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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