Post on 06-Feb-2016
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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 155.52 Mbit/s defined as the aggregate rate for STM-1. STM- 4 622.080 Mbit/s STM-16 2488.32 Mbit/s STM-64 9953.28 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
A1
A1
X Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
Read: A1
Source: Z
Expected: A1
Alignment Example
C1
A1
A1
A1
X
Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
Read: A1
Source: X
Expected: A1
Alignment Example
C1
A1
A1
A1
X Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
Read: A1
Source: Y
Expected: A1
Alignment Example
C1
A1
A1
A1
X Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
No reading because of attenuation
Alignment Example
C1
A1
A1
A1
X
Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
Read: C1
Source: X
Expected: C1
Alignment Example
C1
A1
A1
A1
X Y
C1
A1
A1
A1
Z
C1
A1
A1
A1
Read: C1
Source: Y
Expected: C1
Alignment Example
C1
A1
A1
A1
X Y
C1
A1
A1
A1
Z
C1
A1
A1
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.