Frequency and Time Synchronization In Packet Based ... - Cisco

Frequency and Time Synchronization In Packet Based Networks Peter Gaspar, Consulting System Engineer

© 2010 Cisco and/or its affiliates. All rights reserved.

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•  Synchronization Problem Statement •  Overview of the Standardization Works •  Frequency Transfer: techniques and deployment Synchronous Ethernet Adaptive Clock Recovery •  Time Synchronization Two-Way Transfer Time Protocols •  Overview of IEEE Std 1588-2008 for Telecom •  Summary


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Problem Statement What and Why Do We Care About?

Presentation_ID


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Why and How are Packet Switched Networks Involved? •  Transition from TDM to Ethernet networks. Access

Subscriber Mobile TV

•  Connect consumers requiring Frequency

and/or Time (F&T) synchronization.

TDM / ATM

•  PSN is built with network elements that

DVB-T/H 3GPP/2

May have to support F&T distribution

WiMAX

May be consumers of F&T

Mobile user

Aggregation

Ethernet Femto-cell

DSLAM

P

xDSL OLT

Enterprise

M-CMTS

P

P

PE

Hub & Spoke or Ring

MS A

P

MSE

Internet

Mesh

Content Network

DOCSIS

VoD TV Portal

Peer ISP

P

PE

PE

xPON Residential SoHO

Backbone

TDM / ATM

Monitoring Billing Subscriber Database

SI P

Identity Address Policy Mgmt Definition

Service Exchange


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•  Single domain vs. multiple domains

Access

Subscriber

Internet is a multi-domain network. Mobile TV

TDM / ATM

Wholesale Ethernet virtual link

•  Frequency and time could use different

DVB-T/H 3GPP/2

distribution methods.

WiMAX

•  Operators may provide synchronization services

to their customers.

Mobile user

Aggregation

Ethernet

Backbone

Peer ISP

TDM / ATM

Femto-cell

DSLAM P

xDSL OLT

Enterprise

DOCSIS


P

PE

Hub & Spoke or Ring

MSA M-CMTS

P

PE

PE

xPON Residential SoHO

P

P

MSE

Mesh

Content Network VoD

TV

Internet

SIP

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•  Frequency TDM interoperability and Co-existence: Circuit Emulation, TDM, MSAN (MGW) Access: Wireless Base Stations, PON, DSL •  Time and Phase alignment Wireless Base Stations SLA and Performance Measurements

BS PON DSL SLA © 2010 Cisco and/or its affiliates. All rights reserved.

: Base Station : Passive Optical Network : Digital Subscriber Line : Service Level Agreement Cisco Confidential

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External Integrated Time and Frequency Server

•  Inter-CO/LAN (WAN) •  Intra-CO, LAN •  Intra-node, -platform © 2010 Cisco and/or its affiliates. All rights reserved.

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The Leading Requirements Application TDM support (e.g. CES, SDH transformation), Access

Frequency PRC-traceability, jitter & wander limitations ITU-T G.8261/G.823/G.824/G.825

GSM, WCDMA and LTE FDD UMTS TDD Mobile Base Stations

TD-SCDMA CDMA2K

Phase Alignment Time Synchronization

N/A (except for MBMS and SFN) Frequency assignment (fractional frequency accuracy) shall be better than •  ± 50ppb (macrocells) •  ± 100ppb (micro- & pico-cells) •  ± 250ppb (femtocells)

Phase alignment between base stations must be < ±2.5µs Phase alignment between base stations must be < ±3µs Time alignment error should be less than 3 µs and shall be less than 10 µs Phase alignment between base stations from ±0.5µs to ±50µs (service degradation)

LTE TDD WiMAX Mobile

Shall be better than ± 15 ppb

Phase alignment between base stations must be < ±1µs

DVB-S/H/T2 SFN

TBD

Cell synchronization accuracy for SFN support must be < ± 3µs

MB SFN Service

Phase/time alignment between base stations requirement can vary but in order of µs

One-way delay and jitter Performance Measurement

To improve precision << 1 ms for 10 to 100µs measurement accuracy need ± 1 µs to ± 10µs ToD accuracy


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Use of GPS (and GNSS alternatives) raises some concerns: •  Cost •  Limited utilization Locations Regulatory & Politics •  Reliability Geography Vulnerability

https://www.gsw2008.net/files/Civ %20Vulnerabilities_GSW2008.pdf

GPS

746th Test Squadron © 2010 Cisco and/or its affiliates. All rights reserved.

