[rescue] VOIP

[Geoffrey S. Mendelson]

Patrick Giagnocavo +1.717.201.3366 wrote:

> Well, I don't think that it would particularly be a problem in most
> cases.  With overhead, etc. the most you can get on 11mbps 802.11 is
> about 3mbps full-duplex .  But you might only need 128kbps or less for
> good voice quality.  Vonage does it with less than 90kbps; as long as
> your latency is not too bad (say under 95ms ping times) you would be OK.

VoIP was designed for poor performance. I think the same people that
developed ATM, went on to develop VoIP. The DATA required is about 16k 
BYTES per second (64k BITS). This is not too difficult to get on modern
networks.

The problem is that the VoIP standards use very small packets with BIG
headers. The header is up to 40 bytes, and often the data is less.

Cisco gets around this by compressing the headers to as little as TWO
bytes, but you need a Cisco ATA (analog telephone adaptor) and Cisco
routers at each end. 

The other problem is that IP networks are not designed to handle the 
performance requirments of VoIP. They are designed to move large amounts
of data from one place to the other effeciently, but they are not designed
to move small amounts of data quickly,  keep them in sequence and do it
consistently for long periods of time.

Geoff.


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Geoffrey S. Mendelson gsm at mendelson.com 972-54-608-069
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