Ethernet Demarcation Devices With Built in OTDR


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Telecoms Carriers and Service Providers use Managed Ethernet Demarcation Devices (EDDs) to provide full end-to-end visibility and control of their Layer-2 infrastructure.

Advanced EDDs incorporate test-traffic generation and protocols such as ITU-T Y.1731 to monitor key service-level characteristics such as Frame Loss, Latency and Jitter.

Now, it is possible to incorporate fibre integrity checking and fault-reporting to such devices. Specifically, Optical Time Domain Reflectometer (OTDR) functionality, integrated directly into EDD fibre interfaces, provides a cost-effective solution to Carriers for fibre fault determination and localisation, reducing costs and time-to-repair for customer services.

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Ethernet Demarcation Devices With Built in OTDR

  1. 1. Metrodata Ltd Fortune House, TW20 8RY U.K.Tel: +44 (0)1784 744700 E-mail: Ethernet ServicesWhite PaperEthernet Demarcation Devices withbuilt-in OTDR for fibre fault-findingTelecoms Carriers and Service Providers use Managed Ethernet Demarcation Devices(EDDs) to provide full end-to-end visibility and control of their Layer-2 infrastructure.Advanced EDDs incorporate test-traffic generation and protocols such as ITU-T Y.1731 tomonitor key service-level characteristics such as Frame Loss, Latency and Jitter. Now, itis possible to incorporate fibre integrity checking and fault-reporting to such devices.Specifically, Optical Time Domain Reflectometer (OTDR) functionality, integrated directlyinto EDD fibre interfaces, provides a cost-effective solution to Carriers for fibre faultdetermination and localisation, reducing costs and time-to-repair for customer services.May, 2013
  2. 2. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 1 of 10IntroductionThe rapid uptake of so-called Next Generation Packet Switched Networks by TelecommunicationsCompanies has led to a similarly rapid rise in the deployment by Carriers of high bandwidth EthernetServices over fibre infrastructure.Whilst the majority of Packet Switched Services actually offered to Corporate customers for siteinterconnection comprise IP VPN overlays, the Infrastructure Carriers themselves predominantly offerLayer-2 Ethernet services over their Fibre Infrastructure for customer-site connectivity. In the increasinglyde-regulated world of Telecoms Services, very often the bandwidth services of Infrastructure Carriers areseparated from the offerings of Service Providers laid over the Carriers infrastructure. Service Providerstypically contract under wholesale arrangements with Infrastructure Carriers in accordance withincreasingly stringent Service Level Agreements relating to both the supply and technical characteristicsof the Infrastructure Services provided.In the case of Fibre Ethernet services much effort, by both Carriers and Telecoms EquipmentManufacturers, principally under the auspices of the Metro Ethernet Forum (MEF), has been put into thedevelopment of management tools for both Connectivity and, latterly, Performance Assurance forEthernet services. End-to-end Ethernet Infrastructure Services are now frequently characterised in termsof Throughput, Packet Loss, Latency and Jitter and managed circuit termination equipment known asEthernet Demarcation Devices (EDDs) now incorporate an array of technologies to provision andmonitor Ethernet Networks according to these characteristics.By adding increasing sophistication to these circuit termination devices, Carriers have been able toreduce costs in commissioning and troubleshooting Ethernet problems on behalf of their clients.Nevertheless, to date, such devices have contained little or no capability to provide information regardingthe physical fibre infrastructure by which they are connected. In the case of fibre damage or breakagealong the route from a Carriers Central Office and/or intermediate Point of Presence to a specificcustomer site, often considerable cost and complexity can be involved in the localisation of a problem,particularly if it presents in the form of an intermittent failure.This White Paper explores the combined benefits of Advanced Ethernet Demarcation Devices withintegrated Optical Time Domain Reflectometer (OTDR) functionality in characterising and monitoringcircuits both at Layer 1 (i.e. the physical fibre) and Layer 2 (i.e. Ethernet), thus maximising the Carriersvisibility to their own connections and minimising their costs in relation to both Commissioning andTroubleshooting activities.Backgrounder - Ethernet Demarcation DevicesOver the past few years, each of three Industry standards bodies, namely the Institute of Electrical andElectronic Engineers (IEEE), the International Telecommunications Union (ITU) and the Metro EthernetForum (MEF) have been active in developing and promoting both capabilities and standards in relation toCarrier (i.e. WAN) Ethernet Services. Most significantly, a number of Operations, Administration andManagement (OAM) protocols have been developed relating to Ethernet WAN deployments.Relatively simple visibility and connectivity checking of single segment Ethernet connections is supportedby the Link OAM, or Ethernet First Mile (EFM) protocol, formalised initially as IEEE 802.3ah, by which itis still generally best known, albeit that this functionality has now been fully incorporated into the core ofthe 802.3 standard itself.An additional level of connectivity assurance is offered by those Demarcation Devices supporting theConnectivity Fault Management (CFM) protocol, formalised under the standard IEEE 802.1ag. CFMoffers the ability for a number of end-point devices to establish and monitor a community of reachableend-points and mid-points corresponding to a customers network, which can offer some degree of pro-activity to the Service Provider with regard to connectivity fault detection.
