Presentation on theme: "Synchronous Digital Hierarchy Eleventh Meeting. History of Multiplexing Synchronous digital hierarchy (SDH) is a world- wide standard for digital communication."— Presentation transcript:
Synchronous Digital Hierarchy Eleventh Meeting
History of Multiplexing Synchronous digital hierarchy (SDH) is a world- wide standard for digital communication network. Two other systems were before it: the plesiochronous digital hierarchy (PDH) and frequency division multiplexing (FDM). Frequency division multiplexing (FDM): a number of signals share a medium that has a much larger bandwidth. Support of many stages
Time Division Multiplexing (two ways)
Plesiochronous Digital Hierarchy Basic data transfer rate is 2048 Kbps It is broken in 30 x 64Kbps 2 x 64Kbps (synchronization and signaling) The exact are of the 2Mpbs is controlled by a clock with some percentage +/- %0.005 What is Justification or Stuffing Extra bits that are need to reconstruct correctly
Synchronous Transport Module (STM) STM-1 Frame STM-1 frame is designed this way because transport the full range of PDH bit- rates provide sufficient flexibility to transport future services based
Building transport (interleaving) The transmission of digital signals over optical fibre allows for transmission rates far in excess of the Mbit/s defined as the aggregate rate for STM-1. STM Mbit/s STM Mbit/s STM Mbit/s
SDH Multiplexing Structure
STM1 Frame Equals to 9 × 270 byte block. AU-4 = payload area (9 × 261) The pointer address is located in row four of the overhead The location of the start of the VC-4 The floating nature of the virtual containers and the pointer is one of the key features of SDH. The VC-4 occupies the whole payload area of the AU-4.
AU-4 Pointer VC-4 holds Lower-order virtual containers, Tributary unit (TU) pointers Indicate the start position of lower- order VCs. The AU-4 pointer marks the location of the beginning of VC-4 TU pointers Have a fixed position within the VC-4. Mark the start of lower-order VCs.
Simple Transmission System Two connected multiplexers on an optical link Containing three regenerators. SDH signals is sent to a distant location, Logical signal is converted to a physical signal. Carried out by the STM-n multiplexer. Signals are attenuated and distorted The regenerator detects the incoming optical signal and ‘regenerates’ a perfectly formed signal with the same information content. The distant STM-1 multiplexer receives the optical signal and reconverts it into a logical signal for processing. Generators
Overhead Overhead functionality two types. operation and maintenance of the SDH signal itself Provides framing, identification and alarm indication. error performance indication and data communications channels, Provide error performance monitoring and an embedded management communication channel.
Section overhead regenerator section overhead (RSOH) multiplex section overhead (MSOH). A1 and A2 bytes together contain a frame alignment word. The frame alignment word is repeated with each frame to maintain alignment and re- alignement. When STM-1 signals are multiplexed into an STM-4, then the C1 byte allows each STM-1 to be uniquely identified. The B2 bytes provide an error monitoring capability (D1 to D12) is to provide an embedded data communications link
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: A1 Source: Z Expected: A1
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: A1 Source: X Expected: A1
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: A1 Source: Y Expected: A1
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 No reading because of attenuation
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: C1 Source: X Expected: C1
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: C1 Source: Y Expected: C1
Alignment Example C1 A1 X Y C1 A1 Z C1 A1 Read: A1 Source: Z Expected: C1 Require Alignment
Path Overhead J1 B3 C2 G1 F2 H4 Z3 Z4 Z5 9 bytes, arranged in one column, dedicated to management and supervision of that path.