We have been working on another troublesome ADSL circuit for a while now at a bank branch on the Gold Coast. As the site is within 1km of the exchange the synchronisation speed is good but the circuit is unstable and therefore unusable so they are running on a slow 3G backup connection.
We have investigated the circuit performance using a modem and special software that enables the circuit performance to be measured along with a frequency plot. We have done it at the MDF and at the socket and there is virtually no difference.
Of all the data provided, two figures stand out the loss over the circuit and the signal to nose ratio. The loss is higher than it should be and the signal to noise ratio is very low. The result is that less signal is available meaning less speed and the modem may have difficulty hearing the signal over the noise.
These are indications that the port in the exchange may be failing. In other cases we have seen the loss rise and signal to noise fall – as if the customer has physically moved further away from the exchange.
The modem used for testing is very sensitive and works very well on long and noisy lines. This was left on site for several days logged into a test account with the carrier and it did not drop out once.
The bank IT department has replaced the router but appears to have transferred the WAN Interface Cards (WIC’s) to the new router.
A new ADSL circuit was provisioned on the fax line and we were asked to go and connect it. My tech arrived on site and was unable to get sync so it hadn’t been connected properly. A fault was raised and a Telstra tech arrived on site the following day. He rang me to ask which pair it was on in the bank so he could test it and I explained what had happened so he went to see whether it was connected at the exchange. Apparently it was connected correctly but the port was faulty and he had trouble finding a good ADSL port – further supporting my theory the port for the original circuit was faulty.
The new circuit is continuing to drop out which raises several possibilities: the port for the new circuit is faulty, the ADSL card in the router is faulty or it just cannot handle the low signal to noise ratio as well as the test modem. We may go back to site to do some more testing or just install a modem like the test modem and connect it to the router.