  3. 3. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 2 of 10Consider the rather simplified Infrastructure diagram below.Fig 1. Simplified end-to-end Ethernet WAN Circuit modelIn this example, a Telecoms Carrier provides an Ethernet service between two customer sites, A and B.In order to facilitate full manageability, right up to the point of connectivity to the customers equipment ateach site, the Carrier provides manageable Ethernet Demarcation Devices as Customer PremiseEquipment (CPE).Above and beyond connectivity management though, customers are increasingly asking of their ServiceProviders that they provision multiple traffic streams across their Ethernet pipe connections, to whichpotentially different criteria may apply for key network performance parameters, including acceptableframe loss ratio, latency (i.e. traffic delay) and jitter (delay variation), together with comprehensive trafficthroughput policing. Providers may then be faced with the challenge to demonstrate to their customer, atthe time of provisioning, that such performance parameters are complied with for each individual Servicedata stream within a given end-to-end Ethernet connection. Such parameters may be detailed within atightly defined Service Level Agreement (SLA), to which compliance should be verified.Furthermore, Service Providers may not only need to demonstrate SLA compliance at the time ofcommissioning, but they may be required to subsequently monitor in-service traffic and take pro-activesteps with regard to any potential breach of SLA.Ethernet Demarcation Devices equipped with more advanced packet processing capabilities can offer avery effective tool to Service Providers in this regard. For example if a Service Provider, from a NetworkOperations Centre, can interact with an EDD in such a manner as to configure this device to issue one ormore test traffic streams across the network to a corresponding remote end-point, at which traffic may belooped and returned, then this can be highly beneficial. Such test stream(s) can enable accuratereporting of throughput, packet loss, latency and jitter, for the end-to-end network link. DemarcationDevices with such capabilities are now available. Necessarily, such devices contain more than simpleswitch and management processing functionality. Dedicated packet processing hardware is required inorder to ensure accurate time-stamping, test collation and reporting in real-time for line rates up to 1Gbpsand beyond.Another of the OAM protocols, this time the ITU-Ts Y.1731 suite, relates to the ability to provide in-service testing and reporting of SLA compliance, which is very much to the fore in the MEFs definitionsfor Carrier Ethernet service and to which is often referred as Performance Assured Ethernet (PAE).All of these capabilities, incorporated within the most recent generation of Advanced EthernetDemarcation Devices, combine to make these an extremely useful addition to the Service Providersportfolio of devices to ensure that their customers experience strength and depth in support.CustomerSite ACarrier CoreNetworkNOCCustomerSite BEthernet CircuitdemarcationEthernet CircuitdemarcationManagementAccessManagementAccessFibreFibre
  4. 4. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 3 of 10Backgrounder - Optical Time Domain ReflectometryOptical Time-domain Reflectometry (OTDR) is a well established technology whereby the length of a fibrecable can be determined. A pulse of light is sent into the fibre from a light source at a precise time. Thepulse is reflected, albeit at much reduced amplitude, back from a discontinuity in the fibre, such as thatdue to a breakage or disconnection, or simply from the end of the fibre. The source detects this returnedpulse and, by measuring the time delay associated with the round-trip to and from the discontinuity, cancalculate the distance between the source and the discontinuity, i.e. the length of the cable. This isillustrated graphically below:Fig 2. Principles of Optical Time-domain ReflectometryThere are indeed many manufacturers of OTDR-based fibre test equipment, but typically OTDR testersare expensive and require some training in operation. When used to determine not just the length of aparticular fibre but, in the event of a breakage, the distance from a particular item of equipment to thatbreakage, then the OTDR tester