While Carrier Ethernet OAM has come a long way, some functionality gaps still exist, and these gaps must be addressed to enable true, carrier-class OAM for Carrier Ethernet services.
By Umesh Kukreja, Atrica Inc.
As the demand for high-bandwidth, mission-critical Ethernet-based applications continues to grow at a rapid pace, a key requirement for the success of any service provider's Carrier Ethernet service portfolio is the ability to offer a wide range of attractive, end-to-end service-level agreement (SLA) options. This crucial capability depends on advanced operation, administration, and management (or maintenance; OAM) capabilities complemented by integrated network management and service management tools.
While Carrier Ethernet OAM has come a long way—thanks to the efforts of many industry standards bodies—some functionality gaps still exist, and these gaps must be addressed to enable true, carrier-class OAM for Carrier Ethernet services. Once these standards are complete, service providers will need advanced service management and delivery tools to ensure their Carrier Ethernet service offerings meet end users' expectations.
The growth of Ethernet
Ethernet services continue to gain momentum. Infonetics Research forecasts Ethernet services to grow from its $2.5 billion mark in 2004 to $22.2 billion in 2009, a compound annual growth rate (CAGR) of 54.7%. And Vertical Systems Group expects 14% of Ethernet services to represent new service deployment while a whopping 86% will come from the replacement of legacy services.
However, before enterprise customers will make the switch from their "tried and trusted" Frame Relay, ATM, and private line services to Ethernet services, they must be assured that Ethernet is carrier grade with the ability to support stringent SLAs and service guarantees. Without SLAs, many enterprises will simply stick with their current services, and operators will miss their chance to grab a part of this burgeoning market.
While Carrier Ethernet has been developed with SLA support as one of its core critical capabilities, the truth is that comprehensive, effective SLA support requires advanced OAM tools that go beyond today's existing standards. Robust, comprehensive service management systems are necessary to manage and monitor end-to-end SLAs and provide reports to end users ensuring service provider compliance.
Carrier Ethernet OAM challenges and requirements
OAM tools provide the functionality for easy and timely OAM of a service provider's network and services. It is commonly understood that OAM functions should be implemented on each layer of the network as well as on the service layer. In general, these functions can be divided into two main categories: the ability to troubleshoot network defects/failures and the ability to measure and assure the quality and service level of network traffic.
More specifically, these functions can be categorized by the following four aspects as defined by the IETF RFC3429:
- Defect/failure detection: Defects/failures affecting the transport of user information are detected by continuous or periodic checking. As a result, maintenance event information, protection actions, or appropriate alarms will be produced.
- Defect/failure reporting: Defect information is given to other management entities (e.g., operations support systems; OSSs) in order to provide the appropriate indications to the maintenance staff for maintaining the quality-of-service (QoS) levels offered to customers.
- Defect/failure localization: Determination by internal or external test systems of a failed entity is performed if defect information is insufficient.
- Performance monitoring: Performance (packet losses, transfer delay, bit errors, etc.) of the user information transport is measured in order to estimate the transport integrity.
Though Ethernet has been used as a local area network (LAN) technology for many years, managing and monitoring Ethernet-based metro (MANs) and wide area networks (WANs) introduces new challenges. Not only are the management practices of MAN and WAN held to a higher standard, but MAN and WAN Ethernet-based services typically involve multiple business entities with contractual SLAs, which requires a more extensive set of OAM functions.
To deliver an Ethernet service over diverse networks like these, the service provider's OAM tools must able to:
- Troubleshoot and isolate problems associated with the connectivity and quality of a specific service in a matter of minutes.
- Isolate and troubleshoot problems on the lower physical layers.
- Provide tools for successful and accurate service turn-up testing.
- Lay out the infrastructure for automatic failure recovery mechanisms (invoking protection routes, for example).
- Offer enough information for the validation and reporting of actual service performance metrics as they relate to specific SLAs.
Furthermore, Carrier Ethernet OAM should provide the means to monitor and manage all types of Ethernet services, including both point-to-point and multipoint services.
Key OAM tools and functions
Following is a checklist of the key characteristics required from OAM functions for Carrier Ethernet service delivery:
- Transparency: The OAM tools should be unintrusive when measuring the relevant data traffic without influencing the results of these measurements.
- Scalability: The tools should be able to measure multiple entities concurrently as relevant to the scales of MAN and WAN transport services.
- Accuracy: Aligned to the objectives of Carrier Ethernet OAM, the tools offered should be as precise as possible. This requirement implies that the tools should use exact measurements and calculations and use the same route as the data route so they can correctly compute the performance measurements.
- Robustness: The tools should provide OAM for the different types of Carrier Ethernet services and should not be confined to specific service types only.
Standardization efforts for Carrier Ethernet OAM
The scope of current Carrier Ethernet OAM standards efforts resides in two main functional layers: the link/transport layer and an end-to-end Ethernet service layer. Carriers need to be aware of these standards so they can establish the right OAM implementation for their Ethernet service portfolios.
With respect to the Transport/Link Layer OAM, the IEEE 802.3 (Clause 57) standard—formerly known as 802.3ah—enables a service provider to manage a single physical Ethernet link. The nature of the standard makes it particularly valuable in the first-mile connection to customer located equipment (CLE). The key functions of the 802.3 Clause 57 OAM are discovery, link monitoring, remote failure indication, and remote loopback.
