1 / 53

Multicast 2

Multicast 2. 2002 년 4 월 2 일 Jeong Ji-Woong. Outline. Introduction Overview of IP Multicast Hop By Hop Multicast End System Multicast Conclusion. What is multicast?. Delivery of Data one-to-many, many-to-many Application 인터넷 방송 ftp Video-conferencing, shared whiteboard benefit

artie
Télécharger la présentation

Multicast 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multicast 2 2002년 4월 2일 Jeong Ji-Woong

  2. Outline • Introduction • Overview of IP Multicast • Hop By Hop Multicast • End System Multicast • Conclusion

  3. What is multicast? • Delivery of Data • one-to-many, many-to-many • Application • 인터넷 방송 • ftp • Video-conferencing, shared whiteboard • benefit • Reducing network load • Reducing server overhead • Single transmission

  4. Multicast vs Unicast Server Network Client Server Network Client

  5. Class D address • Class D : 224.0.0.0 ~ 239.255.255.255 • Well known address • Reserved : 244.0.0.0~224.0.0.255(topology discovery,maintenance) • 224.0.0.1 : all multicast systems on subnet • 224.0.0.2 : all routers on subnet • Map into Ethernet:01.00.5E.00.00.00+lower 23bits • 224.10.8.5 → 01005E.0A0805

  6. Fundamental algorithms • Multicast Routing algorithm • Reverse Path Broadcasting(RPB) • Truncated Reverse Path Broadcasting(TRPB) • RPB+truncated • group member를 가지지 않은 leaf로는 forwarding하지 않음 • Reverse Path Multicasting(RPM) • TRPB+prune • TRPB를 이용하여 multicast packet을 forwarding • member가 없는 leaf router는 source를 향하여 prune 메시지를 전송

  7. Fundamental algorithms • join algorithm • Implicit join: source로부터 multicast packet이 도착 후 tree 형성 • explicit join: host가 router 또는 source를 향해 join message 를 전송함으로써 트리 형성

  8. Example

  9. IP Multicast Routing Protocol • DVMRP(Distance Vector Multicast Routing Protocol) • MOSPF(Multicast Extensions to OSPF) • PIM-DM(Protocol Independent Multicast-Dense Mode) • CBT(Core Based Tree) • PIM-SM(Protocol Independent Multicast-Sparse Mode)

  10. Source Based Tree(SBT) • DVMRP • Operation • RPM + grafting • DVMRP router 간의 주기적인 routing table update • PIM-DM • Similar to DVMRP • MOSPF • OSPF link state routing protocol에 의해서 topology 파악 • Explicit join • Drawback • 주기적인 multicast traffic이 전체 network으로 전송 • Not scalable(member 수가 증가함에 따라)

  11. Center Based Tree(CBT) • CBT • group내의 모든 member는 같은 tree를 공유(shared tree) • Bidirectional tree • Explicit Join • PIM-SM • Similar to CBT • Unidirectional tree • source에서 RP로 tunneling • Drawback • Multicast packet을 전송할 때 delay가 커진다. • core 또는 Rendezvous Point 근처에서 bottleneck

  12. Example • JOIN REQUEST

  13. Example • CBT Forwarding

  14. Outline • Introduction • Hop By Hop Multicast • REUNITE • HBH • End System Multicast • Conclusion

  15. IP Multicast component • Service Model • 여러 Receiver들이 하나의 주소를 가지는 Group으로 Aggregate 됨 • 어떤 호스트도 Receiver들의 Group으로 전송가능 • Receiver들은 Dynamic하게 Join과 Leave가 가능 • Routing Protocol • Membership Information의 유지 • Multicast Distribution Tree의 형성

  16. Problem of IP Multicast • 기존 Service Model의 문제점 • 일반적인 ISP의 Billing Model과 맞지 않음 • Sender를 제한할 수 있는 방법이 없음 • Globally Unique한 Multicast 주소 할당의 어려움 • 기존 Routing Protocol의 문제점 • 모든 Router는 Distribution Tree가 자신을 지나가는 모든 Group에 대한 Forwarding Entry를 가지고 있어야 함 • Incremental Deployment의 어려움

