Carrier Ethernet Services

Transcription

1 White Paper Ethernet Demarcation Devices with built-in OTDR for fibre fault-finding 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. May, 2013 Metrodata Ltd Fortune House, TW20 8RY U.K. Tel: +44 (0) sales@metrodata.co.uk

2 Introduction The rapid uptake of so-called 'Next Generation' Packet Switched Networks by Telecommunications Companies has led to a similarly rapid rise in the deployment by Carriers of high bandwidth Ethernet Services over fibre infrastructure. Whilst the majority of Packet Switched Services actually offered to Corporate customers for site interconnection comprise IP VPN overlays, the Infrastructure Carriers themselves predominantly offer Layer-2 Ethernet services over their Fibre Infrastructure for customer-site connectivity. In the increasingly de-regulated world of Telecoms Services, very often the bandwidth services of Infrastructure Carriers are separated from the offerings of Service Providers laid over the Carriers' infrastructure. Service Providers typically contract under wholesale arrangements with Infrastructure Carriers in accordance with increasingly stringent 'Service Level Agreements' relating to both the supply and technical characteristics of the Infrastructure Services provided. In the case of Fibre Ethernet services much effort, by both Carriers and Telecoms Equipment Manufacturers, principally under the auspices of the 'Metro Ethernet Forum' (MEF), has been put into the development of management tools for both Connectivity and, latterly, Performance Assurance for Ethernet services. End-to-end Ethernet Infrastructure Services are now frequently characterised in terms of 'Throughput, Packet Loss, Latency and Jitter' and managed circuit termination equipment known as 'Ethernet Demarcation Devices' (EDDs) now incorporate an array of technologies to provision and monitor Ethernet Networks according to these characteristics. By adding increasing sophistication to these circuit termination devices, Carriers have been able to reduce 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 regarding the physical fibre infrastructure by which they are connected. In the case of fibre damage or breakage along the route from a Carrier's 'Central Office' and/or intermediate 'Point of Presence' to a specific customer 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 with integrated Optical Time Domain Reflectometer (OTDR) functionality in characterising and monitoring circuits both at Layer 1 (i.e. the physical fibre) and Layer 2 (i.e. Ethernet), thus maximising the Carrier's visibility to their own connections and minimising their costs in relation to both Commissioning and Troubleshooting activities. Backgrounder - Ethernet Demarcation Devices Over the past few years, each of three Industry standards bodies, namely the Institute of Electrical and Electronic Engineers (IEEE), the International Telecommunications Union (ITU) and the Metro Ethernet Forum (MEF) have been active in developing and promoting both capabilities and standards in relation to Carrier (i.e. WAN) Ethernet Services. Most significantly, a number of 'Operations, Administration and Management' (OAM) protocols have been developed relating to Ethernet WAN deployments. Relatively simple visibility and connectivity checking of single segment Ethernet connections is supported by the 'Link OAM', or 'Ethernet First Mile' (EFM) protocol, formalised initially as IEEE 802.3ah, by which it is still generally best known, albeit that this functionality has now been fully incorporated into the core of the standard itself. An additional level of connectivity assurance is offered by those Demarcation Devices supporting the 'Connectivity Fault Management' (CFM) protocol, formalised under the standard IEEE 802.1ag. CFM offers the ability for a number of end-point devices to establish and monitor a 'community' of reachable end-points and mid-points corresponding to a customer's network, which can offer some degree of proactivity to the Service Provider with regard to connectivity fault detection. Page 1 of 10

