William Stallings Data and Computer Communications 7th Edition

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

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3. 3 Multicasting Examples: Multimedia � video or audio transmission to group of people Teleconferencing Database � concurrent update Distributed computing � intermediate results sent to all participants Real time workgroups � groupwork

4. 4 Multicast Environments � LAN Environment LAN environment - simple Only one copy of the packet is transmitted Sending server does not need to know the location of all members Message is transmitted, and only those nodes that are members of the multicast group recognize the address and respond

5. 5 Mulitcast Environments � WAN Environment � More Difficult If sending server does not know the location of all members of the multicastgroup, the message is broadcast to each network in the configuration. The receiving network then transmits a single copy to the members of the LAN Again, only multicast group members respond If sender KNOWS location of all members of the multicast group Only send packets to those networks that contain members (Multiple Unicast) Both of these methods are not practical � both sends multiple copies, increasing congestion

6. 6 Solution: True Multicast Determine least cost path to each network that has host in group Gives spanning tree configuration of those networks containing multicast group members Sending server transmits a single packet along spanning tree Routers replicate packets at branch points of spanning tree

7. 7 Requirements for Multicasting (1) Need to identify a multicast address IPv4 � Class D address reserved for multicast � 1110 in high-order bit IPv6 � 8-bit prefix of all 1�s plus other control Each node (router or source participating in routing algorithm) must know names of networks that contain multicast members Router must translate between a WAN IP multicast address and a LAN multicast address

8. 8 Requirements for Multicasting (2) Mechanism required for hosts to join and leave a given multicast group dynamically (IGMP � discussed later) Routers must exchange info Which networks include members of a given multicast group? Need sufficient info to work out shortest path to each network containing group members Need a routing algorithm to calculate shortest path to all group members Routers must determine routing paths based on source and destination addresses

9. 9 Internet Group Management Protocol (IGMP) Used by hosts and routers to exchange of multicast group info over a LAN Supports two principle operations: Hosts send messages to subscribe and unsubscribe from a multicast group defined by a given multicast address Routers periodically check which multicast groups are of interest to which hosts

10. 10 IGMP v3 Allows hosts to specify muticast groups from which they want to receive traffic Traffic from other groups blocked at routers Allows hosts to block packets from sources that send unwanted traffic

11. 11 IGMP Message Format All IGMP messages are transmitted as IP datagrams Two types of messages Membership query Membership report

12. 12 Membership Query Query sent by multicast router SubTypes General query Learn which groups have members on attached network Group-specific query Learn if a particular group has any members on an attached network Group-and-source specific query Learn if any attached device wants packets sent to specified multicast address (From any of specified list of sources)

13. 13 IGMP Operation - Joining Host using IGMP wants to make itself known as group member to other hosts and routers on LAN IGMPv3 can signal group membership with filtering capabilities with respect to sources EXCLUDE mode � all group members except those listed INCLUDE mode � Only from group members listed To join group, host sends IGMP membership report message Address field multicast address of group Sent in IP datagram with Group Address field of IGMP message and Destination Address encapsulating IP header same Current members of group will receive learn of new member Routers listen to all IP multicast addresses to hear all reports

14. 14 IGMP Operation � Keeping Lists Valid Routers periodically issue IGMP general query message In datagram with all-hosts multicast address Hosts that wish to remain in groups must read datagrams with this all-hosts address Hosts respond with report message for each group to which it claims membership Router does not need to know every host in a group Needs to know at least one group member still active Each host in group sets timer with random delay Host that hears another claim membership cancels own report If timer expires, host sends report Only one member of each group reports to router

15. 15 IGMP Operation - Leaving Host leaves group, by sending leave group message to all-routers static multicast address Send membership report message with EXCLUDE option and null list of source addresses Router determines if there are any remaining group members using group-specific query message

16. 16 Group Membership with IPv6 IGMP defined for IPv4 Uses 32-bit addresses IPv6 internets need functionality IGMP functions incorporated into Internet Control Message Protocol version 6 (ICMPv6) ICMPv6 includes all of functionality of ICMPv4 and IGMP ICMPv6 includes group-membership query and group-membership report message Used in the same fashion as in IGMP

17. 17 Routing Protocols Routers receive and forward packets through the interconnected set of networks Each router makes routing decision based on knowledge of topology and traffic/delay conditions Attempts to avoid congestion and failure

