Determinism and Ethernet
In a carrier environment, the connectionless behavior of traditional Ethernet implies a level of unpredictability that is troublesome in a high availability environment. A recent development in the Ethernet world has been the work on a connection-oriented technique known as Provider Backbone Transport (PBT). PBT builds on the hierarchical nature of PBB (or MAC-in-MAC) by using the backbone address and VLAN tag as identifiers for a deterministic “tunnel” through the network. PBT is being actively worked in the IEEE 802.1Qay committee where it is known as Provider Backbone Bridges — Traffic Engineering.
PBT provides Ethernet with a connection-oriented forwarding mode, which enables dedicated Ethernet links with guaranteed, deterministic performance levels. In this way, PBT delivers QoS over an Ethernet network without the added cost of connection- oriented alternatives. PBT also delivers the following benefits to the service provider:
•Scalability — PBT does not rely on the traditional Ethernet MAC address learning methods. This explicit learning approach removes the undesirable MAC flooding behavior that otherwise limits the size of the network.
•Resiliency — Since PBT allows creation of point-to-point connections across the network, working and protection routes can be provisioned to provide end-to-end resiliency across arbi- trary mesh topologies.
•Network utilization — The ability to fully manage traffic paths and know exactly which customer traffic is being carried over which path allows customer SLAs to be met without over- provisioning and under-utilizing network capacity.
•Manageability — Since the operations support system (OSS) is aware of the route taken by each service, functions such as alarm correlation, service-fault correlation and service- performance correlation are simplified.
•Security — Using point-to-point Ethernet tunnels across the network protects traffic from misconfiguration errors or inter- ception by those with malicious intent. Furthermore, by avoiding the flooding behavior of conventional Ethernet, unintentional leakage of packets to endpoints for which they were not intended can be avoided.
With Provider Backbone Transport (PBT) technology, efficient trunks can be engineered thru the network to deliver end-to-end traffic with deterministic routing and QoS in support of individual multiple-priority services or aggregrated services being backhauled across the MAN. PBT avoids the inefficiencies and lack of carrier-class resilience that otherwise arise from use of the traditional spanning tree algorithm. Rolled out as a software release on the Metro Ethernet Routing Switch 8600, PBT functionality can be deployed as needed, and need not be deployed uniformly across the entire network.
Figure 1 shows the Metro Ethernet Routing Switch 8600 deployed in support of triple play services including video (broadcast TV, video on demand), voice over IP (VoIP) and high-speed Internet access over a common network. Residential subscribers are connected to the network via various access technologies (xDSL, cable, direct fiber, Ethernet access ring, etc.) while enterprise subscribers are connected via direct Ethernet VPNs using the same access infrastructure. A mix of residential and enterprise services are supported on every port, creating a truly shared Ethernet-based infrastructure without compromising on performance.
Triple play services can be further distributed via an Ethernet access ring topology using Nortel Metro Ethernet Services Units. The Metro Ethernet Routing Switch 8600 supports services through other access topologies, such as point-to-point fiber, IEEE 802.1ad access networks and broadband aggregation devices.
