[Asterisk-Users] Codecs and bandwidth

[Waldo Rubinstein]

You are correct. Bandwidth is bidirectional. All those references  
mentioned in the thread may be misleading. However, the bottom line  
is that it does use 64Kbps up/down plus overhead. This does not mean  
that to transport a single conversation you need ~150Kbps. You simply  
need to make sure your upload and download capacity have at least  
~75Kbps available.

In the case of most standard DSL services (and even cable broadband)  
sold in the US, the service sold is Asymmetrical. For these  
scenarios, Dan's explanation should suffice.

For most dedicated Internet services (such as T1, fractional T1s,  
Ethernet, etc), the capacity is Symmetrical. In the case of a full T1  
of Internet service, you can assume you could transport ~20  
simultaneous calls (~75Kbps x 20 = ~1500Kbps), which, unfortunately,  
turns out to give you less capacity than a channelized T1 or even a  
PRI using standard trunk services. I guess, at this point you need to  
evaluate codec use and a couple of other factors in order to maximize  
your capacity.

- Waldo

On Jul 18, 2005, at 3:58 PM, Dan Perik wrote:

> If you include down + up, yes, it's actually about 150-160 using  
> uLaw + IP/UDP/RTP/signaling overhead.  But that's a little  
> misleading, I think.
> 1/2 of that (~75-80) is down, 1/2 of that (~75-80) is up.  So if  
> you have, say, a 1.5Mbps down/384 up DSL connection, you can do up  
> to 4 calls simultaneously.  80*4 = 320.  You'd be using 320kbps  
> down and 320kbps up, which is within your 1500kbps down / 384 kbps up.
>
> Someone please correct me if I'm wrong.
>
> - Dan
>
> Tim Pushor wrote:
>
>
>> Of course - ISDN is bi-directional. I guess saying that ULAW takes  
>> 130K+ bandwidth depending on the framing type (local lan, w/1 hop,  
>> vlan, etc) is not very clear. Thats total bandwidth. With lots of  
>> us at home and small business using asynchronous connections - we  
>> need to keep that in consideration.
>>
>> Thanks for helping clear that up.
>>
>> Tim
>>
>>
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