Networking / Beginners

---

Step 2: Intrusively testing: Looping the CSU

Your carrier can intrusively test a circuit, which renders the circuit useless to you during the duration of the test. Every channel of the circuit being tested must be engaged so you won't have any room left to either make or receive calls.

Remember As soon as your carrier begins intrusive testing on your circuit, all the active calls on your circuit will be disconnected. The testing environment usurps all the bandwidth. Your hardware can't grab any DS-0 to make or receive a call during an intrusive test. If your circuit is already down, you should release it for intrusive testing. If the circuit is bouncing, or only slightly impaired, you need to make a judgment call. Can your business stand to have the circuit down for 30 to 60 minutes now, or should you wait until after your office closes to release it for intrusive testing?

Tip You don't have to release your circuit for intrusive testing at your carrier's discretion when you open your trouble ticket. If your circuit is bouncing, ask the carrier to do some preliminary work first (such as accessing the system's performance monitors). You can always release the circuit for testing after hours, say at 7 p.m. central standard time. This way, you can get basic information, and when you get in tomorrow morning, you can get more information about what the carrier found during the intrusive test.

An intrusive test involves looping the CSU. Looping is a general term used in telecom that describes the act of sending an electrical signal to a specific piece of hardware where it's bounced back to your carrier. Your carrier technicians actually send a stream of data down the circuit, possibly consisting of all 1s or all 0s. If every "1" the technician sends in a test effectively hits the desired endpoint and comes back to your carrier, your circuit has solid continuity from your carrier to that point.

If the idea of looping doesn't make sense to you, imagine it another way. If you have a garden hose with leaks, the easiest way to find them is by placing a spray nozzle on the end of the hose and closing it so no water can escape. After the end is sealed off, you can check for leaks by turning on the faucet and looking for any water springing out of it. Intrusive testing does the same thing, but with data. If you send a series of 27 consecutive 1s down the circuit and only 25 return, you know that a pair of your 1s were lost somewhere between the point at which the data originated and the looped piece of hardware that is sending it back to you. Losing data means that you have a problem in that section of your circuit.

There are many tests that your carrier can use when looping a piece of hardware. They have names like QUAZI, 4 and 8, 6 and 2, and my personal favorite, all 1s. Some tests are more rigorous on a circuit than others, so have your carrier try a few of them if you don't feel confident with the results of the first test.

Intrusively testing a dedicated circuit follows a very methodical sequence. Your carrier's first test is attempting to loop your CSU.

Dealing with synch issues caused by Dialogic cards

Remember If you are using Dialogic cards as the multiplexing interface on your side of the circuit, you may have problems when you reboot your hardware. There is a known issue that exists between Dialogic cards and some switches that the carriers use. If you find that your Dialogic cards don't automatically synch up when you reboot, or if individual channels lock up when you dial to a bad phone number (where you receive a recording or a fast busy signal), you need to enable the CRC-6 setting on your Dialogic card to resolve the issue. You might also need to reboot your Dialogic card before the programming change takes effect. After the setting is enabled, your channels shouldn't fall out of sync with your carrier any more.

Remember Not all CSUs are identical. Your CSU might not be a free-standing piece of hardware and might instead be an integrated card housed within your multiplexer. It's uncommon, but not unheard of, for a CSU to not be loopable. This isn't a huge stumbling block, but you simply need to be aware of this bit of trivia. Your carrier might try to imply that your hardware is defective, because the carrier can't loop your CSU.