3 Consider the rather simplified Infrastructure diagram below. Customer Site A Management Access NOC Management Access Customer Site B Fibre Carrier Core Network Fibre Ethernet Circuit demarcation Ethernet Circuit demarcation Fig 1. Simplified end-to-end Ethernet WAN Circuit model In 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 customer's equipment at each site, the Carrier provides manageable 'Ethernet Demarcation Devices' as 'Customer Premise Equipment (CPE). Above and beyond connectivity management though, customers are increasingly asking of their Service Providers that they provision multiple traffic streams across their Ethernet 'pipe' connections, to which potentially different criteria may apply for key network performance parameters, including acceptable frame loss ratio, 'latency' (i.e. traffic delay) and 'jitter' (delay variation), together with comprehensive traffic throughput 'policing'. Providers may then be faced with the challenge to demonstrate to their customer, at the time of provisioning, that such performance parameters are complied with for each individual Service data stream within a given end-to-end Ethernet connection. Such parameters may be detailed within a tightly 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 of commissioning, but they may be required to subsequently monitor 'in-service' traffic and take pro-active steps with regard to any potential breach of SLA. Ethernet Demarcation Devices equipped with more advanced packet processing capabilities can offer a very effective tool to Service Providers in this regard. For example if a Service Provider, from a Network Operations Centre, can interact with an EDD in such a manner as to configure this device to issue one or more test traffic streams across the network to a corresponding remote end-point, at which traffic may be 'looped' and returned, then this can be highly beneficial. Such test stream(s) can enable accurate reporting of throughput, packet loss, latency and jitter, for the end-to-end network link. Demarcation Devices with such capabilities are now available. Necessarily, such devices contain more than simple switch and management processing functionality. Dedicated packet processing hardware is required in order to ensure accurate time-stamping, test collation and reporting in real-time for line rates up to 1Gbps and beyond. Another of the OAM protocols, this time the ITU-T's Y.1731 suite, relates to the ability to provide inservice testing and reporting of SLA compliance, which is very much to the fore in the MEF's definitions for 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 Ethernet Demarcation Devices, combine to make these an extremely useful addition to the Service Provider's portfolio of devices to ensure that their customers experience strength and depth in support. Page 2 of 10

4 Backgrounder - Optical Time Domain Reflectometry Optical Time-domain Reflectometry (OTDR) is a well established technology whereby the length of a fibre cable can be determined. A pulse of light is sent into the fibre from a light source at a precise time. The pulse is reflected, albeit at much reduced amplitude, back from a discontinuity in the fibre, such as that due to a breakage or disconnection, or simply from the end of the fibre. The source detects this returned pulse and, by measuring the time delay associated with the 'round-trip' to and from the discontinuity, can calculate the distance between the source and the discontinuity, i.e. the length of the cable. This is illustrated graphically below: 1. Source emits light pulse, which travels to the end of the fibre ( Xns Ym ) 2. Light Reflects back from end to Source 3. Source measures the round-trip travel time for the Light Pulse and calculates the length of the fibre Fig 2. Principles of Optical Time-domain Reflectometry There are indeed many manufacturers of OTDR-based fibre test equipment, but typically OTDR testers are expensive and require some training in operation. When used to determine not just the length of a particular fibre but, in the event of a breakage, the distance from a particular item of equipment to that breakage, 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 the solution offered by Metrodata in association with Optical Zonu Corporation. The Role of EDDs in end-to-end Circuit Characterisation and Monitoring Carriers today must be sure that the infrastructure circuits which they offer meet the exacting demands of their customers. Basic Ethernet 'connectivity' services may be nothing more than a high-speed conduit for IP VPN traffic, across an MPLS core network, but increasingly customers are demanding Ethernet circuits for pure Layer-2 networks, either for simple point-to-point Layer-2 'LAN extension' or alternatively for more complex multi-point networking, typically using VPLS. In such cases, at the customer interface point, a number of options may need to be offered by the Carrier, such as support for various VLAN designations within the customer's traffic stream, or perhaps support for the 'tunnelling' of various 'layer 2 Control Protocols' such as 'Spanning tree', to which the Carrier's own Switched network infrastructure should necessarily be transparent. Moreover, in a pure Layer-2 environment, a customer may demand one or more 'virtual circuits' with specific subsets of bandwidth to be designated within the overall service 'pipe', which may require traffic 'policing' 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 internet access stream might be more tolerant to latency and/or jitter. Page 3 of 10

