Selt Melt Delt

DSLAM vendors offer integrated "SELT, DELT and MELT" as a full solution for testing a customers line.

SELT = Single Ended Line Test
DELT = Double Ended Line Test
MELT = Metallic Line Test

The DSLAM is capable of generating masses of statistics on DSL performance, it can also pull off statisticss from the customer's DSL modem: -if the customer is using a compatible modem!

Loads of "useful" information can be derived from this data. Unfortunately it is only of very limited use in solving real customer service problems, because SELT and DELT only works while there is a DSL connection established.

The customer is calling the service desk or helpline becuase his or her DSL connection does not work. In these circumstances SELT and DELT will tell you that it is not possible to establish a DSL connection. It cannot tell you why! The fault may be due to a faulty line card port on the DSLAM, a faulty DSL modem at the customer's end or neither of these, it could be a real copper line fault!

SELT and DELT enable the CSPs call centre operative to confirm that there is a fault but it cannot identify the source of the fault.

Some DSLAM vendors claim that they can test the copper line using their built in "MELT" functionality. This is not entirely true. Yes the DSLAM can carry out AC tests on the line but these tests are of little value as they cannot identify common line faults such as Leg to Ground leakage. All of the really useful line tests require DC coupling of the test circuitry to the line. This is however not possible on the line card because the DSLAM port is AC coupled to the line via a line transformer.

Faced with a "don't know" answer from the integrated SELT DELT and MELT, the service desk operator at the call centre is left with a few options. He can ask the customer to cold start his PC and Modem and check the status of the modem indicator LEDs. These LEDs again only verify that there is no service but cannot identify the cause of the fault.

Unable to sort out the problem with a reboot the call centre operative escalates the fault to the"technical helpdesk" who lacking a proper testhead and test access switch will not be able to do much either.

The first thing they will do is to annoy the customer more by asking him again to cold start his PC and Modem.

If this fails (again) they will try to eliminate the line. In the case of an "unbundled" copper pair this will mean asking the incumbent operator to do a proper line test. If the line tests OK, then the CSP will usually be charged for the test. If it tests OK it still leaves the big question open – has the DSLAM line card port failed or is there a problem with the customer's DSL modem. The only way that this can be checked is to send a technician to the DSLAM to manually break the line and to carry out tests with a hand held tester or plug a known good working modem onto the line at the customer's premises.

Costs are now mounting due to expensive truck rolls and engineers time. The customer is also still waiting and becoming unhappy with the service provider.

True Test Access with remote test and diagnostics is the real answer. The solution is here.