[Asterisk-Users] Newbie Questions

[Greg Broiles]

You can plug several phones into an FXS port, but they look like the
same phone/extension to Asterisk - so they will all ring together, if
one is in use the others will be as well, etc.

The big question I see here is whether or not you want each individual
phone instrument (or group of instruments) to have their own identity
- e.g., do you want to be able to call the kitchen from the bedroom?
Do you want to be able to have someone on the phone in the kitchen
having a conversation with X in Florida, while someone else in the
bedroom is having a conversation with Y in New York? Do you want to be
able to set things up so that some phones don't ring late at night, or
such that it's possible for an outside caller to be routed to a
particular instrument?

If you want those sorts of things, you will want to have several FXS
ports (or several VoIP phones) so that each phone can have its own
identity.

If you don't need that sort of thing, then it's not important that
each phone get its own FXS port. That being said, you don't want to
plug so many phones in that you exceed the REN capacity of the port
(the ability of the device to provide the higher voltage used to
signal (and, on older phones, to generate) the ringing sound). I don't
know what the REN capacity of the cards is, but I know you don't want
to go above it. Once upon a time, most phones had a REN of 1, and the
telco would guarantee at least 5 REN worth of juice. In the modern
age, I've got no idea, but my impression is that modern electronic
telephones, particularly those with their own power supplies, are more
likely to have a REN in the neighborhood of 0.1, or similar.

If you want to use VoIP to get long distance service for your Asterisk
box, you don't need to monkey around with a T1 interface - you can use
your existing Ethernet and cable/DSL connection to get service, so
long as your bandwidth needs are modest. This works smoothest if you
sign up with one of the LD providers who's set up to interconnect with
Asterisk.

If you wanted to, you could also sign up for Vonage or one of the
other more consumer-oriented VoIP providers, and plug their network
device into an FXO port, and just pretend it's an old-fashioned POTS
line. The theoretical downside to that is that you're doing an extra
digital -> analog -> digital conversion, which may cost you some voice
quality. The practical downside to that is that the consumer-oriented
services are also more expensive, at least at a low call volume, since
they're more likely to be priced at $20-30-40-50/month for many
minutes or unlimited service, whereas the Asterisk-friendly providers
are probably going to charge you on a per-minute (or fractional
minute) basis for time used, plus a flat rate per incoming number (if
you even want/need one).

I have Vonage's 500 minutes/month service and never come close to
using up my 500 minutes. Also, I've found voice quality to be better
using Asterisk and SIP phones - I suspect it's because I've got more
control over the codecs used, but it's hard to say for sure.

-- 
Greg Broiles, JD, EA
gbroiles at gmail.com (Lists only. Not for confidential communications.)
Law Office of Gregory A. Broiles
San Jose, CA