
Also why do we see 3 ENDS, is it just to make sure that, the END pkt reaches the other end if there are any pkt loss? Please explain.
 
Thanks,
Raghul


      
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