1. 15-744: Computer Networking L-15 Multicast Address Allocation and Reliability

2. L -15; 3-7-01© Srinivasan Seshan, 20012 Multicast Issues Address allocation Reliable transfer Congestion control Assigned reading F+97] A Reliable Multicast Framework for Ligh- Weight Sessions and Application Level Framing [MJV96] Receiver-driven Layered Multicast

3. L -15; 3-7-01© Srinivasan Seshan, 20013 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

4. L -15; 3-7-01© Srinivasan Seshan, 20014 Multicast Address Allocation Unicast IP addresses Allocated statically to hosts Allocated hierarchically by hosts’ org Multicast IP addresses Allocated per session Groups cross admin boundaries

5. L -15; 3-7-01© Srinivasan Seshan, 20015 Address Allocation Solutions Central server? Blocks of addresses for internal groups Leases for global addresses Random allocation? Send to group to ask if address is in use Need conflict resolution protocol

6. L -15; 3-7-01© Srinivasan Seshan, 20016 Multicast Address-Set Claim (MASC) Address allocation goals Efficient utilization of address space Aggregation of routing entries Robust and scalable Distributed, collaborative allocation Dynamic claim and listen protocol Claim “prefixes” from parent Communicate prefixes to local addresss allocation

7. L -15; 3-7-01© Srinivasan Seshan, 20017 MASC Domain A 224.0.0.0/16 Domain B 224.0.128.0/24 Domain C 224.0.1.0/24 Domain FDomain G A1 B1 B2 F1 C1 C2 G1

8. L -15; 3-7-01© Srinivasan Seshan, 20018 Prefix Selection Collect available prefixes Remove those that have been claimed Randomly select one of remaining prefixes with shortest mask (largest range) Claim first sub-prefix of desired size

9. L -15; 3-7-01© Srinivasan Seshan, 20019 Interaction with Multicast Routing Need an easy way to find/allocate core for CBTs How can address allocation help? Address for group should allocated by domain that has core Reasonable choice, since initiator is usually largest transmitter

10. L -15; 3-7-01© Srinivasan Seshan, 200110 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

11. L -15; 3-7-01© Srinivasan Seshan, 200111 Loss Recovery Sender-reliable Wait for ACKs from all receivers. Re-send on timeout or selective ACK Per receiver state in sender not scalable ACK implosion Receiver-reliable Receiver NACKs (resend request) lost packet Does not provide 100% reliability NACK implosion

12. L -15; 3-7-01© Srinivasan Seshan, 200112 R1 Implosion S R3R4 R2 21 R1 S R3R4 R2 Packet 1 is lostAll 4 receivers request a resend Resend request

13. L -15; 3-7-01© Srinivasan Seshan, 200113 Retransmission Re-transmitter Options: sender, other receivers How to retransmit Unicast, multicast, scoped multicast, retransmission group, … Problem: Exposure

14. L -15; 3-7-01© Srinivasan Seshan, 200114 R1 Exposure S R3R4 R2 21 R1 S R3R4 R2 Packet 1 does not reach R1; Receiver 1 requests a resend Packet 1 resent to all 4 receivers 1 1 Resend request Resent packet

15. L -15; 3-7-01© Srinivasan Seshan, 200115 Ideal Recovery Model S R3R4 R2 2 1 S R3R4 R2 Packet 1 reaches R1 but is lost before reaching other Receivers Only one receiver sends NACK to the nearest S or R with packet Resend request 11 Resent packet Repair sent only to those that need packet R1

16. L -15; 3-7-01© Srinivasan Seshan, 200116 R1 Aside: Using the Routers S R3R4 R2 Routers do transport level processing: Buffer packets Combine ACKs Send retransmissions Model solves implosion and exposure, but not scalable Violates end-to-end argument NACK RTX Router

17. L -15; 3-7-01© Srinivasan Seshan, 200117 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

18. L -15; 3-7-01© Srinivasan Seshan, 200118 SRM Originally designed for wb Receiver-reliable NACK-based Every member may multicast NACK or retransmission

19. L -15; 3-7-01© Srinivasan Seshan, 200119 R1 SRM Request Suppression S R3 R2 21 R1 S R3 R2 Packet 1 is lost; R1 requests resend to Source and Receivers Packet 1 is resent; R2 and R3 no longer have to request a resend 1 X X Delay varies by distance X Resend request Resent packet

20. L -15; 3-7-01© Srinivasan Seshan, 200120 Deterministic Suppression d d d d 3d Time data nack repair d 4d d 2d 3d = Sender = Repairer = Requestor Delay = C 1  d S,R

