1. CIS460 – NETWORK ANALYSIS AND DESIGN CHAPTER 12 Optimizing Your Network Design

2. Introduction –Optimization is a critical design step for organizations that use high-bandwidth and delay sensitive applications –We are going to look at IP multicast techniques that minimize bandwidth utilization for multimedia applications –Then we are cover methods for optimizing network performance to meet QoS requirements

3. Optimizing Bandwidth Usage with IP Multicast Technologies –High-bandwidth multiple-user multimedia distance learning, videoconferencing and collaborative computing –Old way - send a data stream to every user –Alternative - use a single stream and use a broadcast destination address Disadvantages - goes to all devices –Multicast - single data stream only stations that request

4. IP Multicast Addressing Transmits IP data to a group of hosts that are identified by a single Class-D IP address Can also be identified by a MAC-layer multicast address. Optimizes network performance since it allows NICs to ignore data streams

5. The Internet Group Management Protocol –Allows a host to join a group and inform routers of the need to receive a particular data stream –Host transmits a membership-report message –Multicast router sends an IGMP query out every port periodically –To lessen bandwidth host sets a random timer to reply to IGMP query –IGMPv2 - recognizes when last host has left a group

6. Multicast Routing Protocols Extend the capabilities of a standard routing protocol to include: –learning paths to destination networks to include multicast destination addresses

7. Multicast Open Shortest Path First –Complements OSPFs capability to develop a link-state database to include l8ink-state record for group memberships –Router running MOSPF computes shortest-path tree within its area Then prunes the branches of the tree that do not lead to group members Optimized for an autonomous system that has a limited number of groups Learns areas and not whole network - inefficient

8. Protocol-Independent Multicast Works in tandem with IGMP and other unicast protocol such as OSPF PIM has two modes dense and sparse –Dense - have many members –Sparse - smaller group of employees

9. Dense-Mode PIM Similar to an older dense -mode protocol (Distance Vector Multicast Routing Protocol (DVMRP) Uses a reverse path forwarding mechanism to compute shortest path When a multicast packet is received from a source to a group it determines if it needs it Uses prune messages to be deleted from paths

10. Spares-Mode PIM Sets up a rendezvous point to provide registration services for a multicast group Hosts join by sending a membership report, depart by sending a leave message A designated router tracks these messages and periodically sends join and prune messages to rendezvous point

11. Optimizing Network Performance to Meet Quality of Service Requirements Two types –Controlled-load service provides a client data flow with a QoS closely approximating the QoS that the flow would receive on an unloaded network –Guaranteed service provides firm bounds on end-to-end packet queuing delays. Guaranteed for applications that need it

12. IP Precedence and Type of service Specifies both precedence and type of service –Precedence - helps router determine which packets to send when several packets are queued –Type of service helps router select a routing path when multiple paths are available Type-of-service byte - 3 bit precedence and 4 bit type-of-service

13. IP Precedence Field Specify importance of packet Congestion control 0-5 are used for applications and user data –5 is typically set for Voice over IP and other real-time applications

14. IP Type-of-Service Field Select a route using route characteristics –Delay bit - minimize delay (Telnet, Rlogin, Voice and video) –Throughput bit - maximize throughput (file transfer) –Reliability bit - maximize reliability (fault- tolerance path) –Cost bit - minimize monetary cost Can only select one

15. Resource Reservation Protocol Alternative to IP type-of-service and precedence capabilities in the IP header Supports more sophisticated mechanisms for QoS requirements for individual traffic flow Deploy on LANs and intranets to support multimedia applications QoS signaling protocols for delivering QoS requirements on a network

16. Resource Reservation Protocol (Cont’d) Setup protocol not a routing protocol Receiver responsible for requesting level of service Provides a general facility for creating and maintaining information on resource reservations More suited for private intranets than the Internet or other public networks

17. Common Open Policy Service Protocol Understands actual services and policies regarding the service Defines a simple client/server model for supporting policy control with QoS signaling protocols A policy server is a policy-decision point and the client is a policy-enforcement point

18. IEEE 802.1 Specification Specifies mechanisms in bridges to expedite the delivery of time-critical traffic Limits the extent of high-bandwidth multicast traffic

19. IP Version 6 Enhances the capability of hosts and routers to implement varying levels of QoS for different traffic flows A source host assigns a flow label to each application flow. The router maintains a cache of flow information indexed by source address and flow label Header includes a 4-bit priority field

20. Real-Time Protocol Used by multimedia applications Provides end-to-end network transport functions suitable for transmitting real-time data Usually runs on top of User Datagram Protocol (UDP) Relies on lower layer services to deliver QoS

21. CISCO Internetworking OS Features for Optimizing Networking Performance Ranges from proxy services which allow delegating of specialized tasks to a router or switch to advanced switching and queuing services to improve throughput and offer QoS functionality