: Global Positioning System

GNSS : Global Navigation Satellite System Cisco Confidential

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•  As Replacement or Backup •  Alternative Radio Navigation LORAN-C  ELORAN •  Atomic Clock Cheap Scale Atomic Clock Molecular Clock •  Network Clock Main topic of this session!

LORAN : LOng Range Aid to Navigation © 2010 Cisco and/or its affiliates. All rights reserved.

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Standardization Development Organizations Who’s doing what?

Presentation_ID


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•  Frequency transfer Parallel (overlay) SDH/SONET network Radio Navigation (e.g., GPS, LORAN) PHY-layer mechanisms Packet-based solutions •  Time transfer (relative and absolute) Radio Navigation (e.g., GPS, LORAN…) Packet-based solutions


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SDO

Techno

Status

Scope

Market

G.8262(2007)+Amend.1 G.8264(2008) G.781 (2008)

PHY-layer frequency transfer

Service Provider (SP) Metro & Core Ethernet

G.8261 (2006)

CES performance

Multiple working items: profile, metrics, modeling…

Packet-based frequency, phase and time transfer

G.8261(2008) Synchronous Ethernet ITU-T

SG15 Q13 Packet-based timing

IEEE1588-2002 1588

PTP

IEEE

IEEE1588-2008 No “Telecom” profile

802.1AS NTP IETF TICTOC

Based on PTP NTP NTPv5 PTP Profile(s)


Ballot NTPv3 Standard NTPv4 (CY09) New WG (approved March 08)

Service Provider (SP) Enterprise: Time

Precise time distribution Precise time distribution Time distribution Frequency and time transfer

SP: Frequency, phase and time  ITU-T & IETF Residential Internet SP domain Internet Specific SP areas Cisco Confidential

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ProfiNet: IEC 61158 Type10 DeviceNet: IEC 62026-3 ControlNet: IEC 61158 Type2 IETF NTP

IETF TICTOC

IEC Profiles

IEEE1588-200 8 (PTPv2)

AVB Profile(s)

Telecom Profile(s) On-going

ATIS Telcordia © 2010 Cisco and/or its affiliates. All rights reserved.

IEEE 802.1AS

ITU-T Q13/15

IEEE 802.3 Timestamping Cisco Confidential

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Frequency Transfer Distribution of Frequency Reference

Presentation_ID


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•  Physical layer options Ex: SONET/SDH, SDSL, GPON, Synchronous Ethernet Pros: “carrier-class”, well defined, guaranteed results Cons: node by node link bit timing, requires HW changes •  Packet-based options Ex: SAToP, CESoPSN, NTP, PTP (protocol of IEEE Std 1588) Pros: flexible, looks simple, some can do time as well Cons: the network and the network traffic, not so simple!


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•  The task of network synchronization is to distribute the reference signal

from the PRC to all network elements requiring synchronization. •  The method used for propagating the reference signal in the network is

the master-slave method.

•  Slave clock must be slaved to clock of higher (or equal) stability. 

hierarchical model

PRC : Primary Reference Clock Source: ETSI EG 201 793 “Synchronization network engineering” © 2010 Cisco and/or its affiliates. All rights reserved.

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•  Synchronization equipments PRC (PRS) and SSU (BITS) do not belong to the Transport network.

•  SEC (SDH/SONET Equipment Clock) belong to Transport network. They are embedded in Network Element : NE.


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•  Synchronization information is transmitted through the network via

synchronization network connections. •  Synchronization network connections are unidirectional and generally

point-to-multipoint.

Stratum 1 level

CO

Stratum 2 level

NE (Stratum level ≥ 3)


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PRC : Primary Reference Clock (≈ PRS) SSU : Synchronization Supply Unit (≈ BITS) SEC : SDH Equipment Clock

Core Network

Aggregation and Access Networks

Source: ETSI EG 201 793 “Synchronization network engineering” © 2010 Cisco and/or its affiliates. All rights reserved.

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Receiver for synchronization reference signal

Source: ETSI EG 201 793 “Synchronization network engineering” © 2010 Cisco and/or its affiliates. All rights reserved.

