Asterisk Hardware Recommendations - Workstation or Server Hardware

>> I have read posts here and elsewhere that you may be better off having the installation on a regular PC/Workstation.

To me, that doesn't make much sense especially if it's going to be used in a call center.  Use a rack mount case and the components should be server grade.  We build our servers and the first 2 used 4U cases, but since then, we've used 1U cases for the other 10 servers.

We use hardware RAID, and since we only have 2 drives in the VoIP servers, we use RAID 1.  All of the other servers in our company have 8 to 12 drives and use RAID 10.

Here are the minimum recommended specs taken from Asterisk: The Future of Telephony http://www.oreilly.com/catalog/asterisk/index.html

Purpose                    Number of Channels            Minimum Recommended
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Hobby System           No more than 5                  400-MHz x86, 256 RAM
SOHO System            5 to 10                             1-GHz x86, 512 RAM
Small Business            Up to 15                           3-GHz x86, 1GB RAM
Med to Lg Business     More than 15                     Dual CPUs, possibly also multiple servers in a distributed architecture

For the phones, we use standard (cheap) phones and connect them to either an iaxy or sip adaptor.  If you go this route, stay away from the D-Link sip adaptors, they have several compatability issues with asterisk which makes them "not ready for prime time".  I'm currently working with their engineers and doing some bata testing of their new firmware which is worse than the version than comes with the adaptor.  The Linksys adaptors (formally Sipura) seem to be the industry standard SIP adaptor.

I dont know when that book was published but those minimum specs are way off now with a relativly modern computer. See http://www.voip-info.org/wiki/view/Asterisk+dimensioning
Running a quad E1/T1 card with a single processor P4 machine works fine and that gives you up to 60 channels. Other people are running a purely VoIP based system with hundreds of simultaneous calls on a single processor machine.

There are a few things which do consume far more load on the server :-

1) Transcoding or converting audio from one compression format to the other. In your cause I would suspect you would use g711/ulaw which is the highest quality codec and will use little cpu converting the audio to and from the raw format used by the telephone card.

2) Echo cancelation. I would recomend you get one of the higher spec cards from Digium which has echo cancelation built onto the card itself instead of asterisk having to do it itself in software.

I would use SIP phones rather than analogue phones with IAX/SIP adapters. Using proper SIP phones you get the extra functionality of being able to handle multiple calls, call waiting, conferencing and even things like transfering calls are easier to do.

Sorry guys for the long delay in getting back to you.  

grblades - Would you mind elaborating on which model Amplicon rack mount server you went with along with the OS you are using.  I have reviewed the site and there are 1U, 2U, and 4U options.  Also I would prefer RH Linux and was wondering if it is worth buying the Enterprise edition (AS - Basic or Standard).  I have also read where some people are using CentOS with Asterisk successfully.  

The reason I mentioned a Dell server in the previous post and one of the Enterprise AS editions is that in some preliminary discussions with some customers about moving to VOIP using Asterisk is that they have been apprehensive because they are not familiar with it and asked what hardware it will run on.  Our thought with these kind of customers was to propose a solution on supported hardware (Dell), a supported OS, and possibly even the Business Edition for Asterisk just to make them more comfortable with the solution.

However, this does not address redundancy and purchasing two Dell servers would drive the price up on the solution significantly.