William Stallings Data and Computer Communications 7 th Edition

1. William StallingsData and Computer Communications7th Edition Chapter 19 Internetwork Operation

2. 19.1 Multicasting组播 • Addresses that refer to group of hosts on one or more networks • Uses • Multimedia “broadcast” • Teleconferencing • Database • Distributed computing • Real time workgroups

3. Example Config 链路 路由器 路由器 局域网 组播服务器 组成员

4. Broadcast and Multiple Unicast • Broadcast a copy of packet to each network • Requires 13 copies of packet • Multiple Unicast • Send packet only to networks that have hosts in group • 11 packets

5. True Multicast • Determine least cost path to each network that has host in group • Transmit single packet along spanning tree • Routers replicate packets at branch points of spanning tree • 8 packets required

6. Multicast Example

7. Internet Group Management Protocol (IGMP)互联网组管理协议 P622 • RFC 3376 • Host and router exchange of multicast group info • Defines two IGMP message types: • Membership Query 询问 ：sent by a multicast router • Membership Report报告: sent by a host IGMP is a group management protocol. It helps a multicast router create and update a list of loyal members related to each router interface.

8. 19.2 Routing Protocols p626 • In a simple internet, a fixed routing scheme is possible. • In more complex internets , dynamic cooperation is needed among the routers. • Routers exchange routing information using routing protocol

9. Autonomous Systems (AS)自治系统 • Set of routers and networks managed by single organization • Group of routers exchange information via acommon routing protocol • A connected network

10. Autonomous systems

11. Interior Router Protocol (IRP)Exterior Routing Protocol (ERP) • IRP(Interior Router Protocol,内部路由器协议) • Passes routing information between routers within AS • e.g. interior gateway protocol, IGP • ERP(exterior router protocol,外部路由器协议) • Routers need some info about networks outside their AS • e.g. exterior gateway protocol, EGP

12. Popular routing protocols

13. Approaches to Routing p627 • three approaches : distance-vector routing, link-state routing, and path-vector routing. • Distance-vector:距离向量路由选择 • Each node (router or host) exchange information with neighboring nodes in the same network • Node maintains vector of link costs for each directly attached network and distance and next-hop vectors for each destination • first generation routing algorithm for ARPANET • Used for RIP (Router information protocol)

14. Approaches to Routing – • Link-state :链路状态路由选择 • When router initialized, it determines link cost on each interface • Advertises set of link costs to all other routers in topology • Each router can construct topology of entire configuration • Router constructs routing table, listing first hop to each destination • Used in second generation routing algorithm for ARPANET • Used for OSPF (Open shortest path first)protocol

15. Approaches to Routing –– • Path-vector :路径向量路由选择 • Provide information about which networks can be reached by a given router and ASs crossed to get there • Does not includedistance or cost estimate • Each block of information lists all ASs visited on this route • Exterior Router Protocols

16. Path vector packets

17. Border Gateway Protocol (BGP) 边界网关协议 P629 • Preferred ERP for the Internet • BGP was designed to allow routers, called gateways in the standard, in different Ass to cooperate in the exchange of routing information.

18. BGP Messages 不可行 • Messages sent • Open • Update • Keep alive • Notification 撤销

19. BGP Messages • Router first Opens TCP connection to the neighbor • Then sends Open message • Includes hold time 保持时间 • 一方从另一方收到保活或更新报文前经过的最大秒数。 • 若路由器在此期间内未收到，认为对方不工作。 • Keep Alive message保活报文 • To tell other routers that this router is still here • Update message更新报文 • Info about single routes through internet • List of routes being withdrawn

20. BGP Messages • Notification Message通知报文 • Message header error • Open message error • Update message error • Hold time expired • Finite state machine error • Cease BGP uses the services of TCP on port 179.

21. Open Shortest Path First Protocol –OSPF 开放最短路径优先协议 p634 • IRP of Internet • Uses Link State Routing • Route computed on least cost based on user cost (Dijkstra algorithm) OSPF packets are encapsulated in IP datagrams.

22. Open Shortest Path First • Topology stored as directed graph • Vertices顶点or nodes 节点 • Router • Network • Transit 转送网络 • Stub 残桩网络 • Edges

23. Sample AS

24. Directed Graph of AS • Arcs (弧)are labeled with the cost • Arcs leading from networks to routers always have a cost of 0

25. SPF Treefor Router 6 SPF：Shortest Path First

26. Routing Table for R6

27. 19.3 Integrates Services Architecture ISA 综合服务体系结构 p637 • ISA, intend to provide QoS (quality of service) transport • Traffic on a network can be divided into two broad categories: • Elastic弹性通信量 • Can cope with wide changes in delay and/or throughput • FTP sensitive to throughput, E-Mail insensitive to delay • Network Management sensitive to delay • Web sensitive to delay • Inelastic 非弹性通信量 • Does not easily adapt to variations. E.g. real time traffic

28. Figure19.10 ISA implemented in Router 路由器中综合服务体系结构的实现 P642 预约协议 准许控制 路由选择协议 管理代理 路由选择数据库 通信量控制数据库 QoS排队 分类程序和路由选择 分组调度程序 尽最大努力排队

29. Token Bucket Traffic Specification令牌桶通信量规约 • Token replenishment（补给）rate R • Continually sustainable(可持续的） data rate • Bucket size B • Amount that data rate can exceed R for short period • During time period T amount of data sent can not exceed RT + B

30. Token Bucket Scheme令牌桶机制 令牌 生成器 令牌补充速率R 桶的大小为B bit 1.路由器以预定速率投放令牌 2.令牌可以累积到桶的大小，丢弃超出的令牌 4.路由器的队列调节器要求令牌的数量等于下一个分组的尺寸 3.通行量寻求网络的许可 5.如果令牌足够，分组排队输出 到达的分组 调节器 离开的分组 6.如果令牌不够，分组或者被标记为超出的，缓存等待稍后传输，或者被丢弃。

31. Resource Reservation Protocol: RSVP资源预约协议 P647 • RFC 2205 • To prevent congestion by allowing applications to reserve network resources at a given QoS • Unicast(单播) • If router can not meet request, application informed • Multicast (组播)is more demanding • May be reduced