FOOD FOR THOUGHT Cat3 Wiring

[David Sabot]

Currently using FreePBX 2.11x and have 3 SIPS coming in. Have 9 internal extensions.

We as a company make VERY FEW external calls. The most calls in a single day we ever had was 130.
We use the extentions to page each other.

So in general, there doesn't seem like a lot of traffic on the line.

We are moving to a new facility and they do not have CAT5 wiring, but rather CAT3.

I really don't want to upgrade the wiring if I don't have to. How well will FreePBX run on CAT3?

 

[MGD4me]

Not to be crass, but the question is similar to "How well will a Model T run on the freeway?", but is a good analogy. They will both run fine, to a point, as they both have speed constraints.

CAT3 cabling is rated to 10 Megabits/sec, and CAT5 is 100. Whether or not you upgrade now, or ever, will depend on how long you plan on staying in the facility. For now, you can figure that each extension only requires approximately 100 Kilobits/sec (.1 Mbs) of bandwidth. If each extension has it's own "home run" CAT3 cable, then that portion of the wiring certainly has ample capacity. It would be at the point where the traffic is combined, such as the leg towards the PBX, which would be more critical. You never want to run at more than 50% capacity here, as data collisions will quickly bring traffic to it's knees. So, even at 5 Mbs capacity say, the CAT3 cable to the PBX could handle 50 extensions theoretically. Next, from the router to the outside world, and whether voice traffic is competing with "other" internet data.

Should you decide to upgrade now for "future-proofing" purposes, then CAT6 is the current standard to shoot for. Beyond 10 years, who knows? You might need fiber optic cabling instead, or the technology might be totally wireless, so the concept of future-proofing has a limited life span.

As an alternative, you may want to have your existing cable plant inspected, tested, and certified. If the CAT3 was properly installed in the first place, and hasn't been modified or disturbed since day one, you might be good to go "as-is".

Just my $.02 ...

 

[David Sabot]

@ MGD4me that was incredibly helpful and much appreciated!

 

[Billy Johnson]

The Cat system is actually rated on Mhz. Cat 3 has a bandwidth of 16 Mhz and Cat 5 and Cat 5e rated to 100Mhz with different ACR values at 100Mhz. There is an unofficial Cat5E with a bandwidth of 350 Mhz. There should be no collisions on a UTP system running full duplex. You have one pair for TX and a seperate pair for RX. Collisions will only happen on the old coax systems or half duplex systems. As far as utilization goes that is going to be dependent upon your switch switching capacity and the processing power of the end nodes. With Cat3 fastethernet is going to have a problem. The signalling 4B5B does not have sificant bandwidth on Cat3. If may appear to be working but if you put an analyzer on the cable you would see a lot of CRC errors and retries.
Just my .02 cents

 

[ou812]

I have a Asterisk server working on a customers site for over a year with No problems, only the phones are on cat3 3pair, I reconfigured the RJ45 jacks so they would also provide poe.

gary.