By Ricardo A. Villa, Senior Engineer, DWDM Systems Engineering, Sudhesh Mysore, PhD., Director, DWDM Systems Engineering and Oleh Sniezko, Vice President, Engineering, AT&T Broadband
In the last two decades, a trend toward metro market clustering under a single operator led to changes in metro market architecture. This trend allowed for significant headend consolidation and for lowering the number of signal processing facilities to the level dictated by local programming requirements and operational issues. A side effect of this benefit was an increase in distances between the processing facilities and the customers. This had not been an issue for traditional broadcast services that did not require two-way communication. However, with the introduction of interactive services with their strict requirements for proper timing and synchronization, the absolute distance from the processing centers and the differential distance between the devices transmitting on the upstream path became critical.
Additionally, requirements for increased network availability on long fiber routes made it necessary to deploy optical switching to reduce the network downtime to a minimum. Optical switching activation results in an instantaneous change in distance that causes a change in delay between the terminal devices affected by the switch and the processing facilities. It also affects differential distances between the terminal devices. Therefore, a reliable and timely recovery from these changes became crucial to achieve network availability targets.
This paper presents the requirements formulated for all interactive service platforms operating in the HFC network with consolidated signal-processing facilities. It also presents and discusses the results of tests performed on several proprietary digital telephony platforms to verify these requirements.