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NE’s External Timing Input a.k.a. BITS IN

NE’s External Timing Output

Figure 4-2. Recommended BITS Implementation with SONET Timing Distribution Source: Telcordia GR-436-CORE . Digital Network Synchronization Plan © 2010 Cisco and/or its affiliates. All rights reserved.

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PRC/PRS Intraoffice

Intra-office

Inter-office

Inter-office

SSU/BITS

SSU/BITS Intra-office

NE

NE

NE

NE

PRS

NE

NE

PRS Intraoffice

Inter-office

Intraoffice

BITS

Inter-office

BITS Intra-office

NE © 2010 Cisco and/or its affiliates. All rights reserved.

NE

NE

NE

NE

NE Cisco Confidential

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What clock quality do I get? Is that the best source I can use? Stratum 1 level

Stratum 2 level

NE level

•  Some of these synchronized trail contain a communication channel, the

Synchronization Status Message (SSM) transporting a quality identifier, the QL (quality level) value. This is a 4-bit field in SDH/SONET frame overhead.

•  Purpose: Traceability (and help in prevention of timing loops)


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SSM Allows Source Traceability Representation of the PRC network connection

Representation of the synchronization network connection in case of failure

Fault

X

Example of restoration of the synchronization

PRC synchronization network connection

SEC synchronization network connection

SSU synchronization network connection © 2010 Cisco and/or its affiliates. All rights reserved.

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•  PHY-layer frequency transfer solution for IEEE802.3 links •  Well-known design rules and metrics Best fit for operators running SONET/SDH •  Fully specified at ITU-T Working Group 15 Question 13 For both 2.048 and 1.544 kbps hierarchies •  Expected to be fundamental to high quality time transfer •  Drawback : hardware upgrades All timing chain shall be SyncE capable.


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External Equipment BITS/SSU)

PRC-traceable signal from BITS/SSU

ITU-T G.8262 (EEC): Synchronous Ethernet Equipment Clock ITU-T G.781: Clock Selection Process

External timing interface outputs External timing interface inputs

IEEE802.3 ± 100ppm

ITU-T G.8261 SyncE interface jitter & wander

Frequency distribution traces

PLL

Synchronous Ethernet capable Line Card © 2010 Cisco and/or its affiliates. All rights reserved.

External timing interface inputs

Synchronous Ethernet capable Line Card

ITU-T G.8264 ESMC and SSM-QL

Synchronous Ethernet capable Equipment

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•  Ethernet Synchronization Messaging Channel Use OSSP from IEEE802.3ay (a revision to IEEE Std 802.3-2005)

•  Key purpose: transmit SSM (QL) Outcome: Simple and efficient But designed to support extensions

•  Protocol model: Event-driven with TLVs •  Two message types Event message sent when QL value change Information message sent every second

•  TLVs QL-TLV is currently the unique defined TLV. Other functions can be developed. OSSP : Organization Specific Slow Protocol © 2010 Cisco and/or its affiliates. All rights reserved.

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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Slow Protocols MAC Address | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Slow Protocol MAC Addr (cont) | Source MAC Addr | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Source MAC Address (continued) | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| |Slow Protocols Ethertype 0x8809| Subtype (10) | ITU-OUI Oct 1 | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | ITU-OUI Octets 2/3 (0x0019A7) | ITU Subtype (0x0001)* | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Vers. |C| Reserved | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Type: 0x01 | Length | Resvd | QL | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Future TLV #n (extension TLV) | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | Padding or Reserved | | | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | FCS | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|

IEEE 802.3 OSSP ITU-T OUI Header ESMC Header QL-TLV Future TLV Extension Payload OSSP

* Allocated by TSB © 2010 Cisco and/or its affiliates. All rights reserved.

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Assuring The Continuity at PHY Layer BITS/SSU PRC/PRS

BITS/SSU BITS/SSU

SONET/SDH ITU-T G.8262 (EEC) Node

PHY SyncE

PHY SyncE ITU-T G.8262 (EEC) Node

ITU-T G.8262 (EEC) Node

ITU-T G.8262 (EEC) Node

•  Extension or replacement of SDH/SONET synchronization chain •  Inherit from previous ITU-T (and Telcordia) recommendations •  Difference: frequency transfer path engineering will define the necessary

upgrades. Only the NE part of the engineered timing chain needs SyncE upgrades. © 2010 Cisco and/or its affiliates. All rights reserved.

