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Chapter 9

Computer Networks

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Chapter Topics

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

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OSI Network Layers

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OSI Network Layers

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.

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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.

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OSI Network Layers

Physical Layer – the layer at which communication between devices actually takes place.

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Mathieson’s Three Layers

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Chapter Topics

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

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Network Topology

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

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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.

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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.

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Network Topology

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Network Topology

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

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Network Topology

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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.

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Network Topology

Physical Topology Star Bus Ring

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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.

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Network Topology

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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.

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Network Topology

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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.

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Network Topology

Ring Topology

Disadvantages: Susceptibility to failure and difficulty adding , deleting and moving nodes.

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Network Topology

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Network Topology

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Network Topology

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Chapter Topics

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

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Media Access Control

Definition of a Collision Methods for dealing with Collisions Carrier Sense Multiple Access with Collision

Detection Token Passing

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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

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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.

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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.

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Media Access Control

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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.

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Chapter Topics

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

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Addressing and Routing

Definition of a Local Area Network Definition of a Wide Area Network Local Area Network Routing Wide Area Network Routing

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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.

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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.

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Addressing and Routing

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Addressing and Routing

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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

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Chapter Topics

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

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Network Hardware

Network Hardware Devices: Network interface units or network interface

cards Hub Bridges Routers Switches

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Network Hardware

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Technology Focus

Home Networks

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TCP/IP

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Chapter Topics

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

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Network Standards

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

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Network Standards

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Technology Focus - Ethernet

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Technology Focus - Ethernet

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Windows Commands

ipconfig ipconfig /all net statistics workstation net use net view

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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.

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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.

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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.