must be taken to site, installed in place of the normal active equipment,and testing conducted. As we shall see, this is operationally complex and expensive compared with thesolution offered by Metrodata in association with Optical Zonu Corporation.The Role of EDDs in end-to-end Circuit Characterisation and MonitoringCarriers today must be sure that the infrastructure circuits which they offer meet the exacting demands oftheir customers. Basic Ethernet connectivity services may be nothing more than a high-speed conduit forIP VPN traffic, across an MPLS core network, but increasingly customers are demanding Ethernet circuitsfor pure Layer-2 networks, either for simple point-to-point Layer-2 LAN extension or alternatively formore complex multi-point networking, typically using VPLS. In such cases, at the customer interfacepoint, a number of options may need to be offered by the Carrier, such as support for various VLANdesignations within the customers traffic stream, or perhaps support for the tunnelling of various layer 2Control Protocols such as Spanning tree, to which the Carriers own Switched network infrastructureshould necessarily be transparent.Moreover, in a pure Layer-2 environment, a customer may demand one or more virtual circuits withspecific subsets of bandwidth to be designated within the overall service pipe, which may require trafficpolicing in order to separate the different services into segments of fully discrete bandwidth. Possibly,each different service may demand different transit characteristics through the core network. for example,a VoIP traffic stream may demand an end-to-end latency of less than 30ms, whereas a regular internetaccess stream might be more tolerant to latency and/or jitter.1. Source emits light pulse, which travels to the end of the fibre3. Source measures the round-trip travel time for the Light Pulse and calculates the length of the fibre2. Light Reflects back from end to Source( Xns ≡ Ym )1. Source emits light pulse, which travels to the end of the fibre3. Source measures the round-trip travel time for the Light Pulse and calculates the length of the fibre2. Light Reflects back from end to Source( Xns ≡ Ym )
  5. 5. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 4 of 10Carriers require to demonstrate to their customers that they are meeting their contractual obligations fornetwork performance, both initially at the time of circuit commissioning, and then subsequently during in-service usage.Modern advanced Ethernet Demarcation Devices support dedicated test traffic generation and loop-backcapabilities, with accurate time-stamping and calculation of key SLA characteristics including throughput,packet-loss, latency and jitter. At the time of circuit commissioning, test profiles such as the recentlystandardised ITU-T Y.1564, can provide comprehensive birth certificate type reporting for Carriers todemonstrate that, under full load conditions, their infrastructure will meet a customers requirements.An example of this process and output is illustrated below.Fig 3. Circuit testing during ProvisioningDuring subsequent in-service usage, the challenge for the Carrier becomes more one of monitoringactual performance of the network under real load conditions. The ITU-T Y.1731 protocol definesmechanisms for enabling periodic test packets to be inserted into live data-streams, which can then beused to monitor latency and jitter characteristics for each service defined across a Layer-2 Ethernetcircuit. The size and frequency of such test packets are low, hence they do not appreciably affect theoverall throughput of customers services.Again, the more advanced Demarcation Devices support the ability to assign alarms to key performanceparameters such that, for example, the Carriers Network Operations Centre might readily be alerted if thelatency of one of a customers services, perhaps representing only a single virtual pathway within anoverall Ethernet pipe, rises above a certain threshold defined within the customers SLA. This scenario isillustrated in the following diagram.EDD BEDD ACore NetworkCustomer Site BCustomer Site ANMCSite ASite BCore1. Expand view2. Test link A<>BProvisioning / SLA Verification TestingA-end: "Site A" MAC Addr.B-end: "Site B" MAC Addr.Test Traffic: L2, MAC Addr. loop-back test256 byte packetsY.1564 test profile to 95% CIR/CBS/EIR/EBSTraffic Parameters Service 1 Service 2EVC Number (S-Tag): 100 100VLAN Number (C-Tag): 101 102Committed SLACIR (Mbps): 200 800CBS (Bytes): 1,000 1,000EIR (Mbps): 80 20EBS (Bytes): 5,000 5,000Frame loss (%): <0.005 <0.0001Frame delay (µs): <30,000 <10,000Frame delay variation (µs): <10,000 <1,000Test ResultsThroughput (Mbps): 190 760Lost frames (%): 0.0005 0.0001Average frame delay (µs): 10,000 5,000Frame delay variation (µs): 1,000 100Pass/Fail Pass PassTest traffic generation Test traffic loop-back1. Testing initiated from NMC2. Circuit characteristics retrievedand reportedManagementConsoleTypical ManagementConsole Screens
