[Asterisk-Users] Re: System Design

[Paul Davidson]

>
>
> Date: Tue, 7 Mar 2006 18:26:12 -0500
> From: "Jason Adams" <jadams at sumosystems.net>
> Subject: [Asterisk-Users] System Design
> To: "Asterisk Users Mailing List - Non-Commercial Discussion"
>         <asterisk-users at lists.digium.com>
> Message-ID:
>         <725FFB0CA3F44B4FB0CE715CABA2A52106E332 at sumosrv.sumosystems.local>
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>
> Hey Everyone,
>
> We are in the works of planning a new * installation for our company.
> We have 20 users in our main office and 5 users in a remote office a
> couple of states away.  Our call volume for the main office will be
> anywhere from 5-10 concurrent calls.  The remote office will have about
> 3 heavy users with two users making calls occasionally.
>
> Right now we have an existing PBX.  We have a T-1/PRI coming into the
> main office and a DSL connection at the remote office.  We have a Cisco
> 2610/PIX 501 at the main office a cheesy linksys router at the remote
> site.
>
> We are planning on purchasing new Cisco IP phones for everyone.
>
> My main question is this:  What type of hardware/network design would be
> best for this situation?  Would a full T-1 at the remote site work with
> a VPN between the offices?  Or would a higher bandwidth DSL work with a
> VPN?  Or should we move to a Point-to-Point connection?  What type of
> hardware would be best for the end-to-end communication in regards to
> QoS?  I know the PIX 501 doesn't support it.
> Would it be best to have two * servers in each office or for that call
> volume at the remote office does it make sense?  I was thinking of a
> Dell Power Edge server with 4GB of ram and a dual processor.. is that
> enough?
>
> Sorry for all the questions!
>
>
> - Jason
>
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>

Jason-

You're right, that's a lot of questions.  Let me try to net it out a little
for you.

First off, it sounds as if you're using the Internet to connect the two
offices.  Understand- nothing presently there will provide QOS over the
Internet- from that perspective, your existing equipment is just fine.  If
you're considering making changes, and budget is not an issue, a private WAN
setup- Frame Relay, for instance, that provides low latency between the two
points, is what you're looking for, as you can perform QOS on it.
Speedwise, however, depending on the level of compression you go with, at 5
simultaneous calls (my assumed maximum with 5 remote users- YMMV), you
really dont need anything faster than a 256K connection between the two
points- assuming the latency can be kept in the 60ms range or less.  DSL,
specificall aDSL is notoriously awful for high-bandwidth VoIP applications,
as it's asymetric (faster download than upload in general), and the speed
will vary at random based on the carrier and time of day.  If you compress,
you can get away with 128K for the voice portion of the link (Remember,
that's 256K for the Voice side, not counting whatever other traffic is going
on at the time)- and if you trunk IAX, you can potentially get even
smaller.  The big question is- at 20 users and 5 users- how many calls are
going on across the VoIP link?

Secondly, consider your PSTN connections.  Are you using a PRI at the main
office, and some POTS lines at the remote? Do you need to use a VoIP
provider for all of it? Want to get rid of those POTs lines and use the PRI
for the remote office as well? All of which will change the equations as far
as how much bandwidth and what kind of hardware you need in each office.

Finally, hardware.  That dual CPU machine is a cadillac for 20 users- even
25 users.  I won't go in to my opinion of Dell, that's a theological
discussion- but I'd sandbox that setup on something far smaller- a 1Ghz
Celeron should be more than up to the task for Asterisk, depending on what
else you're doing at the time, even with transcoding going on.  I personally
would recommend two low cost servers- look in to astlinux and a Soekris box
for the remote office (might be pushing it, but again, it depends on your
apps and transcode requirements), and a cheap commodity machine for the main
branch- it should be just fine for what you're looking to do.  Trunk the two
machines together, and you've got all the power in the world- Dundi or IAX
switched dialplans will take care of most of the headache for you.

If you want to dig deeper into details, I'd be happy to offlist- I'm posting
this here as more of a general selection/architecture guide.

-Paul Davidson
 PlanCommunications, LLC
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