21. L -15; 3-7-01© Srinivasan Seshan, 200121 SRM Star Topology S R2 21 R3 Packet 1 is lost; All Receivers request resends Packet 1 is resent to all Receivers X R4 Delay is same length S R2 1 R3R4 Resend request Resent packet

22. L -15; 3-7-01© Srinivasan Seshan, 200122 SRM: Stochastic Suppression data d d d d Time NACK repair 2d session msg 0 1 2 3 Delay = U[0,D 2 ]  d S,R = Sender = Repairer = Requestor

23. L -15; 3-7-01© Srinivasan Seshan, 200123 SRM (Summary) NACK/Retransmission suppression Delay before sending Delay based on RTT estimation Deterministic + Stochastic components Periodic session messages Full reliability Estimation of distance matrix among members

24. L -15; 3-7-01© Srinivasan Seshan, 200124 What’s Missing? Losses at link (A,C) causes retransmission to the whole group Only retransmit to those members who lost the packet [Only request from the nearest responder] Sender Receiver A B E F S CD 0.99 00 0 00

25. L -15; 3-7-01© Srinivasan Seshan, 200125 Local Recovery Application-level hierarchy Fixed v.s. dynamic TTL scoped multicast Router supported

26. L -15; 3-7-01© Srinivasan Seshan, 200126 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

27. L -15; 3-7-01© Srinivasan Seshan, 200127 RMTP Reliable Multicast Transport Protocol by Purdue and AT&T Research Labs Designed for file dissemination (single- sender) Deployed in AT&T’s billing network

28. L -15; 3-7-01© Srinivasan Seshan, 200128 RMTP: Fixed Hierarchy Rcvr unicasts periodic ACK to its Designated Receiver (DR) DR unicasts its own ACK to its parent Rcvr chooses closest statically configured (DR) Mcast or unicast retransmission Based on percentage of requests Scoped mcast for local recovery D R2 R5 S R3 R4 R1 RRRR D RR D D DR R Receiver R* Router

29. L -15; 3-7-01© Srinivasan Seshan, 200129 RMTP: Comments  : Heterogeneity Lossy link or slow receiver will only affect a local region  : Position of DR critical Static hierarchy cannot adapt local recovery zone to loss points

30. L -15; 3-7-01© Srinivasan Seshan, 200130 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

31. L -15; 3-7-01© Srinivasan Seshan, 200131 Pragmatic General Multicast Cisco’s reliable multicast protocol NACK-based, with suppression Repair only forwarded to the NACKers

32. L -15; 3-7-01© Srinivasan Seshan, 200132 R1 Pragmatic General Multicast S R3R4 R2 21 R1 S R3R4 R2 Packet 1 reaches only R1; R2, R3, R4 request resends Packet 1 resent to R2, R3, R4; Not resent to R1 1 1 X 11 1 Routers remember resend requests 11 1 Resend requestResent packet

33. L -15; 3-7-01© Srinivasan Seshan, 200133 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

34. L -15; 3-7-01© Srinivasan Seshan, 200134 Light-weight Multicast Service (LMS) Enhance multicast routing with selective forwarding LMS extends router forwarding - what routers are meant to do in the first place No packet storing or processing at routers Strictly IP: no peeking into higher layers

35. L -15; 3-7-01© Srinivasan Seshan, 200135 The LMS Concept Heavy-weight model LMS: Receiver acts as surrogate R Control messages R Router stores packets, receives NACKs and sends retransmissions Router chooses a receiver as a surrogate Router steers all control messages to surrogate Router relays messages from surrogate to the subtree

36. L -15; 3-7-01© Srinivasan Seshan, 200136 LMS: Definitions Replier Receiver volunteered to answer requests Turning point Where requests start to move downstream Directed mcast Mcast to a subtree R1 S R3R6 R2 Replier link R4R5 Turning point Replier

37. L -15; 3-7-01© Srinivasan Seshan, 200137 R1 LMS with Replier Links S R3R6 R2 21 Packet 1 reaches only R1; R2 requests resend Resend requests from each receiver follow replier links 1 X Resend request Replier link R4R5 R1 S R3R6 R2 Resend request Replier link R4R5

38. L -15; 3-7-01© Srinivasan Seshan, 200138 R1 LMS with Replier Links S R3R6 R2 Request from replier links go up towards the Source Packet 1 is resent to all Receivers Resend request Replier link R4R5 R1 S R3R6 R2 1 Resent packet Replier link R4R5

39. L -15; 3-7-01© Srinivasan Seshan, 200139 LMS: Comments Replier problems Selection? Fault tolerance? How well will repliers scale w.r.t. group size? Works with unidirectional shared trees (PIM) Needs to relay requests from core/RP to sender Difficulties with bi-directional shared trees Needs per-source state