18. 18 Autonomous Systems (AS) Group of routers managed by a single organization Exchange information via a common routing protocol (Interior Router Protocol � IRP) A connected network There is at least one path between any pair of nodes

19. 19 Interior Router Protocol (IRP) Shared routing protocol Passes routing information between routers within an AS May be more than one AS in internet Routing algorithms and tables may differ between different AS

20. 20 Exterior Router Protocol (ERP) Routers need some info about networks outside their AS ERP is to pass routing information between routers in different Ass ERP generally passes less info than an IRP. Only needs to figure out how to get the message from sending AS to receiving AS. AS responsible for getting the message to final destination

21. 21 Application of IRP and ERP

22. 22 Approaches to Routing Distance-Vector Routing Link-State Routing Path-Vector Routing

23. 23 Approaches to Routing � Distance-vector (IRP only) Each node (router or host) exchanges information with neighboring nodes Neighbors are adjacent nodes both directly connected to same network First generation routing algorithm for ARPANET Node maintains vector of link costs for each directly attached network and distance and next-hop vectors for each destination Used by Routing Information Protocol (RIP) Requires transmission of lots of information by each router Distance vector to all neighbors Contains estimated path cost to all networks in configuration Changes take long time to propagate

24. 24 Approaches to Routing � Link-state (IRP only) Designed to overcome drawbacks of distance-vector When router initialized, it determines link cost on each interface Advertises set of link costs to all other routers in topology Not just neighboring routers From then on, monitor link costs If significant change, router advertises new set of link costs Each router can construct topology of entire configuration Can calculate shortest path to each destination network Router constructs routing table, listing first hop to each destination Router does not use distributed routing algorithm Use any routing algorithm to determine shortest paths In practice, Dijkstra's algorithm Open shortest path first (OSPF) protocol uses link-state routing. Also second generation routing algorithm for ARPANET

25. 25 Approaches to Routing � Path Vector (ERP) Disregards routing metrics Provides information about which networks can be reached by a given router and ASs crossed to get there Does not include distance or cost estimate Each block of information lists all ASs visited on this route Enables router to perform policy routing E.g. avoid path leading to a particular AS May want to avoid or focus on certain AS�s for security reasons Better focus onlink speed, capacity, tendency to become congested, and overall quality of operation, security May want to minimize number of transit ASs

26. 26 Border Gateway Protocol (BGP) Designed for use with TCP/IP internets Preferred ERP of the Internet Functions as messages sent over TCP connections Open � create relationship with neighbor Update Keep alive � open and confirm a relationship Notification � error message Procedures Neighbor acquisition Neighbor reachability Network reachability

27. 27 Open Shortest Path First (1) OSPF Widely used IRP of Internet Replaced Routing Information Protocol (RIP) Uses Link State Routing Algorithm Each router keeps list of state of local links to network Transmits update state info Little traffic as messages are small and not sent often Route computed on least cost based on user cost metric

28. 28 Integrated Services Architecture (ISA) Suite of standards developed by IETF Intended to provide QoS transport over IP-based networks

29. 29 Internet Traffic � Classified as Elastic or Inelastic Elastic Can adjust to wide changes in delay and/or throughput Traditional type of traffic for which internets were designed Elastic applications: FTP SMTP Telnet SNMP HTTP Inelastic Does not easily adapt to variations e.g. real time traffic

30. 30 Requirements for Inelastic Traffic Minimum required throughput Minimal delay Minimal jitter Delay variation Minimal packet loss Require preferential treatment for certain types of traffic Require elastic traffic to be supported as well

31. 31 Integrated Services Architecture (ISA) Approach to Handling Internet Traffic Provide QoS support Congestion controlled by Routing algorithms Packet discard Associate each packet with a flow � distinguishable stream of related IP packets that results from a single user activity and requires the same QoS Can be unidirectional Can be multicast

32. 32 How do you Identify a member of a Flow? Typically, an IP packet is identified as a member on the basis of source and destination IP addresses and port numbers, and protocol type

33. 33 ISA�s congestion control and QoS Admission Control � if routers determine there are insufficient resources to handle required QOS, the flow is not admitted Routing Algorithm � routing based on more than minimum delay � may also select routes based on QoS Queuing Discipline � Queuing based on flow requirements � not FIFO Discard Policy � drops select packets when buffers are full

