清华大学：计算机科学与技术（PPT讲稿）组播 Multicast

Multicast Dan lI CS Department, Tsinghua University 2021/2/11

Multicast 2021/2/11 1 Dan LI CS Department, Tsinghua University

Today's Lecture Why Multicast? iP multicast service models Host-Router Signaling: IGMP Multicast Distribution Trees and Forwarding Multicast Routing protocols Reliable multicast ulticast Overlay Reading List 2021/2/11

Today’s Lecture  Why Multicast?  IP multicast service models  Host-Router Signaling: IGMP  Multicast Distribution Trees and Forwarding  Multicast Routing Protocols  Reliable multicast  Multicast Overlay  Reading List 2021/2/11 3

Multicast Routing Unicast: one source to one destination w Multicast: one source to many destinations Main goal: efficient data distribution Avoid data duplication within network 2021/2/11 4

Multicast Routing  Unicast: one source to one destination  Multicast: one source to many destinations  Main goal: efficient data distribution  Avoid data duplication within network 2021/2/11 4

Multicast- Efficient Data Distribution Src Src ↓↓| 2021

Multicast – Efficient Data Distribution 2021/2/11 5 Src Src

EXample Applications Broadcast audio/video Push-based systems(e. g. BGP updates Software distribution Web-cache updates Teleconferencing (audio, video, shared whiteboard, text editor) Multi-player games Other distributed applications 2021/2/11

Example Applications  Broadcast audio/video  Push-based systems (e.g., BGP updates)  Software distribution  Web-cache updates  Teleconferencing (audio, video, shared whiteboard, text editor)  Multi-player games  Other distributed applications 2021/2/11 6

Multicast Advantages Enhanced Efficiency: Co and reduces serverand ctpplsoaetwork trattic Optimized performance: Eliminates traffic redundancy Distributed Applications: Makes multipoint applications possible Example: Audio Streaming □ Multicast All clients listening to the same 8 Kbps audio 口 Unicast 0.8 0.6 Traffic Mbps 0.4 0.2 20 40 60 80 100 20 40 60 80 100 2021/2/11 f clients

Multicast Advantages  Enhanced Efficiency: Controls network traffic and reduces server and CPU loads  Optimized Performance: Eliminates traffic redundancy  Distributed Applications: Makes multipoint applications possible 2021/2/11 7 1 20 40 60 80 100 Example: Audio Streaming All clients listening to the same 8 Kbps audio 0 0.2 0.4 0.6 0.8 Traffic Mbps 1 20 40 60 80 100 # Clients Multicast Unicast

Multicast Disadvantages Multicast is udP based!!! Best Effort Delivery k Drops are to be expected No Congestion Avoidance Lack of TCP windowing and"slow-start mechanisms can result in network congestion Duplicates Out of Order Delivery 2021/2/11

Multicast Disadvantages  Multicast Is UDP Based!!!  Best Effort Delivery:  Drops are to be expected  No Congestion Avoidance:  Lack of TCP windowing and “slow-start” mechanisms can result in network congestion  Duplicates  Out of Order Delivery 2021/2/11 8

Today's Lecture Why Multicast? IP multicast service models Host-Router Signaling: IGMP Multicast Distribution Trees and Forwarding Multicast Routing protocols Reliable multicast ulticast Overlay Reading List 2021/2/11

Today’s Lecture  Why Multicast?  IP multicast service models  Host-Router Signaling: IGMP  Multicast Distribution Trees and Forwarding  Multicast Routing Protocols  Reliable multicast  Multicast Overlay  Reading List 2021/2/11 9

IP Multicast Architecture Service model Hosts Host-to-router protocol (IGMP) Routers Multicast routing protocols varIous 2021/2/11

IP Multicast Architecture 2021/2/11 10 Hosts Routers Service model Host-to-router protocol (IGMP) Multicast routing protocols (various)

IP Multicast service Model Each group identified by a single IP address Variable size. k groups of any size sparse or dense Variable location mem bers may be located anywhere on Internet Dynamic membership Members can join and leave at will 2021/2/11 11

IP Multicast Service Model  Each group identified by a single IP address  Variable Size:  Groups of any size; sparse or dense  Variable Location:  Members may be located anywhere on Internet  Dynamic membership:  Members can join and leave at will 2021/2/11 11