QUESTION: Are there any further synchronisation requirements that telecom operators need to be aware of to support SDSL technologies over & beyond what is currently provided to support ADSL technology? Has the ITU-T carried out any work in this area for example?
ANSWER: On the face of it, the synchronization requirement for SDSL is not that different from ADSL. In both cases the DSLAM has to be provided a Stratum-1 traceable reference (from the local SASE) since it is required in the Standards to provide a Network Timing Reference (NTR) to the xTU-R (customer premise located).
At a somewhat deeper level, it should be noted that the DSLAM is being positioned as the principal access mechanism and the xTU-R positioned as an Integrated Access Device (IAD) to allow the Network Operator to carry a wide variety of services over the copper loop. These services include legacy services, including ISDN BRI and PRI. In a "data only" application, it is quite easy to ignore the NTR; however, with synchronous applications it suicidal to do so.
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