  17. 기존 Routing Protocol의 문제점 모든 Router는 Distribution Tree가 자신을 지나가는 모든 Group에 대한 Forwarding Entry를 가지고 있어야 함 Assuming Multicast Group들의 수는 많아도 대다수의 Group들은 대단히 Sparse 할 것 REUNITE

  18. Forwarding Algorithm • Multicast Forwarding Table • Key : <root_addr, root_port, dst> • Value : <rcv1, rcv2, …, rcvn> • Branching Router에 존재 • Forwarding Algorithm • MFT에 Entry가 존재하면 Receiver List에 있는 Receiver에게 Packet을 복사해서 전송 • 단순한 Unicast Packet 처럼 전송

  19. Tree Maintenance • Multicast Control Table • Format : <root_addr, root_port><dst> • Non-Branching Router에 존재 • Question • 결국 REUNITE도 MFT나 MCT 둘 중의 하나를 모든 Router들이 가지고 있는데 왜 더 Scalabe 한가? • Answer • Data Packet은 Forwarding 시 MFT 만을 참조 • MCT는 Tree 유지를 위한 Control 목적으로만 사용

  20. Two Control Messages JOIN (Receiver->Root) : MFT의 Receiver Entry를 만들고 갱신 TREE (Root->Distribution Tree) : MFT와 MCT의 Group Entry를 만들고 갱신 두 가지 Control Message를 쓰는 이유 Asymmetric Unicast Routes Tree Maintenance S 1 2 R R

  21. Tree Maintenance

  22. Tree Maintenance

  23. Advantages • Enhanced Scalability • Non-Branching Router에는 Forwarding State를 유지하지 않음 • Incremental Deployment • Unicast Address를 사용하기 때문에 Multicast가 구현되지 않은 Router가 Tree에 참여 가능 • Load Balancing • Overload된 Router는 JOIN Message를 무시할 수 있음

  24. Advantages • Unique Group Identification • Root가 Locally Unique한 Port Number를 만들면 Globally Unique한 Group Address가 됨 • Support for Access Control • Root만이 Multicast Traffic을 Inject할 수 있기 때문에 Access Control이 용이 • Shortest Path Tree • JOIN과 TREE의 두 Message를 사용함으로써 Asymmetric Routes가 존재하는 경우에도 SPT를 구성

  25. REUNITE’s Problem • Addressing • Group Identifier로 Class-D Address를 쓰지 않음 • Member Departure의 효과 • 첫 번째로 JOIN한 Receiver가 Deparutre할 경우 그 파급 효과가 큼

  26. REUNITE’s Problem • Asymmetric Routes에 의한 Packet Duplication • 한 Link로 같은 Packet을 두 번 전송하는 경우가 발생 • RPF 기반 Algorithm에 비해 Cost가 클 수 있음

  27. HBH’s Addressing • REUNITE와 차이점 • Data Packet의 Destination Address가 첫 번째의 Receiver의 Address가 아닌 다음 Branching Router의 Address • Multicast Group Identifier • EXPRESS의 Channel Abstraction을 사용 • <Source IP Address, Class D address>

  28. HBH’s Tree Management • Three Control Messages • JOIN (Receiver->Source) : MFT의 Receiver Entry를 만들고 갱신 • TREE (Sender->Distribution Tree) : MFT와 MCT의 Group Entry를 만들고 갱신 • FUSION (Branching Router->Source) : Tree 구조를 정제 • REUNITE와 차이점 • 첫 번째 JOIN Message를 Intercept하지 않음 • 같은 Source에게 다른 TREE Message를 받으면 Source에게 FUSION Message를 보냄

  29. HBH’s Tree Management

  30. HBH’s Tree Management • Member Departure의 효과 • 첫 번째로 JOIN한 Receiver가 Departure할 경우에도 작은 파급 효과 • Worst Case에는 REUNITE보다 하나 많은 Change 필요 • Asymmetric Routes에 의한 Packet Duplication • FUSION Message로 해결

  31. Outline • Introduction • Hop By Hop Multicast • End System Multicast • Conclusion

  32. Key Concerns with IP Multicast • group의 수에 따른 scalability • Router는 per-group state를 유지 • higher level functionality를 지원하기가 어려움 • IP Multicast : best-effort multi-point delivery service • Deployment가 어렵고 느리다