40. L -15; 3-7-01© Srinivasan Seshan, 200140 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

41. L -15; 3-7-01© Srinivasan Seshan, 200141 Multicast Congestion Control What if receivers have very different bandwidths? Send at max? Send at min? Send at avg? R R R S ???Mb/s 100Mb/s 1Mb/s 56Kb/s R

42. L -15; 3-7-01© Srinivasan Seshan, 200142 Video Adaptation: RLM Receiver-driven Layered Multicast Layered video encoding Each layer uses its own mcast group On spare capacity, receivers add a layer On congestion, receivers drop a layer Join experiments used for shared learning

43. L -15; 3-7-01© Srinivasan Seshan, 200143 Layered Media Streams S R R1 R2 R3 R 10Mbps 512Kbps 128Kbps 10Mbps R3 joins layer 1, fails at layer 2 R2 join layer 1, join layer 2 fails at layer 3 R1 joins layer 1, joins layer 2 joins layer 3

44. L -15; 3-7-01© Srinivasan Seshan, 200144 Drop Policies for Layered Multicast Priority Packets for low bandwidth layers are kept, drop queued packets for higher layers Requires router support Uniform (e.g., drop tail, RED) Packets arriving at congested router are dropped regardless of their layer Which is better? Intuition vs. reality!

45. L -15; 3-7-01© Srinivasan Seshan, 200145 RLM Intuition Uniform Better incentives to well-behaved users If oversend, performance rapidly degrades Clearer congestion signal Allows shared learning Priority Can waste upstream resources Hard to deploy RLM approaches optimal operating point Uniform is already deployed

46. L -15; 3-7-01© Srinivasan Seshan, 200146 RLM Intuition

47. L -15; 3-7-01© Srinivasan Seshan, 200147 Receiver-Driven Layered Multicast Each layer a separate group Receiver subscribes to max group that will get through with minimal drops Dynamically adapt to available capacity Use packet losses as congestion signal Assume no special router support Packets dropped independently of layer

48. L -15; 3-7-01© Srinivasan Seshan, 200148 RLM Join Experiment Receivers periodically try subscribing to higher layer If enough capacity, no congestion, no drops  Keep layer (& try next layer) If not enough capacity, congestion, drops  Drop layer (& increase time to next retry) What about impact on other receivers?

49. L -15; 3-7-01© Srinivasan Seshan, 200149 Join Experiments 1 2 3 4 Time Layer

50. L -15; 3-7-01© Srinivasan Seshan, 200150 RLM Scalability? What happens with more receivers? Increased frequency of experiments? More likely to conflict (false signals) Network spends more time congested Reduce # of experiments per host? Takes longer to converge

51. L -15; 3-7-01© Srinivasan Seshan, 200151 RLM Receiver Coordination Receiver advertises intent to add layer Other receivers Avoid conflicting experiments If experiment fails, will see increased drops => don’t try adding layer! (shared learning) OK to try adding lower layer during higher layer experiment Won’t cause drops at higher layer!

52. L -15; 3-7-01© Srinivasan Seshan, 200152 Overview Address Allocation Reliability Scalable Reliable Multicast Reliable Multicast Transport Protocol Pragmatic General Multicast Lightweight Multicast Service Receiver-driven Layered Multicast Other Issues

53. L -15; 3-7-01© Srinivasan Seshan, 200153 Inferring Topology What if packet is lost on link? All children of link will not get packet Idea: use loss “fingerprints” to identify siblings Siblings will have the most similar fingerprints Various techniques to build tree from collection of fingerprints

54. L -15; 3-7-01© Srinivasan Seshan, 200154 Session Messages SRM Identify what node knows about global state Multimedia & other applications Identify list of members Communicate loss rates  possibly for congestion control or other feedback What if it is a large group? Periodic transmissions can flood network!!

55. L -15; 3-7-01© Srinivasan Seshan, 200155 Application-level Multicast (Alternative) Do we really need network level multcast? Efficiency Logical rendezvous Can we get efficiency by creatively using the actual members or a few infrastructure nodes?

56. L -15; 3-7-01© Srinivasan Seshan, 200156 Application-level Multicast (Alternative) S R3R4 R2 S R3R4 R2

57. L -15; 3-7-01© Srinivasan Seshan, 200157 Next Lecture: Mobile Routing No lecture on March 12 Mobile IP Ad-hoc network routing Assigned reading [Joh96] Scalable Support for Transparent Mobile Host Internetworking [BMJ+98] Performance Comparison of Multi- Hop Wireless Ad Hoc Routing Protocols