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Reference Clock

Recovered Clock PSN

•  Three key steps: Generation: from signal to packet Transfer: packet transmission over packet network(s) Recovery: from packet to signal


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•  ITU-T Recommendation G.8261 (2008) Adaptive Clock Recovery

Definition “In this case the timing recovery process is based on the (inter-) arrival time of the packets (e.g., timestamps or CES packets). The information carried by the packets could be used to support this operation. Two-way or one-way protocols can be used.” ACR Protocol / Method

One-Way

Two-Way

Timestamp

CES (SAToP, CESoPSN)

X

IETF NTP

(X)

X

X

IEEE Std 1588-2008 PTP

X

X

X

IETF RTP

X

X

X


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Independent Timing Stream TDM PW bit stream IWF

IWF TDM

TDM

Recovered TDM timing based on the adaptive clock recovery

ACR Packet Stream

Reference Clock

Reference Clock

PEC

TDM

IWF & PEC

ACR Packet Stream

TDM PW bit stream

IWF & PEC

TDM

Clocking method a.k.a. “out-of-band” (here, used for CES clocking) © 2010 Cisco and/or its affiliates. All rights reserved.

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Source: Diagram from “Time Domain Representation of Oscillator Performance”, Marc A. Weiss, Ph.D. NIST


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•  Frequency Accuracy ≤ ±50ppb at base station radio interface (specified) Turns into ≤ ± 16ppb at base station traffic interface (not specified*) •  Frequency Stability For T1, it shall comply to G.824 traffic mask (specification; 3GPP Rel8) Sometimes* G.824 synchronization mask preferred

* Note: real requirements are variable as they are dependent on base station clock servo.


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•  Phase measurement Measure signal under test against a reference signal •  Phase deviation plot TIE : Time Interval Error •  Analysis MTIE TDEV


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Step 1 : Phase Measurements

Ref.





Signal

























+0.1 -0.1

-0.2

+0.1 -0.2

•  At a certain signal threshold, time stamp the edges of timing

signal. •  Signal edges are the significant instants. •  PHY-layer signals have high frequency (e.g., 1544 kHz) © 2010 Cisco and/or its affiliates. All rights reserved.

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Step 2 : Phase Deviation

•  Phase deviation or TIE (Time Interval Error)


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Step 3: Analysis •  Analysis cover different aspects of the Clock (oscillator) e.g. in free-running or holdover mode Signal •  Primary used measurement analysis are: Phase (TIE) Frequency (fractional frequency offset) Frequency accuracy MTIE TDEV


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Signal with jitter and wander present


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Jitter:

Filter out low-frequency components with high-pass filter 10 Hz


Jitter range

Frequency

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Wander: Filter out high-frequency components with low-pass filter Wander range


10 Hz

Frequency

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•  Both MTIE and TDEV are measures of wander over ranges of values. From very short-term wander to long-term wander •  MTIE and TDEV analysis shows comparison to standard requirements. Defined by ATIS/ANSI, Telcordia/Bellcore, ETSI & ITU-T E.g., ITU-T G.824, ANSI T1.101 or Telcordia GR-253-CORE •  MTIE is a peak detector: simple peak-to-peak analysis. •  TDEV is a highly averaged “rms”-type of calculation.


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Frequency Accuracy (Frequency Offset) ITU-T G.823 Traffic Interface (MRTIE mask) ITU-T G.823 Synchronization Interface (MTIE mask)


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•  Physical layer signals can be characterized. •  Recommendations exist for node clock and interface limits. •  Synchronous Ethernet Equipment Clock (EEC) inherits from SONET NE

clock specifications.

•  The performance of SyncE-capable NE and SyncE interface are fully

specified and metrics exist.


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•  How to guarantee the packet-based recovered clock quality?

OK Reference Clock

DS1

DS1

Recovered Clock

PSN Master/ Server

?

Slave/ Client

Packet Delay Variation is key impairment factor for timing. © 2010 Cisco and/or its affiliates. All rights reserved.

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•  TIE is still a valid measurement for characterizing the packet-based

servo (slave). Oscillators and timing interfaces •  How can the PSN behavior be characterized? Algorithms use minTDEV value Need sufficient numbers of minimal latency packets Packet Delay Variation (PDV) as metric? •  First approach is to reuse known tools to PDV analysis/measurement. Some can be applied to PDV as to TIE.