  33. routers end systems multicast flow IP Multicast • 아주 효율적 • Good delay

  34. B C C Overlay Tree D B A D E A F E F What is End System Multicast? • multicast와 관련된 functionality (group management, packet replication) 가 End System에서 구현

  35. A A A B B B C C C E E D D D E F F F High latency High degree (unicast) “Efficient” overlay End System Multicast • Efficient overlay tree • low stress • low resource usage • the out-degree of each member must reflect the bandwidth of connection to Internet

  36. End System Multicast • Self-organizing의 two component • group management component • overlay는 dynamic change와 failure 에도 robust • overlay optimization component • quality of overlay remains good

  37. NARADA Design • First, • “Mesh”: Richer overlay that may have cycles and includes all group members • Second, • Source rooted shortest path spanning trees of mesh를 구성

  38. NARADA Design • Group Management • 각각의 member는 주기적으로 refresh message를 발생 • Optimizing mesh quality • addition of link • member는 주기적으로 다른 member(at random)를 probe • Utility Gain of adding link > Add Threshold 이면 link 추가 • dropping of link • member는 주기적으로 existing links를 감시 • Cost of dropping link < Drop Threshold 이면 link drop • Data Delivery • NARADA run distance vector protocol on top of mesh • The per-source tree used for delivery tree are constructed from the reverse shortest path between each S and R

  39. Supporting Conferencing app. • conference app. 의 작은 그룹 크기와 지속적인 session 의 특성은 overlay design에 적합 • framework • 각 overlay link 상에 Unicast congestion control • packet drop 정책을 사용하여 data rate를 adapt

  40. Enhancements of Overlay Design • Optimizing Overlay for dual metric • latency 보다는 bandwidth(widest)에 더 우선순위를 부여 • 같은 bandwidth를 가진 multiple path 가 있다면, lowest latency(shortest path)를 선택 • Optimizing for dynamic metric • Adapt overlay trees to changes in network condition • Monitor bandwidth and latency of overlay links • Link measurements can be noisy • Aggressive adaptation may cause overlay instability • transient: do not react • persistent: react • Capture the long term performance of a link • Exponential smoothing, Metric discretization

  41. Experiment Methodology • adopt following strategy • Interleave experiments with various protocol schemes • Repeat same experiments at different time of day • Average results over 10 experiments • For each experiment • 모든 member들은 동시에 join • Single source, CBR traffic • Each experiment lasts for 20 minutes

  42. Adapt to network congestion • Reach a stable overlay • Acquire network information • Self-organization Mean Bandwidth averaged over all receivers • 처음 몇 분간 overlay는 많은 topology 변화 • overlay의 quality를 향상시키기 위해 더 많은 정보를 획득

  43. Performance metric • Application Level Metrics • Bandwidth: throughput observed by each receiver • Latency: RTT between source and each receiver along overlay • Network perspective • resource usage • consumption of network resource of overlay tree • Overlay link RU = propagation delay • Tree RU = sum of link RU • protocol overhead • (total non-data traffic) / (total data traffic)

  44. BW, Primary Set, 1.2 Mbps • Random’s poor performance: because of the inherent variability in Internet path characteristics

  45. BW, Extended Set, 2.4 Mbps • Optimizing only for latency has poor bandwidth performance • no strong correlation between latency and bandwidth

  46. RTT, Extended Set, 2.4Mbps • Optimizing only for bandwidth has poor latency performance • Bandwidth-Only cannot avoid poor latency links or long path length

  47. Protocol overhead • Results • Average overhead : 10~15% • Overhead의 약 90% 이상이 bandwidth probe 때문이다 • Current scheme employs active probing for available bandwidth • Simple heuristics to eliminate unnecessary probes

  48. Adapting to network dynamic • Primary Set, CBR traffic at 1.2 Mbps • parent 와 victim간에 congestion 발생

  49. Adapting to network dynamic • Recovery time • Detection time • Reaction time • Repair time • Detection time 이 recovery time의 가장 중요한 fraction이다 • overlay 의 빠른 adapt : unstable을 초래할 수 있음 • overlay 의 느린 adapt : 일시적인 시간 동안 performance penalty

  50. Outline • Introduction • Hop By Hop Multicast • End System Multicast • Conclusion • Summary • References

More Related