MEDEIROS, E.; MEDEIROS, Eugênio.
Resumo:
Local networks of ring-shaped computers with deterministic access protocols and optical fibers as a means of transmission are an important alternative for integrating communication services (data, image, voice) at the local level. The bit-level transmission system generally associated with this type of network configures a synchronous chain of regenerative repeaters. The most appropriate bit-level synchronization scheme for the repeater chain of a ring network is the master-slave scheme. Basic-band transmission results in the simplest and most economical transceiver. The master-slave synchronization scheme may be implemented in a ring network by transmitting the clock information in the data signal itself. In this case, the master repeater node provides a stable time base and the other repeaters retrieve the clock information by passing the data signal received by a non-lincarity and then a filter. Phase-Locked Loop (PLL) circuits can perform these two operations and have been used in various embodiments. The clock recovery process produces jitter in the recovered clock phase. The cumulative effect of dazzling repeater nodes can make jitter a strong limitation on the performance of the synchronization system. The accumulation of jitter causes two basic problems: the need to place a synchronization buffer in the master repeater node, and the possibility of network failures by the occurrence of cycle-slips in PLLs. In this work, the jitter accumulation caused by the Symbols Interference (IES) is evaluated for a chain of repeaters in a computer network configured in ring and with fibers as a transmission medium. The transmission in basic band is considered using the code Manchester (Bifase) and a PLL of 2nd order like circuit recuperador of the clock. The performance of the bit-level synchronization system in relation to the jitter caused by the IES is evaluated as a function of the dispersion in the optical fiber, the number of repeater nodes in the communication subnet and the average length of the optical links. Additionally, the length of the ring synchronization buffer required in the master repeater node is estimated and the design of the PLLs synchronizers is analyzed.
