第五章Internet组播v4.pptVIP

Internet组播简介 徐 恪 清华大学计算机系 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 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 单播和组播的比较 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 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 组播的应用 Multimedia Streaming media, IPTV Training, corporate communications Conferencing—video/audio Net Game Any one-to-many data push applications 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 组播地址 组播地址 组播地址 组播地址 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 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 组播地址 Static Group Address Assignment Temporary method to meet immediate needs Group range: - 55 Your AS number is inserted in middle two octets Remaining low-order octet used for group assignment Defined in IET