# Presentation: 489231

## Combining Synchronous Ethernet and IEEE-1588TM for use inTelecom

**Silvana Rodrigues**
**Phone: +1 613 2707258**
_**[silvana.rodrigues@zarlink.com](mailto:silvana.rodrigues@zarlink.com)**_
_**[http://timing.zarlink.com/](http://timing.zarlink.com/)**_

## AGENDA

**Background**
**The Basic Problem**
**Definition of Synchronous Ethernet**
**Combining Synchronous Ethernet with 1588**
**Summary**

- IEEE-1588TM is trademark of its respective owner

## Background

**Next Generation Networks (NGN) are migrating to a packet-based network**
**Service providers worldwide are faced with major challenges: **
**Increasing service revenue **
**Lowering network costs and **
**Delivering QoS (quality of service)**
**Service providers are moving from voice services to  networked services and solutions **
**TDM  transport continues to represent significant revenue for carriers**
**TDM must be supported in this new model**

## Background cont’d

**There are applications that still require synchronization in a PSN (packet switched network)**
**Cellular base station**
**Synchronization allows smooth call hand-off between base stations, it minimizes dropped calls, it reduces customer churn**
**Legacy services: E1, fax, modem**
**Increases bandwidth utilization**
**Improves QoS**
**Synchronization is essential for wireless and wireline carriers to move to NGN**

## Synchronous Networks

**No problem with synchronous network...**
**Current synchronization distribution in circuit switched networks**
**T1/DS1 or E1 **
**Sonet or SDH**

**Broadband**
**DLC**
**(FTTx)**

**Digital**
**Loop**
**Carrier**

**IAD**

**Base**
**Station**

**Synchronous Network**

## Packet Switched Networks           The Basic Problem

**Broadband**
**DLC**
**(FTTx)**

**Digital**
**Loop**
**Carrier**

**IAD**

**Base**
**Station**

**Packet Switched Network**

**In the PSN the synchronization chain is broken...**
**But... there is still a need for synchronization to support time-sensitive services over PSN**

## ITU-T Recommendation G.8261

**Recommendation published in May 2006**
**Defines timing and ****synchronization elements of packet networks**
**Specifies the minimum equipment tolerance to jitter and wander at the boundary of the packet networks at TDM interfaces**
**Outlines the minimum requirements for the synchronization function of network elements**
**Two methods for clocking distribution**
**Plesiochronous and network synchronous methods **
**Synchronous Ethernet**** **
**Packet based methods**** **
**IEEE-1588 is an example of this method, but ITU does not refer to it**
**Four clocking methods**
**Network - synchronous operation **
**Differential methods**
**Adaptive methods**
**Reference clock available at the TDM end systems**

## Standards for Synchronization

**E1 standards (2.048 Mbps)**
**Traffic interface ****(G.823, Table 2)**
**18 ********s over 1000s**

**T1 standards (1.544 Mbps)**
**Traffic interface ****(G.824, Table 2) **
**18 ********s over 24 hours**

**Central Office**

**Remote Terminal **

**CESoP IWF**

**CESoP IWF**

**T1/E1**

**Max. end-to-end wander (traffic interface) 18 ********s**

**G.8261 - CES induced wander:**
**< 4.3********s or 4.5********s for Deployment Case 1**
**< 16********s for Deployment Case 2**

**PRS**

**Customer**
**Premises**

**TDM**
**Equipment**

**T1/E1**

## Synchronous Ethernet Concept

**Uses the PHY clock**
**Generates the clock signal from “bit stream”**
**Similar to traditional SONET/SDH/PDH PLLs**
**Each node in the Packet Network recovers the clock**
**Performance is independent of network loading**

**Stratum 1**
**Traceable**
**reference**

**Packet Network**

**L2-L7 (Packet)**

**Data**

**Timing Flow**

**Data Flow**

**Recovered Clock**

**Data**

**Physical Layer**

**L2-L7 (Packet)**

**Physical Layer**

**L2-L7 (Packet)**

**Physical Layer**

## G.8261 – Synchronous Ethernet

**A reference timing signal traceable to a PRC is injected into the Ethernet switch using an external clock port**

**Figure 4/G.8261 - Timing to Ethernet IWF provided over Ethernet PHY**

## G.8261 – Synchronous Ethernet cont’d

**Synchronous Ethernet clocking distribution can be considered an extension of the current synchronization distribution network**
**It does not impact any existing IEEE 802.3 specifications such as frequency tolerance, but refers to the new additional network element clock functionality**
**Uses the OAMPDUs (protocol data units) to pass SSM (synchronization status message) **
**ITU is working on a new recommendation G.paclock**
**Outlines requirements such as clock bandwidth, frequency accuracy, holdover and noise generation**
**Proposal is to model Synchronous Ethernet as an SDH equipment slave clock (as defined in recommendation G.813)**

## G.8261 – Architecture for Synchronous Ethernet

**Figure A.1/G.8261 – Reference Clock Location**

- Edge

- Core

- Access

## Example of IEEE-1588 and Synchronous Ethernet 

- Example of IEEE-1588 and Synchronous Ethernet

**Ethernet**

**CES **
**IWF**

- Core

- Access

**Ethernet**

**CES **
**IWF**

- Edge

**PRS**

## IEEE-1588 and Synchronous Ethernet

**IEEE-1588**
**Independent of the physical layer **
**Can distribute time of the day and frequency **
**Can be affected by impairments of the telecom network such as packet delay variation**

**Synchronous Ethernet**
**Uses the physical layer of Ethernet**
**Can only distribute frequency, it can not distribute time of the day**
**It is not affected by impairments introduced by the higher levels of the network**

**Applications like billing and SLA (service level agreements) can benefit from a network that is aware of the time of the day**
**Some networks are very noisy and there is a need to have carrier class synchronization**
**In these conditions Synchronous Ethernet can be used to deliver frequency and IEEE-1588 can be used to deliver time of the day**

## Summary

**Work done at ITU-T is complementary to the work done at IEEE-1588 standards committees**
**There are new technologies being proposed at ITU that will complement the use of IEEE-1588**
**Synchronous Ethernet**
**There is a lot of interest in IEEE1588 in the Telecom Industry**
**The work in IEEE-1588 to support Telecom is going well**
**Committee is reviewing version 2 draft that includes key features for telecom**

## Thank you!