22. Proxy Services –Allows a router to act as a surrogate for the service that is not available locally –Support a router performing tasks beyond its typical duties to minimize delay and bandwidth usage –Can convert a frame type to a new type that causes less traffic –Improve performance for applications that are time sensitive

23. Switching Techniques Router switches switch packets from incoming interfaces to outgoing interfaces Speed router can do this is a major factor in determining network performance In general should use fastest switching available

24. Classic Methods for Layer-3 Packet Switching Process switching is the slowest of the switching methods –Processor interrupted to process packet information –Fast switching uses an entry in the fast-switch cache –Autonomous switching uses an autonomous switching cache

25. Classic Methods for Layer-3 Packet Switching (Cont’d) –Silicon switching speeds up autonomous switching by using silicon switching cache –Optimum switching is faster due to an enhanced caching algorithm and the optimized structured of the cache –Distributed switching supports very fast throughput because the switching process occurs on the interface card

26. NetFlow Switching New switching that is optimized for environments where services must be applied to packets to implement security, QoS features, and traffic accounting Identifies traffic flows and then quickly switches packets in the flows when it applies services

27. Cisco Express Forwarding Technique for switching packets very quickly across large backbones networks and the Internet Evolved to accommodate Web-based applications and other interactive applications that are characterized by session of short duration to multiple destinations addresses

28. Tag Switching –Optimizes packet-switching through a network of tag switches –A tag switch is a router or switch that supports tag switching –Tagging the first packet of information will expedite following packets –Three major components Tag Edge routers, Tag switches and the Tag Distribution Protocol

29. Queuing Services Allows a network device to handle an overflow of traffic using queuing methods First In, First Out Priority Queuing Custom Queuing Weighted fair queuing

30. First In, First Out Queuing Basic store and forward functionality Stores when network is congested and forwards them in order Provides no QoS functionality

31. Priority Queuing Ensures that important traffic is processed first Designed to give strict priority to a critical application Is appropriate where WAN links are congested from time to time Has four queues: high, medium, normal and low

32. Custom Queuing Designed to allow a network to be shared among applications with different minimum bandwidth or latency requirements Assigns different amounts of queue space to different protocols and handles the queues in round-robin order

33. Weighted Fair Queuing Sophisticated set of algorithms designed to reduce delay variability and provide predictable throughput and response time for traffic flows Goal is to offer uniform service to light and heavy network users alike Recognizes an interactive application and schedules that traffic to the front of the queue

34. Weighted Fair Queuing (Cont’d) Adapts automatically to changing network traffic conditions and requires little or no configuration Can allocate bandwidth based on precedence

35. Random Early Detection A new class of congestion-avoidance algorithm Monitors traffic loads at points in a network and randomly discards packets if congestion begins to increase Source nodes detect dropped traffic and slow their transmission rate Uses a randomization process

36. Weighted Random Early Detection Combines the capabilities of standard RED algorithm with IP precedence Provides preferential traffic handling for higher-priority packets Selectively discards lower priority traffic

37. Traffic Shaping Allows management and control of network traffic to avoid bottlenecks and meet QoS requirements Avoids congestion by reducing outbound traffic for a flow to a configured bit rate while queuing bursts to that rate Configured on a per-interface basis

38. Committed Access Rate Supports specifying policies regarding how traffic that exceeds a certain bandwidth allocation should be handled Looks at received traffic, compares it to a configured maximum and takes action based on the result

39. Cisco WAN Switching Optimization Techniques Techniques to dynamically allocate bandwidth where it is needed and avoids using bandwidth unnecessarily and prioritize, manage, and control bandwidth usage –Voice Activity Detection –Prioritization and Traffic Management on Wan Switches

40. Voice Activity Detection Saves bandwidth by generating data only when someone is speaking Voice conversations tend to be 60 percent silent so VAD is an effective way to dynamically free up bandwidth Test default setting for VAD to ensure they are appropriate for the network and users

41. Prioritization and Traffic Management on WAN Switches WAN switch features: –Advanced Class of Service (CoS) management - provides dedicated queues and queuing algorithms for the different sub-classes of serviced defined in a network –Optimized Bandwidth Management - an implementation of version 4.0 of the ATM Forum Traffic Management Specification that enables a switch to continually monitor trunk utilization

42. Prioritization and Traffic Management on WAN Switches (Cont’d) Automatic Routing Management provides end-to-end connection management services via a source-based routing algorithm –selects a route based on network topology, class of service, trunk loading and relative distance to the destination

43. Summary Optimization provides the high bandwidth, low delay, and controlled jitter required by many critical business applications Multimedia and other applications that are sensitive to network congestion and delay can inform routers in the network of their QoS requirements using both in-band and out of band methods