Wipro Confidential 1Synchronization in Optical Networks

Synchronization in Optical Networks

Name:

Designation:

Date: February, 2004

Copyright © Wipro Technologies 2005

Name : Vinay Sasi

Date : 1st April, 2005

Wipro Confidential 2Synchronization in Optical Networks

Agenda

Network Synchronization – What and Why?

Sync Module & Components

Synchronization sources & timing modes

Stratum Levels

Timing Generation & Distribution block

Timing Reference Protection block

NE timing States & transition

Clock signal flow in NE

Sync Status Messaging

Alarms & Faults related to Sync

Wipro Confidential 3Synchronization in Optical Networks

Network Synchronization – What & Why

Clocking A series of repetitive pulses to keep the bit rate of data constant To indicate the location of 1 and 0 in a data stream

All network elements need a clock to operate To enable the accurate Detection & Demultiplexing of the Inflow signals To enable the accurate Multiplexing & Generation of the Outflow signals

Network Synchronization - What Distribution of a clock over the network to align the time and frequency scales of all

network element clocks

Network Synchronization – Why To ensure that all the digital signals of the network are effectively clocked by a single

frequency. This allows efficient bit sampling and consequently, minimizes bit errors.

Wipro Confidential 4Synchronization in Optical Networks

Asynchronous Networks

During multiplexing, extra bits are added (bit-stuffing) to account for the variations of each individual stream

Asynchronous multiplexing uses multiple stages (DS0 – DS1 – DS2 – DS3)

To access a low speed signal, full demultiplexing is required. E.g. to access a DS-1 within a DS-3 for purposes such as add and drop, the entire DS-3

has to be demultiplexed and then multiplexed

Requires complicated multiplexing/demultiplexing

Time

/ 100 pulses

/ 99 pulses

Bit Stream A

Bit Stream B

Must stuff a dummy pulse into stream B prior to multiplexing

Transitions of the signals do not necessarily occur with the same nominal rate or at same instants of time

Network Elements use their own clocks (no reference – not synchronized) Large variations occur in the clock rate and thus the signal bit rate

Wipro Confidential 5Synchronization in Optical Networks

Synchronous network

Digital transitions of the Signals occur with exactly the same rate and at same

instants of time

Small phase difference possible due to propagation delays

All NE clocks are traceable to one Primary Reference Clock (PRC)

Deterministic multiplexing - lower signal can directly be accessed from the high

speed signal.

Use of accurate network clocking allows SONET to use byte Multiplexing -

simple/efficient

Facilitates Add/Drop

Enables Drop and Repeat (continue)

Synchronous Optical NETwork

Synchronous Digital Hierarchy

Synchronous N/W

Easy Mux/Demux

Scalable

Standard rates

Synchronous N/W

Easy Mux/Demux

Scalable

Standard rates

Advantages

Low Cost H/W

Flexible

Interoperable

Advantages

Low Cost H/W

Flexible

Interoperable