5 Carriers require to demonstrate to their customers that they are meeting their contractual obligations for network performance, both initially at the time of circuit commissioning, and then subsequently during 'inservice' usage. Modern advanced Ethernet Demarcation Devices support dedicated test traffic generation and loop-back capabilities, 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 recently standardised ITU-T Y.1564, can provide comprehensive 'birth certificate' type reporting for Carriers to demonstrate that, under full load conditions, their infrastructure will meet a customer's requirements. An example of this process and output is illustrated below. Test traffic generation EDD A Core Network Test traffic loop-back EDD B Customer Site A Management Console NMC 1. Testing initiated from NMC 2. Circuit characteristics retrieved and reported Provisioning / SLA Verification Testing A-end: B-end: Test Traffic: Customer Site B "Site A" MAC Addr. "Site B" MAC Addr. L2, MAC Addr. loop-back test 256 byte packets Y.1564 test profile to 95% CIR/CBS/EIR/EBS Traffic Parameters Service 1 Service 2 EVC Number (S-Tag): VLAN Number (C-Tag): Expand view Typical Management Console Screens Site A Core 2. Test link A<>B Site B Committed SLA CIR (Mbps): CBS (Bytes): 1,000 1,000 EIR (Mbps): EBS (Bytes): 5,000 5,000 Frame loss (%): <0.005 < Frame delay (µs): <30,000 <10,000 Frame delay variation (µs): <10,000 <1,000 Test Results Throughput (Mbps): Lost frames (%): Average frame delay (µs): 10,000 5,000 Frame delay variation (µs): 1, Pass/Fail Pass Pass Fig 3. Circuit testing during Provisioning During subsequent 'in-service' usage, the challenge for the Carrier becomes more one of monitoring actual performance of the network under 'real load' conditions. The ITU-T Y.1731 protocol defines mechanisms for enabling periodic test packets to be inserted into live data-streams, which can then be used to monitor latency and jitter characteristics for each service defined across a Layer-2 Ethernet circuit. The size and frequency of such test packets are low, hence they do not appreciably affect the overall throughput of customers' services. Again, the more advanced Demarcation Devices support the ability to assign alarms to key performance parameters such that, for example, the Carrier's Network Operations Centre might readily be alerted if the latency of one of a customer's services, perhaps representing only a single virtual pathway within an overall Ethernet 'pipe', rises above a certain threshold defined within the customer's SLA. This scenario is illustrated in the following diagram. Page 4 of 10

6 Live customer traffic Customer Site A EDD A Background SLA monitoring via Y.1731 Core Network Background SLA monitoring via Y.1731 EDD B Customer Site B NMS Alarm if SLA parameters breached e.g. latency > 30mS Fig 4. Service performance monitoring and alarming via Y.1731 Fibre Network Monitoring and Reporting Whilst advanced capabilities exist within many EDDs for Layer-2 and, to a certain extent layer-3 performance baselining and monitoring, what about the underlying physical, or Layer-1 network? In the case of Wide-Area Ethernet networks, such infrastructure is inevitably fibre-based and until recently EDDs have offered little by way of assessment or monitoring of the status of the physical fibre infrastructure. Recently, advanced EDDs have started to offer the facility to report the 'Digital Diagnostics Monitoring' parameters captured by suitably equipped Optical Transceivers. By far the most common type of Transceivers used for services up to 1Gbps today are the 'Small Form Pluggable' (SFP) type, and these now increasingly incorporate facilities for reporting on the following characteristics: Optical signal transmission power, measured in dbm Optical received signal power, measured in dbm Bias current applied at the SFP, measured in ma SFP temperature, measured in o C SFP power supply, measured in V Since the transmission distance parameters of optical transceivers are normally 'rated' on the basis of optical transmission power. received power sensitivity, then the ability of such transceivers to report on power reception levels in particular provides a useful tool to determine whether the fibre link between two points is well within tolerance or maybe 'borderline' and likely to cause some problems affecting the integrity of the link. Some EDDs are able to link measurements through to 'threshold level alarms' to alert the Carrier to potential problems associated with the fibre link as seen directly from fibre transceiver interfaces. But, what of the situation of fibre breakages and/or disconnections? To date, EDDs have not brought any value in this respect. Now, from at least one vendor, i.e. Metrodata Ltd. of the UK, in association with Optical Zonu Corporation of California, USA, this situation has been addressed. Metrodata has worked with Optical Zonu to incorporate software drivers for Optical Zonu's isfc Fast Fiber Fault Finder transceivers, such that whenever a disconnect or breakage occurs in the fibre connected to one of Metrodata's EDD family, then automatically alerting to both the loss of signal and, Page 5 of 10

