Evaluating Carrier-Class Ethernet Services

Transcription

1 Technical Paper Evaluating Carrier-Class Ethernet Services Demand for Ethernet-based services is on the rise, and the key driving force behind this is continuous growth of data traffic in the metro/access networks. Many service providers and enterprise network operators are already moving towards the evaluation and deployment of next-generation Ethernet services, which promise not only a new source of revenue, but also improved efficiency in the delivery of data services. The challenge is that Ethernet is a 'best-effort' service, and now industry bodies and equipment manufactures are making considerable efforts to ensure Ethernet services are 'carrier class'. Key areas of concerns such as quality of service (QoS), resiliency and scalability required to deliver carrier-class services are being addressed. Therefore, testing is an essential first step in ensuring carrier-class Ethernet services are delivered to subscribers. This paper presents an overview of Ethernet services, and an appreciation of the challenges involved in evaluating carrier-class services being developed and deployed.

2 Introduction A Metro Area Network (MAN) is a network operated by a single network operator, which provides access and services in a metropolitan region. Typically, MANs span distances up to 150km. As MANs resides between Local Area Networks (LANs) and Wide Area Networks (WANs), they have become bottlenecks as data traffic rates surge. Traditionally, MANs have been developed using telecom technologies such as SONET/SDH or TDM-based access. However SONET/SDH infrastructures were originally developed for voice traffic and do not support the granularity, scale, low cost and on-demand bandwidth provisioning required by data traffic. Ethernet services are in demand in Metro Area Networks due to their cost effectiveness, simplicity, and flexibility. For example, additional bandwidth can be provisioned 'on demand' much faster and with finer granularity than with existing technologies. Also, Ethernet interfaces and networking equipment are usually cheaper than using Frame Relay or ATM. Upgrading MANs to use this new technology will prepare the network for convergence of voice, data, and video traffic. Since Ethernet is prevalent throughout the LAN, there are many advantages to extend this technology throughout the MAN also. New standards are emerging from industry bodies such as Metro Ethernet Forum (MEF), making Ethernet more suitable for carrier networks and to use Ethernet as an access technology of choice, enabling the deployment of broadband services to both business and residential users. The Metro Ethernet Forum (MEF) is a consortium of network equipment manufactures and service providers, actively involved in defining the scope, concepts and terminology for deploying Ethernet services in the metro. Other standard bodies including the IETF have also defined ways of scaling Ethernet services through the use of MPLS. The MEF has defined a set of attributes and parameters that describe the Ethernet services and how to set service level agreements between carriers and end users. The basic model for Ethernet services defined by MEF is shown below in Figure 1. Figure 1: MEF Ethernet Service Basic Model Copyright Agilent Technologies, Inc

3 The User-to-Network Interface (UNI) is a standard Ethernet interface that is the point of demarcation between the customer equipment (CE) and the service provider's metro Ethernet network (MEN). Ethernet Virtual Connection (EVC) defined by MEF as "an association of two or more UNIs", is a key Ethernet service attribute. EVC is a logical tunnel that connects two or more customer sites, enabling the transfer of Ethernet frames between them. The EVC also enables data privacy and security between different customers. Two basic service types have been identified: Ethernet Line (E-Line) service for point-to-point connectivity. (Figure 2) Ethernet LAN (E-LAN) services for multipoint-to-multipoint (any-to-any) connectivity. (Figure 3) E-line services will be used to create Ethernet private line services, Ethernet-based Internet access services, and point-to-point Ethernet VPNs. E-LAN Services are designed for multipoint Ethernet VPNs and native Ethernet Transparent LAN services such as VPLS. Figure 2: MEF Ethernet Line Services Figure 3: MEF Ethernet LAN Services Copyright Agilent Technologies, Inc

