Is Rj45 ethernet the same as PARTNER phone sytem cabling?

October 17, 2005 7:29 AM

Is phone system cabling the same as straight-thru ethernet?

I'm trying to set up a vintage PARTNER system in my office. It has a couple 206 modules, a brain module, and a 400 module. All the jacks are RJ45's. When I connect the phone lines to the line jacks via Rj11's, and then plug a phone into an extension jack with Rj45, the phone passes the self test. I've found this piece of info surprisingly hard to google for. Do I just use regular old ethernet cables to attach the phones to the system?

posted by jeb to technology (10 comments total)

There's lots of posts out there on message boards that have people looking for this information (and it not being in the documentation for the system), but this USENET post both states that AT&T (who Avaya was spun off from) always used straight-through CAT-5 patch cables (which would indeed be the same as your regular old Ethernet cables). The post also has support numbers for Avaya so that you can confirm.

There's no technical reason why this couldn't be the case, so chances are that you're fine.
posted by eschatfische at 7:51 AM on October 17, 2005

I've seen similar things in the past. I'm not an expert, but RJ-45 is basically multiple (4?) phone lines wound together and terminated so the inside connections work as a phone line.

You can also take one ethernet cable and split it to have multiple phone lines with one cable.

I'm sure someone more knowledgeable will come along with more precise answers and terminology, but for anecdotal evidence I can offer a firm yes, this will work.
posted by gus at 7:53 AM on October 17, 2005

Indeed, as long as the Ethernet was Cat-5 and pinned straight through, you can definitely use the cabling. I have done a couple of build-outs where we just did straight-through Cat-5 on every jack home-runned to a patch panel, which could then be used to make any jack work as either a network jack or a phone jack as we needed it.
posted by briank at 8:41 AM on October 17, 2005

gus is correct, regular phones only need 1 pair of wires, while Cat5 uses 4 pairs.
posted by falconred at 8:59 AM on October 17, 2005

The million dollar question: are those RJ-45s pinned USOC or TIA-568A or B?

The original way to terminate these was USOC, and it was simple. Pair one on 4-5 (in the middle.) Pair 2 on 3-6 (just outside of that), Pair 3 on 2-7, Pair 4 on 1-8.

This worked fine for phones, which don't need very high quality lines. Indeed, USOC was usually wired with flat cable, not twisted pair.

Now, we add ethernet, and we start ramping up the speeds. The importance of noise rejection leaps, and we use twisted pair. The problem with USOC, though, is the pairs. Pair one is great. Pair four, however, sucks -- it's split across the entire jack, so the crosstalk from Pair 3, and overall noise, is horrible.

Enter TIA-568. This changes pair 3 and 4 to 1-2 and 7-8. This means that only one pair (Pair 2) is split at all, and it is not split very far. This works great. The kicker is that AT&T came up with the same answer, almost -- they put White/Green as Pair 2, while TIA-468 put White/Orange. So, now were somewhat stucky with two standards. The trick is to make sure you use the same one at both ends, unless you're making a crossover.

So, if those jacks are wired USOC, they will, at best, suck for ethernet, probably won't work at all. They will almost certainly fail at 100mb, and they won't work with Gigabit ether.

How to tell? Look at em. First sign. The wire pairs, four of them, should be colored White/Orange, White/Blue, White/Green and White/Brown. If they are Red, Green, Black, Yellow, Orange, Blue, Slate and Brown, it's flat cable, and it will suck for either.

Now, assuming you've got White/Color pairs. Look at pairs 1 and 4. They should be White/Blue on pins 4-5, and White/Brown on pins 7-8. If so, it's TIA-568A or B, and it'll work for ethernet just fine. For 100Mb, you can even still use phone on the same wire -- phone goes to Pair 1, Ethernet to 2 and 3. Gigabit uses all four pairs.

That should be enough. If you need to know which version of TIA-568 you have, check pins 1 and 2. If that's White/Green, you have TIA-568A. If it's White/Orange, TIA-568B.
posted by eriko at 9:39 AM on October 17, 2005

Oops. On reread, I answered the wrong question.

On both USOC and TIA-568, pair one is pinned on 4-5. Thus, for phones, it will work.
posted by eriko at 9:40 AM on October 17, 2005

I was puzzled by the lack of RJ-11 modules for a modular wiring system (Pass & Seymour/Legrand) until I wrote the company asking where I could get some. Answer: use RJ-45 jacks. RJ-11 male ends fit and use the wires in the center of the RJ-45 female. Helpful PDF's.
posted by Dick Paris at 9:54 AM on October 17, 2005

So a so-called "System Phone" only needs one pair?
posted by jeb at 11:57 AM on October 17, 2005

proprietary stuff sucks.

And just about every PBX built until maybe 3 years ago is proprietary. The only way you're going to get a definitive answer is from someone who is - or was - a licensed Avaya tech.

Don't expect a lot of help from the company - they'll point you to a licensed tech near you.

IMO, if the thing will choke along with properly-wired Ethernet*, use it. You'll be happier in three years when you want to switch over to the IP phones that will probably be selling at Sam's club for $30/ea in blister packs at that point.

(* Test it on a full roll of cable. If it'll handle that, it'll almost certainly be fine)
posted by Orb2069 at 5:58 PM on October 17, 2005

Thanks to everyone. It does seem to use only the innermost (pin 4, pin 5) pair, so cat5 ethernet works fine, as does the rj11-terminated cabling that was left stapled all over the office and dropped into modular jacks, which is convenient.
posted by jeb at 6:38 AM on October 18, 2005