Stealth Multicast - A New Paradigm for Incremental Multicast Deployment

1. Stealth Multicast - A New Paradigm for Incremental Multicast Deployment Dr. Aaron Striegel Dept. of Computer Science & Engineering University of Notre DameNSF CAREER

2. Talk Overview • Information Dissemination • Motivation • Stealth Multicast • Basic Architecture • Recent work: Wireless, ALM • Preliminary Results • Future Research • Inter-domain Peering • Network stack enhancement Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

3. Information Dissemination • Distribute rich content in a timely fashion to users • Problem: Internet evolved as point-to-point • Inefficient but currently manageable via unicasts • Two main approaches • Active involvement - Multicast • Close temporal proximity • Applications, network can participate • Community participation -> network efficiency • Passive involvement - Caching • Multiply-accessed data over time • No required participation of apps/network • Exploit existing characteristics of network • HTTP Caching, Packet-level caching Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

4. Multicast • Operation • Tree structure • Network state - replication • Benefits • Reduced bandwidth • N receivers << N bandwidth • Bottleneck relief • Relief close to source • Simplifies sender management • Send to group vs. individuals Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

5. Caching vs. Multicast • Caching • Cannot handle rapidly changing data • Data w/close temporal proximity • Easy deployment • No global participation • Multicast • Deployment problems • Global participation • Addressed by ALM • Delay-sensitive traffic, rich user base • Economic incentive • Bandwidth glut, ISP benefit • Can handle close temporal data • Group-oriented activities - synchrony is an issue Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

6. Current State • Caching: Yes Multicast: ?? • Several recent studies [2000, 2003] • Lackluster adoption 150 (99) -> 250 (2001) • Most groups are single source (SSM) • Why have *, G, CBTs, etc.? • Harder form of multicast anyway • Key lesson from caching • Incremental deployment is key • Big-bang theory is impossible • Transition as easy as possible (FUD inertia) • Immediate benefit • Large benefit with minimal investment • Directable economic benefit • Avoid “If you build it, they will come…” Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

7. Motivation • Research premise • Transparent bandwidth conservation technique • Best of caching and multicast • Incremental deployment • Zero dependence on external forces • Immediate benefit • Exploit the redundancy in the network, first/last mile & core • Economics • Offer a significant and quantifiable benefit • Stealth Multicast • Dynamically convert packets to/from multicast • Target • Small to medium group-oriented apps 5-500 users • Delay-sensitive apps • On-line gaming, video streaming Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

8. Stealth Multicast • Two governing principles • Externally transparent • Zero modification - application (server/client) • Zero modification - external Internet • Seamless operation • Negligible QoS impact? • Should not noticeably impact QoS • What are noticeable QoS changes? • Depends upon application • Large buffer - streaming video • On-line game - zero buffer • Informal definition • Additional delay should not make the application unusable versus separate unicasts Talk Overview Introduction Multicast Motivation Stealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

9. Stealth Multicast Model (Core) Conversion Other Domains Servers ISP Domain Clients Company LAN (Content Provider) Unicast Multicast Unicast

10. Multicast Detection VGDM - Virtual Group Detection Manager Virtual Group Mgr Disp Checksum Calculation Tree Construction H State Management Rules Filter Edge Router Incoming Traffic (Unicast only) Outgoing Traffic (Unicast+Multicast)

11. Further Examination • Benefits • Dynamic conversion • Zero modification • Multicast transport via virtual groups • Exact billing • Drawbacks • Non-zero queuing delay • Aggregation effects • Imperfect virtual groups • Not a universal solution Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack Too much delay Benefit Delay Not enough gain Virtual Group Delay Minimum gain Maximum delay

12. Multicast Transition Options

13. Dynamic Trees • Implementation of stealth multicast • Dynamically grow/shrink physical multicast groups • Virtual group - snapshot at current time • Physical group - superset of potential clients • Defines key issues of stealth multicast • Triggers- Virtual group release • Transport - Dynamic groups • State management - Where to place state Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

14. Virtual Group Triggers • Trigger • Dilemma: Gain for waiting • When to release the virtual group • MHT - Maximum Hold Time • TSW - Time Search Width • PSW - Packet Search Width Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack Target packet MHT TSW PSW time

15. Triggers - Continued • Triggers/thresholds • MinGS - Minimum group size • MaxGS - Maximum group size • MVG - Maximum virtual groups New group Multicast Unicast VG 0 .. MVG MaxGS MinGS VG N

