Overlay Multicast Mechanism Student : Jia-Hui Huang Adviser : Kai-Wei Ke Date : 2006/5/9

2 Outline Introduction Topology-Aware Grouping End system multicast Simulation Summary

3 Introduction IP multicast Drawback  Require router to maintain per-group state  Reliability, congestion control, flow control more difficulty Overlay multicast  Build an overlay multicast tree on top IP layer  Unicast data along tree links  Application level multicast

4 Overlay multicast mechanism Topology-Aware Grouping (TAG) End system multicast (ESM)  Narada

5 Outline Introduction Topology-Aware Grouping End system multicast Simulation Summary

6 TAG(1/2) Exploits underlying network topology information Use path overlap among member to reduces  Delay  Link Stress TAG node maintain IP and paths for parent and children – Family table (FT)

7 TAG(2/2) Definition  A path from node A to node B  The spath of A where S is the root of the tree  Length of a path or is the number of routers in the path  if is a prefix of where s is the root of the tree

8 Complete path matching(1/2) Like longest prefix match Algorithm consider three mutually exclusive conditions  Select a node A such that A is child of C  Select children of C  No child of C satisfying 1 or 2 N : new member C : the node being examined

9 Complete path matching(2/2) Recursive algorithm until condition 2 or 3 is meet Tree management  Member join  Member leave  Fault resilience Parent and children periodically exchange messages Child failure : discards the child from it’s FT Parent failure : rejoin

10 Outline Introduction Topology-Aware Grouping End system multicast Simulation Summary

11 ESM Shift multicast feature to end system  Group membership  Multicast routing  Packet duplication Using a self-organizing and fully distributed algorithm  Narada algorithm Two steps of Narada algorithm  Construct a mesh  Construct per-source spanning tree for mesh

12 ESM Concept Link Stress (Si): number of identical copies of a packet carried by a physical link Distance (di) Resource usage A BD C R A BD C IP Multicast Resource Usage : 30 IP Unicast Resource Usage : 57 End System Multicast Resource Usage : 32 Complete virtual graph

13 Narada Design (1/2) objectives of Narada algorithm  Self-organizing  Overlay efficiency  Self-improving Narada algorithm  Group Management  Mesh Performance  Data delivery

14 Narada Design (2/2) Two steps of algorithm  Group management functions are abstracted out and handled at the mesh  Distributed heuristics for repairing mesh partition  We may leverage standard routing algorithms for construction of data delivery trees Mesh Tree

15 Group management (1/5) Distributed manage membership  Every member maintain a list of other members in the group  List need update when join, leave or fail Refresh message mechanism  Each member periodically generate a refresh message with sequence number  Dissemination refresh message along the mesh

16 Group management (2/5) Member i keeps track of the information for every other member k in the group  Member address k  Last sequence number  Time of first receive Reduce overhead of refresh message  Each member periodically exchange its knowledge of membership with neighbors

17 Group management (3/5) Three operation of group management  Member join  Member leave and failure  Repairing mesh partitions Member join process  It assume can get a some member list  Random select member from list to send join message  The join message request added as a neighbor of that member  Repeat process until successful join the group  Refresh message mechanism to obtain group info.

18 Group management (4/5) Member leave and failure  Member must notifies its neighbors before leave  Leave information will propagated to the rest of group members  Abrupt Detected by neighbors when stop receive refresh Propagate information to other members  Ex of failure if node c fail E F BA D G C

19 Group management (5/5) Repairing mesh partitions  Member failure may cause partition  Each member maintain a queue that stopped receive refresh message for at least time  Periodically run a scheduling algorithm to probe and delete member from head of queue

20 Mesh performance (1/3) The constructed mesh can be suboptimal because  Random selection neighbor when join  Link add in partition repair my not useful in long time  Underlying network conditions may vary Using utility mechanism to add or drop link dynamically and improve quality

21 Mesh performance (2/3) Utility function depends on the what kind of performance metric specific  Example latency and bandwidth ( conferencing application ) Addition of links  Every member periodically probe some random members that is not neighbor  And evaluate the utility of adding a link to this member  Determine if add link by a given threshold

22 Mesh performance (3/3) Dropping of links  Every member periodically computes the cost of its link to every neighbor using the cost algorithm  The cost of a link between I and j in I’s perception is the number of group members for which I use j as next hop  Picks the lowest cost link and drops it if it falls below threshold

23 Data delivery The per-source trees constructed from the reverse shortest path between each recipient and source

24 Outline Introduction Topology-Aware Grouping End system multicast Simulation Summary

25 Simulation (1/2) Properties of simulation topology  Power-law Larger number of low-degree routers than high-degree routers  Small-world Avg. shortest distance between two randomly chosen nodes is approximately six hops

26 Simulation (2/2) Property of constructed overlay tree  High-degree high-bandwidth router more likely traversed by links near the source Simulation metrics  Number of hops vs. overlay tree level  Relative delay penalty (RDP)  Longest Latency  Mean Bandwidth

27 Number of hops vs. overlay tree level Number of hops decreases as the host level increases

28 Relative delay penalty (RDP) ESM < MDDBST < TAG

29 Longest Latency Latency & RDP for ESM decrease as more hosts join  Lower latency paths become available ESM > TAG > MDDBST