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minTDEV

10 Switches, 40% Load

10 Switches, 80% Load


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•  One metric would not be sufficient characterizing the various possible

conditions.

Reference Clock

PSN

Master/ Server

Recovered Clock

Classification (metric) Common, generic PSN metrics for timing performance characterization?

  Today, very close relationship between metric (packet classification) and implementation specific algorithm.


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  minTDEV used in algorithms, but still not adopted as metric   Even with (still to be agreed) metrics, other parameters will remain critical. Reference Clock

Recovered Clock

PSN Metrics PSN

Master/ Server

?

•  Master implementation

? ?

Slave/ Client

  Slave implementation

•  Protocol parameters •  Influenced by : the PSN design, the HW & SW NE configuration, the

traffic.


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1. 

PHY-layer Synchronization Distribution guarantees the quality.

2. 

Packet-based Synchronization Distribution provides the flexibility.

3. 

Mixing the option for getting best of both solutions.

SyncE consumer SEC



PHY-layer Freq Transfer e.g. SyncE

 EEC

Packetbased consumer

Consumer

PHY-layer method e.g., SDH/SONET, SyncE

PHY-layer Freq Transfer e.g. SyncE

EEC

 

PHY-layer Freq Transfer PHY-layer Freq Transfer EEC EEC

Non-capable PHY Layer Synchronization Network Packet-based method (ACR)


PRC/PRS Thru BITS/SSU Cisco Confidential

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Time Synchronization What Specific Challenges Does the Time Distribution Introduce?

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•  Transmitting time reference can be absolute (from national standards) or

relative (bounded timekeeping system).

•  Time synchronization is one way achieving phase synchronization. Phase alignment does not mandate giving a time value. © 2010 Cisco and/or its affiliates. All rights reserved.

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•  This is not phase locking which is

often a result of a PLL in a physical timing transfer. Phase locking implies frequency synchronization and allows phase offset. •  The term phase synchronization

(or phase alignment) implies that all associated nodes have access to a reference timing signal whose significant events occur at the same instant (within the relevant phase accuracy requirement). Figure xxx/G.8266 – Phase Synchronization


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

Target from ±1µs to tens of µs (alignment between BS)



Target from ≤ ±0.5µs to tens of µs (from common reference) 



Time Source








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•  Strictly speaking, the term synchronization applies to alignment of

time and the term syntonization applies to alignment of frequency. •  The master/server and slave/client clocks each have their own time-

base and own wall-clock and the intent is to make the slave/client “equal” to the master/server.

•  The notion of frequency synchronization (or syntonization) is making the

time-bases “equal”, allowing a fixed (probably unknown) offset in the wall-clocks. The notion of time synchronization is making the wall-clocks “equal”.


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NTP vs. PTP Message Exchange As part of time recovery, there’s always a frequency recovery process. PTP

NTP


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•  Forward and backward delays and delay variations are not identical.


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•  Each Node and Link can introduce asymmetry.

•  There are various sources of asymmetry.


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•  Link Link delays and asymmetry Asymmetric (upstream/downstream) link techniques Physical layer clock •  Node Different link speed (forward / reverse) Node design LC design Enabled features •  Network Traffic path inconsistency Interface speed change


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Summary and Introduction to IEEE Std 1588 •  Basis of all packet time transfer protocols (NTP, IEEE1588) is the two

way time transfer mechanism. •  TWTT consists of a time transfer mechanism and a time delay “radar”. •  Assumes path symmetry and path consistency. •  IEEE1588 incorporates some in-network correction mechanisms to

improve the quality of the transfer. •  IEEE1588 has the concept of asymmetry correction. But the correction values are not dynamically measured - they need to be statically configured.


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IEEE Std 1588-2008 for Telecom Challenges of IEEE 1588-2008 applied in Service Provider networks

Presentation_ID


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•  A set of event messages

consisting of:

•  A set of general messages

consisting of:

- Sync

- Follow_Up

- Delay_Req

- Delay_Resp

- Pdelay_Req

- Pdelay_Resp_Follow_Up

- Pdelay_Resp

- Announce - Management - Signaling

  Transmission modes: either unicast or multicast (can be mixed)   Encapsulations: L2 Ethernet, IPv4, IPv6 (others possible)   Multiple possible values or range of values, TLVs (possible extensions), … © 2010 Cisco and/or its affiliates. All rights reserved.

