Prepared by Natalie Rose 1 Network Lecture 6. Prepared by Natalie Rose2 Overview of Communication A...

Prepared by Natalie Rose 1

Network

Lecture 6


Overview of Communication

A Message (data and information) iscommunicated in the form of a signal via a transmission medium.


Data communicationsData communications: The transfer of digital : The transfer of digital data over a transmission medium.data over a transmission medium.

Components: sender, receiver, medium (“channel”), Components: sender, receiver, medium (“channel”), messagemessage


Network: This is a collection of computers and hardware connected for communications and using programs to provide the capabilities of sharing resources.

Basic Network Anatomy



A computer network is any system of two or more computers that are linked together.

How is networking important? People share computer hardware, thus reducing costs. People share data and software programs, thus increasing

efficiency and production. People work together in ways that are otherwise difficult or

impossible.


Basic Network AnatomyNetworks Near and Far In a local area network (LAN) computers are physically

close to each other, usually in the same building. Computers are linked within a building or

cluster of buildings. Each computer and peripheral is an individual

node on the network. Nodes are connected by cables, which may be

either twisted pair (copper wires) or coaxial cable.

In a wireless network each node has a tiny radio (or, less commonly, infrared) transmitter connected to its network port. Computers send and receive data through the air rather than through

cables.


Basic Network Anatomy A metropolitan area network (MAN) links two or more

LANs within a city. A wide area network (WAN) extends over a long distance.

Each networked LAN site is a node on the WAN. Data transmitted over common pathways called a backbone.


LAN vs WAN

Local area network (LAN): operates within a restricted geographic area such as within one building; usually owned by a single organization

Wide area network (WAN): operates over a large geographic area; usually includes computers owned by the network user and communications channels owned by someone else, such as a telephone company

LAN vs. WAN Comparison: LAN transmission speed is usually greater than WAN, and LAN usually has lower error rates than WANs, due to LAN’s shorter travel distance; LANs share more than data, e.g., peripherals, programs, processing power


LAN

All network users within an office building can connect to each other’s devices for fast communication. For example, A users in research and development could sent a document from her computer to be printed at a printer located in the desktop publishing center.


WAN

Wide Area Network are basic long-distance networks used by organisation and individuals around the world. The actual connection may be any combination of satellites, microwave, or cabling. When you make a long-distance telephone call you are using a WAN.


Basic Network Anatomy Communication frequently happens between LANs

and WANs Routers: hardware devices or software programs

that route messages as they travel between networks

Mesh networks: an alternative to today’s networks; rely on centralized routers

Used to set up small, temporary communication systems

Example: emergency personnel use at fire scenes to coordinate actions


Basic Network AnatomySpecialized Networks: From GPS to Financial Systems Global Positioning System (GPS)

GPS is a specialized network developed by U.S. Department of Defense.

It includes 24 satellites that circle the Earth. Each satellite contains a computer, an atomic clock, and a

radio. On the ground, a GPS receiver can use signals broadcast

by three or four visible satellites to determine its position.


Basic Network Anatomy Networks that keep our global financial systems running:

Automated Teller Machine (ATM): a specialized terminal linked to a bank’s main computer through a commercial banking network


Basic Network AnatomyThe Network Interface A network interface card (NIC) permits direct network

connection: Adds an additional serial port to the computer Controls the flow of data between the computer’s RAM and the network cable

The most common types of networks today require some kind of Ethernet card or port in each computer. Ethernet is a popular networking architecture developed in

1976 at Xerox. Most newer PCs include an Ethernet port on the main

circuit board, so they don’t require NICs to connect to Ethernet networks.


Basic Network AnatomyThe Modem

Modem: a hardware device that connects a computer’s serial port to a telephone line (for remote access)

May be internal on the system board or external, sitting in a box linked to a serial port

Modem transmission speed measured in bits per second (bps)

Transmit at 28,000 bps to 56.6K bps


Basic Network Anatomy Computers send digital signals. The modem (modulator/demodulator) converts the

digital signals to analog so that the message can be transmitted through telephone lines and converts it back on the other end.



Broadband connection—a connection with much greater bandwidth than modems have

DSL (Digital Subscriber Line) uses standard phone lines and is provided by phone companies in many areas.

Cable modems provide fast network connections through cable television networks in many areas.

High-speed wireless connections can connect computers to networks using radio waves rather than wires.

Satellite dishes can deliver fast computer network connections as well as television programs.


Basic Network AnatomyFiber Optic Connections

DSL and cable modems have nowhere near the bandwidth of the fiber optic cables that are replacing copper wires in the worldwide telephone network.

A fiber optic network can rapidly and reliably transmit masses of multimedia data at the same time that it’s handling voice messages.


Basic Network AnatomyWireless Network Technology

A lightning-fast network connection to your desktop is of little use if you’re away from your desk most of the time; when bandwidth is less important than mobility and portability, wireless technology can provide practical solutions.

The fastest growing wireless LAN technology is known as Wi-Fi or 802.11b.


Basic Network AnatomyBluetooth: another type of wireless technology

Named for a Danish king who overcame his country’s religious differences

Overcomes differences between mobile phones, handheld computers, and PCs, making it possible for all of these devices to communicate with each other regardless of operating system


Basic Network Anatomy With Bluetooth it’s possible to create a

personal area network (PAN)—a network that links a variety of personal electronic devices so they can communicate with each other.

