# B/W calculation

Jul 23rd, 2008

Hi,

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.

Regards,

Hi,

This is how you calculate this...

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%

Overall Rating: 5 (1 ratings)

## Replies

Ayodeji Okanlawon Wed, 07/23/2008 - 02:41
• Super Bronze, 10000 points or more
• Cisco Designated VIP,

2017 IP Telephony

Hi,

This is how you calculate this...

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%

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