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Synce Explained WHITEPAPER Joan d’Austria, 112 - Barcelona - SP - 08018 Chalfont St Peter - Bucks - UK - SL9 9TR www.albedotelecom.com Synchronous Ethernet explained 1. FROM ASYNCHRONOUS TO SYNCHRONOUS ETHERNET Synchronous Ethernet is an ITU-T standard that provides mechanisms to trans- fer frequency over the Ethernet physical layer, which can then be made trace- able to an external source such as a network clock. On this case Ethernet links are part of the synchronization network (see Figure 2). The proposal to specify the transport of a reference clock over Ethernet links was brought by operators to ITU-T Study Group 15 in September 2004. The aim of Synchronous Ethernet is to avoid changes to the existing IEEE Ethernet, but to extend to work as a proper synchronous network. On many respects the evolution to a synchronous Ethernet network is equiva- lent to the one that occurred from PDH/T-Carrier to SDH/SONET and the causes are similar. The higher bit rates are the most important is to keep transmission synchronized by a unified clock in order to keep clock fluctuations and offsets under control as they are a main cause of errors a poor QoS. Despite being an IEEE standard, Ethernet architecture has been described in ITU-T G.8010 as a network made up of an ETH layer and a ETY layer. Written in simple terms, the ETY layer corresponds the physical layer as defined in IEEE 802.3, while the ETH layer represents the pure packet layer. Ethernet MAC Figure 1 ALBEDO Ether.Sync is a field tester for Synchronous Ethernet equipped with all the features to deploy SyncE infrastructures, Precision Time Protocol (PTP / IEEE 1588v2) and Gigabit Ethernet supporting legacy while new test such as eSAM Y.1564 All rights reserved. No part of this document may be stored, copied or transmitted, by any means, without the permission in written of the Legal Owner © 2012 ALBEDO Telecom T EST- LABOS- EST- ALBEDO Telecom - Registered in Barcelona, Book 41613, Page 155, Sheet B-390886 - VAT : ESB6523022 TAPS Figure 2 - WAN EMULATION - E1 - GBE - SYNCE -WLESS - LTE - 3G - IPTV - 3G -IPTV LTE- - E1 -GBESYNCE -WLESS - - WANEMULATION Central timing G.8262 EEC Synchronous Ethernet Archit ±4.6 ppm SSU Ext. Reference clock Backplane Networking & Telecoms Synchronus Ethernet • • Standard Ethernet Standard ETH ETH ±100 ppm covered thereincludethefollowing: different recommendations: ITU-T G. three procedures mechanisms arefoundfundamentallyin and age. These ment inorderforthemtohaveaunifiedsynchronization networktoman- betweenSD internetworking achieve A key issuein Synchronous isthe definition of the mechanisms necessary to theEthernetarchitecture. of description ITU-T G.8010 nology, ETY layer1, is ETH layer2. frames attheETHlayerarecarriedlayer. asaclient InOSItermi- oftheETY erence Clock (PRC) traceability at the interfaces (see Figure theinterfaces at traceability Clock (PRC) erence 2). addition, bytiming the Ethernet clock, it ispossible Primary achieve to Ref- EECs bewithin±100ppm. to clocks Ethernet specifies Whileclocks. standard theIEEE802.3 Slave Equipment Ethernet as referred are clocks These andnoisegeneration. erance, noise tol- performance, holdover noise transfer, of accuracy, in terms fined clocks, Ethernet Synchronous clocks. clocks Ethernet Synchronous defines ITU-T G.8262 Ethernet and vice-versa. over be SDHcan transported for chronization SDH.Syn- that network the samesynchronization to be connected to ment block networkequip- Ethernet (ITU-T G.8261). Synchronous This enables network of the synchronization Extension SyncE timing Professional TelecomSolutions ecture and comparison withecture andconventional comparison Ethernet. ETY ETY Master Slave - Synchro Data Synchronous Ethernetexplained Synchronous Data Rx Rx Tx Tx VoIP - QoS - SLA - ONEWAY - DATACOM - POLQA - PTP - JITTER -WAND -JITTER - ONEWAY -DATACOM -POLQAPTP QoS -SLA VoIP - Synchronus Ethernet Synchronus Standard Ethernet Standard ETY ETY ±100 ppm Synchronous Ethernet isbasedon the Ethernet Synchronous accuracy must be within ±4.6 ppm. In bewithin±4.6ppm. must accuracy 8261, G.8262 and G.8264. Theaspects G.8264. and G.8262 8261, SyncE timing based on ITU-T G.813 clocks, are de- are G.813 clocks, on ITU-T based H and Synchronous Ethernet equip- H andSynchronous to consider Ethernet as a building a as Ethernet consider to ETH ETH compatible with SDH with compatible Backplane Central timing SSU G.8262 EEC ±4.6 ppm SSU 2 / 8 A L B E D O - W H I T E P A P E R E R T EST- LABOS- EST- ALBEDO Telecom - Registered in Barcelona, Book 41613, Page 155, Sheet B-390886 - VAT : ESB6523022 TAPS Figure 3 - WAN EMULATION - E1 - GBE - SYNCE -WLESS - LTE - 3G - IPTV - 3G -IPTV LTE- - E1 -GBESYNCE -WLESS - - WANEMULATION TDEV [ns] MTIE [ns] ITU-T G.8262 states MTIE and TDEV limits forEECs and TDEVlimits MTIE states ITU-T G.8262 MTIE TDEVmasksMTIE and Networking & Telecoms Ethernet