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Archive 27 Mar 2007 #58Ethernet's New Frontier: "Self-Insured" Ethernet - Part 2 By Vladimir Kaminsky, Contributing Editor and Sr. Consultant This is Part II from a two-part paper prepared by Flanagan Consulting on an emerging Ethernet protocol whose goal is to compete with MPLS and Ethernet-over-SONET transport techniques for Carrier-Grade transmission. To date, the combination of MPLS with Ethernet over SONET (EoS) have been the prevailing technology option that supports Carrier-Grade applications requirements, specifically: -- Scalability, -- Reliability, -- Hard QoS / traffic management, -- Service management, and -- Support for TDM services. PBT FOR A CONNECTION-ORIENTED CORE This ViewsLetter introduces a new technology called Provider Backbone Transport (PBT), which can be employed in the service provider domain of a Provider Backbone Bridge Network (802.1ah) to allow configuration of engineered, resilient, SLA driven point-to-point Ethernet trunks, also called Ethernet Virtual Circuits (EVCs) by the MetroEthernet Forum. PBT trunks allow carriers to engineer traffic-managed circuits which may be monitored, along with the rest of the 802.1ah network, using the 802.1ag protocols. PBT focuses on applying Ethernet technology directly to the transport of Ethernet services. Introduced in October, 2005, PBT is a connection-oriented Ethernet technology combining telecom network and Ethernet technology characteristics. It is based on, but is not equal to, 802.1 MAC-in-MAC, the encapsulation of one Layer 2 frame in another using the Ethernet Media Access Control (MAC) header. PBT maintains the advantages of Ethernet, such as simplicity, scalability, and ubiquity, while addressing carrier grade quality concerns without the need for MPLS. The idea is to subtract certain things from Ethernet properties to make it more carrier-friendly. For example: rather than allow Ethernet to learn the surrounding network, as it was created to do, PBT lets carriers dictate network knowledge to switches. The core concepts of PBT are to: -- configure Ethernet services in network switches via network management and the network control plane, thereby creating connection-oriented Ethernet services, -- disable self-learning functions, such as the Spanning Tree protocol, and VLAN features in order to avoid broadcast packet flooding, -- reuse forwarding tables in the switches, and -- discard all packets not found in the PBT forwarding table. Carriers tell a node where to forward traffic, giving it multiple options and the ability to define protection paths which provide for <50-ms service recovery. With the introduction of Ethernet Virtual Circuits (EVCs) a carrier realizes such functions as protection switching, OAM, QoS, and traffic engineering. Each EVC may be assigned performance parameters such as a committed information rate (CIR) and committed burst size (CBS) that assure throughput, and similar limits for "excess" traffic to be carried if capacity is available. Discard thresholds are also available to limit throughput to what the subscriber ordered. The reason to do all this is to create determinism, the lack of which is the main issue Ethernet has always had against it in a carrier environment. SCALABILITY PBT offers a mechanism to permit scalable point-to-point trunks to be configured or signaled in an Ethernet subnetwork. Such trunks perform the functions of a packet switched network (PSN) and supports pseudowires to replace TDM circuits. PBT builds upon the concepts of Provider Bridging in 802.1ad (Q-in-Q), which is limited by the VLAN address space of 4096. Provider Backbone Bridging, in 802.1ah, doubles the length of the MAC address space (which squares an already large number) to provide an extremely scalable solution. That is, both the customer's original frame and the carrier's encapsulation header contain source and destination addresses in the form of Ethernet MAC addresses. PBT forwarding decisions are made based on a Backbone MAC destination (B-MAC) address (associated with an EVC) and Backbone VLAN ID (B-VID), the encapsulated header. With these enhancements, PBT provides a “pure” Ethernet backbone solution, which meets carrier class requirements without the need for additional protocol layers such as MPLS or new generation SONET (NGS). By basing the solution on existing standards and technologies, PBT also ensures that existing Ethernet network deployments can be re-used and enhanced to support this new concept. PBT leverages the existing IEEE 802.1ah frame format, without modification. PBT may be deployed in place of PBB (Provider Backbone Bridging), or may run in parallel with PBB. In both cases, PBT eliminates the need for backbone core devices to perform learning and flooding. Instead, point-to-point tunnels to transport L2 VPNs are provisioned using a sophisticated management platform. Rather than using RSTP/MSTP to prevent loops, the management platform traffic engineers the provider backbone network utilizing significantly more capacity. BACKUP TUNNEL FOR H.A. Primary and backup PBT tunnels may be pre-configured by a management system. This enables the operator to traffic engineer according to path, bandwidth, and service requirements. Customers and services are associated with tunnels taking into account the aggregate committed information rate (CIR) and excess information rate (EIR) bandwidth requirements. Tunnels are monitored through the use of IEEE 802.1ag Connectivity Fault Management (CFM) Continuity Check Messages (CCM). CCM control frames are sent and received every few milliseconds across PBT tunnels. If the primary tunnel should experience a fault, the tunnel endpoints automatically begin using the backup tunnel. The forwarding database entries are pre-configured along the backup path to minimize the failover and restoration times. PBT has been proposed to the IEEE, IETF, and ITU-T. It is expected that IEEE 802.1 will standardize this innovative and increasingly popular transport technology. BT has selected Nortel (www.nortel.com) and Siemens (www.siemens.com) as key suppliers of carrier-scale Ethernet equipment for its 21CN network. BT plans to use PBB-TE (Provider Backbone Bridging with Traffic Engineering), an emerging IEEE standard, for PBT)deployment. The network will be used to transport high-bandwidth services, from mission critical business applications to full-streaming video. BT has selected Nortel's Metro Ethernet Routing Switch 8600 and Metro Ethernet Services Unit 1850 for the Ethernet component of its 21CN. Meriton Networks (www.meriton.com) is combining PBT, what they call Carrier Ethernet Transport, with their wave division multiplexing optical switch. Provider Backbone Transport transforms Ethernet technology, traditionally restricted to small-scale, local networks, into a more reliable, scalable and deterministic technology making it suitable as the basis for fixed and mobile carrier networks to deliver live video and broadcast, multimedia, broadband data, and voice services. Traditional connectionless, best-effort Ethernet poses challenges for service providers needing to guarantee service delivery and quality of service for real-time applications. PBT is a simple point-to-point tunneling technology that adds determinism to Ethernet, enabling service providers to specify the path that an Ethernet service should take across the network. PBT allows for QoS guarantees by reserving bandwidth for real-time services. NEXT TIME: Perspective on carrier Ethernet compared to other transport methods. ================================ How Can Flanagan Consulting Help You? We understand not only the technology of network architectures but also the surrounding business processes: procurement, bid preparation/analysis, statements of work, financial analysis, consensus building, and more. "Flanagan
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