[SIPForum-discussion] Switching RTP packets based on ptime(For G729)

pradeep kumar pradeep872k at gmail.com
Tue Oct 15 09:57:34 UTC 2013

Dear All,

    One of our client ask to switch media based of caller & callee ptime.
For example, If caller sends 120ms ptime in INVITE and callee sends 20ms
ptime in 200OK, So Media proxy should Split/Merge the packets and sent to
caller/callee. We achieved this but the problem is client says we have some
Qos problem in few calls. After some analysis i found that problem with
time stamp. As per my understanding

For example

packetNo   sequence  RxedTime     ssrc                   timeStamp
7209          8354         67.270726    0xB5CA2D17    1991040
7223          8355         67.390467    0xB5CA2D17    1992000

Time difference between two packets is 0.119741, So approximately 120 ms

120ms (Of data) * 8 kHz(sampling rate) =  960ms  ----> time stamp
difference between two packets

My question is now the third packet comes with delay, what will be the time
stamp i have to set in that rtp packet ?
third packet details are,
packetNo   sequence  RxedTime     ssrc                   timeStamp
7333            8356        68.110467   0xB5CA2D17    1992960 (Here i
increment only 960ms)

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