ebook carrier ethernet basics chap 1and2 ang

Carrier Ethernet Basics Educational Series 2 3 4 5 6

CarrierEthernetBasics

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AUTHORS

SYLVAIN CORNAY, Marketing Manager, EXFOHAMMADOUN DICKO, Product Specialist, EXFOTHIERNO DIALLO, Product Specialist, EXFOSOPHIE LEGAULT, Product Line Manager, EXFOSUE JUDGE, Consultant

EXFO Inc.March 2011

CarrierEthernetBasics

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1. CARRIER ETHERNET BASICS 1– 4

1.1 What Is Carrier Ethernet? 1– 4

1.2 Transport Media 1– 4

1.2.1 Copper 1– 5

1.2.2 Microwave 1– 5

1.2.3 Fiber 1– 5

1.3 Carrier Ethernet Network Services 1– 6

1.3.1 Ethernet Line (E-Line) 1– 6

1.3.2 Ethernet LAN (E-LAN) 1– 7

1.4 Carrier Ethernet Applications: 1– 8

1.4.1 Business Services 1– 8

1.4.2 Mobile Backhaul Services 1– 9

1.4.3 Key Performance Indicators 1– 9

1.5 Key Technologies Overview 1– 10

1.5.1 MPLS 1– 10

1.5.2 MPLS-TP 1– 10

1.5.3 PBB-TE 1– 10

1.5.4 PTN 1– 11

1.5.5 PWE3 1– 11

1.5.6 Circuit Emulation Services 1– 11

1.5.7 Ethernet OAM 1– 12

1.5.8 Synchronization 1– 13

Also coming soon to the Carrier Ethernet Basic Educational Series, modules that will focus on the following aspects of Carrier Ethernet, including service turn-up, service monitoring and troubleshooting.

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ETHERNET ACCESS

CARRIER ETHERNET BASICS1As technologically sophisticated businesses and residential consumers continue to drive the demand for premium, high-bandwidth data services such as voice and video, service providers worldwide must evolve their transport infrastructures to support these bandwidth and quality-intensive services. No longer is an all-IP core suffi cient—providers must now expand their IP convergence to the edge/metro network, in a cost-effective, quality-assured manner.

1.1 What Is Carrier Ethernet?Ethernet has long been accepted as an inexpensive, scalable data-networking solution in LAN environments; however, the stringent quality of service (QoS) expectations of today’s service offering require that service providers fi nd solutions to tap into the cost-effectiveness of Ethernet without sacrifi cing the benefi ts of connection-oriented (albeit it costly) time-domain multiplexing (TDM) solutions such as SONET/SDH

Comprehensive Ethernet testing immediately at service turn-up is now essential in order to ensure service quality and increase customer satisfaction. Customer service level agreement (SLAs) dictate certain performance criteria that must be met, with the majority documenting network availability and mean-time-to-repair (MTTR) values, which are easily verifi ed. However, Ethernet performance criteria are more diffi cult to prove, and demonstrating performance availability, transmission delay, link burstability and service integrity cannot be done precisely with only a single ping command. Carrier Ethernet, therefore, is the extension of Ethernet that enables service providers to provide premium Ethernet services.

1.2 Transport MediaThe diagram below outlines the different media used within a Carrier Ethernet network and indicates where they are commonly deployed:

Carrier Ethernet Basics

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1.2.1 CopperTo this day, copper cabling (i.e., insulated twisted copper wires) is still one of the most widely used media in Carrier Ethernet due to its existing vast deployment and its relatively low cost. It is almost everywhere as it was the media of choice to deliver plain old telephony service (POTS) to homes and businesses. Leveraging this infrastructure, service providers can avoid building out new and costly networks, as they address markets with lower-rate traffic of up to 1 Gigabit per second (Gbit/s) and begin to carry higher-speed traffic (in some cases up to 10 Gbit/s). Ethernet’s inherent scalability gives carriers a highly flexible platform for delivering incremental services to smaller enterprises, branch offices, cellular towers and other sites. However, copper is subject to both electromagnetic interference and cross-talk, which can negatively affect the reliable transfer of digital data—and at high speeds, the problem is even worse.

1.2.2 MicrowaveEthernet is also used for mobile backhaul, the distance from a cell tower to a switching office or between switching offices. The medium used is actually microwave-over-the-air. Microwave radio is a popular infrastructure choice for wireless operators. Ethernet-enabled microwave is becoming an increasingly important component of a wireless infrastructure. The increasing interest in microwave is driven by the higher bandwidth demands at the base station sites and the requirement to provide a substantial reduction in operational costs of backhauling the data traffic. The growth of the wireless industry combined with the proliferation of the mobile backhaul will only contribute to increase the use of microwave radio as a transport medium.

1.2.3 FiberSince fiber can carry much more information than copper, carrier Ethernet service providers typically use fiber to transport high-speed traffic (usually 1 Gbit/s or more) over long distances or within the network core. Fiber is used with SONET/SDH, dense wavelength-division multiplexing (DWDM) or optical transport networks (OTNs). Fiber cabling may have an initial higher cost, but even at the fastest speeds, it is entirely resistant to both cross-talk and electromagnetic interference, therefore it can provide much more reliable data transmission. As the demand for bandwidth and speed increases, the need to implement fiber on networks, even at the business site, is growing. However, the main issue with fiber is the high cost of deployment and maintenance.


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1.3 Carrier Ethernet Network ServicesThe two basic Ethernet service types defi ned by the Metro Ethernet Forum (MEF) are:

1.3.1 Ethernet Line (E-Line)Delivering point-to-point connectivity, E-Line services are used to create Ethernet private line services, Ethernet-based Internet access services and point-to-point (P2P) Ethernet VPNs.

