Overlay Networking

1. Overlay Networking Overview

2. Outline • Overview • Overlay multicast • Overlay QoS Overview

3. Overlay Networking Overview

4. Q: What new services/applications enabled? Q: What are the new technical challenges? Overlay Networking Overview

5. Large-scale file sharing Multicast Routing End-to-end commutations QoS Security Network Integration What new services/applications enabled? Overview

6. Why Overlay Multicast? • Why not IP Multicast? • Potential benefits of Overlay Multicast • Concerns of Overlay Multicast Overview

7. Routers with multicast support IP Multicast Gatech Stanford CMU Berkeley • No duplicate packets • Highly efficient bandwidth usage • Key Architectural Decision: Add support for multicast in IP layer Overview

8. Key Concerns with IP Multicast • Scalability with number of groups • Routers maintain per-group state • Analogous to per-flow state for QoS guarantees • Aggregation of multicast addresses is complicated • Supporting higher level functionality is difficult • IP Multicast: best-effort multi-point delivery service • End systems responsible for handling higher level functionality • Reliability and congestion control for IP Multicast complicated • Inter-domain routing is hard. • Deployment is difficult and slow • ISP’s reluctant to turn on IP Multicast Overview

9. Overlay Multicast CMU Stan1 Gatech Stanford Stan2 Berk1 Berkeley Berk2 Overlay Tree Stan1 Gatech Stan2 CMU Berk1 Berk2 Overview

10. Potential Benefits • Scalability (number of sessions in the network) • Routers do not maintain per-group state • End systems do, but they participate in very few groups • Easier to deploy • Potentially simplifies support for higher level functionality • Leverage computation and storage of end systems • For example, for buffering packets, transcoding, ACK aggregation • Leverage solutions for unicast congestion control and reliability Overview

11. Concerns of Overlay Multicast • Performance • Self-organization Overview

12. Delay from CMU to Berk1 increases Stan1 Gatech Stan2 CMU Duplicate Packets: Bandwidth Wastage Gatech Berk2 Stan1 Berk1 Stan2 CMU Berk1 Berk2 Performance Concerns Overview

13. The delay between the source and receivers is small Ideally, The number of redundant packets on any physical link is low Heuristicwe use: Every member in the tree has a small degree Degree chosen to reflect bandwidth of connection to Internet What is an efficient overlay tree? CMU CMU CMU Stan2 Stan2 Stan2 Stan1 Stan1 Stan1 Gatech Gatech Berk1 Berk1 Berk1 Gatech Berk2 Berk2 Berk2 High latency High degree (unicast) “Efficient” overlay Overview

14. Delay from CMU to Berk1 increases Stan1 Gatech Stan2 CMU Berk1 Berk2 Performance Metrics • Delay between members Berk2 Overview

15. Stan1 Stress = 2 Stan2 CMU Berk1 Performance Metrics (Cont.) • Stress, defined as the number of identical copies of a packet that traverse a physical link Berk2 • Overhead Overview

16. Why is self-organization hard? • Dynamic changes in group membership • Members join and leave dynamically • Members may die • Limited knowledge of network conditions • Members do not know delay to each other when they join • Overlay must self-improveas more information available • Dynamic changes in network conditions • Delay between members may vary over time due to congestion Overview

17. Overlay OoS Routing End control Benefits Flexibility Concerns No fully control QoS guarantees is difficult to achieve. A Whole Picture on Overlay QoS Overview

18. Conclusions • Overlay network is more flexible • Overlay network can enable many “new” networking applications • Overlay network can provide better QoS, but still without guarantees Overview