Few questions about the physical cabling for my system

hey all

I’m the sound engineering instructor for a charity music organisation that provides music lessons and education to kids among many other things. We have outgrown our current premises and have managed to find a custom built music rehearsal/studio complex thats been lying empty for a couple of years and will be perfect for our needs.

We have to lay out a phone and internet system for several users (explained below) and I have just came across Asterisk and it looks perfect for us, in terms of the software and programming it looks fairly straight forward but just a couple of questions about the physical wiring i’ll have to lay out in the building to get it all to work.

The senario…

The complex as a whole will be run as a semi seperate business from our current music charity and will house the charity along with several other things. For our use we will need two phonelines, one for members of the public outside that charity who just want to book time in a rehearsal room and one for people who call with regards to the music lessons and things. Both numbers will be routed by Asterisk to the same reception, but hopefully with a way to show the person answering which number has been dialed so they can then answer with the appropriate greeting (hi welcome to such and such, or hi welcome to the other such and such). The will the have the ability to deal with a simple inquiry themselves or to transfer the call to four maybe 5 different extensions if it has to come to me or someone else.

We also plan to dedicate some space as a business hub however, where other local small music and media organisations such as small record labels, promotion companies, graphics designers etc etc can rent a desk/phoneline/net connection from which to run. We may build it up to as many as ten or more, so would need a further collecton of phonenumbers that would come through asterisk but bypass reception and go straight to that person/desk. All of the numbers would require an answering machine and we may also offer a second line to each desk if they want a fax.

My plan for all of this is to get a PRI line (well BT over here calls it an IDSN30 line but i asume that what they mean) so that we have lots of channels and can just buy as few or many Direct Dial numbers as we need and use asterisk to send them where they need to go as the various businesses come and go.

In addition, we will have a separate phone connection comming in so we can have a DSL connection (which I assume cant just be run down one of the channels of the PRI?) and then network that throughout the building using a mixture of wired and wireless connections.


OK so thats the plan, now the questions:

Firstly with the use of a card such as the Digium ones that have the t1/e1/j1 ports on them the PRI line will just plug straight into the pc thats running Asterisk? or will some other sort of adapter be needed in between?

Now to save some money and hassle I was hoping to use VoIP handsets and softphones throughout so that I could maybe run the internet/dsl connection and the handsets through the one set of cabling. Is this doable/recomended?

How does the VoIP get out of the Asterisk box and into the system of handsets, just through an normal ethernet port?

In terms of wiring up the VoIP handsets, i’m not totly sure of VoIP not something ive never worked with before, but I assume you just use cat 5 or cat 6 (prob cat 6 for futureproofing) and each handset/softphone has a subnet IP just like a PC on a network? so does every handset need a direct line all the way to the Asterisk box or can I just use switches/hubs and normal topologies to be a bit more efficient about getting the signals about everywhere, and use the IP addresses so they all find their way to the Asterisk box.

What i’m thinking of here particularly is for the business hub room, where it would be great to just run a single cable to it then a hub to split to each desk, rather than having to run 10 or 12 different cables all the way from the initial control room.

And overall, can i use VoIP like this? Even though i’m not actually using a VoIP carrier, will VoIP (using SIP or IAX) work from the handsets to the Asterisk box and be converted inside Asterisk to then go down the PRI line.

Then mixing the internet in? Would i run the DSL line through the Astrisk box as well and then into the system or would this line bypass the astrisk box and plug the DSL straight into the hub thats distributing the various call lines. Will the connections all sort themselves out with thin the subnet using the IP addresses so calls get to phones and data gets to the PCs, or is it better just to separate the two within their own systems in case a large file transfer or network print ties up the bandwidth and affects the phone quality?

LOl sorry I know thats a bit of a barrage of questions all at once but really appreciate everyone’s help.


Your wiring will be pretty standard. As you said cat 5E or cat 6 every where there will be a station (computer or telephone). There are different type of VOIP telephones, some have two ports on them. One is the connection to the wall and the second goes to your computer.

Voip telephones need power from the wall or you can get a POE switch which will suppy the power to run the telephone.

In the states, some carriers will supply a combo T-1 with a channel bank that will separate the internet connection from the telephone lines. Or you could run the T-1 just for internet connection and future VOIP carrier connections.

Take a few moments to sketch out your building and lay out every possible connection (phone, fax, and computer and don’t for get others like alarm).

Asterisk telephones (VOIP) run over the local network and connect to your asterisk server.
hope this helps to get you started, post back with questions.

brilliant, so just to confirm a few things…

The two connections inside some handsets act like a little switch themselves so the pc can connect to the net and the larger wiring system through the handset?

With it all on the one systems like this, the subnet IP’s will let everything get to where it has to go (i.e. phones to asterisk and comps to DSL router) without any troubles. Will DHCP sort all the IPs out and if so which one (the asterisk box or the DSL box) will be the assigning host, or is it better to just address everything in the whole system myself?

Will there be any noticeable loss of quality or even dropped calls this way if someone does something silly with data? Obviously even if people are using the full speed of the DSL there will be plenty of bandwidth left over on even a 100mb network but what if someone does some silly large file transfer from pc to pc and uses up the majority of even the 100mb? what kind of bandwith is needed for say 10 simultaneous calls as that’s about the maximum i think will ever happen.

Ok based on what you said (and subject to the answers to those questions) here is a very rough overview of the kind of thing i’m thinking of. Obviously it’ll become far more refined once i can actually plan out how many handsets where the physical locations will be etc etc, but just in terms of overall topology is this then kind of thing that would work?..

Looks good so far.
You can set the asterisk server to static IP and the phones to static. and you can use a separate subnet for the phone system.
In you router setup, you can shape network traffic to give the phone system priority on data. (traffic shaping).
You might not to need to that right now, but keep it in mind.