Source: Metro Ethernet Forum

E-LINE VARIANTS

Ethernet Private Lines

This service consists of a P2P connection that uses dedicated bandwidth, either virtually concatenated SONET/SDH channels or reserved packet bandwidth in a packet-switched network. The customer’s Ethernet frames stay strictly separated from others’ at the Ethernet layer, and the customer will always have the contracted bandwidth rate available (also known as the committed information rate (CIR)). In this regard, the Ethernet private line is much like legacy TDM-based private lines, yet offers the benefi t of a native Ethernet interface to the customer and to the network operator’s edge equipment. Like typical TDM private lines, the Ethernet private line can be deployed to support a number of different carrier services such as Ethernet Internet, network services access or LAN-to-LAN interconnect—in which the customer owns one or both ends of the connection. The Ethernet private line is the simplest E-Line service to deploy. Service providers typically provide these services from a multiservice provisioning platform (MSPP), which acts as the demarcation between the customer’s network and the carrier’s SONET/SDH transport network.


E-LINE SERVICE TYPE


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Ethernet Virtual Private Line

For the Ethernet virtual private line, the rules are slightly different. In this service, the customer still gets point-to-point connectivity, but over shared bandwidth instead of dedicated. The shared bandwidth can be a TDM channel in the transport network or the switched-fabric bandwidth of switches and routers in the packet network. The service can either be offered as best-effort or with SLAs specifying CIR and other critical network parameters, such as latency. This service is quite similar to frame relay and its model of creating networks using permanent virtual circuits (PVCs). MEF defi nes Ethernet virtual private line service as a P2P Ethernet virtual connection (EVC) between two subscribers. Multiple EVCs can be combined to provide hub-and-spoke architectures in which multiple remote offi ces all require access to a head offi ce, or multiple customers all require access to managed services from an operator’s point of presence (POP).

1.3.2 Ethernet LAN (E-LAN)Delivering multipoint-to-multipoint (any-to-any) connectivity, E-LAN services are designed for multipoint Ethernet VPNs and native Ethernet transparent LAN services.


E-LAN VARIANTS

Ethernet Private LAN

An Ethernet private LAN (EPLAN) service provides multipoint connectivity over dedicated bandwidth, i.e., it can connect two or more subscribers. Subscriber data sent from one customer site can be received at one or more of the other customer sites. Each site is connected to a multipoint-to-multipoint Ethernet virtual circuit (EVC) and uses dedicated resources so that the different customers’ Ethernet frames are not multiplexed together. As new sites are added, they are connected to the same multipoint EVC, thus simplifying provisioning and service activation. From a subscriber standpoint, an EPLAN makes multiple LAN sites look like a single, yet immense, LAN.

E-LAN SERVICE TYPE


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Ethernet Virtual Private LANThe Ethernet virtual private LAN (EVPLAN) has gone by many names over the past two years, from virtual private LAN service (VPLS) to transparent LAN service (TLS) to virtual private switched network (VPSN). Regardless of how it is termed, the EVPLAN is a network service providing layer 2 multipoint connectivity between Ethernet-edge devices. Customer separation is accomplished via encapsulation using VLAN tags or other encapsulation technologies such as MPLS. The EVPLAN is a cost-effective service for the service provider, as it can leverage shared transmission bandwidth in the network. However, because it is a multipoint service, it can be complex to administer. The operator must implement protection, bandwidth profi les, congestion management, buffering, etc.—these are much more complex to implement in EVPLANs when compared to P2P services.

1.4 Carrier Ethernet Applications:Carrier Ethernet services are mainly used in two segments:

1.4.1 Business ServicesThe deployment of carrier Ethernet services within businesses will continue to grow with the demand of higher and higher bandwidth; this is driven by the requirements of enterprises—not only for data services, but also for voice and video services over their network.

Site-to-site access, data centers, server consolidations, disaster recovery, service orientated architecture, internet access, software-as-a-service (SaaS) and converged networking are just a few applications that require high bandwidth and low latency.

One of the major benefi ts of Ethernet for business services is cost reduction. Global availability of standardized services reduces the cost of implementation. The familiarity of IT departments with Ethernet makes the implementation of Carrier Ethernet services easier and cheaper. In essence, Carrier Ethernet brings the benefi ts of the Ethernet cost model to metro and wide-area networks. New applications requiring high bandwidth and low latency—which was previously not possible or prohibited due to high costs—can now be implemented.

Another major benefi t of Carrier Ethernet is performance. That is, in part because inherently, Ethernet networks require less processing to operate and manage. They also operate at higher bandwidths than other technologies. It is also the most suited solution for voice, video and data because of its low latency and delay variation. Carrier Ethernet services also provide a high level of fl exibility, which is ideal for applications such as site-to-site access that by the nature can have unpredictable and varying bandwidth requirements.

Carrier Ethernet services also provide a high level of fl exibility, which is ideal for applications such as site-to-site access that by the nature can have unpredictable and varying bandwidth requirements.


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1.4.2 Mobile Backhaul ServicesAs the backhaul network infrastructure evolves to support packet-based transmission, mobile operators face numerous challenges, resulting from the shift from managing network performance to managing service performance. Testing the network with a simple ping is no longer an option. In addition to assessing the network’s performance, operators now must constantly validate and measure key performance indicators on a per-service basis.

Today, and in the years to come, backhaul networks will be made of a mixture of both E1/T1 (for voice) and Ethernet/IP (for data services) technologies. This hybrid-network approach offers an economical solution for potential traffic bottlenecks with the increased traffi c of non-real-time data.

As carrier Ethernet networks mature, wireless backhaul will eventually become totally packet-based; this will simplify network architecture, reduce costs and provide the necessary scalability for expected growth with data-centric applications.

1.4.3 Key Performance IndicatorsKey performance indicators (KPIs) are specifi c traffi c characteristics that indicate the minimum performance of a specifi c traffi c profi le. The following KPIs directly infl uence the performance of backhaul networks.

• Framedelay,orlatency,isthedifferenceintimefromthemomentaframeorpacket leaves the origination port and the moment it arrives at the destination port. It has a direct impact on the quality of real-time data, such as voice or video. Management services such as synchronization protocols, which communicate between the BSC and mobile devices, must have a very fast response time. This helps to ensure quality voice transmission, cell handoffs, signaling and reliable connectivity.

• Framelossisaseriousproblemforallreal-timeservicessuchasvoiceorlivevideo, as well as for synchronization and management of traffi c control. Lost packets cause poor perception quality, and lost control packets increase latency and may cause connectivity failures—and even dropped calls.

and provide the necessary scalability for expected growth with data-centric applications.

