Chapter 9 Computer Networks

1. Chapter 9Computer Networks

2. Chapter 9Computer Networks Chapter Outline Network Topology Addressing and Routing Media Access Control Network Hardware OSI Network Layers TCP/IP Focus– Voice over IP Network Standards Focus- Ethernet Focus- Upgrading Network Capacity (Part II)

3. Chapter Goals • Compare and contrast bus, ring, and star network topologies • Describe packet routing across local and wide area networks • Describe the CSMA/CD media access control protocol • Describe network hardware devices, including network interface units, routers, and switches • Describe the OSI network model, the TCP/IP protocol suite, and IEEE network standards

4. Chapter 9Computer Networks

5. Network Topology • Spatial organization of network devices, physical routing of network cabling, and flow of messages from one network node to another • Can be physical or logical • Three types – star, bus, ring – differentiated by • Length and routing of network cable • Type of node connections • Data transfer performance • Susceptibility of network to failure

6. Point-to-Point Network Topology Impractical for all but very small networks

7. Point-to-Point Network Topology Impractical for all but very small networks

8. Point-to-Point Network Topology Impractical for all but very small networks

9. Advanced Network Topologies Improve practicality for most networks

10. Store and Forward System Centralizes the work of networking

11. Network Topologies

12. Star Topology Uses a central node to which all end nodes are connected Relatively simple wiring

13. Bus Topology Connects each end node to a common transmission line Low susceptibility to failure Relatively simple wiring

14. Ring Topology Connects each end node to two other end nodes Long maximum network length Susceptible to failure and difficulty in adding, removing, or moving nodes Low susceptibility to noise and distortion

15. Physical Star / Logical Bus Topology The strengths of two different topologies can be combined by using one topology for physical layout and another for message routing.

16. Addressing and Routing • How messages sent by end nodes find their way through transmission lines and central nodes to their ultimate destination • Local area networks (LANs) • Interconnected to form WANs • Wide area networks (WANs)

17. Local Area Network Routing • Each central node maintains and uses a routing table to make routing decisions • LAN hub or switch usually handles packet routing • Logical network topology determines exact procedure for routing a message between two end nodes in the same LAN

18. Example of a WAN • Includes • end nodes • LANs • zone • networks • backbone • network • central • nodes

19. LAN Central NodeRouting Decisions

20. Wide Area Network Routing • Packet routing uses a store and forward approach • Forwarding stations can be implemented using • Bridges • Routers • Switches

21. Media Access Control • Uses a protocol that specifies rules for accessing a shared transmission medium • Carrier Sense Multiple Access/Collision Detection (CSMA/CD) • Commonly used in bus networks to detect and recover from collisions • Token passing MAC protocol • Used by ring network topologies

22. CSMA/CD Protocol • Process • Listen and wait for an idle state • Transmit a packet • Listen for a collision • If a collision is detected • First wait for a random period of time • Then retransmit the same packet • Primary Advantage • Simplicity • Primary Disadvantage • Potentially inefficient use of data transfer capacity

23. Token Passing MAC Protocol • Token passes from node to node • in a predetermined order • includes all nodes on network • in a specified time interval • Only the node that “possesses” the token is allowed to transmit messages • All others can only receive and repeat messages • No longer used in LANs; rarely in WANs

24. Effect of CSMA/CD Protocol on Network Throughput

25. Network Hardware Devices

26. Network Interface Units(NIUs) • Interface between network node and network transmission medium • Scan destination address of all packets • In bus network • ignores packets not addressed to it • In ring network • retransmits all packets not addressed to it • Implement media access control functions

27. Hubs • Connect nodes to form a LAN • Most are Ethernet devices • Combine separate point-to-point connections between nodes and the hub into a single shared transmission medium by repeating all incoming packets to every connection point • Low-cost alternative for home and small office networks

28. Bridges • Connect two networks or network segments and copy packets between them • Look at source addresses and update internal tables of node addresses on each network segment • Common uses • Construct a virtual LAN from two separate LANs • Divide a network into segments in order to minimize congestion

