VoIP bandwidth fundamentals Part II
Calculating the bandwidth for a VoIP call is not difficult once you know the method and the factors to include. The chart below, “Calculating one-way voice bandwidth,” demonstrates the overhead calculation for 20 and 40 byte compressed voice (G.729) being transmitted over a Frame Relay WAN connection. Twenty bytes of G.729 compressed voice is equal to 20 ms of a word. Forty bytes of G.729 compressed voice is equal to 40 ms of a word.
The results of this method of calculation are contained in the next table, “Packet voice transmission requirements.” The table demonstrates these points:
* Bandwidth requirements reduce with compression, G.711 vs. G.729.
* Bandwidth requirements reduce when longer packets are used, thereby reducing overhead.
* Even though the voice compression is an 8 to 1 ratio, the bandwidth reduction is about 3 or 4 to 1. The overhead negates some of the voice compression bandwidth savings.
* Compressing the RTP, UDP and IP headers (cRTP) is most valuable when the packet also carries compressed voice.
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Written by Lovely on August 4th, 2007 with no comments.
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