SynchronizationMessagingChannel • The ITU-TG.8264definesabackgroundor SP), in currently specified IEEE 802.3ay. defined by the ITU-T is based onthe Organization Specific Slow Protocol (OS- by theITU-TinG.8264cooperationwi nisms needed to transportthe SSMover Synchronous Ethernet are defined However, inEthernet there isnoequivalent ofafixed frame. The mecha- carriedin is In SDH,theSSMmessage to achievefull interoperability withSDHequipment. therefore required to extendtheSSMfunctionality Synchronous Ethernet traceability provides SSM SDH, the In network. Ethernet theSynchronous through of theSSM propagation for is Channelused (ESMC) Message Synchronization chain. The Ethernet of thecl the qualitylevel of dication TheSSM equipment. Ethernet contain an in- (SSM) Synchronous by Message the usability G.707 ITU-T ofthe extends ITU-T G.8264 sages with a new SSM quality level aregenerated immediately. continuous indication of the clock quality level. However, event type mes- Professional TelecomSolutions - Synchronous Ethernetexplained Synchronous Ether.Sync VoIP - QoS - SLA - ONEWAY - DATACOM - POLQA - PTP - JITTER -WAND -JITTER - ONEWAY -DATACOM -POLQAPTP QoS -SLA VoIP - verified with ALBEDO Ether.Sync and Ether.Genius. verifiedEther.Sync withALBEDO ock thatisdriving thesynchronization fixed locations within the SDH frame. SDH within the locations fixed ofsynchronization andit signals is th IEEE. More specifically, the th IEEE.Morespecifically, ESMC, heart-beat Synchronus Ethernet Synchronus Synchronization Status Synchronization message toprovidea IP 3 / 8 A L B E D O - W H I T E P A P E R E R Networking & Telecoms - Synchronous Ethernet explained 4 / 8 R The ESMC protocol is composed of the standard Ethernet header for a slow E protocol, an ITU-T specific header, a flag field, and a type length value (TLV) P A structure (see Figure 5.). The SSM encoded within the TLV is a four-bit field P E whose meaning is described in ITU-T G.781. T I H W - O D 2. HANDS-ON: TESTING SYNCHRONIZATION E B L A 2 Several phenomena in packet networks can affect the performance of packet 2 0 3 2 timing, such as network congestion, outage, and routing changes, causing 5 6 B some disturbance in packet networks that can lead to packet loss, packet de- S E : lay, and packet jitter (packet delay variation). The ALBEDO Ether.Genius de- T A liver SyncE, Ethernet and E1 test functionality for metro and access V - 6 applications in the field and lab. 8 8 0 9 3 - B Key factors for verifying packet timing include: t e e h S • Connectivity at TDM and packet interfaces , 5 5 1 • TDM jitter/wander e g a P , • Synchronous Ethernet jitter/wander 3 1 6 1 4 k o o B Basic TDM and Packet Test , a n o l e c r The very first step in verifying TDM service is to conduct a bit error rate test a B (BERT) between the end (TDM) nodes. If bit errors are present, performing n i d e various tests within the enclosed packet network such as basic Ping test can r e t s i verify connectivity at Ethernet (OAM Loopback) or IP (ICMP Ping) layer. Fur- g e R ther characterization of the packet network involves testing the throughput - m delay, and delay variation (jitter) across the packet network. o c e l e T O D E B L STS1/STM0 1 STM-1/STS-3 9 A 1 1 A1* A2* J0* A1* A1* A1* A2* A2* A2* J0* X* X* J0: Section Trace A1= 11110110, A2= 00101000: Frame Alignment B1 E1 F1 B1 ^ ^ E1 ^ F1 X X B1: Section Parity Code BIP-8 D1 D2 D3 D1 ^ ^ D2 ^ D3 B2: Bit interleaved parity, D1-D3: 192-kbit/s OA&M data H1 H2 H3 Pointer (s) D4-D12: 576-kbit/s OA&M data E1, E2: 64-kbit/s orderwire channels B2 K1 K2 B2 B2 B2 K1 K2 F1: 64-kbit/s user channel H1, H2, H3: pointer bytes D4 D5 D6 D4 D5 D6 K1, K2: Request /answer APS channels D7 D8 D9 D7 D8 D9 F1: 64-kbit/s user channel M0, M1: Resending of B2 errors D10 D11 D12 D10 D11 D12 Z0: reserved 9 S1 M1 E2 9 S1 M1 E2 X X S1: SSM (Synchronization Status Messages) Figure 4 Sections overheads in SDH / SONET. Synchronization Status Messages (SSM): This is used to inform the remote multiplexer on the quality of the clock used to generate the signals. 0x: Unknown, 2x: G811, 4x: G.812 transit, 8x: G.812 local, Bx: G.813, Fx: Not used for synchronization. Professional Telecom Solutions TEST- LABOS - TAPS - WAN EMULATION - E1 - GBE - SYNCE -WLESS - LTE - 3G - IPTV - VoIP - QoS - SLA - ONEWAY - DATACOM - POLQA - PTP - JITTER - WANDER T EST- LABOS- EST- ALBEDO Telecom - Registered in Barcelona, Book 41613, Page 155, Sheet B-390886 - VAT : ESB6523022 TAPS Figure 5 - WAN EMULATION - E1 - GBE - SYNCE -WLESS - LTE - 3G - IPTV - 3G -IPTV LTE- - E1 -GBESYNCE -WLESS - - WANEMULATION ESMC message ITU-T G.8264 Ethernet Synchronization Ethernet Message Channel (ESMC) Networking & Telecoms TDM Jitter / WanderMeasurements interfaces. der that must be provided at thebounda G.8261 alsospecifies themaximum equipment tolerancetojitter andwan- maximum networklimits ofjitterwhich mustnotbeexceeded.
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