SDH Network Topologies: Linear, Ring, Mesh, and Point-to-Point

This page describes different types of SDH networks, including two-fiber ring and four-fiber ring configurations. It explains the unidirectional and bi-directional ring concepts used in SDH networks.

Synchronous Digital Hierarchy (SDH) is a standardized digital communication technology used in telecommunications networks to transport data, voice, and video signals over optical fiber networks. It provides a flexible and efficient way to multiplex and transport multiple digital signals over a single optical fiber infrastructure.

SDH networks are based on a hierarchy of standardized bit rates, with each level representing a multiple of the basic transmission rate called the STM-1 (Synchronous Transport Module level 1). The most common SDH rates are multiples of STM-1, such as STM-4, STM-16, STM-64, etc. These rates determine the capacity of the SDH network.

The following section provides an overview of the types of SDH networks.

Point-to-Point SDH Network

In a point-to-point SDH network, two nodes are directly connected through an SDH link. This type of network is commonly used for connecting two locations over a long distance. It provides a dedicated and reliable connection between the two points.

Linear SDH Network

A linear SDH network is a simple point-to-point or point-to-multipoint connection where nodes are arranged in a linear fashion. This type of network is suitable for connecting remote locations or extending network coverage along a linear path, such as a railway line or highway.

As shown in Figure 1, a simple SONET/SDH network is composed of a sequence of nodes referred to as Add/Drop Multiplexers (ADMs). There will be either two fibers or four fibers connected between them. In the case of four fibers, one set acts as a protection or backup pair.

Ring SDH Network

In the case of a linear network, even if both sets of fibers were used between the nodes, there is a possibility of both getting cut at the same time, which would hamper communication services.

The most common topology is the ring network in SDH. They are popular because they provide an alternate path to communicate between two nodes. A two-fiber ring can be operated either as a unidirectional ring or as a bi-directional ring.

In the unidirectional case, traffic is limited to one fiber and flows only in one direction. The second fiber is used as a protection fiber. In the unidirectional case, there will be propagation delay (PD) between two nodes. As shown in the figure, if node B sends traffic to node A, the PD is one link, and if node A sends to node B, then it will be 3 links.

In the four-fiber case, one set is the working fiber, and the other set is the protection fiber. Also, data flows in both directions, and hence the propagation delay between nodes will be less.

Mesh SDH Network

This SDH network type consists of multiple interconnected nodes forming a mesh topology. Each node in the mesh network is connected to multiple other nodes, providing multiple paths for data transmission. Mesh networks offer high scalability and flexibility, allowing for efficient resource utilization and network optimization. They are commonly deployed in large-scale telecom networks where multiple connections and high fault tolerance are essential.

Conclusion

Overall, various types of SDH networks, including point-to-point, ring, mesh, and linear configurations, provide flexibility, scalability, and fault tolerance to meet different network requirements. Whether used in backbone networks, access networks, or metropolitan area networks, SDH technology plays a crucial role in ensuring reliable and high-capacity communication services worldwide.