4 Challenges involved in ensuring carrier-class Ethernet's simplicity, widespread adoption in the LAN and cost-effectiveness has led many public network operators to embrace this technology. However, despite the excitement surrounding Ethernet, it is not considered a carrier-class solution because it does not offer SONET-like resiliency and quality of service (QoS) mechanisms, required to support real-time services such voice and video. As a result, equipment manufacturers are moving in different directions to enhance the capabilities of Ethernet, making it more resilient and enabling network operators to offer bandwidth guarantees and service level agreements (SLAs) so carriers can offer support for service, such as voice and video, as well as mission-critical applications. Considerable efforts are also being made by the industry bodies including MEF, IETF and ITU-T to standardize Metro Ethernet services, thereby making it more important to validate whether these services conform to the QoS performance, reliability and scalability measures required to ensure 'carrier-class' status. Quality of Service (QoS) Ethernet has often been relegated to 'best-effort' class, because the Ethernet service interface is unable to differentiate between Ethernet frames carrying an message or a voice over IP call. Thus, no true service multiplexing was possible, in which different services are carried over the same UNI. Various solutions are currently being proposed to overcome this shortcoming. The MEF specification supports multiple Ethernet classes of service (CoS) tiers based on physical port, MAC addresses, VLAN ID, (IEEE 802.1Q), user priority bits (802.1p), MPLS EXP bits, or DiffServ/IP Type of Service value. However, no standards exist for Ethernet traffic management to support Ethernet CoS. Therefore, proprietary solutions or solutions based on other standards have been implemented. Service Resiliency Resiliency in a MAN is essential in order to prevent significant downtime and service frame loss. Native Ethernet protection protocols, such as Spanning Tree, take tens of seconds to reroute around fibre or node failures in the network, in contrast with a 50ms provided by SONET/SDH automatic protection switching (APS). Re-routing times spanning tens of seconds negatively affects the quality of voice, video and mission critical traffic. Other technologies such as Resilient Packet Rings (RPR), MPLS Fast Reroute, and proprietary solutions promise faster network re-convergence times after a failure, which will enable service providers to deliver more reliable services. Service Scalability In enterprise networks, Ethernet has the ability to logically separate distinct user groups using the virtual LAN (VLAN) concept. However, the IEEE 801.Q standard only defines 4096 VLAN tags, which is not sufficient to accommodate the large provider networks. Other service delivery mechanisms that use subscriber frame encapsulation such as VLAN tag stacking and MPLS are being proposed to scale the network resource. Service Interoperability The proposed solutions to overcome the above limitations hold a lot of promise towards making Ethernet service carrier-class. However, there are no standards on how to implement QoS, resiliency and scalability in a uniform manner, giving rise to proprietary solutions from different vendors trying maintain their competitive edge. The crucial step enabling carrier-class Ethernet services is achieving conformance and multi-vendor interoperability. Many network failures can be attributed to differences in the implementation causing two network elements to interoperate in unpredictable manner compromising network reliability. Copyright Agilent Technologies, Inc

5 Testing Ethernet Services Ethernet testing is undergoing a paradigm shift, towards services testing. It is no longer about validating Ethernet devices' ability to forward traffic but instead its ability to support multiple services. Following are some typical test scenarios that will enable service providers and network operators to verify the quality of service, service performance, protection and restoration, data plane, control plane and VLAN transparency of Ethernet services. E-Line Service Validation Ethernet service must be transparent in order to ensure the subscriber's traffic at the egress UNI associated with an EVC is identical to their counterparts at the ingress UNI. In other words data and control plane traffic must pass through the MEN transparently; and must not alter the data in any way, even if traffic is being forwarded at full line rate The MEF has defined the EVC Layer 2 Control Protocol Processing Service Attribute as a key attribute defining an Ethernet Service. It is critical to verify that when a Layer 2 control protocol is tunneled, the Layer 2 control frame at each egress UNI is identical to the ingress Service Frame, as it allows subscribers significant control over their extended corporate networks. Figure 4: Testing Ethernet Line Service Test Methodology This test verifies that data and control plan traffic is transparently transmitted over the network. 1 Generate an Internet-Mix (Imix) of data, voice and video traffic with a range of service frame sizes from ingress test port. 2 Simultaneously generate some control-plane traffic, such as Spanning Tree BPDUs and Cisco's CDP frames originating from the same ingress port. 3 Transmit all traffic types at full line rate. 4 On the egress test port, check the data-integrity statistics to ensure that the traffic is not being corrupted. Ensure there is no service frame loss, and that latency, jitter, and throughput measurements are acceptable. Copyright Agilent Technologies, Inc

6 E-LAN Service Validation Ethernet LAN services allow subscribers to extend their corporate LANs over the WAN by providing multipoint-to-multipoint connectivity across several UNIs. End-to-end security is important for this service type, as it is critical to ensure traffic from one LAN did not get switched to another customer's LAN. To isolate the subscribers' traffic and avoid VLAN conflicts between customers, the service provider may insert an additional VLAN tag into the service frame. This VLAN tag stacking mechanism is referred to as Q-in-Q. Figure 5: Testing Ethernet LAN Service Test Methodology This test verifies that VLAN tagged data is correctly handled by the metro Ethernet network, and the data is transmitted to the correct destination. 1 Configure the ingress test port to simulate its participation in a MEN by transmitting Q-in-Q traffic. 2 Specify the expected destination ports to ensure that traffic is arriving at the correct egress port. 3 Generate full line rate Q-in-Q traffic from ingress test port. 4 Validate the traffic stream statistics to ensure the traffic is not being sent to an incorrect port. Copyright Agilent Technologies, Inc