16. Scalability & Storage • Examine worst case constraints • Worst case delay is MHT • 10% of an RTT of 50 ms • 5 ms MHT • Average delay is MHT / 2 • Worst case storage • PSW and TSW yield MHT, no matches • 1 Gb/s link, 1000 byte group overhead • 1 Gb/s @ 8 bit/byte * 5 ms = 625 kB • 625 kB/sec / 64 bytes = 9765 packets • 625 kB + 9765 * 1000 = ~ 11 MB Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

17. Multicast Transport • Issue • Members (clients) not known a priori • Dynamically construct tree • Approaches • Exhaustive tree construction • All variations, all egress points • Broadcast/hold • Costly - queuing at edge • Encapsulation-based • Embed tree inside the packet • Dynamic tree construction • Grow/shrink tree as necessary • Multicast or ALM • Broadcast (wireless) Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

18. Application State

19. Control Messages

20. State Management • Issue • Unique portions of packet • Compress multiple packets for different destinations into a single packet • Dest port, dest IP • Who is responsible for exporting? • Egress A vs. Egress B vs. Egress C • Approaches • Include in packet • Similar to encapsulation-based approach • Distributed knowledge • Egress points share knowledge Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

21. Application-Assisted Method • Virtual group detection • Imprecise nature - best guess • Application-assist • Application knows about VGDM • Application sends 1 packet w/state to VGDM • VGDM constructs tree • Benefits • No change to the client - deployment • Precise group construction • Issues • Billing • Requires change to server app Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

22. Other Issues - TCP, IPSec, IPv6 • TCP • Limited benefit • Why? • Extra state • Retransmit of lost packets • Potential benefit • Web serving - initial request • Assume no cookies • CNN on 9/11 • IPSec / VPNs • XBox Live (on-line gaming) • IPv6 Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

23. Wireless Stealth Multicast • Apply stealth to the last mile • Guarantee of B/W issues • Exploit broadcast nature of wireless • Design issues • Discovery • Partial group coverage • Bitmask on UDP header • Linkage on client • Spoof packet back through stack • Open issues • Ad hoc networks Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

24. Passive ALM (PALM) • Avoid reliance on IP multicast • Leverage existing ALM work • Dynamically convert to/from ALM • AC, AHD, non-ALM clients • New services to leverage • Design issues • Reliability constraints on ALM • Tree consistency • Partial tree subsets • Discovery • VGDM outwards, client to client Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

25. Simulation Studies • Simulation setup • Ns-2 simulator • Freely available simulator • GenMCast module for ns-2 • GIPSE for simulation management • Network setup • Medium-sized multicast groups • On-line gaming apps - 8 to 64 clients • UDP traffic - 40 server apps • Compare various approaches • Based on VGDM location + others • Local, Stealth, None, App-Assist, ALM • Evaluation metrics • Bandwidth savings • End-user QoS Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

26. Effect of Clients - Link BW No savings, unicast Higher up-link cost

27. Effect of clients - Domain BW Increasing savings vs. unicast Trades B/W for client B/W

28. Effect of Clients - QoS (Delay) Only amenable packets are queued Limited impact of queuing

29. Results – Wireless Stealth • Interesting performance • Remove entire queuing penalty • 3+ clients, huge B/W savings • Need larger search space • Inter-packet spacing from network • Prototype work • Concurrent development • Wireless Stealth, PALM • Beta: Jan 2005 • COTS, COTS + HW Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

30. Future Research Areas • Inter-domain peering / super-proxy • Transparent bandwidth conservation • Packet caching and stealth multicast • Edge routers of domains exchange info • Stealth multicast • Avoid conversion to/from multicast/unicast • Construct tree for new domain • Packet caching • Share cache in other domains • Issues • Billing, QoS • Resource management • Protocol / security Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

31. Future Research Areas • Network stack modification • Present: Minimize overhead • Avoid extra IP/TCP or IP/UDP headers • Premise • Can we increase redundancy but increase overall system performance? • Enhance network stack • Add End of Data marker - TCP • Modify sendmail / Apache to use • Issues • Benefit to the network • Downstream impact -> net system impact Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack

32. Conclusions • Stealth multicast • New paradigm for multicast • Offers several key benefits • Solves multicast deployment issue • Zero modification outside of the domain • Inherent resource management • Offers directable economic benefit • Interesting research problems • Transport, state management • Inter-domain peering, stack optimization Talk Overview Introduction Multicast MotivationStealth Multicast Virtual Groups Triggers Scalability Transport State Mgmnt Other Issues Wireless Stealth PALM Simulations Dynamic Trees Wireless Future Research I-D Peering Network Stack Conclusions

33. Questions? striegel@cse.nd.edu http://www.cse.nd.edu/~striegel GenMCast Package (ns-2) http://www.cse.nd.edu/~striegel/GenMCast