29. Routers • Intelligently route and forward packets among two or more networks • Forward packets based on information other than destination address • Build internal “map” of the network • constantly scan the netework to monitor traffic patterns and network node changes

30. Switches • High-speed devices that create virtual LANs on a per-packet basis • Each input connection is treated as a separate LAN • Dramatically increase network performance • Connection decisions made by hardware are based only on destination address • Each virtual LAN has only one sending and one receiving node • eliminates congestion

31. OSI Network Layers Open System Interconnection (OSI) model • ISO conceptual model that divides network architecture into seven layers • Each layer uses services of layer below and is unaware of other layer’s implementations • Uses: • General model of networks • Framework for comparing networks • Architectural roadmap that enhances interoperability among network architectures and products

32. OSI Network Model

33. Application Layer • Network service request and response • Contains programs that make and respond to high-level requests for network services • End-user network utilities • Network services embedded in the OS • Network service providers

34. Presentation Layer • Converts and formats data • Ensures correct interpretation of transmitted data • Encryption and decryption • Compression and decompression • Converting data between EBCDIC and ASCII • Font substitution • Primarily used by applications that format data for user display

35. Session Layer • Negotiates and implements high-level protocol parameters • timeout • half or full duplex • synchronization • quality of service • Establishes and manages communication sessions • Monitors communication to detect and resolve problems that arise once protocol has been established

36. Transport Layer • Formats messages into packets suitable for transmission over the network • Places messages within a packet data area and adds header/trailer information (network addresses, error detection data, packet sequencing data) • Gives packets to network layer for delivery • Examines packets for errors; requests retransmission if necessary (when receiving packets)

37. Network Layer • Routes packets to their proper destination • Those within central node interact with one another to exchange routing information and update internal routing tables

38. Data Link Layer • Transmits packets and bits • Interface between network software and hardware

39. Physical Layer • Transmits bit streams • Where communication between devices actually takes place • Includes hardware devices that encode and decode bit streams and the transmission lines that transport them

40. OSI Network Model

41. TCP/IP • The core Internet protocol suite • Delivers most services associated with the Internet • File transfer via FTP • Remote login via Telnet protocol • Electronic mail distribution via SMTP • Access to Web pages via HTTP • Predates and corresponds poorly to OSI model

42. IPInternet Protocol • Provides connectionless packet transport across LANs and WANs • Translates datagrams into format suitable for transport by physical network • IP layer can divide datagram into smaller units and transmit them individually • Attaches header information to each unit, including its sequence in the datagram

43. IPInternet Protocol • Assumes datagram will traverse multiple networks via nodes called gateways • Determines transmission routes via related protocols (ICMP, RIP) • IP nodes • Identified by unique 32-bit address (nnn.nnn.nnn.nnn) • Periodically exchange routing information to keep tables current

44. Only the IP layer is implemented within the gateways

45. TCPTransmission Control Protocol • Provides connection-oriented packet transport to higher-level Internet service protocols, including HTTP, FTP, and Telnet • Provides framework to check for lost messages; explicitly establishes connection with intended recipient before transmitting messages • Performs connection management functions (verifying receipt, verifying data integrity, controlling message flow, securing message content)

46. TCPTransmission Control Protocol • Sender and recipient TCP layers maintain information about one another (message routes, errors encountered, transmission delays, status of ongoing data transfers) • Uses positive acknowledgment protocol to ensure data delivery • Establishes connections through a port and an socket

47. VoIPVoice over IP • Technologies/standards that carry voice messages and data over single packet-switched network • Lower cost than traditional public switched telephone network (PSTN) • Complex and competing standards • Transmission quality problems • packet loss • latency • jitter

48. H.323 is an umbrella for many component protocols

49. Network Standards • IEEE 802 standards • Describe network hardware, transmission media, transmission methods, and protocols • Help ensure compatibility among products from competing vendors • Developed by committees whose membership is drawn from industry, government, and academia • Ethernet standard (802.3) - very successful

50. IEEE 802Network Standards