An easy yet effective way to test if existing network cabling will be ok for GbE?

Question

OK, so the story is this: I'm a school governor for my daughter's primary school here in the UK (roughly equivalent to being 'on the school board' in the USA, I think).

I'm the IT governor (pretty much by default) because I work in IT but my work has never included network engineering. So I don't know much about this specific area.

The school is being extended and refurbished soon, and we want to upgrade the network from 100 Mbit/s to GbE. The new part of the building will be fitted out with appropriate cabling for GbE. We'll be buying new switches for the the whole school.

The existing part of the building is being refurbished and we have the opportunity to replace the existing network cabling. Or we can save money and keep the existing cabling.

So the question that I'd like to find a way to answer is: is the existing cabling capable of working properly at GbE speeds?

If it's the case that an upgrade from 100 Mbit/s to GbE always requires new cabling, then I guess my question is answered quite simply: we just need to replace the cabling. But I'm not clear whether that's the case.

Ideally I'd like to answer this question without paying for an expensive survey from an external company, since the school has fixed budgets and any money that we save here is freed up to be spent on teacher salaries, educational resources, etc...

I don't want to start making holes in the walls and physically looking at the existing cabling - every part of the school is in constant use by teachers and children at the present time.

Neither the school nor the local authority has yet located any plans or diagrams or other details of how the network is cabled and what standard of cabling was used.

The network may well have been added to gradually over the years, rather than installed all-in-one-go. I know that none of it has been installed within the past 7 years. The walls have RJ45 sockets.

I can see a variety of devices billed as 'network cable testers' are available - I could buy one of those but I'm not clear if this is really the purpose they're intended for, or if they're just for checking that a new installation is wired up correctly. Some of them just have LEDs showing a quality result from 1 to 10 - I'm not clear how to interpret that in the context of "is this good enough for GbE?".

We have plenty of laptops supporting GbE that we could plug into the network if there's a way of testing this using them.

Any advice much appreciated. Thanks.

Answer 1

A E said: OK @MikePennington, so what's the "right way"?

Either hire a professional cable installer to check out your cable installation, or get something similar to a Fluke CableIQ. These meters perform detailed tests on the cable that reveal what you're dealing with. GigE has Signal to Noise requirements that simple continuity testers will not check. Cheaper continuity testers are typically what you'll find at lower prices in consumer electronics stores.

After you have satisfied one of the conditions above, test every cable. That's expensive and time-consuming, but it's the only way to be sure you won't deal with flaky connections down the road.

Some might argue that you could merely look at the jacket of the cable and see whether it's at least Cat5e; however, that's still inadequate to truly know whether you can use this for GigabitEthernet because:

• Someone could have used the wrong cable connectors or patch panels
• Someone could have crimped / punched down the correct equipment poorly
• Someone could have made errors pulling the cabling (i.e. used excessive force)
• Someone could have run the cabling across sources of significant electronic noise
• Someone could have violated cable run length requirements

If you're willing to gamble, you can test every cable with a couple of cheap 1GE switches from Wal-Mart, ensure each cable links to 1GE, and hope that those results are repeatable. However, I don't recommend this approach for anyone who cares about whether every cable is done right.

Answer 2

The standard for Gigabit Ethernet was ratified in 1999, so it's certainly possible that the building was wired to cat 5E or better, if it was wired some time this century. However, as Mike Pennington notes, using the right components doesn't guarantee the installation will meet the specification. The higher the rating, in general the more careful you have to be.

You could certainly look at the cable and panels to see whether it could meet the 5E at least standard before you waste your money getting it professionally tested.

You also have to consider how much effort nursemaiding a potentially dodgy installation would be. If you don't have the expertise on site, which I'm guessing you won't it could get expensive. The worst scenario is that it works at Gigabit rates but unreliably.

Answer 3

You can use cable qualification testers that perform tests to decide whether an existing cabling link will support the requirements Gigabit Ethernet.