Thursday, August 5, 2010

How Much Hardware Do You Need

A question I've seen a lot lately is about how much hardware at the network and in the rack you need to run an Asterisk VOIP environment for the enterprise.  The real answer is "not much".

The Network Matters
On the network side, you're looking for Quality of Service (QOS) and the ability to put your voice traffic on a Virtual LAN (VLAN) so that it is "invisible" to data traffic.  Of the two, QOS is more important and generally easier to manage.  However, if you VLAN your VOIP infrastructure, and you are wired with CAT 5e end to end as a minimum, then the lack of QOS shouldn't bite you.

If you aren't going to VLAN your VOIP infrastructure, depending on what other type of network traffic you have and how many stations, then you might have issues.  Particularly if you are not wired gigabit to the desktop and then plan on using "HD" voice codecs.  "Bursty" traffic like streaming media and large file transfers can saturate a wire resulting in lost voice traffic, which is sent over "expendable" UDP.

Big Irons
As far as which server you get, the biggest issue is not horsepower.  Generally speaking, 1CPU @ 1Ghz + 1Gb RAM + 10Gb disk = 100 conncurent calls (PRI <=> SIP) based on my experience.  Transcoding, recording, conferencing, virtual FAX, or database services running on the PBX will each cost you about 10% of that number.

The real issue in buying a server is reliability.  This is your enterprise telephony stack...  your communications line to your customers.  Hardware RAID-1, dual power supplies, hot-swappable drives and PCI cards, and "can't kill it" features are excellent.  Either that, or buy two cheaper servers and rig them in a Highly Available fail-over cluster.

My House
My home Asterisk server is an IBM PC-700 with 512Mb of RAM and 40Gb of disk.  It supports a Fax server, a Ruby/Rails configuration GUI, and three phones.  There is a VOIP trunk to an ITSP, and a DAHDI PCI card for hook to the PSTN.  The machine is asleep, even while receiving a fax and with my wife on the phone on an LD call.  I'm wired internally with 100M/bit every where in the house, except my wireless at 54M/bit.

JKL5's Cloudphones PBX, which is our growing multi-tenant service, currently has 15 end points for 5 tenants, plus six VoIP trunks split between IAX2 and SIP.  There are calls in progress at any point of of the day.  It is an Intel(R) Xeon(R) CPU @ 3.00GHz, 500Mb of RAM (100mb free) and 28Gb of disk.  Its in a data center with dual OC3 connectivity, so the only bandwidth issues are with the end-stations, usually home XDSL or Cable Modem.  Current load average at 9am on a business day is 0.09.

Wrapping Up
I personally suggest to clients be more worried about having a good network environment and a good T1 card than worry about needing a massive server.  The only thing you need to worry about with the hardware is what your plan is if there is a component failure.

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