  6. 6. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 5 of 10Fig 4. Service performance monitoring and alarming via Y.1731Fibre Network Monitoring and ReportingWhilst advanced capabilities exist within many EDDs for Layer-2 and, to a certain extent layer-3performance baselining and monitoring, what about the underlying physical, or Layer-1 network? In thecase of Wide-Area Ethernet networks, such infrastructure is inevitably fibre-based and until recentlyEDDs have offered little by way of assessment or monitoring of the status of the physical fibreinfrastructure.Recently, advanced EDDs have started to offer the facility to report the Digital Diagnostics Monitoringparameters captured by suitably equipped Optical Transceivers. By far the most common type ofTransceivers used for services up to 1Gbps today are the Small Form Pluggable (SFP) type, and thesenow increasingly incorporate facilities for reporting on the following characteristics:Optical signal transmission power, measured in dBmOptical received signal power, measured in dBmBias current applied at the SFP, measured in mASFP temperature, measured in oCSFP power supply, measured in VSince the transmission distance parameters of optical transceivers are normally rated on the basis ofoptical transmission power. received power sensitivity, then the ability of such transceivers to report onpower reception levels in particular provides a useful tool to determine whether the fibre link between twopoints is well within tolerance or maybe borderline and likely to cause some problems affecting theintegrity of the link. Some EDDs are able to link measurements through to threshold level alarms to alertthe Carrier to potential problems associated with the fibre link as seen directly from fibre transceiverinterfaces.But, what of the situation of fibre breakages and/or disconnections? To date, EDDs have not brought anyvalue in this respect. Now, from at least one vendor, i.e. Metrodata Ltd. of the UK, in association withOptical Zonu Corporation of California, USA, this situation has been addressed.Metrodata has worked with Optical Zonu to incorporate software drivers for Optical Zonus iSFC®FastFiber Fault Finder transceivers, such that whenever a disconnect or breakage occurs in the fibreconnected to one of Metrodatas EDD family, then automatically alerting to both the loss of signal and,EDD BEDD ACore NetworkCustomer Site BCustomer Site ANMSLive customer trafficBackgroundSLA monitoringvia Y.1731BackgroundSLA monitoringvia Y.1731Alarm if SLA parameters breachede.g. latency > 30mS
  7. 7. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 6 of 10more critically, the distance to the fault, becomes immediately available to the Carriers NetworkOperations Centre.The general principle of this operation is illustrated in the diagrams below.Fig 5a. EDD/SFC combination provides a basis for alerting andlocalising fibre breakages or disconnectsFig 5b. Typical single-ended deployment scenarioThe iSFC®family transceivers transmit and receive at the same wavelength and should thereforegenerally be used in pairs. Within the family are variants both with and without embedded OTDRfunctionality, so it is possible to pair these devices such that the OTDR variant is at just one end of a fibrelink, or both, as required. The scenario above illustrates deployment of this capability in a single-endedmanner, although if EDDs exist at both ends of such a link and both are equipped with OTDR-equippedtransceivers, then provided that independent management access is available to the EDDs in both1. SFC emits light pulse (up to +13 dBm), which travels along fibre to the fault3. SFC measures the roundtrip travel time for the Light Pulse and stores it in memory4. SFC reports