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IP MULTICAST Adiseshu Hari, T. V. Lakshman and Gordon Wilfong Nokia - PowerPoint PPT Presentation

IP MULTICAST Adiseshu Hari, T. V. Lakshman and Gordon Wilfong Nokia Bell Labs DIMACS Workshop on Algorithms for Data Center Networks Rutgers University, NJ Bell Labs 1 1 Why is IP Multicast not deployed in public networks?


  1. IP MULTICAST Adiseshu Hari, T. V. Lakshman and Gordon Wilfong Nokia Bell Labs DIMACS Workshop on Algorithms for Data Center Networks Rutgers University, NJ Bell Labs 1 1

  2. Why is IP Multicast not deployed in public networks? • Denial-of-Service (DoS) attack amplification • Complex Control Plane • Large Forwarding state - Non aggregable Multicast state flow Multicast data flow Multicast control plane Multicast data plane Bell Labs 2 Nokia 2017

  3. Can SDN help with Multicast? • Denial-of-Service (DoS) attack amplification  • Control state  • Forwarding state  Multicast state flow Multicast data flow Multicast SDN Controller Multicast SDN switch Bell Labs 3 Nokia 2017

  4. Can we eliminate multicast forwarding state in SDN? • Eliminate unicast forwarding state in SDN: - Path Switching: per-flow routing without per-flow state - New data path suitable for SW switches and programmable packet processors - Encode path in the packet headers - DIMACS 2016 Bell Labs 4 Nokia 2017

  5. Eliminating unicast forwarding state in SDN using Path Switching SDN Controller Bell Labs 5 Nokia 2017

  6. Can we eliminate multicast forwarding state in SDN? Can we extend Path Switching to encode multicast paths? Can we create an efficient encoding of a multicast path? No blowup in packet size (e.g. using bitmaps) No blowup in storage state (e.g,. encode each multicast tree by a unique identifier) Bell Labs 6 Nokia 2017

  7. Can we reduce multicast forwarding state in SDN? • Unicast Branching (UB) - Use branching nodes in the network to replicate unicast flows. - Use SDN Flow Table at ingress and egress - Use SDN Group Table at branching nodes • Reduces multicast forwarding state from linear to sublinear in number of forwarding nodes Bell Labs 7 Nokia 2017

  8. Unicast Branching (UB) Reference Diagram Central Controller Branching Nodes With Group Tables Transit Switches First Hop Switches First Hop Switches Endpoints Endpoints Bell Labs 8

  9. Reducing multicast forwarding state in SDN using Unicast Branching (UB) UB state flow UB data flow UB SDN Controller Unicast switch Ingress, Egress, Branching SDN switch Bell Labs 9 Nokia 2017

  10. Added advantages of Unicast Branching (UB) • Tunable knob to switch between unicast replication and full multicast • Allows for an NFV based implementation • Allows Traffic Engineered branches - Fast Reroute, Per branch QoS • Works at all protocol layers – protocol agnostic - Ethernet, IP, MPLS • Enables unicast only protocols like Segment Routing and TCP to be multicast capable* - HTTP Adaptive Streaming multicast - Efficient content caches • Enables Policy Based Multicast * Requires stateful NFV elements, not just SDN switches for branching points Bell Labs 10 Nokia 2017

  11. Policy Based Multicast • Policy based networking: Rules for non default routing - Geofencing - QoS - Membership filtering • UB enables Policy Based Multicast - Number, location and type of branching nodes Bell Labs 11 Nokia 2017

  12. Where are the Algorithms? Bell Labs 12 Nokia 2017

  13. Building Efficient Policy Based Multicast Trees • Problem 1 definition: Given an ingress node, a set of egress nodes and a set of branching nodes, build an “optimal” - multicast tree. What is “optimal” - - Usual definition is based on link cost. - Steiner tree problem (NP-complete) Bell Labs 13 Nokia 2017

  14. Building Multicast Trees using UB – Major Issue • UB based multicast tree is not a tree!!! It is a “configuration” - • Cannot apply Steiner tree approximation solutions directly. • Problem: How to create minimum cost configurations? r 2 b r G r 1 Bell Labs 14 Nokia 2017

  15. Transformation to Steiner tree problem on H Define : • Edge-weighted graph H = (O,E). O is set of branching nodes (including terminals) e=(b,b’) ∊ O, w(e) = length shortest path containing no internal O nodes • r r 2 2 5 b b 2 r r 4 H 5 G r r 1 1 Theorem: Minimum cost configuration problem in G is equivalent to Steiner tree problem in H Bell Labs 15

  16. Minimum cost configuration problem Theorem: There is a polynomial-time 1.39-approximation algorithm for min cost configuration problem. [BGRS10] Theorem: The minimum cost configuration problem is APX-hard. Proof: Follows from APX-hardness of Steiner problem for complete graphs with weights 1 and 2. [BP89] Bell Labs 16

  17. Problem 2: Minimize branching nodes • Problem 1: Minimize cost given a set of branching nodes . MIN COST PROBLEM • Problem 2: Minimize number of branching nodes given a fixed cost. MIN BRANCHING PROBLEM Bell Labs 17 Nokia 2017

  18. Min Branching Problem • For a subset X of the transit nodes, let C X be the minimum cost valid configuration using X as the set of extra branching nodes. • We are given a graph G = (V, E), a multicast demand d = (r, r1, r2,..., rt), a bound k and an attainable cost c. • Does there exists a branching set X with least cost valid configuration C X satisfying d where  X  <= k and cost(C X ) <= c. Bell Labs 18 Does anybody

  19. Min Branching Problem Theorem: This problem is NP-complete. Proof: Follows from a construction using Set Cover. Corollary: For this problem the best possible approximation is ≈ ln n . Proof: Follows from bounds for Set Cover. Bell Labs 19 Does anybody

  20. Theorem: Min Branching is NP-complete   r  , 1  demand r r , , r n    C r , r , r , r c e f 1 1 C C   1 m  C r , r , r , r m a b e n r r r r r r r b c e a 1 f n Bell Labs 20

  21. Policy Driven Software Defined Multicast Using Efficient Selection of Unicast Branching Points • Conclusion: - Unicast Branching based multicast provides for efficient, policy driven Software Defined Multicast. Bell Labs 21 Nokia 2017

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