1.4.3 Key Performance Indicators


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• Bandwidth refers to themaximumamountofdata thatcanbe forwarded.This measurement is a ratio of the total amount of traffic forwarded during a measurement window of one second. Bandwidth can either be ‘committed’ or ‘excess’ with different performance guarantees.

• Framedelayvariation,orpacket jitter, referstothevariability inarrival timebetween packet deliveries. As packets travel through a network, they are often queued and sent in bursts to the next hop. Random prioritization may occur, resulting in packet transmission at random rates. Packets are therefore received at irregular intervals. This jitter translates into stress on the receiving buffers of the end nodes, where buffers can be overused or underused when there are large swings of jitter. Real-time applications are especially sensitive to packet jitter. Buffers are designed to store a certain quantity of video or voice packets, which are then processed at regular intervals to provide a smooth and error-free transmission to the end user. Too much jitter will affect the quality of experience (QoE)—where packets arriving at a fast rate will cause buffers to overfill, leading to packet loss; while packets arriving at a slow rate will cause buffers to empty, leading to still images or sound.

1.5 Key Technologies Overview

1.5.1 MPLSIP/multi-protocol label switching (MPLS), an IEEE standard, is an established transport method that transparently switches data (packets or frames) from multiple protocols (ATM, frame relay, Ethernet, etc.) across an all-IP backbone. With full class-of-service (CoS) and virtual LAN (VLAN) support, MPLS is an ideal solution for carriers wanting to extend the life of legacy TDM-based services in the core. Modifications are being made to the standard to increase traffic engineering capabilities (MPLS-TP), which will enable IP/MPLS to support the advanced quality of service needed to extend the solution out to the metro edge.

1.5.2 MPLS-TPWith the movement toward packet-based services, transport networks have to encompass the provision of packet-aware capabilities while enabling carriers to leverage their installed transport infrastructure investments. MPLS transport profile (MPSL-TP) is a derivative of MPLS designed for transport networks. It supports the capabilities and functionalities needed for packet-transport network services and operations through combining the packet experience of MPLS with the operational experience and practices of existing transport networks. MPLS-TP enables the deployment of packet-based transport networks that efficiently scales to support packet services in a simple and cost-effective way.

1.5.3 PBB-TEProvider backbone bridge traffic engineering or PBB-TE (also referred to as PBT) is an alternative Ethernet-based implementation that enables carrier-grade provisioning and management of connection-oriented transport services across an


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all-IP MAN and core network by disabling the flooding/broadcasting and spanning tree protocol features. It is an evolution of MAC-in-MAC by making it connection-oriented. PBB-TE separates the Ethernet service layer from the network layer; its flexibility also allows service providers to deliver native Ethernet initially and MPLS-based services—i.e., virtual private wire service (VPWS) or virtual private LAN service (VPLS)—if and when they are required.

1.5.4 PTNThe packet transport network (PTN) is the next generation of networks designed around the best elements of traditional TDM technologies and the emergent packet technologies. It is typically deployed at two layers. At the access layer, PTN provides convergence of multiple services by converging TDM and packets into the PTN cloud. TDM packets are encapsulated and forwarded as packets in the PTN cloud while native Ethernet/IP packets are encapsulated and forwarded in the same PTN cloud.

PTN networks overcome many of the challenges of carriers by providing the efficient data transport of packetized technologies with the fault detection and resiliency of TDM-based networks. Service providers can now leverage the inherent advantages of Ethernet and TDM technologies, such as cost effectiveness, flexibility, multiservice applications as well as quality of service.

1.5.5 PWE3Pseudo wire emulation edge-to-edge (PWE3) is a mechanism that emulates the essential attributes of a service such as ATM, frame relay or Ethernet over a packet switched network (PSN). PWE3 only provides the minimum required functionality to emulate the wire. From the customer perspective, it is perceived as an unshared link or circuit of the chosen service. PW3 specifies the encapsulation, transport, control, management, interworking and security of services emulated over PSNs.

To maximize the return on their assets and minimize their operational costs, many service providers are looking to consolidate the delivery of multiple service offerings and traffic types onto a single IP-optimized network. PWE3 is a possible solution since it emulates Ethernet frame formats over IP networks.

1.5.6 Circuit Emulation ServicesCircuit emulation services (CES) is a technology used to carry T1/E1 services over asynchronous networks such as ATM, Ethernet. This paper focuses specifically on CESoS (Circuit Emulation over Ethernet). Service providers can now manage and provision TDM (Time Division Multiplexing) leased lines via CESoS and endpoints terminating in the PSTN (public switched telephone network) or between enterprise endpoints. With this technology, service providers can now use TDM applications to leverage the advantages inherent in Ethernet such as: flexibility, cost-effectiveness and simplicity.


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1.5.7 Ethernet OAMEthernet OAM draws on and includes existing standards such as IEEE 802.1ag for connectivity fault management (CFM), ITU-T Y.1731 for performance monitoring, 802.3ah or EFM (Ethernet in the fi rst mile) for link monitoring, fault signaling and remote loopback for the access network.

OAM standards are used to troubleshoot networks, monitor performance, verify confi guration and manage security. OAM functionality allows network operators to measure QoS attributes, such as availability, frame delay, frame delay variation (jitter) and frame loss. Ethernet OAM can also provide remote loopback, a feature often used to troubleshoot networks where all inbound traffic is immediately refl ected back on the link.

At the device level, OAM protocols generate messages that are used by operations staff to help identify problems in the network. In the event of a fault, the information generated by OAM helps the operator troubleshoot the network to locate the fault, identify which services have been impacted and take the appropriate action. Also, just as it is important to keep the customers’ services running, operators must be able to prove that is the case, this is usually measured against an SLA, and the operator must have the performance measurements to manage customer SLAs. Finally, administration features include collecting the accounting data for the purpose of billing and network usage data for capacity-planning exercises.

Effective end-to-end service control also enables carriers to avoid expensive truck rolls to locate and contain faults, thereby facilitating reduction of maintenance costs. Intrinsic OAM functionality is therefore essential in any carrier-class technology and is a ‘must have’ capability in intelligent Ethernet network termination units.


