SDH Networks - Linear, Ring, Mesh, Point to Point

This page of SDH networks describes type of SDH networks which include two fibre ring and four fibre ring. It explains unidirectional and bi-directional ring concepts used in SDH network.

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. Following section describes 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 the figure-1, simple SONET/SDH network is composed of sequence nodes referred as Add/Drop Multiplexers (ADMs). There will be either two fibres or four fibres connected between them. In case of four fibres one set acts as protection or back up pair.

SDH network fig1

Ring SDH Network

In the case of linear network even if both sets of fibres were used between the nodes there will be possibility of both getting cut at the same time and communication services will be hampered. The most common topology is of type ring network in SDH. They are most popular as they provide alternate path to communicate between two nodes. A two fibre ring can be operated either as unidirectional ring or as bi-directional ring.

In unidirectional case, traffic is limited to one fibre and flows only in one direction. The second fibre is used as protection fibre. In uni-direction 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.

SDH network fig2

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

SDH network fig3

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.

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