7 more critically, the distance to the fault, becomes immediately available to the Carrier's Network Operations Centre. The general principle of this operation is illustrated in the diagrams below. When a fibre break occurs, EDD alerts Network Management Systems and SFC reverts to Micro-OTDR mode: 1. SFC emits light pulse (up to +13 dbm), which travels along fibre to the fault 2. Light Reflects back from fault to SFC (as little as -42 dbm) 3. SFC measures the roundtrip travel time for the Light Pulse and stores it in memory 4. SFC reports failure status and distance to fault to EDD 5. EDD software reads data from SFC and reports to Network Management Systems Fig 5a. EDD/SFC combination provides a basis for alerting and localising fibre breakages or disconnects isfc transceiver FCM9004 Remote equipment Core Network (i) Alarm: Customer Site Connection Fault (SNMP 'Trap') Fibre discontinuity (breakage or disconnection) NMS (ii) Log into FCM9004: SFP Management "Fibre breakage at 1,200m" Fig 5b. Typical 'single-ended' deployment scenario The isfc family transceivers transmit and receive at the same wavelength and should therefore generally be used in pairs. Within the family are variants both with and without embedded OTDR functionality, so it is possible to pair these devices such that the OTDR variant is at just one end of a fibre link, or both, as required. The scenario above illustrates deployment of this capability in a single-ended manner, although if EDDs exist at both ends of such a link and both are equipped with OTDR-equipped transceivers, then provided that independent management access is available to the EDDs in both Page 6 of 10

8 locations (as is commonly the case via back-up xdsl circuits for critical services), then fault detection can be 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 'historic event' information and that they respond rapidly in the event of a fibre discontinuity. This facilitates detection and localisation of even intermittent problems. It is often the case that when using external OTDR test equipment, by the time this has been brought to site, connected and testing conducted, then a temporary but potentially intermitted fault may not be evident at the time of a test. In contrast the isfc is able 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 a Metrodata FCM9004 EDD and an isfc. In the first case, no fibre fault exists within the monitored network segment. Note that the isfc facilitates measurement of the initial length of the deployed fibre. SFP DETAIL OTDR status No LOS No Fault Detected Fibre Length 1,200m Fig 6a. EDD Management Screen reflecting Fibre Connection status and parameters Fig 6b. Alternative screen indicating Fibre Fault condition OTDR status LOS Fault Detected Distance to Fault: 825m Extended Applications Examples Aside from the clear example of determination of the length of an individual fibre strand and point of breakage or disconnection, this unique capability lends itself to further applications including protection coverage for multiple fibre/copper cables or other transmission media. Since fibre cables invariably comprise many individual fibre strands within a single protective sheath, it is most 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 even hundreds of separate services. Moreover, it is frequently the case that fibre bundles are run in conjunction with copper cables or even other services which may be afforded a degree of 'protection' (to the extent of generation of alarms and provision of immediate localisation information in the event of a breakage, allowing Engineers to start immediate rectification works) by a single isfc OTDR-enabled link. There is no imperative, in fact, that Page 7 of 10

