Wipro Confidential 1 Synchronization in Optical Networks Name: Designation: Date: February, 2004 Copyright © Wipro Technologies 2005 Name : Vinay Sasi Date : 1st April, 2005

Wipro Confidential 2 Synchronization 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 3 Synchronization 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 4 Synchronization 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 5 Synchronization 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