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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

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Multicast 2

Multicast 2

2002년 4월 2일

Jeong Ji-Woong


Outline

Outline

  • Introduction

    • Overview of IP Multicast

  • Hop By Hop Multicast

  • End System Multicast

  • Conclusion


What is multicast

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


Multicast vs unicast

Multicast vs Unicast

Server

Network

Client

Server

Network

Client


Class d address

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


Fundamental algorithms

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


Fundamental algorithms1

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


Example

Example


Ip multicast routing protocol

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)


Source based tree sbt

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)


Center based tree cbt

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


Example1

Example

  • JOIN REQUEST


Example2

Example

  • CBT Forwarding


Outline1

Outline

  • Introduction

  • Hop By Hop Multicast

    • REUNITE

    • HBH

  • End System Multicast

  • Conclusion


Ip multicast component

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


Problem of ip multicast

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


Reunite

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


Forwarding algorithm

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


Tree maintenance

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


Tree maintenance1

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


Tree maintenance2

Tree Maintenance


Tree maintenance3

Tree Maintenance


Advantages

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


Advantages1

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


Reunite s problem

REUNITE’s Problem

  • Addressing

    • Group Identifier로 Class-D Address를 쓰지 않음

  • Member Departure의 효과

    • 첫 번째로 JOIN한 Receiver가 Deparutre할 경우 그 파급 효과가 큼


Reunite s problem1

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


Hbh s addressing

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>


Hbh s tree management

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


Hbh s tree management1

HBH’s Tree Management


Hbh s tree management2

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


Outline2

Outline

  • Introduction

  • Hop By Hop Multicast

  • End System Multicast

  • Conclusion


Key concerns with ip multicast

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


Ip multicast

routers

end systems

multicast flow

IP Multicast

  • 아주 효율적

  • Good delay


What is end system multicast

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


End system multicast

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


End system multicast1

End System Multicast

  • Self-organizing의 two component

    • group management component

      • overlay는 dynamic change와 failure 에도 robust

    • overlay optimization component

      • quality of overlay remains good


Narada design

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


Narada design1

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


Supporting conferencing app

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


Enhancements of overlay design

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


Experiment methodology

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


Mean bandwidth averaged over all receivers

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


Performance metric

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)


Bw primary set 1 2 mbps

BW, Primary Set, 1.2 Mbps

  • Random’s poor performance: because of the inherent variability in Internet path characteristics


Bw extended set 2 4 mbps

BW, Extended Set, 2.4 Mbps

  • Optimizing only for latency has poor bandwidth performance

  • no strong correlation between latency and bandwidth


Rtt extended set 2 4mbps

RTT, Extended Set, 2.4Mbps

  • Optimizing only for bandwidth has poor latency performance

  • Bandwidth-Only cannot avoid poor latency links or long path length


Protocol overhead

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


Adapting to network dynamic

Adapting to network dynamic

  • Primary Set, CBR traffic at 1.2 Mbps

  • parent 와 victim간에 congestion 발생


Adapting to network dynamic1

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


Outline3

Outline

  • Introduction

  • Hop By Hop Multicast

  • End System Multicast

  • Conclusion

    • Summary

    • References


Summary

Summary

  • Hop By Hop Multicast

    • REUNITE

      • Recursive Unicast라는 개념을 제안

      • 기존의 Routing Protocol 보다 Scalability 향상

    • Hop By Hop Multicast

      • EXPRESS + 개선된 REUNITE

  • End System Multicast

    • dynamic 하고 heterogeneous한 Internet 환경에서 conferencing app. 이 수행될 수 있음

    • Overlay 를 구성하는데 있어서 bandwidth와 latency는 중요한 metric이다.

    • sparse 하고 작은 size의 group에 적당


References

References

  • Ion Stoica, T. S. Eugene Ng, Hui Zhang “REUNITE: A Recursive Unicast Approach to Multicast”, IEEE INFOCOM, March 2000

  • Luis Henrique M. K. Costa, Serge Fdida, Otto Carlos M. B. Duarte “Hop By Hop Multicast Routing Protocol”, ACM SIGCOMM, August 2001

  • Yang-hua Chu, Sanjay G. Rao, Hui Zhang “A Case for End System Multicast”, SIGMETRICS 2000

  • Yang-hua Chu, Sanjay G. Rao, Srinivasan Seshan, Hui Zhang “Enabling Conferencing Applications on the Internet Using an Overlay Multicast Architecture”, SIGCOMM, August 2001


References1

References

  • Chuck Semeria, Tom Maufer, “Introduction to IP Multicast Routing”, Internet-Draft, July 1997.

  • Stephen E. Deering, “Multicast Routing in Internetworks and Extended LANs”, ACM SIGCOMM 1988


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