30 Mean Bandwidth Trade-off between latency and bottleneck bandwidth MDDBST > TAG > ESM

31 Outline Introduction Topology-Aware Grouping End system multicast Simulation Summary

32 Summary Both delay and number of hops between parent and child decrease as the level increase Balance the trade-off between delay and bandwidth

33 Reference Yang-hua Chu, Sanjay G. Rao, Srinivasan Seashan, and Hui Zhang, “A Case for End System Multicast,” IEEE Journal On Selected Areas In Communications, VOL. 20 ISSUE 8, Oct. 2002, pp Sherlia Y. Shi, Jonathan S. Turner and Marcel Waldvogel, “Dimensioning Server Access Bandwidth and Multicast Routing in Overlay Networks,” Proceedings of NOSSDAV Minseok Kwon and Sonia Fahmy, “Topology-Aware Overlay Networks for Group Communication,” Proceedings of NOSSDAV'02, May Minseok Kwon and Sonia Fahmy, “Characterizing Overlay Multicast Networks,” IEEE International Conference on Network Protocols, pp. 61

34 Outline Introduction Dimensioning server multicast routing Topology-Aware Grouping End system multicast Simulation Summary

35 Dimensioning server multicast routing(1/2) Use AMcast network architecture  Deploy application servers on the networks  Spawn a start topology from each server to its end users  End users send/receive exactly one copy of packet  Work shifted from source to all servers Design routing algorithms from two objectives

36 Dimensioning server multicast routing(2/2) Delay Optimization  Minimum diameter, degree-bounded spanning tree (MDDBST) Load balancing  Bounded diameter, residual-balanced spanning tree (BDRBST) Two objectives are orthogonal

37 MDDBST(1/4) Definition given G=(V,E) : undirected complete graph : degree bound : cost for edge e Find A spanning tree T of G for each and degree of v satisfies diameter (the cost of the longest simple path) of T is minimized

38 MDDBST(2/4) Longest path of u to any other nodes in T

39 MDDBST(3/4) A B E DC A BCDE A B CD E A B E D C

40 MDDBST(4/4) A B E DC A B E DC

41 BDRBST(1/3) Definition given G=(V,E) : undirected complete graph : degree bound : cost for edge e B : cost Bound Find A spanning tree T of G for each and degree of v satisfies diameter (the cost of the longest simple path) of T < B and maximize (residual bandwidth)

42 BDRBST(2/3) Introduce balance factor M Algorithm similar MDDBST Main difference  Select a set of M smallest nodes  Select the largest residual bandwidth (smallest degree) node as parent node Special cases  M=1 : algorithm same as MDDBST  M= # of servers : only considers load balancing

43 BDRBST(3/3) Increase system capacity by increase end-to- end delay Small values of M provide good load balance while still meeting the diameter bound

44 AMcast architecture

45 MDDBST algorithm

46 Family table (FT) FT Parent Children …...

47 Topology aware definition S R1 D1 D5 D3 D4 D2 R5 R3 R2 R4 Path from S to D5 ( spath of D5 )

48 Path match condition S C A N Path match S C A1A2A3 S C A1A2A3 N Path match S C A2A1 S C A2A1N Path match Condition 1 Condition 3Condition 2

49 Complete path match algorithm

50 CPM Member join Root Member1 Member2 Path Matching New Member Join Request/Reply ….. CPM Join process S R1 R2 R4 R3 D5 D2D3 D4 D1 FT D1 : (R1) FT D2 : (R1,R2,R4) FT D3 : (R1,R2,R4) FT D4 : (R1,R2) FT D2 : (R1,R2,R4) FT D2 : (R1,R2,R4) D5 : (R1,R2,R3)

51 CPM Member leave Send LEAVE message Parent remove entry Parent add entry S R1 R2 R4 R3 D5 D2D3 D4 D1 FT D1 : (R1) FT D3 : (R1,R2,R4) FT D4 : (R1,R2) FT D2 : (R1,R2,R4) D5 : (R1,R2,R3) FT D2 : (R1,R2,R4) D5 : (R1,R2,R3)

52 Partial path matching process S R1 R2 R4 R3 D2 D3 D1 R5 R6 FT D1 : (R1,R2) D2 : (R1,R3,R4) Bwthresh = 100kbps D1-D3 : 300kbps D2-D3 : 50kbps S R1 R2 R4 R3 D2 D3 D1 R5 R6 FT D2 : (R1,R3,R4) D4 : (R1,R3,R7) D5 : (R1,R3,R2) R7 D4 D5 FT D1 : (R1) FT D3 : (R1,R3,R5,R6) FT D2 : (R1,R3,R4) D4 : (R1,R3,R7) Bwthresh = 100kbps D1-D3 : 50kbps D2-D3 : 600kbps D4-D3 : 80kbps Join processLeave process

53 Scheduling algorithm Time exceed T According probability

54 Utility function Latency as metric

55 Addition of links Berk1 Stan2 CMU Gatech1 Stan1 Gatech2 Probe Berk1 Stan2 CMU Gatech1 Stan1 Gatech2 Probe Delay improves to Stan1, CMU but marginally. Do not add link! Delay improves to CMU, Gatech1 and significantly. Add link!

56 Cost algorithm

57 Dropping of links Gatech1 Berk1 Stan2 Stan1 Gatech2 Gatech1 Berk1 Stan2 CMU Stan1 Gatech2 Used by Berk1 to reach only Gatech2 and vice versa: Drop!!