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1.5.8 SynchronizationAs the network moves toward Ethernet as the transport technology of choice, synchronization remains a major issue. As Ethernet and TDM technologies continue to coexist, technologies like circuit-emulation services (CES) provide capabilities to map TDM traffi c on Ethernet infrastructure and vice versa, enabling a smooth changeover for network operators transitioning to an all-packet network.

To interconnect these two technologies, frequency synchronization is key since the TDM technologies have frequency-offset tolerances that are much more restrictive than the asynchronous Ethernet technologies. Ethernet relies on inexpensive holdover oscillators and can stop transmitting traffi c or buffer data, while TDM technologies rely on the continuous transmission and presence of synchronization reference. Synchronous Ethernet solves these issues by ensuring frequency synchronization at the physical level.

However, since SyncE is a synchronization technology based on layer 1, it requires that all ports on the synchronized path be enabled for SyncE. Any node that is non SyncE-enabled on the path will automatically break the synchronization from this node. This is an issue for network providers that have a multitude of Ethernet ports between the primary synchronization unit and the edge device that needs synchronization as all the ports must be SyncE-enabled to synchronize to the edge. Such requirements can increase the cost of deployments as hardware and software upgrades can dramatically increase the total cost of ownership. SyncE also only focuses on frequency synchronization and does not guarantee phase synchronization—although the phase requirements can be somewhat assessed via SyncE.

This diagram shows an example of Ethernet synchronization.

Many services need synchronization, but wireless base stations today have the largest stake in frequency and time distribution. The frequency stability of the air interface between the cell tower and the handset supports handing off a call between adjacent base stations without interruption. Synchronization for base stations is therefore central to the QoS that an operator provides.

This diagram shows an example of Ethernet synchronization.


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The next packet synchronization technology, the Precise Time Protocol (PTP) also referred to as the “IEEE 1588v2”, is specifi cally designed to provide high clock accuracy through a packet network via a continuous exchange of packets with appropriate timestamps. In this protocol, a highly precise clock source, referred to as the “grand-master clock” generates timestamp announcements and responds to timestamp requests from boundary clocks, thus ensuring that the boundary clocks and the slave clocks are precisely aligned to the grand-master clocks. By relying on the handover capability and the precision of the integrated clocks in combination with the continuous exchange of timestamps between PTP-enabled devices, frequency and phase accuracy can be maintained at a sub-microsecond range, thus ensuring synchronization within the network. In addition to frequency and phase synchronization, ToD synchronization can also ensure that all PTP-enabled devices are synchronized with the proper time, based on coordinated universal time (UTC).

The great advantages of PTP is that as a packed-based technology, only boundary and slave clock needs to be aware of the nature of the packets and therefore synchronization packets are forwarded as any other data packets within the network. This fl exibility reduces the cost of ownership as the main upgrade to the networks are limited to synchronization equipment contrarily to the SyncE approach that requires both synchronization equipment and upgrade of all Ethernet ports on the link to SyncE specifi cations.

This diagram shows an application of IEEE 1588v2 PTP in a mobile backhaul to establish synchronization.

Ethernet ports on the link to SyncE specifi cations.

This diagram shows an application of IEEE 1588v2 PTP in a mobile backhaul to establish synchronization.

Carrier Ethernet Testing TECHNOLOGIES

AND METHODOLOGIES

Carrier Ethernet Basics Educational Series 3 4 5 621

AUTHORS

SYLVAIN CORNAY, Marketing Manager, EXFOHAMMADOUN DICKO, Product Specialist, EXFOTHIERNO DIALLO, Product Specialist, EXFOSOPHIE LEGAULT, Product Line Manager, EXFOSUE JUDGE, Consultant

EXFO Inc.March 2011

Carrier Ethernet Testing Technologies and Methodologies

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2. OPTIMIZING QUALITY OF SERVICE AND QUALITY OF EXPERIENCE 2– 4

2.1 RFC-2544 2– 5

2.2 ITU-T Y.1564 2– 7

2.2.1 Service Definitions 2– 7

2.2.2 Test Rates 2– 7

2.2.3 Methodology 2– 8

2.2.4 Burst (CBS and EBS) Tests 2– 10

2.2.5 Metrics 2– 11

2.2.6 Benefits 2– 12

2.3 BERT over Ethernet 2– 12

2.4 Synchronization 2– 13

2.4.1 Ethernet Synchronization Methods 2– 14

2.4.2 Synchronization Metrics 2– 16

2.4.3 PTP Metrics 2– 16

2.5 Service Lifecycle Management 2– 17

2.5.1 Fault Management 2– 17

2.5.2 Performance Monitoring 2– 18

Also coming soon to the Carrier Ethernet Basic Educational Series, modules that will focus on the following aspects of Carrier Ethernet, including service turn-up, service monitoring and troubleshooting.

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OPTIMIZING QUALITY OF SERVICE AND QUALITY OF EXPERIENCE2

The increasing demand for data-centric services driven by smartphone technologies, along with the growth of social networking (e.g., Facebook, Twitter, etc.) and multimedia applications (e.g., gaming, YouTube, etc.), has prompted operators to shift toward packet-based Ethernet/IP technologies across their access and core networks in order to cost-effectively support the rapidly escalating bandwidth requirements.

In fact, according to the latest report from Cisco’s Visual Networking Index Global Mobile Data Traffi c Forecast, it is predicted that global mobile data traffi c will grow by 26 times between 2010 and 2015, to 6.3 exabytes—one billion gigabytes—per month. Additionally, the report foresees that by 2015, two-thirds of all mobile data traffic will be video, underscoring the challenges operators face as they try to manage the tidal wave of mobile data set to fl ood their networks.

While there is little doubt about the cost efficiencies and scalability of Ethernet, the time- and delay-sensitive nature of established voice services, in addition to the growing popularity of new mobile video services, cannot be ignored and necessitate an advanced approach to Ethernet networking and testing to maintain the customer expectations for quality of service (QoS) and quality of experience (QoE).

