Budapest University of Technology and Economics Department of Telecommunications and Media Informatics Optimized QoS Protection of Ethernet Trees Tibor Cinkler, András Kern, István Moldován

BME-TMIT Ericsson, January 2006, ● Ethernet is the most dominating LAN technology ●Cheap equipment + high speed (up to 10 Gbps) ● Switched Ethernet - Carrier grade properties are required: ●Traffic Engineering ●Resilience Ethernet in Metro Access Networks

BME-TMIT Ericsson, January 2006, Spanning Tree Protocol (STP) ●Reverse learning + broadcast based packet switch ●Tree–like topology desired ●STP: ●Defines loop-free logical packet forwarding topology ●Spans a tree between the switches ●Problems:  Slow convergence (improved by RSTP)  Bad network utilization

BME-TMIT Ericsson, January 2006, Multiple Spanning Tree Protocol ●MORE VLAN based spanning trees ●Multiple spanning tree instances ●Each tree runs a separate RSTP instance ●1 VLAN  1 tree ●Number of trees is decision of the operator ●By default tree spanning is “Topology-Driven”: ●Port costs based on topology and link capacities ●Costs can be set manually (to obtain desired trees)

BME-TMIT Ericsson, January 2006, Protection switching ●802.3ad Link Aggregation ●uses redundant links for load balancing and protection ●Using MSTP ●2 MSTI trees, two paths: red and green ●VLAN 1 -> MST 1, VLAN 2 -> MST 2 ●A and B uses VLAN 1, in case of failure switch to VLAN 2 LAN VLAN 1 MST 1 VLAN 2 MST 2 (backup) A B

BME-TMIT Ericsson, January 2006, ●Typical Metro Topology: ●Aggregated traffic (demands) goes from the access to the edge nodes. ●Root of the trees at Edges node  one or more trees per edge node Model assumptions Traffic Source Traffic Destinatio n

BME-TMIT Ericsson, January 2006, Optimization framework ●Optimize the spanning trees ●Goal is to minimize the used network resources to maximize network throughput ●Provide 1:1 protection ●To protect all traffic is expensive - protect only a part of the traffic: the prioritized traffic ●Best Effort can use the protection paths

BME-TMIT Ericsson, January 2006, Formal description: ILP ●Integer Linear Program is used ●Result is a global optimal solution ●Constraints ●Total load does not exceed the link capacities and QoS limits ●If a demand uses a link the assigned tree will also use it ●Tree constraints (no cycles) ●Backup paths must be disjoint

BME-TMIT Ericsson, January 2006, Evaluation Criteria ●Maximal Throughput of the network ●Scaling up the offered load ●The allocated capacity for protection ●Resilience vs. Throughput: the amount of traffic lost in case of failure ●Complexity

BME-TMIT Ericsson, January 2006, Throughput gain

BME-TMIT Ericsson, January 2006, Throughput w/ protection

BME-TMIT Ericsson, January 2006, Capacities allocated

BME-TMIT Ericsson, January 2006, Heuristic ●Decomposition: ●Demand Routing (DR) ●Based on Simulated Allocation (SAL) ●Tree Assignment and Placement (TAP) ●Tree construction algorithm ●Results verified by simulations ●comparison to ILP solution

BME-TMIT Ericsson, January 2006, Heuristic Results

BME-TMIT Ericsson, January 2006, Relative throughputs

BME-TMIT Ericsson, January 2006, Conclusion ●We present an optimization TE Framework for QoS and protection ●ILP – not scalable ●Heuristics – scalable, close to optimal ●We show that: ●With optimization we can use redundant links –Throughput doubles compared to STP ●Optimized 1:1 protection –The same throughput as STP but all protected ●Protecting QoS traffic only is reasonable tradeoff

BME-TMIT Ericsson, January 2006, Thank you for your attention!

BME-TMIT Ericsson, January 2006, The End…

BME-TMIT Ericsson, January 2006, QoS model ●Priority based scheduling: ●Lower priority traffic is not served until there is higher priority traffic in the queue. ●To ensure low delay for each QoS class: amount of higher priority traffic should be limited for each link ●The ratios are examples, and should be determined individually for each operator 10% 20% remaining 30%

BME-TMIT Ericsson, January 2006, QoS provisioning ●Edges: ●Classification - VLANs ●Admission control, policing ●All nodes ●Queuing, scheduling ●Preprovisioned VLAN based QoS pipes ●Traffic engineered paths for VLAN pipes ●Resources assigned to pipes ●Optimization ensures that QoS requirements are met for each link

BME-TMIT Ericsson, January 2006, Loss in case of failure ●Throughput loss is compared to the network throughput without failure ●losses are measured immediately after the link failure, so the restoration capability of the STP is not considered