1,清华大学计算机系,Internet组播简介,2,主要内容,为什么需要组播？ 组播地址 主机和路由器的交互：IGMP 组播分发树 组播转发 域内组播路由协议 域间组播路由协议 IPv6,3,主要内容,为什么需要组播？ 组播地址 主机和路由器的交互：IGMP 组播分发树 组播转发 域内组播路由协议 域间组播路由协议 IPv6,4,Server,Router,Unicast,Server,Router,Multicast,单播和组播的比较,5,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,组播的优势,Enhanced Efficiency: Controls network traffic and reduces server and CPU loads Optimized Performance: Eliminates traffic redundancy Distributed Applications: Makes multipoint applications possible,6,组播带来的问题,Best Effort Delivery: Drops are to be expected. Multicast applications should not expect reliable delivery of data and should be designed accordingly. Reliable Multicast is still an area for much research No Congestion Avoidance: Lack of TCP windowing and “slow-start” mechanisms can result in network congestion. If possible, Multicast applications should attempt to detect and avoid congestion conditions,组播是基于UDP的！,7,组播带来的问题,Duplicates: Some multicast protocol mechanisms (e.g. Asserts, Registers and SPT Transitions) result in the occasional generation of duplicate packets Out of Order Delivery: Some protocol mechanisms may also result in out of order delivery of packets,8,组播的应用,Multimedia Streaming media, IPTV Training, corporate communications Conferencingvideo/audio Net Game Any one-to-many data push applications,9,主要内容,为什么需要组播？ 组播地址 主机和路由器的交互：IGMP 组播分发树 组播转发 域内组播路由协议 域间组播路由协议 IPv6,10,IPv4 Multicast Group Addresses 224.0.0.0239.255.255.255 Class “D” Address Space High order bits of 1st Octet = “1110” Reserved Link-local Addresses 224.0.0.0224.0.0.255 Transmitted with TTL = 1 Examples: 224.0.0.1 All systems on this subnet 224.0.0.2 All routers on this subnet 224.0.0.4 DVMRP routers 224.0.0.5 OSPF routers 224.0.0.13 PIMv2 routers,组播地址,11,Administratively Scoped Addresses 239.0.0.0239.255.255.255 Private address space Similar to RFC1918 unicast addresses Not used for global Internet traffic Used to limit “scope” of multicast traffic Same addresses may be in use at different locations for different multicast sessions Examples Site-local scope: 239.253.0.0/16 Organization-local scope: 239.192.0.0/14,组播地址,12,32 Bits,28 Bits,25 Bits,23 Bits,48 Bits,01-00-5e-7f-00-01,1110,5 Bits Lost,组播地址,IP Multicast MAC Address Mapping (FDDI and Ethernet),239.255.0.1,13,224.1.1.1 224.129.1.1 225.1.1.1 225.129.1.1 . . . 238.1.1.1 238.129.1.1 239.1.1.1 239.129.1.1,0x0100.5E01.0101,1 - Multicast MAC Address (FDDI and Ethernet),32 - IP Multicast Addresses,组播地址,Be Aware of the 32:1 Address Overlap,IP Multicast MAC Address Mapping (FDDI & Ethernet),14,组播地址,Dynamic Group Address Assignment Historically accomplished using SDR application Sessions/groups announced over well-known multicast groups Address collisions detected and resolved at session creation time Has problems scaling,15,组播地址,Future dynamic techniques under consideration Multicast Address Set-Claim (MASC) Hierarchical, dynamic address allocation scheme Extremely complex garbage-collection problem Long ways off MADCAP Similar to DHCP Need application and host stack support,16,组播地址,Static Group Address Assignment Temporary method to meet immediate needs Group range: 233.0.0.0 - 233.255.255.255 Your AS number is inserted in middle two octets Remaining low-order octet used for group assignment Defined in IETF RFC3180 GLOP Addressing in 233/8,17,主要内容,为什么需要组播？ 组播地址 主机和路由器的交互：IGMP 组播分发树 组播转发 域内组播路由协议 域间组播路由协议 IPv6,18,Routers solicit group membership from directly connected hosts RFC 1112 specifies version 1 of IGMP RFC 2236 specifies version 2 of IGMP RFC 3376 specifies version 3 of IGMP Supported on latest service pack for Windows and most UNIX systems,How hosts tell routers about group membership,主机和路由器的交互：IGMP,19,H3,Host sends IGMP Report to join group,H1,H2,Joining a Group,主机和路由器的交互：IGMP,20,Router sends periodic Queries to 224.0.0.1,One member per group per subnet reports,Other members suppress reports,Maintaining a Group,主机和路由器的交互：IGMP,21,Host quietly leaves group,H1,H3,Router sends 3 General Queries (60 secs apart),No IGMP Report for the group is received,Group times out (Worst case delay = 3 minutes),H2,Leaving a Group (IGMPv1),主机和路由器的交互：IGMP,22,Host sends Leave message to 224.0.0.2,H1,H3,Router sends Group specific query to 224.1.1.1,No IGMP Report is received within 3 seconds,Group 224.1.1.1 times out,H2,Leaving a Group (IGMPv2),主机和路由器的交互：IGMP,23,IGMPv3,RFC3376 Enables hosts to listen only to a specified subset of the hosts sending to the group,24,Source = 1.1.1.1 Group = 224.1.1.1,H1 - Member of 224.1.1.1,R1,R3,R2,Source = 2.2.2.2 Group = 224.1.1.1,H1 wants to receive from S = 1.1.1.1 but not from S = 2.2.2.2 With IGMP, specific sources can be pruned back - S = 2.2.2.2 in this case,IGMPv3: Join 1.1.