NTL Broadcast deploy Astricom ISDN Loopback Device to enable Remote Testing of Basic Rate ISDN Lines

Background
With an extensive UK transmitter and telecommunications network, NTL supply broadcast services to most UK commercial radio stations from their national operations centre at Emley Moor near Huddersfield in West Yorkshire, NTL wanted to be able to test the availability and quality of ISDN basic rate lines going to each radio station studio and transmitter. They needed the flexibility to run these tests outside normal office hours to ensure minimum disruption.

Automated Call Generation to the Radio Stations
Our sister company Packet Data Systems provided a call generation system capable of dialing an unlimited range of telephone numbers automatically while recording all the protocol messages exchanged between the ISDN network and the call generator. The system provided a clear indication of call success or failure together with the clearing cause to provide a good indication of the fault.

The Challenge
The difficulty now was to provide a method of answering every call at each remote site. This had to be carried out automatically whatever the time of day or night and needed to loop back any B channel data such as a bit error rate test so that line quality tests could be carried out if required. It was also necessary that the device used to answer the calls at the remote site would only answer calls sent by the call generator at Emley Moor.

Solution
Our solution was to use the versatile Astricom automatic Loopback device at each of the radio stations. For NTL, each device was pre-programmed to respond to a called party subaddress received with each of the calls sent by our call generator. On receipt of a call containing this subaddress, the Loopback device would answer the call immediately and apply a loop to return any data received.

The call generator was programmed to send calls out to every connected device using the chosen subaddress, upon successful connection the call generator automatically clears each call after just one second with a 'normal' clearing cause and if any of the calls were not successful, the Network would clear the call using a cause that is immediately presented on the call generator display.

If subaddress had not been available on NTL's lines, the ISDN line-powered Loopback device could have been programmed to only answer calls from a particular number or after a user defined delay which would have been just as effective.

NTL's forward thinking approach allows them to be confident of the availability and quality of the service that they provide and they have been deploying more loopback devices as the number of customers benefiting from their service increases.