Hardware recommendations for medium-large office (PRI+POTS)


#1

Getting ready to purchase hardware for new Asterisk system.
The book says not to use more than one Digium board per server.

We have an ISDN PRI coming into an AltiGen switch with 36 extensions,
and 5 POTS lines coming into a second AltiGen switch with 4 extensions.
These are separate business divisions with their own (800) #'s & Caller ID.

I want to provision a system that will combine the two, yet maintain their individual identity. Currently, we can’t transfer calls from one switch to the other without using an outside line. Yuk. They should just be like any other extension, except when calling out. (Assigned outbound circuits.)

It will also need to be expandable. We anticipate growth for as many as 75-100 employees, plus additional phone circuits. Perhaps a second PRI, and more POTS lines. With a remote facility, VoIP over a private circuit or VPN.

My preliminary guess is that I will want a Digium Quad T-1, and several TDM2400P’s for all the analog phones and POTS lines, with a mix of FXO & FXS daughter boards…

The questions I haven’t been able to find in the book are:

  • How many servers will I need?
  • Will a channel bank be required in my plans?
  • Will I get better mileage with dual CPU/FPPU motherboards?
  • Multi-server configuration details?

I’ll keep reading, but it is always nice to find some bread crumbs along the trail from those who have gone before…

Thank you!


#2

hello again! I assume from your post that you are planning on dumping the AltiGen gear and going to a straight asterisk setup. So here is another somewhat useless and very long rambly reply.

When they say only one Digium board, that generally means not more than one quad-PRI board (~100 channels). Unless your server motherboard sucks, you won’t have IRQ issues, and as long as each card has its own IRQ to itself youw ill be fine.

So you have 24ch PRI -> 36users, and 5POTS -> 4users. I am also assuming that all your users use analog (ughk) telephones. How are they connected? I’m assuming they are plugged into interface boards on the AltiGen system…

Since you are diving into VoIP, you have somewhat of a decision to make- if you are going to transition to a mostly voip-based infrastructure, now is the time.
FXS interfaces for analog phones will be at least about $70/port no matter how you slice it, and that assumes everybody has a phone and wiring.
IP phones are a bit more expensive, depending on what you get they start at around $100/phone(port) ($80 for a sipura-841 which is quite capable) (assuming you have adequate ethernet infrastructure), however over time and as you expand, they may save you money in lower hardware requirements (with reinvites, you can put many more than 100 IP phones on a server, so you don’t need a second box for quite a while). Also, IP to IP calls don’t require echo cancellation on the server, in fact they don’t require much of anything unless you’re talking on an outside line or recording something (because if allowed to do so, IP phones will send the voice data directly to each other; only using the server to set up the call).
Also- what kind of phones do you have now? Your AltiGen analog phones may not work correctly with a standard analog channel, in which case they will be useless and you have to replace them anyway.

My preference would be to (if you can sell it to those holding the credit cards) give everybody a VoIP phone. This will drastically simplify your backend needs, and with it you will be able to (unless your server sucks) expand to at least 100 users without needing any more servers or hardware.
If the Ethernet infrastructure isn’t there (which can be worked around by getting dual-port phones) and/or you think you aren’t ready for that, then dont bother; but if you think you will and you can afford it, now is the time.

That said, if you do go then analog route, you’d have to consider if you want to use PRI cards and channel banks or TDM2400 cards. Like I said, it comes out to be $70/port either way, and (assuming your mobo will correctly give each Digium 2400 card its own IRQ), i’d still go with 100channels/server max (although 4 cards/server is sort of pushing it).

As for dual-cpu boards- the advantage of this comes when you are crunching something. That means either encoding to a low-bitrate codec such as G.729 or iLBC, or echo cancellation for very large numbers of channels. IMHO, get one GOOD cpu and you will be fine.

As for multi-server, there are a few ways to set it up. How you do it will depends on what your calling patterns are, and how your company is organized.
If your users make a good quantity of internal phone calls, what will work well is to have a front and back system. Have one server with a bunch of TDM2400 cards that connect to your phones. Link it via a dedicated Ethernet span (TDMoE) or IAX trunk (both support more than 24 channels per span) to the other server. The other server will have your Dual- or Quad-PRI board and up to 100 channels of PRI T1 to your telco. This way loads such as echo suppression are balanced between the two systems.
If your users rarely call internally, then this system won’t save you much. For now it might be better to put everything in one server and then expand later as needed.

lastly, at least as an option- setup a system with FXS ports now for your existing users, but add voip phones for new users as you expand. This isn’t as efficient as going all-IP, but it greatly reduces your investment in old technology.


#3

Great advice. This is beginning to make some sense.

Yes, I am replacing the AltiGen switches. All phones are analog. A mix of off the shelf handsets and headsets. All have “Flash” features, some with CID dsplays, but nothing fancy. Buying new phones now is not going to happen.
VoIP is way down the road.

As for usage, mostly outbound calls to existing clients. Some sales calls.
Autodialer in the near future for sending deadline reminder notices, etc.
Internal calls are infrequent.

Sounds like I should get two boxes.
One for the Quad T-1, and the other for all the analog phones & POTS lines.
If each 2400 can handle 24 extensions, then 4 boards would do it.
If we grow beyond the need for more than 100 channels, I’ll get another.

I assume that these two servers can either be directly connected.
If not, I have a Gigabit switch. Traffic between them would be isolated.

Anywho, I just need some specs on form factors, available board slots, motherboard options, disk space, memory, etc., and I can start spending.

Let’s see, fast CPU, FPU, Gb NIC, no video, no audio, lots-o-memory, disk…

Recommendations? (Considering IRQs, compatibility, driver issues?)

Thanks again. You’ve been very helpful, patient, and kind.


#4

yeah, you can directly connect them. Either over the GB switch or with separate ethernet cards in each one, i’d use a system called TDMoE. It sets up a fake-PRI interface over Ethernet (level2, no TCP/IP involved as i recall) with as many channels as you want. Never used it personally so I have no idea how well it works, but it seems like it might be ‘better’ than an IAX trunk.

as for recommendations- mostly the normal server crap (raid1 disks, ECC memory, etc). Also for your cases, remember that the 2400’s are full height full length boards, so you will (as i recall) want at least a 3-4u chassis and make sure it has the length for a full length board.

One last idea to consider- a gateway appliance. It’s a 1u(usually) device thats basically a channel bank but with SIP instead of PRI on the other end. You should at least consider such a thing, as it would probably remove the need for a second * server. This would simplify your setup- put the Quad-T1 and possibly 1-2 TDM400’s in a server, connect all your phones to the gateway, setup SIP and call it a day. IIRC, they cost about the same as a channel bank + pri card, but they save you money in that you don’t need a second server. Then you have 1 * server with everything connected to it. This also leaves you room to grow, because you can add more gateways pretty easily and a quad-PRI card has plenty of growth room esp. if you only have one T1 now.
It’s worth considering at least.

Good luck!