As Carrier Ethernet technology matures, networks will eventually become entirely packet-based; this will greatly simplify the network architecture, reduce costs and provide the necessary scalability for expected growth with data-centric applications. But as the network infrastructure evolves to support packet-based transmission, operators must also evolve from only managing network performance to also managing service performance. This means that testing the network with a simple ping is no longer an option as operators must now constantly validate and measure the key performance indicators (KPIs) on a per-service basis.


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2.1 RFC-2544The Internet Engineering Task Force’s (IETF’s) RFC 2544 is a benchmarking methodology for network interconnect devices. This request for comment (RFC) was created in 1999 as a methodology to benchmark network devices, such as hubs, switches and routers, as well as to provide accurate and comparable values for comparison and benchmarking.

RFC 2544 provides engineers and network technicians with a common language and results format. RFC 2544 describes the following six subtests:

• Throughput: This test measures the maximum rate at which none of the offered frames is dropped by the device/system under test (DUT/SUT). This measurement translates into the available bandwidth of the Ethernet virtual connection.

• Back-to-back or burstability: This test measures the longest burst of frames at maximum throughput or minimum legal separation between frames that the device or network under test will handle without any loss of frames. This measurement is a good indication of the buffering capacity of a DUT.

• Frame loss: This test defines the percentage of frames that should have been forwarded by a network device under steady state (constant) loads that were not forwarded due to lack of resources. This measurement can be used for reporting the performance of a network device in an overloaded state, as it can be a useful indication of how a device would perform under pathological network conditions, such as broadcast storms.

• Latency: This test measures the round-trip time of a test frame to travel through a network device or across the network and back to the test port. Latency is the time interval that begins when the last bit of the input frame reaches the input port and ends when the first bit of the output frame is seen on the output port. It is the time taken by a bit to go through the network and back. Latency variability can be a problem. With protocols like voice over Internet protocol (VoIP), a variable or long latency can cause degradation in voice quality.

• System reset: This test measures the speed at which a DUT recovers from a hardware or software reset. This subtest is performed by measuring the interruption of a continuous stream of frames during the reset process.

• System recovery: This test measures the speed at which a DUT recovers from an overload or oversubscription condition. This subtest is performed by temporarily oversubscribing the device under test and then reducing the throughput at normal or low load while measuring frame delay in these two conditions. The difference between delay at overloaded conditions and the delay and low-load conditions represent the recovery time.


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From a laboratory and benchmarking perspective, the RFC 2544 methodology is an ideal tool for automated measurement and reporting. From a service turn-up and troubleshooting perspective, RFC 2544, although acceptable and valid, does have some drawbacks:

• ServiceprovidersareshiftingfromonlyprovidingEthernetpipestoenablingservices. Networks must support multiple services from multiple customers, while each service has its own performance requirements that must be met even under full load conditions and with all services being processed simultaneously. RFC 2544 was designed as a performance tool with a focus on a single stream to measure maximum performance of a DUT or network under test and was never intended for multiservice testing.

• WithRFC2544’sfocusonidentifyingthemaximumperformanceofadeviceornetwork under test, the overall test time is variable and depends heavily on the quality of the link and subtest settings. RFC 2544 test cycles can easily require a few hours of testing. This is not an issue for lab testing or benchmarking, but becomes a serious issue for network operators with short service maintenance windows.

• PacketdelayvariationisaKPIforreal-timeservicessuchasVoIPandInternetprotocol television (IPTV) and is not measured by the RFC 2544 methodology. Network operators that performed service testing with RFC 2544 must typically execute external packet jitter testing outside of RFC 2544—as this KPI is not defi ned or measured by the RFC 2544.

• TestingisperformedsequentiallyononeKPIafteranother.Intoday’smultiserviceenvironments, traffi c is going to experience all KPIs at the same time, although throughput might be good, it can also be accompanied by very high latency due to buffering. Designed as a performance assessment tool, RFC 2544 measures each KPI individually through its subtest and therefore cannot immediately associate a very high latency with a good throughput, which should be a cause for concern.


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2.2 ITU-T Y.1564Next-Generation Carrier-Ethernet Testing

To resolve issues with RFC 2544, ITU-T has introduced a new test standard: the ITU-T Y.1564 methodology, which is aligned with the requirements of today’s Ethernet services. EXFO is the first to implement EtherSAM—the Ethernet service testing methodology based on this new standard—into its Ethernet-testing products.

ITU-T Y.1564 is designed around the three following key objectives:

1. To serve as a network service-level-agreement (SLA) validation tool, ensuring that a service meets its guaranteed performance settings in a controlled test time.

2. To ensure that all services carried by the network meet their SLA objectives at their maximum committed rate, proving that under maximum load, network devices and paths can support all the traffic as designed.

3. To perform medium- and long-term service testing, to validate that network elements can properly carry all services while under stress during a soaking period.

2.2.1 Service Definitions

ITU-T Y.1564 defines test streams with service attributes linked to the Metro Ethernet Forum (MEF) 10.2 definitions.

Services are traffic streams with specific attributes identified by different classifiers, such as 802.1q VLAN, 802.1ad and class of service (CoS) profiles. These services are defined at the user-to-network interface (UNI) level with different frame and bandwidth profiles, such as the service’s maximum transmission unit (MTU) or frame size, committed information rate (CIR) and excess information rate (EIR).

2.2.2 Test RatesITU Y.1564 defines three key test rates based on the MEF service attributes for Ethernet virtual circuit (EVC) and UNI bandwidth profiles.

• CIRdefinesthemaximumtransmissionrateforaservicewhereitisguaranteedcertain performance objectives; these objectives are typically defined and enforced via SLAs.

• EIRdefinesthemaximumtransmissionrateabovethecommittedinformationrate considered as excess traffic. This excess traffic is forwarded as the capacity allows and is not subject to meeting any guaranteed performance objectives (best effort forwarding).

• OvershootratedefinesatestingtransmissionrateaboveCIRorEIRandisusedto ensure that the DUT or network under test does not forward more traffic than specified by the CIR or EIR of the service.