failure status and distance to fault to EDD5. EDD software reads data from SFC and reports to Network Management Systems2. Light Reflects back from fault to SFC (as little as -42 dBm)When a fibre break occurs, EDD alerts Network Management Systemsand SFC reverts to Micro-OTDR mode:FCM9004CoreNetworkCustomer SiteNMSRemote equipmentFibre discontinuity(breakage or disconnection)(i) Alarm:Connection Fault(SNMP Trap)(ii) Log into FCM9004:SFP Management"Fibre breakage at 1,200m"iSFC® transceiverFCM9004CoreNetworkCustomer SiteNMSRemote equipmentFibre discontinuity(breakage or disconnection)(i) Alarm:Connection Fault(SNMP Trap)(ii) Log into FCM9004:SFP Management"Fibre breakage at 1,200m"iSFC® transceiver
  8. 8. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 7 of 10locations (as is commonly the case via back-up xDSL circuits for critical services), then fault detection canbe reported from both directions, helping to pin-point the problem most accurately.It is worth mentioning that the iSFC®Fast Fiber Fault Finder transceivers maintain a degree of historicevent information and that they respond rapidly in the event of a fibre discontinuity. This facilitatesdetection and localisation of even intermittent problems. It is often the case that when using externalOTDR test equipment, by the time this has been brought to site, connected and testing conducted, then atemporary but potentially intermitted fault may not be evident at the time of a test. In contrast the iSFC®isable to record the locality of a discontinuity even of sub-millisecond duration.As example is shown below of a typical management screen, illustrating the interworking between aMetrodata FCM9004 EDD and an iSFC®. In the first case, no fibre fault exists within the monitorednetwork segment. Note that the iSFC®facilitates measurement of the initial length of the deployed fibre.Fig 6a. EDD Management Screen reflectingFibre Connection status and parametersFig 6b. Alternative screen indicatingFibre Fault conditionExtended Applications ExamplesAside from the clear example of determination of the length of an individual fibre strand and point ofbreakage or disconnection, this unique capability lends itself to further applications including protectioncoverage for multiple fibre/copper cables or other transmission media.Since fibre cables invariably comprise many individual fibre strands within a single protective sheath, it ismost likely that breakage of a single strand, protected by the in-built OTDR capabilities described above,will in fact have resulted from a breakage of the entire fibre cable, carrying potentially many tens or evenhundreds of separate services.Moreover, it is frequently the case that fibre bundles are run in conjunction with copper cables or evenother services which may be afforded a degree of protection (to the extent of generation of alarms andprovision of immediate localisation information in the event of a breakage, allowing Engineers to startimmediate rectification works) by a single iSFC®OTDR-enabled link. There is no imperative, in fact, thatSFP DETAIL-----------------SFP DETAIL-----------------OTDROTDR statusstatus No LOSNo Fault DetectedFibre Length 1,200mOTDROTDR statusstatus LOSFault DetectedDistance to Fault: 825mLOSFault DetectedDistance to Fault: 825m
  9. 9. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 8 of 10the fibre terminated by EDDs bearing iSFC®transceivers, should itself be carrying user services. Such alink might simply be used as a health monitoring/alarm circuit, run alongside critical Telecoms or otherservices (including, for instance, oil or gas pipelines in territories potentially subject to damage for eithergeological or political/terrorism reasons).The diagram below illustrates that, in the case of the existence of a separate management network(which might in fact comprise wireless technologies, offering independence from the main transmissionpath itself), extended links or ring topologies might be very accurately monitored using a number of EDDsequipped with iSFC®transceivers:Fig 7. Extended or Ring Topology deploymentMetrodata Ltd. is the first EDD vendor to incorporate full commercial support for automated OTDR-basedfault detection in this manner, and is pleased to be working in co-operation with Optical Zonu Corporationto bring not only comprehensive Ethernet service monitoring in