# Understanding telephony hardware

**URL:** <https://community.asterisk.org/t/understanding-telephony-hardware/22865>\
**Category:** Asterisk General\
**Created:** [September 4, 2008, 5:18pm UTC](https://community.asterisk.org/t/understanding-telephony-hardware/22865 "2008-09-04T17:18:06Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![helpmhost](https://avatars.discourse-cdn.com/v4/letter/h/f4b2a3/32.png) [@helpmhost](https://community.asterisk.org/u/helpmhost)\
**Post date:** [September 4, 2008, 5:18pm UTC](https://community.asterisk.org/t/understanding-telephony-hardware/22865/1 "2008-09-04T17:18:06Z")

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Hi,

I’ve been trying to find good websites and books that explain the choices of hardware for setting up an asterisk box.

I dont want a simple comparison of vendors and specific products. What I want, is either a good book or good teaching web site that explains the options:

1. FXS
2. FXO
3. ATA

Why would I chose either one?

A site/book that explains what kind of hardware I would want for specific scenarios like:

1. A SOHO with 1 or 2 phone lines
2. A Small Business with a dozen lines
3. A larger business with a T1

What about using a VOIP provider where all you need is an internet connection (pros/cons).

I’ve also read that it is possible to use a regular old modem, but not recommended. Why?

I am not asking anyone to answer all these questions, just refer me to some books or sites that explain these.

Thanks.

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**Author:** ![swaterhouse](https://avatars.discourse-cdn.com/v4/letter/s/3da27b/32.png) [@swaterhouse](https://community.asterisk.org/u/swaterhouse)\
**Post date:** [September 5, 2008, 12:24pm UTC](https://community.asterisk.org/t/understanding-telephony-hardware/22865/2 "2008-09-05T12:24:09Z")

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The following book is an excellent resource

[http://oreilly.com/catalog/9780596510480/index.html](http://oreilly.com/catalog/9780596510480/index.html)

Also try the wiki

[http://www.voip-info.org/wiki/](http://www.voip-info.org/wiki/)

Finally you cannot use any old modem, you need a true analog or digital voice card if you want to connect to the PSTN and/or to analog phones. There are cheap clone cards out there but the Digium hardware is very nice and well worth the extra money especially since you get free supprt with them and you support further development of Asterisk.