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2.2.3 MethodologyThe ITU-T Y.1564 is built around two key subtests, the service-confi guration test and the service-performance test, which are performed in order:

Service Confi guration Test

Forwarding devices such as switches, routers, bridges and network interface units are the basis of any network as they interconnect segments. If a service is not correctly confi gured on any one of these devices within the end-to-end path, network performance can be greatly affected, leading to potential service outages and network-wide issues such as congestion and link failures.

The service confi guration test is designed to measure the ability of the DUT or the network under test to properly forward in three different states:

• IntheCIRphase,whereperformancemetricsfortheservicearemeasuredandcompared to the SLA performance objectives

• IntheEIRphase,whereperformanceisnotguaranteedandtheservicestransferrate is measured to ensure that CIR is the minimum bandwidth

• Inthediscardphase,wheretheserviceisgeneratedattheovershootrateandthe expected forwarded rate is not greater than the committed information rate or excess rate (when confi gured)

Service Performance Test

As network devices come under load, they must prioritize one traffi c fl ow over another to meet the KPIs set for each traffi c class. With only one traffi c class, there is no prioritization performed by the network devices since there is only one set of KPIs. As the amount of the traffi c fl ow increases, prioritization is necessary and performance failures may occur.

The service performance test measures the ability of the DUT or network under test to forward multiple services, while maintaining SLA conformance for each service. Services are generated at the CIR, where performance is guaranteed, and pass/fail assessment is performed on the KPI values for each service according to its SLA.


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Service performance assessment must also be maintained for a medium- to long-term period as performance degradation will likely occur as the network is under stress for longer periods of time. The service performance test is designed to soak the network under full committed load for all services and measure performance over medium and long test times.

Bidirectional Test

EtherSAM can perform round-trip measurements with a loopback device. In this case, the results refl ect the average of both test directions, from the test set to the loopback point and back to the test set. In this scenario, the loopback functionality can be performed by another test instrument in Loopback mode or by a network interface device in Loopback mode.

The same test can also be run in simultaneous bidirectional mode (dual test set). In this case, two test sets, one designated as local and the other as remote, are used to communicate and independently and run tests per direction. The tests are performed simultaneously as well. This provides much more precise test results such as independent assessment per direction and the ability to quickly determine which direction of the link is experiencing failure. This allows service providers to test asymmetrical links. This test uncovers more confi guration errors than the EtherSAM test with one loopback device on the other end especially when testing multiple services with different EIRs and CIRs.

multiple services with different EIRs and CIRs.


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2.2.4 Burst (CBS and EBS) Tests:Committed burst size (CBS) and excessive burst size (EBS) tests are still considered preliminary and experimental only. The bandwidth profile contains attributes of CBS and EBS that some service providers may wish to test at the time of service activation to verify proper attribute configuration. Today, these types of SLA parameters are only offered for more complex/advanced Ethernet commercial services offerings. As these mechanisms work independently for each service direction, testing CBS and EBS in a round-trip confi guration (one end in loopback) has little to no value. It is essential that these parameters be tested independently for each service direction. Burst testing is mainly important for high bandwidth Ethernet user network interfaces that have a small fraction of the line capacity provisioned to carry customer traffi c.

Burst test methodologies assume a token bucket algorithm to police and shape the traffi c. The token bucket is a control mechanism that dictates when traffi c can be transmitted, based on the presence of tokens in the bucket–an abstract container that holds aggregate network traffi c to be transmitted.

The burst test is provided for non-color aware and color aware applications. In advanced business Ethernet services, it is possible to have traffi c that is tagged with different colors (green and yellow) within the same service. The colors are a method allowing the end customer to tell the network that specifi c traffi c has higher priority in case of congestion. Color Aware mode is also offered only in more complex/advanced Ethernet Services. Color mode testing consists in verifying that the traffi c policers and shapers properly respects the Color mode. Testing Color mode is a complex test and will not be tested frequently in the fi eld. On the other hand Non-Color Aware mode requires only one color per service. It is the most common mode.


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2.2.5 MetricsY.1564 focuses on the following KPIs for service quality:

• Bandwidth: This is a bit rate measure of the available or consumed data communication resources expressed in bits/second or multiples of it (kilobits/s, megabits/s, etc.).

• Frame transfer delay (FTD): Also known as latency, this is a measurement of the time delay between the transmission and the reception of a frame. Typically this is a round-trip measurement, meaning that the calculation measures both the near-end to far-end and far-end to near-end directions simultaneously.

• Frame delay variations: Also known as packet jitter, this is a measurement of the variations in the time delay between packet deliveries. As packets travel through a network to their destination, they are often queued and sent in bursts to the next hop. There may be prioritization at random moments, also resulting in packets being sent at random rates. Packets are therefore received at irregular intervals. The direct consequence of this jitter is stress on the receiving buffers of the end nodes where buffers can be overused or underused when there are large swings of jitter.

• Frame loss: Typically expressed as a ratio, this is a measurement of the number of packets lost over the total number of packets sent. Frame loss can be due to a number of issues such as network congestion or errors during transmissions.


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2.2.6 Benefits:ITU-T Y.1564 provides numerous benefits to service providers, offering mobile backhaul, commercial and wholesale Ethernet services.

• MeasurementofallKPIsinasingletest:While existing methodologies like RFC 2544 only provide the capability to measure the maximum performances of a link, EtherSAM uses a validation approach where KPIs are measured and compared to the expected values for each service. This approach focuses on proving that KPIs are met while in guaranteed traffic conditions.

• Significantlyfaster:The RFC 2544 methodology uses a sequential approach where each subtest is executed one after the other until they have all been completed, making it a time-consuming procedure. Additionally, the completion of a subtest heavily relies on the quality of the link.

In opposition, ITU-T Y.1564 uses a defined ramp-up approach where each step takes an exact amount of time. Link quality issues are quickly identified without necessarily increasing test time because a pass/fail condition is based on the KPI assessment during the step.

• Multiservicetestingcapabilities:As described earlier, the majority of Ethernet services deployed today include multiple classes of service within the same connection. A major drawback of RFC 2544 is the fact that it can only test a single service at a time; Y.1564 on the other hand can test multiple services simultaneously.