34. 34 ISA Services Guaranteed � most demanding service Assured data rate Upper bound on queuing delay No queuing loss Real time playback Controlled load Approximates behavior to best efforts on unloaded network No specific upper bound on queuing delay Very high delivery success Best Effort

35. 35 Queuing Discipline Traditionally FIFO, but not with ISA because: No special treatment for high priority flow packets Large packet can hold up smaller packets Greedy connection can crowd out less greedy connection Fair queuing � ISA method Queue maintained at each output port Packet placed in queue for its flow Round robin servicing Skip empty queues Can have weighted fair queuing

36. 36 Resource Reservation Protocol: RSVP Provides supporting functionality for ISA Prevents congestion by allowing applications to reserve network resources at a given QoS Useful for both unicast and multicast transmissions

37. 37 Soft State When route changes, the resource reservations must be changed. Soft State -Set of state info in router that expires unless refreshed If a route for a given transmission changes, some soft states will expire and new resource reservation will invoke the appropriate soft states on the the new routers

38. 38 RSVP Characteristics Unicast and Multicast reservations � adapt dynamically to changing membership, routes, and reserving resources Simplex � RSVP makes reservations for unidirectional data flow. If two ends need to send and receive, need to simplex reservations Receiver initiates and maintains resource reservation for the flow RSVP maintains soft state at intermediate routers and end users are responsible for maintaining the reservations Provide different reservation styles Transparent operation through non-RSVP routers � they rely on best effort Support for IPv4 and IPv6

39. 39 Differentiated Services Alternative to ISA and RSVP (both overhead intensive) Provide simple, easy to implement, low overhead tool to support range of network services differentiated on basis of performance IP Packets labeled for differing QoS using existing IPv4 Type of Service or IPv6 Traffic class Service level agreement established between provider and customer prior to use of DS Built in aggregation Good scaling to larger networks and loads Implemented by queuing and forwarding based on DS octet No state info on packet flows stored

40. 40 Differentiated Services (DS) As the Internet and its applications grow, there is immediate need to provide differing levels of QoS to different traffic flows DS provides a simple, easy-to-implement, low-overhead tool to do this, differentiated on performance Most widely accepted QoS method in enterprise networks Establish a Service Level Agreement (SLA) service provider and customer prior to use of the DS Each DS is classified. Identical classifications are treated the same � provides good scaling to larger networks and traffic loads

41. 41 SLA Parameters Detailed service performance Expected throughput Drop probability Latency Constraints on ingress and egress points Traffic profiles Disposition of traffic in excess of profile

42. 42 Example Services Level A - low latency Level B - low loss Level C - 90% of traffic < 50ms latency Level D - 95% in profile traffic delivered Level E - allotted twice bandwidth of level F traffic Traffic with drop precedence X higher probability of delivery than that of Y

43. 43 Required Reading Stallings chapter 19 Comer, S. Internetworking with TCP/IP, volume 1, Prentice-Hall All RFCs mentioned plus any others connected with these topics Loads of Web sites on TCP/IP, routing protocols etc.

44. 44 Chapter 19 � Review Questions What is multicasting? Provide examples of its use. Discuss the required functions for multicasting Explain why multicast within a WAN is difficult than multicasting within a LAN. What is the purpose of the Internet Group Management Protocol (IGMP)? Describe how it works. Discuss how IGMP memberships are maintained. Discuss the purpose of a routing protocol.

45. 45 Chapter 19 � Review Questions (cont.) Discuss the concept of Autonomous System (AS). What is its relation to an Interior Router Protocol (IRP); an Exterior Router Protocol (ERP)? Compare and contrast the following types of Internet routing: distance-vector routing, link-state routing, and path-vector routing. Discuss the function of the Border Gateway Protocol (BGP) Discuss the function of Open Shortest Path First (OSPF) Compare and contrast the following categories of Internet Traffic: Elastic and Inelastic. What is a flow? How do you identify a member of a flow? Describe ISA�s method of congestion control and QoS Describe ISA�s method of fair queuing, as opposed to FIFO What is Soft State? How does this relate to RSVP? Compare and contrast ISA, RSVP, and Differentiated Services. What is a Service Level Agreement (SLA)? Discuss its potential parameters.