General questions

Hi there,

I’ve setup an asterisk server at home like that :
Installed centos 5.2 then asterisk on it.
Got a DID from a provider.
Have a cisco 7960 at home which connects to my router so it can reach the asterisk server (which contact then the did provider).

Everything works well considering this very simple setup.

Now, my boss is interested in getting into voip at the office. I’ve read a lot about voip but still, there are many points unclear in my mind, especially about hardware since my setup at home required none.

Here is our current office setup : 15 telephone numbers, all pstn phones, 4 fax dedicated lines and it is not uncommon that 10 persons talk at the same time.

I guess this is not unsual setup but it confuses me a lot!

  1. At home, I have cable connection between my asterisk server and the provider (900k/sec). From what I saw, digital cards are mainly made for T1 lines. So do I really have to use T1 for the office setup or should a 1mb/sec cable line could do it?

  2. I plan about using PCI card for fxo-fxs. I also noticed that adapter exists. What would be the best choice. Is it that pci cards are less expensive when having a lot of pstn to plug?

  3. I can see that there is very few digital pci card with only 1 input. It seems that 2 or even 4 ports is more common. How is that? Is it only to accomodate very large compagnies or am I missing something?

  4. Should we decide to get a T1 for our voice needs, do you have to pay for bandiwth or is is unlimited?

  5. I read that a T1 is 24 pair of copper wires. Does it means that it can accomodate 24 different DID so max 24 person can talk simultaneiously?

As you can see, I’m confused. There is a lot of accurate information about voip on the internet but few for general questions like these.

Can anyone help me pointing me the right direction?

Thank you!

I’ll try to answer your questions in order.

It looks as though if you have the possibility of 10 concurrent calls then a T1 would be the way to go. A T1 is a digital circuit that is not actually 24 copper wires but rather 4 wires that can carry 24 channels (though one is generally used as a d-channel to control signalling for the circuit.) I have done similar installations and used a partial or fractional t1. Most providers will sell you say 12 channels or so at a lower rate than the full 24. Digium makes a card ( 1TE122BF) that is a single span T1 card you could use. The T1 will have a monthly cost that is not based on usage. Basically you have 24 channels of “bandwidth” (if you went with a full T1) no matter if you are using all that capacity or not. Also it can accomodate as many DID’s as you want but will only be able to have as many concurrent conversations as it has channels, ie. if you have a 12 channel t1 then you will be able to have 11 people talking at once or if you had a full t1 you could have 23 people talking at once because one channel will be reserved as the d-chan. I’ve always found it easier to deal with a single t1 span than a large number of FXO lines. You could leave the fax lines as they are or run them through the phone system. It would be a little more work and require a channel bank or analog gateway to run them through the t1 and the phone system but it might be cheaper in the long run, you’d just have to look at the prices from your telco.
Hope this helps