• Morerepresentativeofreal-lifeconditions:The worst-case scenario for a network is handling multiple traffic types during a congestion period. Since RFC 2544 only tests a single stream at a time, it cannot simulate worst-case scenarios.

The ITU-T Y.1564 service subtest can generate all configured services at the same time, providing the ability to stress network elements and data paths in worst-case conditions. The service test provides powerful test results since all KPIs are measured simultaneously for all services with clear pass/fail indication, as well as identification of failed KPIs. This ensures that any failure or inconsistency is quickly pinpointed and reported, again contributing to an efficient and more meaningful test cycle.

2.3 BERT over EthernetSince transparent transport of Ethernet over physical media is now a common service, Ethernet is increasingly carried across a variety of media over longer distances. There is, therefore, a growing need to certify Ethernet carriage on a bit-per-bit basis. This can be done using bit error-rate testing (BERT).

BERT is a concept taken from the SONET/SDH world. In a BERT, a data stream is sent through the communications medium and the resulting data stream is compared with the original. Any changes are noted as data errors. BERT uses a pseudo-random binary sequence (PRBS) encapsulated into an Ethernet frame, making it possible to go from a frame-based error measurement to a BER (bit error rate) measurement.


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BERT still remains a very popular testing methodology because it is suited for applications that are transparent to the transport medium and also because it has been used for a long time and most telecom engineers and technicians are very comfortable with it. However if the network to be tested is switched-based and includes overhead processing and error verification, the BER approach is not the best one. This is because a network processing element will discard frames or packets if an error is found, which means that most errors will never reach the test equipment. These lost frames are more difficult to translate into a BER value.

2.4 SynchronizationSynchronization can be defined as the coordinated and simultaneous relationship between time-keeping among multiple devices. For people outside of the telecom world, synchronization typically refers to time synchronization where one or more devices have the same time as a reference clock, typically the universal time clock (UTC); when synchronized, two devices will have the proper time of day (ToD) in reference to the universal time reference, regardless of their geographical location.

However for network engineers, synchronization has a very precise and critical use. Telecom networks, such as SONET and SDH networks, are based on a synchronous architecture, meaning that all data signals are synchronized and clocked using virtually the same clock throughout. This ensures that all of the ports that carry data do so at the same frequency or with very little offset, and therefore, network throughput is deterministic and fixed for a specific transport rate.

Ethernet on the other hand is an asynchronous technology where each Ethernet port has its own independent clock circuit and oscillator. Because each port is clock independent, frequency offsets between interconnected ports can be relatively high. To solve this issue, Ethernet devices typically implement buffers that can store traffic and then mitigate the effect of offsets between two ports. Therefore, telecom networks require two other types of synchronization in addition to time synchronization, that is, frequency synchronization and phase synchronization.

Frequency synchronization is typically a physical synchronization where the output clocks between devices is synchronized. When two devices are frequency synchronized, they basically generate the same number of bits over an integration period (typically 1 second). When they are not frequency synchronized, one device will generate more bits per second than the other, which can cause overflow and eventually bit errors or traffic loss.

Phase synchronization refers to the simultaneous variation of clocks between devices. When phase-synchronized, the two devices will shift at exactly the same time from one clock pulse to the other. A real-world example would be to compare two watches side-by-side. When synchronized, these two watches will increment at exactly the same time; when unsynchronized, one device will count faster than the other and in the network world, these variations are the equivalent of phase offset.


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2.4.1 Ethernet Synchronization MethodsThere are currently two techniques available:

• SyncEEthernet SyncE achieves frequency by timing the output bit clocks from a highly accurate stratum 1 traceable clock signal in a fashion similar to traditional TDM and SONET/SDH synchronization. SyncE supports the exchange of synchronization status messages (SSM) and now includes a newly introduced Ethernet synchronization messaging channel (ESMC), which ensures that the Ethernet node with SyncE enabled always derives its timing from the most reliable source.

However, since SyncE is a synchronization technology based on layer 1, it requires that all ports on the synchronized path be enabled for SyncE. Any node that is non SyncE-enabled on the path will automatically break the synchronization from this node; this is an issue for network providers that have a multitude of Ethernet ports between the primary synchronization unit and the edge device that needs synchronization, as all the ports must be SyncE-enabled to synchronize to the edge. Such requirements can increase the cost of deployments as hardware and software upgrades can dramatically raise the total cost of ownership. Also, SyncE only focuses on frequency synchronization and does not guarantee phase synchronization—although the phase requirements can be somewhat assessed via SyncE.


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• PreciseTimeProtocol(PTP)The 1588v2 standard, defined by the ITU and also known as Precise Time Protocol, (PTP) is specifi cally designed to provide high clock accuracy through a packet network via a continuous exchange of packets with appropriate timestamps. In this protocol, a highly precise clock source, referred to as the “grand-master clock” generates timestamp announcements and responds to timestamp requests from boundary clocks, thus ensuring that the boundary clocks and the slave clocks are precisely aligned to the grand-master clocks. By relying on the holdover capability and the precision of the integrated clocks in combination with the continuous exchange of timestamps between PTP-enabled devices, frequency and phase accuracy can be maintained at a sub-microsecond range, thus ensuring synchronization within the network. In addition to frequency and phase synchronization, ToD synchronization can also ensure that all PTP-enabled devices are synchronized with the proper time, based on the coordinated universal time clock (UTC). The advantage of PTP is that as a packed-based technology, only the boundary and slave clock need to be aware of the nature of the packets and therefore, synchronization packets are forwarded as any other data packets within the network. This flexibility reduces the cost of ownership as the main upgrade to the networks are limited to synchronization equipment, contrarily to the SyncE approach which requires both synchronization equipment and upgrade of all Ethernet ports on the link to SyncE specifi cations.

However, the major weakness of PTP is due to its packet nature. As the synchronization packets used by PTP are forwarded in the network between grand master and hosts, they are subject to all the network events, such as frame delay (latency), frame-delay variation (packet jitter) and frame loss. Even with the best practice of applying high priority to synchronization fl ows, these synchronization packets still experience congestion and possible routing and forwarding issues, such as out-of-sequence and route fl aps. This means that the host clock’s holdover circuit must be stable enough to maintain synchronization where the synchronization packets experienced network events.

