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Power-User

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LAN Telephone (Help)

11/10/2012 3:32 AM

Dear Sir,

We have LAN Network in our department. currently there is 24+24 port two Ethernet switches working & approximately 30 computer are connected with this device. we are planning to arrange small telephone exchange for communication between all user pc. My question is, Can I take advantages of LAN cable which is already laid on every spot where we will lay telephone cable??? I want to save cable & intercom set cost. kindly advice can i use existing cable pair for telephone or any software/device available for communication through Ethernet cable. Please share your experience with me.

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#1

Re: LAN TELEPHONE (Help)

11/10/2012 3:51 AM
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#2

Re: LAN Telephone (Help)

11/11/2012 7:51 AM

The simple answer to your question is YES. However I looked at some of the links Joshi supplied and while what they do will work it's not the correct way to do it.

First off the Blue/White pair are the one you should be using for telephone signals rather than the Brown/White pair that some sites quote.

Next off the best way to break into the cable so you have access to the unused pairs is to terminate you 4 pair Ethernet cables in at Krone modules mounted in a frame. These are extensively used in telephone exchanges to terminate the lines that run between exchanges and create interconnections between cables and equipment. The termination modules come in a range of colours and types with the one in the image below being designed to terminate two four pair CAT4 cables.

However, you can also get modules that are rated for CAT5 and I believe CAT6. The great thing about terminating everything with these modules is that it gives you access to each individual pair.

What you would do is rather than terminating the building cables at RJ45 sockets then using patch leads to you hub/router they would be terminated at Krone module similar to the one in the image above mounted in a frame. You would then take the patch leads that come from your routers/hubs, cut of the RJ45 connectors from one end and then terminate the ends at other Krone module in the same frame.

Now to connect a port on the router to a wall outlet you use a 2 pair jumper cable (Green/White & Orange/White) and jumper the Green/White & Orange/White termination from you building cable to an unused Green/White & Orange/White termination module that is connected to the ports your Router/hub. You now have ethernet available at the wall outlet.

You can now connect the phone line to the Blue/White pair on the building cable module to send the phone line down the same Ethernet cable.

This technique sounds somewhat convoluted, but believe me, it will make it easy for you to change cabling around as required by just changing jumper wires at the termination frame. That's why they use them so extensively in telephone exchanges.

I've seen this system used to cable the Ethernet and phone connections for an entire university with over 10,000 separate ports being used together as phone and Ethernet.

One thing I would however recommend is that at the wall plate you terminate you CAT5 or CAT6 cable as normal to an RJ45 socket. Then using a short piece of Blue/White twisted pair jumper the Blue/White connections on the RJ45 socket to the phone socket you intend to use. That way if you do decide to use Gigabit you still have all 4 pairs connected to the RJ45 socket. However, you will need to unplug the telephone from its socket to get it to work and perhaps cover it some way so that people knew it shouldn't be used.

The only problem you will have is that you will not be able to use Gigabit Ethernet over a cable that also has a phone signal running down it so you will be limited to 100 Mb/s. Having said that we had no problems with interference or loss of performance by terminating CAT5 cables at Krone frames and using jumpers to interconnect the building wiring with hubs/routers/switches/PABX units and so on. We have also used the same termination system to send all sorts of other signals down CAT5 cables like RS-232, RS-485 et cetera simply because we had access to each of the individual pairs in the CAT5 cable when it's terminated at a Krone module.

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#5
In reply to #2

Re: LAN Telephone (Help)

11/12/2012 1:31 AM

I found this image of what's called a High Band Krone Module. Basically is a standard Krone module that clips into their standard frames but instead of being designed to terminate 10 pairs of phone cable it's designed to terminate two CAT5 cables with four pairs in each cable. It's also certified to CAT5 signal standards so you'll have no problems pushing 100 Mb/sec through it while still having access to the unused Blue/White and Brown/White pair. It's also colour coded for CAT5 cable so there's less chance of mixing up which pair is terminated where. Krone also sell record cards that can be put in binders that keep track of what's terminated at which module and where the interconnecting jumpers in a frame go from and to. If you wan't to learn more about how to use Krone modules and frames just go to your nearest telephone exchange and you likely see frames containing thousands upon thousands of them.

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Guru

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#3

Re: LAN Telephone (Help)

11/11/2012 10:05 AM

Masu is right 1 GP from me. The blue/white (center pair on rj45) is unused because it is the phone line in early com cables. The Ethernet twisted pair setup avoided the center pair to prevent the phone signals running 45-110v from getting mixed up with the lower voltage Ethernet signals.

If you are using POTS (Plain Old Telephone Signaling) type phone system, then you will be limited to 100Mbps on the other pairs. But if you are using VOIP then you should have no troubles at all. In fact, you shouldn't need to break out anything. Use the network and switches as they are.

If you break out the pairs on a block like Masu suggests, then keep the twists as far up to the punch down as you can to preserve the impedance of the lines. You should have no more than half an inch from last twist to punch.

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Power-User

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#4

Re: LAN Telephone (Help)

11/11/2012 11:39 PM

Dear Sirs,

Glade to see your positive replies on my request. I have founded said free pair which will full fill my requirement. bundle of thanks.

Once again Thanks,

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