Availability model of bidirectional line switched ring

This paper analyzes the availability of a bidirectional line switched ring (BLSR). Some reasons for the introduction of synchronous digital hierarchy are listed as well as a survey of protection mechanisms development. The main concepts related to availability are defined as well as the availability of serial and parallel structures. Further, the working principle is explained and analysis of BLSR availability is made. The availability model of the nodes is examined and their influence is analysed as well as the influence of optical cable availability to the total availability of a 2 Mb/s signal between two nodes inside BLSR. Calculation of the availability of BLSR is made using data pertaining to the failures of optical cables and equipment which are obtained during years-long observation of the SDH network of HPT Mostar as well as those obtained from manufacturers.