From: none (alsontra@hotmail.com)
Date: Sun Oct 10 2004 - 00:52:20 GMT-3
Just as I had decided to fortify my voice skills Cisco removes it from the
exam, figures.
In an event, below are a few helpful links for anyone that is still
interested in learning how to calculate voice bandwidth, by codec. This
journey is more about the knowledge and less about the number everyday. :-)
****Voice Bandwidth Calculation Formulas
The following calculations are used:
Total packet size = (L2 header: MP or FRF.12 or Ethernet) + (IP/UDP/RTP
header) + (voice payload size)
PPS = (codec bit rate) / (voice payload size)
Bandwidth = total packet size * PPS
Sample Calculation
For example, the required bandwidth for a G.729 call (8 Kbps codec bit rate)
with cRTP, MP and the default 20 bytes of voice payload is:
Total packet size (bytes) = (MP header of 6 bytes) + ( compressed IP/UDP/RTP
header of 2 bytes) + (voice payload of 20 bytes) = 28 bytes
Total packet size (bits) = (28 bytes) * 8 bits per byte = 224 bits
PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps
Note: 160 bits = 20 bytes (default voice payload) * 8 bits per byte
Bandwidth per call = voice packet size (224 bits) * 50 pps = 11.2 Kbps
Ref:http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a
0080094ae2.shtml
****Cisco Voice Codec Bandwidth Calculator****Great tool for checking your
work!
http://tools.cisco.com/Support/VBC/do/CodecCalc1.do
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