Bluetooth technology is currently limited to simple device connectivity, but in the future it will open up all kinds of possibilities: A pacemaker senses a heart attack and notifies the

victim’smobile phone to dial 911.

A car radio communicates with parking-lot video camerasto find out where spaces are available.


Basic Network Anatomy More examples of Bluetooth possibilities:

A pen scans business cards and sends the information to a PDA inside a briefcase.

A medical wristband transmits an accident victim’s vital information to a doctor’s handheld computer.

A cell phone tells you about specials on clothes that are available in your size as you walk past stores in a mall.


Basic Network AnatomyCommunication Software

Protocol is a set of rules for the exchange of data between a terminal and a computer or between two computers.

Communication software establishes a protocol that is followed by the computer’s hardware.



Communication software takes many forms: Network operating system (NOS)

System handles communications among many workstations.

Client/server model One or more computers act as dedicated servers

and all the remaining computers act as clients. Peer-to-peer model

Every computer on the network is both client and server.

Many networks are hybrids, using features of theclient/server and peer-to-peer models.



A Home Computer Network

USB cable

DSL modem

Multiplayer games

Firewall/routerWireless laptop

Wireless access point


Types of Media

Twisted-Pair Coaxial Cable Fiber-Optic Cable Microwave Transmission Infrared


Transmission Media

Twisted-Pair Wire: most common medium, widely used by local phone companies; usually twisted-pair wires; relatively inexpensive but low-speed medium


Transmission Media

Coaxial cable: widely used for long-distance connections and in local area networks (LANs); faster data transmission than wire pairs because of greater bandwidth


Transmission Media

Optical fiber: This is the most secure medium. It is preferred in locations such as hospital operating rooms with extensive electrical equipment as well as a critical need for accurate data, because its laser light signals are not affected by electrical or magnetic interference.


Transmission Media

Microwave: both terrestrial and satellite systems use line-of-sight signals (transmitter and receiver must be in a straight line with no barriers between them); signals are subject to distortion by weather; many satellite systems are in geosynchronous orbit 22,000+ miles above the equator.


Transmission Media Satellites: Communication satellites are relay

stations that receive signal from one earth station and rebroadcast them to another.


Transmission Media

Infrared: line-of-sight signals being used in some wireless local area networks; security of transmission is an issue unless data is encrypted (scrambled).


Communications Hardware


Data Communication Hardware

Modem: Allows users to transmit digital data over analog medium.

Bridge: A device (usually a computer) used to connect two homogeneous networks, i.e., with the same protocols and topologies.

Gateway: A device used to connect two heterogeneous networks, i.e., with different protocols and topologies

Router: A device that makes decisions as to channel (route) that a message will take to its destination

Multiplexer: A device that can send several signals over a single line.


A Bridge


Gateway


Multiplexer


Network Topology

A topology is the physical or logical layout of the nodes in a network. There are different types of topology:

Star Bus Ring


Star Topology

Star: one central computer is connected by point-to-point channel to each of the other computers; failure of the central computer would shut down the entire network, although failure of one link affects only the one computer connected to the central computer


Bus Topology

All the computers are connected to a single cable with terminators at each end.


Ring Topology

Ring: uses point-to-point channels to connect ring repeaters in a loop; computers are connected to the ring repeaters. No terminators are required because there are no unconnected ends.


Intranet vs Extranet

Intranet: This is an Internal network that uses Internet technology for private business operations.

Extranet: uses Internet technology for business-to-business operations, in which one business has access to data located within another business’ intranet; parts of two business’ intranets may be linked


Basic Processing Strategies

Centralized processing: Decentralized processing Distributed processing:


Centralized Processing

Processing is performed in one computer or in a cluster of coupled computers in a single location. Centralized processing was the architecture that evolved from the very first computers; however, user access was via dumb terminals that performed none of the primary processing. Today, centralized computers use terminals that are mostly full-featured desktop computers.


Decentralized Processing

Computer systems in different locations. Although data may be transmitted between the computers periodically, it has limited daily communications.


Distributed Processing

Distributed is defined as data and programs are spread out over several locations, and computers share the workload.

Client/server system: This is a distributed system in which a server (usually a combination of special hardware and software) provides services to other computer(s) called clients; server and client may both be PCs, and one computer may be a server for some activities and a client for other activities. It also use of multiple computers networked throughout a wide geographical area, or the world via the Internet.


Strategic Network Issues

Planning and implementation network the following issues must include:

Throughput, i.e., how much data can be sent in a time period

Response time from user request to receipt of response

Consistency in speed and quality of service Reliability of network system to keep functioning Availability of network when needed


Strategic Network Issues

Security of data Flexibility when changes in network are

needed Backup/recovery provisions in case any

computers quit working Efficiency in use of resources without

unnecessary waste, such as in transmission time and storage space


Telecommunication and its Application

Video conferencing allows participants to conduct long-distance meeting for face-face while eliminating long-distance traveling cost.


Electronic Data Interchange (EDI)

Many organisation insist that their suppliers operate using EDI System. Often the EDI connect is made directly between the vendor and the customer. Alternatively, the link may be provided by a third-party clearinghouse which provides data conversion and other services for the participants.


Public Network Services Public Network

Services provide users with the lastest information required to remain competitive. For example, yahoo enables registered users to obtain up-to-minute stock quotes.

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Prepared by Natalie Rose 1 Network Lecture 6. Prepared by Natalie Rose2 Overview of Communication A...

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