Ring protection for transport network based on PDH digital microwave links with k/spl times/2Mbit&s and E1 like frame

In this paper we discuss possibilities for ring protection in a network based of PDH digital microwave links (DML), which is typical for interconnection of base stations in mobile telephony. Since such DML network has huge density, and relatively small hop distances, usage of higher frequency bands (13 GHz and above) is preferable. At such frequencies rain attenuation is critical, so path diversity is the only way for performances improvement. Therefore the ring topologies may be more efficient than 1+1. We describe the hardware solution of hitless switch for such purpose. The main design problem is signal delay equalization. We restricted to E1 like frame structure.