9 the fibre terminated by EDDs bearing isfc transceivers, should itself be carrying user services. Such a link might simply be used as a 'health monitoring/alarm' circuit, run alongside critical Telecoms or other services (including, for instance, oil or gas pipelines in territories potentially subject to damage for either geological 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 transmission path itself), extended links or ring topologies might be very accurately monitored using a number of EDDs equipped with isfc transceivers: OTDR Fibre breakage OTDR FCM9004-A OTDR FCM9004-B OTDR FCM9004-C Management Network NMS (i) Alarm sent to NMS from FCM9004 units either side of a fibre breakage (in this case, from A & C) (ii) OTDR measurements are read from FCM9004 units A & C to determine accurately the position of the break (iii) Historic events are maintained such that even short, intermittent disconnects can be reported Fig 7. Extended or 'Ring' Topology deployment Metrodata Ltd. is the first EDD vendor to incorporate full commercial support for automated OTDR-based fault detection in this manner, and is pleased to be working in co-operation with Optical Zonu Corporation to bring not only comprehensive Ethernet service monitoring in terms of throughput, packet-loss, latency and jitter, but now also physical layer fibre fault detection and localisation, to Telecoms Carriers, Ethernet Service Providers and the wider marketplace. Page 8 of 10

10 About Metrodata Ltd & MetroCONNECT Ethernet Demarcation Devices Metrodata Ltd. is a long-standing UK developer and manufacturer of Interface Conversion and Network Access solutions. The company has been a supplier to Governments, Corporations and Telecoms Service Providers worldwide since Within the company's MetroCONNECT range of Ethernet Service Delivery solutions, Metrodata offers cost-effective products with Advanced functionality for use with both wires-only IP VPN and Layer-2 Ethernet WAN solutions. The FCM9002 product supports Copper (RJ45) or Fibre (SFP) Network Connection up to 1Gbps with RJ45 connectivity to Customer equipment. Management visibility is offered to Customer site connections and the product supports the OAM protocols of IEEE 802.3ah (EFM), IEEE 802.1ag (CFM) and ITU-T Y One of the most common frustrations experienced by Service Providers is that of network faults being reported from customers which eventually are found to be due to simple power-downs of interface equipment. The FCM9002 provides indication of local power-down to the Service Provider via both SNMP Trap and OAM protocol alerting when power is withdrawn from the device (or alternatively should the PSU of the EDD itself fail). Test-traffic generation, loop-back and SLA verification features are supported by the product. The FCM9004 supports more sophisticated facilities for test-traffic profiling and additionally supports multiple LAN-ports with advanced Service multiplexing and powerful multi-level VLAN handling capabilities. 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 found here: Page 9 of 10

11 About Optical Zonu Corporation & Zonu isfc Transceivers Optical Zonu Corporation (OZC) is a privately owned high technology company located in the San Fernando Valley of the City of Los Angeles, specializing in the design and manufacturing of Fibre Optic Components for Analogue Transmission, Digital Transmission, Business Class Services and Coarse Wavelength Division Multiplexing (CWDM). OZC is the leading supplier of Full Duplex, Single Fibre, Single Wavelength Transceivers and RF over Fibre Optic Links. OZC maintains important strategic and global relationships in the Industry and cooperates with major vendors and suppliers of optical, communication and electronic devices, to enable rapid production of cutting-edge solutions. isfc Fast Fiber Fault Finder transceivers with micro-otdr, function as normal Single Fibre, Full Duplex CWDM Transceivers, but with the ability to switch into OTDR operation, capable of detecting and localising optical fibre faults. isfc Fast Fiber Fault Finder transceivers transmit and receive at the same wavelength, which allows them be used for Optical Fiber Fault Detection and Localization. The isfc transmitter can be switched to operate in Micro-OTDR mode where it transmits optical pulses of +13 dbm. The receiver will detect any reflected pulses down to -42 dbm optical power. Total ORL detection range is at least 55dB, enabling detection of fibre break/cut. Full information regarding Optical Zonu Corporation's isfc transceiver family may be found here: Metrodata Ltd. Fortune House, Eversley Way EGHAM, Surrey TW20 8RY U.K. +44 (0) sales@metrodata.co.uk Page 10 of 10