For instances where the end-to-end Ethernet virtual circuit (EVC) traverses a Layer 2 multiprotocol label-switched (MPLS) segment, such segments are managed using standards defined by the IETF MPLS OAM specifications and the ITU Y.1711 specification. IETF MPLS OAM includes various categories, such as MPLS OAM, pseudowire OAM, and service-level OAM. The main functions are to detect data plane connectivity across label-switched paths (LSPs) using LSP Ping and Traceroute, as well as the MPLS-level health of the complete virtual circuit/pseudowire via Virtual Circuit Connection Verification (VCCV) protocol. ITU MPLS OAM specifications primarily discuss the OAM functionality for Ethernet-MPLS interworking scenarios.
With respect to the service layer OAM, which is concerned with the end-to-end connectivity of a service, there are complementary efforts by the ITU-T Y.1731 and the IEEE 802.1ag working groups. While IEEE 802.1ag addresses OAM improvements for fault management (Connectivity Fault Management), ITU-T Y.1731 extends these efforts with specifications for both fault management and performance monitoring for Ethernet services. The Metro Ethernet Forum (MEF) has issued a summary requirements document offering a framework for OAM in metro Ethernet. This document is aligned to the joint contributions of the ITU and IEEE.
The definitions in the different standards bodies are primarily focused on point-to-point (i.e., E-Line) services.
Surpassing Carrier Ethernet OAM standards
As the demand for Carrier Ethernet services grows, service providers are faced with creating and meeting SLAs that meet demanding mission-critical applications.
Service providers need OAM functionality that goes beyond the ability to manage the data plane user traffic (as defined by the standards bodies). They need OAM that offers management of the control plane of the physical network. Furthermore, OAM on the physical layer needs to consider not only the health of the links but also the ability to manage and monitor the health of the network nodes.
Advanced OAM functions must offer both a rich set of tools for connectivity and fault management and also a set of functions for performance/SLA monitoring. Going above and beyond the specifications in the standards bodies, these OAM tools must offer service-layer performance monitoring features not only for point-to-point services but also for multipoint services. This can be accomplished using a breakthrough model for accurately measuring performance metrics between the different end points of a specific virtual private LAN service (VPLS).
Performance monitoring—SLA measurements. The ability to measure performance/SLA parameters of services is critical because it enables service providers to 1) provide a tool that will assure and validate that SLAs are correctly provided to end customers (i.e., history-based SLA reports), and 2) troubleshoot and isolate problems in a service.
In advanced OAM tools, dedicated, unintrusive SLA measurement frames are used to perform measurements of an individual service's end-to-end SLA parameters. These frames traverse the same route as the user traffic. Different sampling and sending rates of these SLA measurement packets are required for two reasons. Fast sampling rate on a temporary basis is required for troubleshooting purposes, whereas more permanent packet transmissions are required for assurance purposes and reporting.
Performance monitoring includes the measurement facilities for:
- Frame loss: Actual (measuring actual user traffic loss) and statistical (statistical sampling, similar to Ping) measurements for point-to-point services and statistical measurements for multipoint services.
- Jitter: Frame delay variation.
- Round trip delay: Frame delay.
- Continuity: The uptime of a connection from a customer's perspective.
It is important that a service provider's network elements offer the option to measure performance on the entire user traffic (committed information rate [CIR] and excess information rate [EIR] traffic) or, as defined in the MEF, to CIR-profiled bandwidth only.
Network management. OAM standardization is a critical step for developing and delivering defined, industry-wide Carrier Ethernet services. However, for successful service offerings, carriers need a service management platform that delivers enhanced service management capabilities with rapid service provisioning, comprehensive network and element management, and seamless integration with existing OSS applications. Implemented correctly, such platforms allow existing craft personnel to provision new Ethernet services without getting into the intricacies of IP-based network technologies and services.
To expand the adoption of Carrier Ethernet services further, the simplicity of provisioning a point-to-point service must be extended to multipoint-to-multipoint services.
For any advanced OAM tools, the network management system's ability to deliver carrier-class Ethernet service management capabilities for a service provider's network operation center (NOC) is crucial.
Advanced network management systems will provide network operators with:
- Integrated end-to-end service planning and provisioning.
- Configuration management of network elements.
- Fault and performance management.
- SLA reporting.
- Security management.
- Plug-and-play management of Simple Network Management Protocol (SNMP) Management Interface Base (MIB)-2 compliant third-party network elements.
- Fast and flexible integration with northbound OSS applications using a set of functional application programming interfaces.
Carrier-grade OAM functions for Ethernet in the WAN and MAN are a vital, strategic part of any service provider's toolset when rolling out Carrier Ethernet services. A combined effort by all the standards bodies has produced a set of specifications to meet this objective, from connectivity management to performance management on both the link and service levels.
However, to truly deliver a wide range of guaranteed, end-to-end SLA offerings to enterprise customers, service providers need OAM functions that go beyond the standards-based specifications. They need OAM features that provide robustness, accurate measurements, scalability, service coverage, and manageability.
On top of these OAM functionalities, carriers also need an advanced service management system that delivers enhanced capabilities with rapid service provisioning, comprehensive network and element management, and seamless integration with existing OSS applications.
Combined, these tools will allow network operators to aggressively and successfully pursue a portion of the growing Carrier Ethernet marketplace.