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where the synchronization packets experienced network events.


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2.4.2 Synchronization MetricsMeasuring synchronization accuracy almost entirely rests on the offset between the significant events of the tested signal compared to the same significant event of the reference clock. Synchronization metrics typically consist of three key measurements: time interval error (TIE), maximum time interval error (MTIE) and time deviation (TDEV).

• TIE: Is a basic measurement of the phase difference between the reference clock and the clock under test, based on the time difference between significant events. This basic measurement, performed over many hours or days of tests, provides immediate offsets between the clocks. Due to its instantaneous nature, this measurement is not ideal for the long-term but provides an assessment of the peak offsets of phase variations, which typically lead to failures.

• MTIE: Is a measurement based on the TIE data designed to provide the maximum deviation of the peak-to-peak value of the TIE within, by widening the observation window. Typically produced after processing the TIE data, the MTIE provides the worst-possible TIE change within different observation windows and can be used to predict the stability of the clock frequency over time.

• TDEV: Is another measurement derived from the TIE data and provides the average phase variations of the clock by expressing the root mean square (RMS) of the variations of the MTIE for specific measurement windows. As MTIE is focused on the worst case, any peak variation will limit the visibility of small variations. TDEV on the other hand averages the worst peak variations and provides a good indication of the periodicities or TIE offsets. TDEV provides information about the short-term stability of the clock and the random noise in the clock accuracy.

2.4.3 PTP MetricsWith the introduction of PTP, network operators must now qualify new packet metrics based on the PTP architecture. In PTP, since packet synchronization is performed via an exchange of messages, the synchronization flow is therefore sensitive to the presence or absence of messages due to frame delay, frame-delay variation and frame loss. Moreover, messages are exchanged unidirectionally, meaning that nodes will exchange and terminate the synchronization packets. This induces the concept of unidirectional performance as a direction can experience more network events than the other directions. Asymmetrical behavior may cause synchronization packets to experience more delays, congestion and possible loss in one direction, while the other direction remains trouble-free.

For such reasons, PTP testing involves not only the synchronization KPIs listed earlier but also new ones such as:

• Framedelay(latency)• Framedelayvariation• Frameloss

The increasing demand on network operators to provide more services at competitive rates has resulted in a paradigm shift in the availability of physical-layer synchronization, requiring not only testing and monitoring of synchronization performance carried out at the physical layer, but the packet-layer performance has to be tested and monitored too.


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2.5 Service Lifecycle ManagementOperation, administration and maintenance (OAM)

OAM functionality in traditional TDM networks is well-defined and is an important building block in ensuring that operators can deliver carrier-grade performance. However, OAM represents a significant challenge for next-generation technologies, such as Carrier Ethernet. Ethernet OAM draws on and includes existing standards such as IEEE 802.1ag for connectivity fault management (CFM) and ITU-T Y.1731 for performance monitoring.

Measurements such as availability, frame delay, frame delay variation (jitter) and frame loss enable identification of problems before they escalate so that users are not impacted by network defects. Furthermore, these capabilities allow the operators to offer binding SLAs and generate new revenues from rate- and performance-guaranteed service packages that are tailored to the specific needs of their customers.

Effective end-to-end service control also enables carriers to avoid expensive truck rolls to locate and contain faults thereby facilitating reduction of maintenance costs. Intrinsic OAM functionality is therefore essential in any carrier-class technology and is a must have capability in intelligent Ethernet network termination units.

There are two main areas of Ethernet OAM:

2.5.1 Fault Management:Fault management ensures that when a defect occurs in the network, it is reported to the network operator who can then take the appropriate action.

• Fault detection: IEEE 802.1ag and ITU-T Y.1731 support fault detection through continuity check messages (CCM). These allow endpoints to detect an interruption in service. CCMs are sent from the source to the destination node at periodic intervals; if either end does not receive a CCM within a specified duration, then a fault is detected against the service.

• Faultverification: IEEE 802.1ag and ITU-T Y.1731 support fault verification through loopback messages (LBM) and loopback reply (LBR).

• Fault isolation: IEEE 802.1ag and ITU-T Y.1731 support fault isolation through linktrace messages (LTM) and linktrace reply (LTR). Under normal conditions, it allows the operator to determine the path used by the service through the network, while under fault conditions, it allows the operator to isolate the fault location without making a site visit.

• Fault notification: ITU-T Y.1731 supports fault notification through alarm indication signal (AIS); this functionality alerts the operator to a fault in the network, before it is reported by customers.


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2.5.2 Performance Monitoring:Carrier Ethernet networks require advanced performance monitoring to enforce customer SLAs and this functionality is introduced by ITU-T Y.1731. The following features are supported:

• Frame loss ratio: This represents the percentage of the traffic that has been lost; it is the percentage ratio of the traffic not received versus the traffic that was sent.

• Frame delay (latency): Two types of delays are measured: one-way delay represents how long it takes traffic to go from one of the network to another; whereas two-way delay represents the duration from one end back to the same end.

• Frame delay variation: This is also referred to as jitter; it represents the variation between different delay measurements.

Another standard used for OAM is 802.3ah, which is a complete standard for Ethernet in the first mile, but it also contains a link level (as opposed to service level) OAM mechanism. 802.3ah detects link failures in both bi-directional links and unidirectional links (link monitoring). Once the failure is detected, it can set a device in Loopback mode that will check when it recovers.

The four major capabilities of 802.3ah are:

• Discovery: Detects the endpoints of a link and their OAM capabilities

• Remote fault detection: Allows one endpoint to inform the other after it has detected a fault

• Remote loopback: Can be used to put the remote port in loopback mode, useful for data-path testing

• Remote monitoring: Allows near-end and far-end statistics similar to those found in SONET/SDH

The emergence of carrier-grade Ethernet has driven the need for improved Ethernet OAM functionality. Ethernet OAM allows the exchange of management information from the network elements to the management layer. Without this capability, it is impossible to provide the comprehensive network management tools that operators have today in their TDM networks. The combination of IEEE 802.1ag and ITU-T Y.1731 provides powerful fault management and performance monitoring capabilities to Ethernet.

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