Using VoIP to Connect Phones Between Offices?

virtualPhoneWire asks: "My office is expanding to include a new facility which is just a few hundred feet just across the parking lot. The building is just far enough away to make running cable a pain in the neck, so to get data over there, we're setting up an 802.11b link, and a couple of simple Linux routers to handle the traffic, no problem. Now, the people in this new building are going to need access to our phone system, a simple Avaya Partner II key system. I would like to think that there is a way that I can patch them into our switch using some kind of VoIP technology. The ideal being that we can issue a couple of IP phones that plug into the Ethernet back-bone, take their queue from my DHCP server, and linkup with a device on the other end that ties them into switch thus giving them access like any other phone. As an after thought, being able to give other people on our network, both inside the building and via our VPN, access to this gateway to make calls would be a real bonus. We're considering an upgrade to a real PBX, but we would like to do this without blowing the pension plan. We would like to having something scaleable, and open source, if possible. Any thoughts?"

Comments

Possible source

[Anonymous Coward]

I used to work for a company that did solutions like that. What we normally did was use ISA Micom cards (FXS). Micom are now owned by Nortel, and last I checked there were thousands of these cards still available through distributers. If you want to roll your own solution, get a rackmount case witha failover power supply, and a small processor ~ 266. Load the _DOS_ software and assign IP's,etc. Tie it into your existing PBX as trunks, and you are set.
If you are not inclined to roll your own, I do recommend Nortel's solutions, quite possibly because they tended to be the most relaible to use.

Hardwire it

[ka9dgx]

Let's face it, the only reliable way to get the phone service there is good old fashioned copper (or fiber). While I could support the idea of networking via 802.11b for a non-critical service such as networking, you really want honest to goodness cabling involved when you need to call 911, etc.

--Mike--

http://www.linuxtelephony.com/

[pauldy]

http://www.linuxtelephony.com/

Phreaks

[finity]

Calling all phone phreaks. Business setting up voip and opening it to anyone sitting in their parking lot with a laptop and 802.11b wireless card. If encryption _is_ used, you may have to sit a while. ;-)

VoIP Bandwidth and Leased Line Alternative

[jpkazarian]

Something to keep in mind: For real time speech quality, wireline TDM bandwidth = 0.15 * IP Bandwidth. Meaning that a 100 Mbps Ethernet link can support approximately 10 T1 lines worth of voice calls (120 simultaneous full duplex conversations). This is based on Ethernet realizing a 33% average throughput on shared media plus allowing 100% headroom for equivalent quality after IP packetization and quantization.

If the throughput of wireless Ethernet is the same as wireline, and by throughput we're not talking about the burst speed of the link, then an 802.11b link should be able to support one T1 worth of voice channels, or twelve simultaneous conversations. If RF interference reduces the throughput, your mileage may vary.

Another alternative is to lease a T1 qualified two twisted pair copper line between the two buildings from the phone company. Other posts are mentioning using channel banks at either end of the line. With leasing, the cost and pain of digging et al belongs to the local phone company. It may be worth the monthly rate for 100 feet to avoid that.

I can see it now:

[Hard_Code]

You. Have. Thirty. One. Thousand. Three. Hundred. and Thirty. Seven. Messages. Last. Message. From. "HAXXOR" At. Two. AM. To. Hear. Message. Press. One.