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MASTER

SLAVE Slave time = TS

Master time = TM

MS_Delay

Timestamps known by slave

SYNC

t1

t2 t1, t2 t3 Delay_Req

SM_Delay

t1, t2, t3

t4 Delay_Resp

t1, t2, t3, t4


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MASTER µP

SLAVE µP MAC/PHY

MAC/PHY

t1

Need to inject the timestamp into the payload at the time the packet gets out.


SYNC

t1 t2

Delay_REQ

t3

t2 t1, t2

t3

t1, t2, t3

t4 t4

Delay_RESP

t1, t2, t3, t4

Hardware assistance necessary to prevent insertion of errors or inaccuracies. © 2010 Cisco and/or its affiliates. All rights reserved.

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MASTER µP

SLAVE µP MAC/PHY

MAC/PHY t1

SYNC() t2


Follow_Up(t1)

Two-step clock mode Vs. One-step (a.k.a. “on-the-fly”) clock mode

t2 t1, t2

Delay_REQ()

t3

t1, t2, t3

t4

Delay_RESP(t4) t1, t2, t3, t4 © 2010 Cisco and/or its affiliates. All rights reserved.

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•  Five basic types of PTP devices (“clocks”) Ordinary clock (master or slave) Boundary clock (“master and slave”) End-to-end Transparent clock Peer-to-peer Transparent clock Management node •  All five types implement one or more aspects of the PTP protocol


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•  BC and TC aims correcting delay variation into intermediate nodes

between OCs. •  Can correct link asymmetry if known.

Ordinary Slave

Ordinary Master

Recovered Clock TC

Transparent Clock


Ref. Clock

BC

Boundary Clock

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•  Can help on scalability when using unicast. •  Equivalent to NTP Stratum (>1) Server  UTC •  Node by node: BC slave function is critical

Ordinary Slave

Ordinary Master

Recovered Clock BC

Boundary Clock © 2010 Cisco and/or its affiliates. All rights reserved.

Ref. Clock

BC

Boundary Clock Cisco Confidential

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•  TC calculates Residence Time (forward / reverse intra node

delays). •  TC are supposed to be transparent but: One-step clock issue

Ordinary Slave

Ordinary Master

Recovered Clock TC

Transparent Clock © 2010 Cisco and/or its affiliates. All rights reserved.

Ref. Clock

TC

Transparent Clock Cisco Confidential

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•  If IEEE 1588-2008 is not planned node to node, with every

node IEEE 1588 aware and in unique domain…

•  Multiple interface types IEEE 802.3, ITU-T G.709, … •  Multiple interface frequencies 10GE, 100GE, STM64, STM192… •  Multiple encapsulations Ethernet, IP MPLS, MPLS-TP, PBB-TE…


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Ordinary Slave Recovered Clock

Ordinary Master TC

TC

Wholesale

BC

Ref. Clock

BC

Boundary Clock

•  Who owns the master? •  Who owns the slaves? •  Who owns the intermediate nodes? © 2010 Cisco and/or its affiliates. All rights reserved.

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•  How to guarantee the recovered clock quality?

Objective: accuracy and stability from reference Slave/ Client Recovered Clock

?

?

TC

Master/ Server

Ref. Clock

PSN BC

?

? ?


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•  IEEE Std 1588-2008 is actually a “toolbox” !

 What does “support of IEEE 1588” really mean ? •  IEEE Std 1588 itself is not sufficient for telecom operator operations. Node characterization, modeling, performance, metrics… •  For phase & time support, it is expected any telecom standardization

would take time.


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Summary

Presentation_ID


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•  Timing is a new service many networks shall have to support. •  Different solutions are necessary to cover disparate requirements,

network designs and conditions. Physical layer solutions required to upgrade routers and switches. Packet-based solutions are more flexible but less deterministic. •  Whatever the timing protocol, it must deal with the same network

constraints. •  Each network is different •  Synchronization Experts are welcome to enter the packet based

networks and assist with the designs


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Thank you.

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Frequency and Time Synchronization In Packet Based ... - Cisco

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