terms of throughput, packet-loss, latencyand jitter, but now also physical layer fibre fault detection and localisation, to Telecoms Carriers, EthernetService Providers and the wider marketplace.FCM9004-AManagementNetworkNMSFCM9004-B FCM9004-COTDROTDROTDROTDR(i) Alarm sent to NMS from FCM9004 units either side ofa fibre breakage (in this case, from A & C)(ii) OTDR measurements are read from FCM9004 units A & Cto determine accurately the position of the break(iii) Historic events are maintained such that even short,intermittent disconnects can be reportedFibrebreakageFCM9004-AManagementNetworkNMSFCM9004-B FCM9004-COTDROTDROTDROTDR(i) Alarm sent to NMS from FCM9004 units either side ofa fibre breakage (in this case, from A & C)(ii) OTDR measurements are read from FCM9004 units A & Cto determine accurately the position of the break(iii) Historic events are maintained such that even short,intermittent disconnects can be reportedFibrebreakage
  10. 10. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 9 of 10About Metrodata Ltd & MetroCONNECT Ethernet Demarcation DevicesMetrodata Ltd. is a long-standing UK developer and manufacturer of Interface Conversion and NetworkAccess solutions. The company has been a supplier to Governments, Corporations and TelecomsService Providers worldwide since 1989.Within the companys MetroCONNECT range of Ethernet Service Delivery solutions, Metrodata offerscost-effective products with Advanced functionality for use with both wires-only IP VPN and Layer-2Ethernet WAN solutions.The FCM9002 product supports Copper (RJ45) or Fibre (SFP) Network Connection up to 1Gbps withRJ45 connectivity to Customer equipment. Management visibility is offered to Customer site connectionsand the product supports the OAM protocols of IEEE 802.3ah (EFM), IEEE 802.1ag (CFM) and ITU-TY.1731. One of the most common frustrations experienced by Service Providers is that of network faultsbeing reported from customers which eventually are found to be due to simple power-downs of interfaceequipment. The FCM9002 provides indication of local power-down to the Service Provider via both SNMPTrap and OAM protocol alerting when power is withdrawn from the device (or alternatively should thePSU of the EDD itself fail). Test-traffic generation, loop-back and SLA verification features are supportedby the product.The FCM9004 supports more sophisticated facilities for test-traffic profiling and additionally supportsmultiple LAN-ports with advanced Service multiplexing and powerful multi-level VLAN handlingcapabilities.Fig. 8: MetroCONNECT FCM9004 Ethernet Demarcation Device(AC and -48V DC PSU variants)Full information regarding the MetroCONNECT family of Ethernet Demarcation Devices, may be foundhere:
  11. 11. Carrier Ethernet ServicesAdvanced EDDs with built-in OTDRPage 10 of 10About Optical Zonu Corporation & Zonu iSFC®TransceiversOptical Zonu Corporation (OZC) is a privately owned high technology company located in the SanFernando Valley of the City of Los Angeles, specializing in the design and manufacturing of Fibre OpticComponents for Analogue Transmission, Digital Transmission, Business Class Services and CoarseWavelength Division Multiplexing (CWDM).OZC is the leading supplier of Full Duplex, Single Fibre, Single Wavelength Transceivers and RF overFibre Optic Links. OZC maintains important strategic and global relationships in the Industry andcooperates with major vendors and suppliers of optical, communication and electronic devices, to enablerapid production of cutting-edge solutions.iSFC®Fast Fiber Fault Finder transceivers with micro-OTDR, function as normal Single Fibre, Full DuplexCWDM Transceivers, but with the ability to switch into OTDR operation, capable of detecting andlocalising optical fibre faults.iSFC®Fast Fiber Fault Finder transceivers transmit and receive at the same wavelength, which allowsthem be used for Optical Fiber Fault Detection and Localization. The iSFC®transmitter can be switchedto operate in Micro-OTDR mode where it transmits optical pulses of +13 dBm. The receiver will detect anyreflected pulses down to -42 dBm optical power. Total ORL detection range is at least 55dB, enablingdetection of fibre break/cut.Full information regarding Optical Zonu Corporations iSFC®transceiver family may be found here: Ltd.Fortune House, Eversley WayEGHAM, Surrey TW20 8RY U.K.+44 (0)1784 744700