1 Chapter 9 Computer Networks

2 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

3 OSI Network Layers

4 Presentation Layer – ensures that data transmitted by one network node is correctly interpreted by the other network node. Session Layer – establishes and manages communication sessions.

5 OSI Network Layers Transport Layer – formats messages into packets suitable for transmission over the network. Network Layer – routes packet to their proper destination. Data Link Layer – interface between network software and hardware.

6 OSI Network Layers Physical Layer – the layer at which communication between devices actually takes place.

7 Mathieson’s Three Layers

8 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

9 Network Topology Definition of Network Topology Point-to-Point transmission Shared Connections Store and Forward Physical Topology (star, bus, ring) Logical Topology

10 Network Topology Network topology refers to: The spatial organization of network devices. The physical routing of network cabling. The flow of message from one network node to another.

11 Network Topology Point-to-Point transmission – the line is laid over the shortest path and connected directly to both nodes. Used for small networks. Shared connections – smaller shared links are connected to larger shared links. Used for larger networks.

12 Network Topology

13 Network Topology Store and Forward - interconnected system of end nodes and transfer points used to route data among end nodes.

14 Network Topology

15 Network Topology Physical topology – refers to the physical placement of cables and device connections to those cables. Logical topology – refers to the path that messages traverse as they travel from node to node.

16 Network Topology Physical Topology Star Bus Ring

17 Network Topology Star Topology Uses a central node to which all other nodes are connected. The central node can be a transfer point. Advantage: simple wiring. Disadvantage: the failure of the hub disables the entire network.

18 Network Topology

19 Network Topology Bus Topology Connects each node to a common transmission line. Transmitted messages travel from a node across the common transmission line. Advantage: simple wiring and low susceptibility to failure.

20 Network Topology

21 Network Topology Ring Topology Connects each network node to two other nodes and the entire network forms a closed loop. Advantages: long maximum network length and low susceptibility to noise and distortion.

22 Network Topology Ring Topology Disadvantages: Susceptibility to failure and difficulty adding, deleting and moving nodes.

23 Network Topology

24 Network Topology

25 Network Topology

26 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

27 Media Access Control Definition of a Collision Methods for dealing with Collisions Carrier Sense Multiple Access with Collision Detection Token Passing

28 Media Access Control Collision – noise or interference in a message. Methods for dealing with collisions: Carrier Sense Multiple Access/Collision Detection (CSMA/CD) Token Passing

29 Media Access Control Carrier Sense Multiple Access/Collision Detection – (Commonly used on bus network topologies) A node that wants to transmit listens (carrier sense) until no traffic is detected. The node then transmits its message.

30 Media Access Control Carrier Sense Multiple Access/Collision Detection – The node listens during and immediately after its transmission. If abnormally high signal levels are heard, which is a collision detection, then the node ceases transmission. If a collision is detected, the node waits for a random time interval and then retransmits its message.

31 Media Access Control

32 Media Access Control Token Passing Used in ring network topologies. A token is passed from node to node. Only the node with the token can pass a message. Advantage: simplicity. Disadvantage: inefficient use of data transfer capacity.

33 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

34 Addressing and Routing Definition of a Local Area Network Definition of a Wide Area Network Local Area Network Routing Wide Area Network Routing

35 Addressing and Routing Local Area Network – a network covering a floor or building. Wide Area Network – a network a network that spans large physical distances, such as multiple buildings, cities, regions, or continents.

36 Addressing and Routing Local Area Network Routing Each time a node is started, it sends a message announcing its presence and its address to the nearest hub. Each hub maintains a table of addresses and transmission lines or connections ports and uses that table to make routing decisions.

37 Addressing and Routing

38 Addressing and Routing

39 Addressing and Routing Wide Area Network Routing Each router knows: The addresses and physical locations of its own nodes Other nearby routers Groups of addresses that they control Default destination for messages to the addresses that it does not know

40 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

41 Network Hardware Network Hardware Devices: Network interface units or network interface cards Hub Bridges Routers Switches

42 Network Hardware

43 Technology Focus Home Networks

44 TCP/IP

45 Chapter Topics OSI network layers Network Topology Media access control Addressing and routing Network hardware Network standards

46 Network Standards The Institute of Electrical and Electronic Engineers (IEEE) has drafted a number of telecommunication and network standards – IEEE 803 standards.

47 Network Standards

48 Technology Focus - Ethernet

49 Technology Focus - Ethernet

50 Windows Commands ipconfig ipconfig /all net statistics workstation net use net view

51 Summary Network topology refers to the spatial organization of network devices, the physical routing of network cabling and the flow of messages from one network node to another. LANs are interconnected to form WANs.

52 Summary A media access control (MAC) protocol specifies rules for accessing a shared transmission medium. Network hardware devices include NIUs, hubs, bridges, routers, and switches.

53 Summary The Open Systems Interconnection (OSI) model is an ISO conceptual model that divides network architecture into seven layers. TCP/IP is the core Internet protocol suite. The IEEE 802 standards cover many types of networks.