esting is that of the signalling place to play in ISDN testing, as they can perform far more complex protocol that is carried in the D channel. and detailed tests that cannot be achieved with the combinational The testing of ISDN Basic Rate circuits has no historical pre- simple testers. cedence but yet can be split into three distinct categories as per the Primary Rate circuits and other non-ISDN circuits, as follows: 61.5.4 Testing philosophies 1. Physical testing, the testing of the physical parameters of the 61.5.4.1 The effect of maturity media used to carry the signals for the appropriate interface. These tests would normally be impedance, continuity, jitter, The types of test which are carried out on transmission installations, signal balance and electrical loading. and the ways in which the test equipment is connected, depend on 2. Transmission testing, the transmission test being designed to the maturity of the service transmitted, as illustrated in Figure 61.16. test the transmission capabilities of the physical media as well In development, conformance with specification is of prime import- 61/18 Telecommunication system measurements Maturity 61.5.5 of service ISDN Basic Rate transmission testing service 61.5.5.1 Basic Rate structure The ISDN Basic Rate signal is a time division multiplexed compo- Functional site of two 64kbit/s channels, known as B channels, plus one Development conformance 16kbit/s control channel, known as the D channel. Basic rate trans- mission is used to connect subscribers to local exchanges, where ISDN line cards or ISDN multiplexers convert the basic rate for transmission over the network. The purpose of basic rate testing is to establish the quality of the Install transmission over the subscriber loop. This is achieved in three phases: Installation / 1. Testing of the physical connection. Conformance and commissioning 2. Establishment of a call. out of service full quality validation 3. Data or speech (voice) transmission testing. repair 61.5.5.2 Basic Rate physical line test