Technology

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NextGen SDH

Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates, data can also be transferred via an electrical interface. SDH was originally designed to transport circuit mode communications (e.g., DS1, DS3) from a variety of different sources, but primarily, it was designed to support real-time, uncompressed, circuit-switched voice encoded in PCM format. The ability to transport ATM traffic was another early application. In order to support large ATM bandwidths, concatenation was developed whereby smaller multiplexing containers (e.g., STS-1) are inversely multiplexed to build up a larger container (e.g., STS-3c) to support large data-oriented pipes.

The introduction of Virtual concatenation (VCAT) allows for a more arbitrary assembly of lower-order multiplexing containers, building larger containers of fairly arbitrary size (e.g., 100 Mbit/s) without the need for intermediate network elements to support this particular form of concatenation. The Link Capacity Adjustment Scheme (LCAS) allows for dynamic changes to bandwidth via dynamic virtual concatenation, multiplexing containers based on the short-term bandwidth needs in the network.
Next-generation SDH is an improvement to the traditional SDH with enhanced features:-

Features of NextGen SDH

  • integrated data transport with Ethernet tributaries in addition to E1/DS1, E3/DS3, STM-1/4/16
  • integrated non-blocking wide-band cross-connects
  • intelligence for topology discovery, route computation, automated provisioning and mesh-based restoration

In addition, it has colored (DWDM) interfaces at STM-16 speeds to feed traffic into DWDM backbone while retaining all other features of SDH/SONET and has rapid (< 50 ms) protection in the event of failures.

Benefits of NextGen SDH

  • flexible mapping of any new service interface
  • more efficient use of installed infrastructure
  • transparency
  • better connection management
  • faster service turn-up/tear down
  • simpler OAM communications

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