MPLS TE Overview Introducing the TE Concept
Outline Overview What Is TE? Business Drivers for TE Congestion Avoidance and TE TE with the Layer 2 Overlay Model TE with the Layer 3 Model TE with the MPLS TE Model Summary
What Is Traffic Engineering? Traffic engineering is manipulating your traffic to fit your network. Network engineering is building your network to carry your predicted traffic. TE is commonly used in voice telephony networks. TE is a process of measures, models, and controls of traffic to achieve various goals. TE for data networks provides an integrated approach to managing traffic at Layer 3.
What Is Traffic Engineering? Traffic Engineering Motivations Reduce the overall cost of operations by more efficient use of bandwidth resources Prevent a situation where some parts of a network are overutilized (congested), while other parts remain underutilized Implement traffic protection against failures Enhance SLA in combination with QoS
Business Drivers for Traffic Engineering Routers forward traffic along the least-cost route discovered by routing protocols. Network bandwidth may not be efficiently utilized: The least-cost route may not be the only possible route. The least-cost route may not have enough resources to carry all the traffic. Alternate paths may be underutilized.
Business Drivers for Traffic Engineering (Cont.) Lack of resources results in congestion in two ways: When network resources themselves are insufficient to accommodate offered load When traffic streams are inefficiently mapped onto available resources Some resources are overutilized while others remain underutilized.
Congestion Avoidance and Traffic Engineering Network congestion can be addressed by either: Expansion of capacity or classical congestion control techniques (queuing, rate limiting, and so on) Traffic engineering, if the problems result from inefficient resource allocation The focus of TE is not on congestion created as a result of a short-term burst, but on congestion problems that are prolonged.
Traffic Engineering with a Layer 2 Overlay Model The use of the explicit Layer 2 transit layer allows very exact control of how traffic uses the available bandwidth. PVCs or SVCs carry traffic across Layer 2. Layer 3 at the edge sees a complete mesh.
Traffic Engineering with a Layer 2 Overlay Model: Example
Traffic Engineering with a Layer 2 Overlay Model (Cont.) Drawbacks of the Layer 2 overlay solution Extra network devices More complex network management: Two-level network without integrated network management Additional training, technical support, field engineering IGP routing scalability issue for meshes Additional bandwidth overhead (“cell tax”) No differential service (class of service)
Layer 3 Model with No Traffic Engineering
Traffic Engineering with a Layer 3 Model (Cont.) The current forwarding paradigm, centered around “destination-based,” is clearly inadequate: Path computation based just on IGP metric is not enough. Support for “explicit” routing (source routing) is not available. Supported workarounds are static routes, policy routing. Provide controlled backup and recovery.
Traffic Engineering with the MPLS TE Model Tunnel is assigned labels that represent the path (LSP) through the system. Forwarding within the MPLS network is based on labels (no Layer 3 lookup).
Traffic Engineering with the MPLS TE Model (Cont.) The MPLS TE LSPs are created by RSVP. The actual path can be specified: Explicitly defined by the system administrator Dynamically defined using the underlying IGP protocol
Summary Traffic engineering measures, models, and controls traffic to achieve various goals. TE is driven by inefficient bandwidth utilization. TE focuses on prolonged congestion problems. With the TE Layer 2 overlay model, routers are not aware of the physical structure and bandwidth available on links. With the TE Layer 3 model, the destination-based forwarding paradigm cannot handle the problem of overutilization of one path while an alternate path is underutilized. TE with the MPLS TE model means that the routers use the MPLS label-switching paradigm.