Please can some one explain to me how to calculate % of overall b/w saved by cRTP for G.729 voip call packetsized at 50pps.
This is how you calculate this...
Bw/call= (Bytes/sample + protocol payload/bytes/sample)X codec badnwidth
Bytes/sample is calculated as (sample size X codec Bw)/8
To determine the sample size, you need to use the packetization period used. Here its 50pps, hence we must have 20ms of speech to generate a full second of converstion.
SO our sample size is 20ms.
hence bytes/sample = 20X8/8 =20bytes.
So to calculate bw/call without cRTP and with cRTP we will need to know the protocol payload for both conditions,
without cRTP, protocol payload = UDP + IP +RTP = 8+20+12 =40bytes
with cRTP, our 40bytes is usually compressed to between 2 and 4 bytes..We will use 4bytes for this..its the maximum...
Hence calculate bw/call without cRTP = (20+40)/20 X 8 = 24kbps
with cRTP = (20 + 4)/20 X 8 = 9.6.
hence bw saved = 24-9.6/24 X 100 =60%