7 Quality of Service Verification Mechanisms supporting explicit rate QoS on a per service basis is the key to meeting differentiated service level agreements. Service level agreements (SLAs) for Ethernet services may define bandwidth profiles to be applied per UNI, EVC or class of service. A bandwidth profile defines the amount of bandwidth a service allocates to a UNI, to an EVC or to Service Frames belonging to a particular Class of service. It is essential for a service provider to test the bandwidth profile capabilities and class of service metrics of all Ethernet services at the UNI because they provide the principal mechanisms ensuring the quality of voice and data applications. Figure 6: Testing QoS implementation of Ethernet Services Test Methodology This test verifies the bandwidth profile and traffic rate enforcement per class of service to guarantee a committed information rate for voice service frames when they are transmitted on an oversubscribed link in the MEN. 1 Configure the ingress and egress test ports to simulate the CE devices. 2 Generate a mixture of data service frames (lower priority) and voice service frames (higher priority). The higher priority traffic is specified using VLAN user priority bits (802.1p). 3 Transmit service frames at full line rate in each direction between two ports. 4 Oversubscribe the traffic streams and measured the service frame rate at the ingress and egress UNIs for both traffic types. Ensure the voice service frames are not affected as the service frames are dropped. Copyright Agilent Technologies, Inc

8 Service Resiliency Verification Ethernet services have the flexibility of being able to be transported over almost any infrastructure, such as SONET/SDH, MPLS and/or RPR. Hence, it is critical to verify the impact on subscribers when outages occur, and accurately measure the protection and restoration performance of the varying mechanisms. Figure 7: Testing resiliency implementation of Ethernet Services Test Methodology This test measures the time taken for the network to restore traffic, and verifies data loss during the failure. 1 Generate traffic streams from the ingress test port, which is simulating a CE-UNI. 2 Monitor the forwarding performance at the egress test port, and ensure no packet loss. 3 Simulate a network failure by pulling a fibre cable or shutting down an interface. 4 Measure the time taken for the network to restore traffic and the number of service frames lost. Copyright Agilent Technologies, Inc

9 Testing with Agilent N2X Agilent N2X provides the most comprehensive solution to validate the scalability and reliability of Ethernet based services as well as emerging hybrid devices such as MSPs, which require both Ethernet and SONET/SDH validation. What distinguishes N2X is its ability to test leading-edge services over the latest converging infrastructures such as MPLS and next-generation SONET/SDH simultaneously in the one test environment. This therefore enables seamless end-to-end service performance verification. Agilent N2X provides a portfolio of hardware test cards for comprehensive testing of Ethernet Services across SONET/SDH networks and infrastructure. Key capabilities include: Patented Ethernet Service Disruption measurements to verify services are 'carrier class' and meets 50ms outage times or SLAs. Real-time multi-stream measurements including Ethernet Packet BER, throughput, loss and latency to verify Ethernet service QoS. Verify the interactions between Ethernet restoration schemes such as Spanning Tree (IEEE 802.1d) and Rapid Spanning Tree (IEEE 802.1w) and the various SONET/SDH restoration schemes. Flexible PDU builder for Q-in-Q (VLAN tag stacking) traffic generation and measurements to verify class of Service and service prioritization. Layer 2 VPN emulation software the easy-to-use topology builder that quickly simulates scalable networks for testing latest technologies such as VPLS (Virtual Private LAN Service). Powerful capture and trigger features for easy troubleshooting and isolation of problems anywhere in the network. Conclusion Ethernet will play a strategic role as service providers open their optical networks to the revenue promise of next-generation Ethernet-based services. Low cost and simplicity are only part of Ethernet's attraction. A new dimension of flexibility, enabling expanded services at reduced operating costs, makes Ethernet the technology of choice in the delivery of these high growth packet services. The key to the wide scale adoption of Ethernet services relies on vendors being able to deliver on carrier-class requirements that are required by service providers to offer differentiated services and honor service-level agreements (SLA). Testing is a critical element in validating these emerging services, to ensure carrier-class requirements including quality of service (QoS), resiliency and scalability and multi-vendor interoperability is achieved. Copyright Agilent Technologies, Inc

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