Wireless Revolution

Ch 7 Connectivity, The Wireless Revolution, and Communications

Competencies

Discuss connectivity, the wireless revolution, and    communications.

Describe physical and wireless communications channels.

Describe conventional modems, T1, DSL, cable modem, and satellite connections.

Discuss bandwidths and protocols.

Discuss networks and network architectures.

Describe local area, metropolitan area, and wide area networks.

Introduction

• Communications has extended our uses for the microcomputer.
• Communication systems are the electronic systems that transmit data over communications lines from one location to another.
• You can set up a network in your home or apartment using existing telephone lines.
• Competent end users need to understand the concept of connectivity, the impact of the wireless revolution, and the elements of a communications system.
• They must also understand the basics of communications channels, connection devices, data transmission, networks, network architectures, and network types.

Connectivity, The Wireless Revolution, and Communication

     Systems

• Computer communications is the process of sharing data, programs, and information between two or more computers.
• Connectivity is a concept related to using computer networks to link people and resources
• Mobile telephone and Bluetooth are technologies of wireless revolution.
• Communication systems transmit data.

Connectivity

• Connectivity is a concept related to using computer networks to link people and resources
• You can use telephone or other telecommunication lines to link to nearly any computer in the world.

The Wireless Revolution

• The single most dramatic change in connectivity and communications in the past five years has been the widespread use of mobile or wireless telephones.
• In 2002, it was estimated that there are over 600 million mobile telephones in use worldwide, and by 2004, almost 1.5 billion.
• This wireless technology allows individuals to stay connected with one another from almost anywhere at any time.
• Originally developed for voice, the wireless revolution can transmit nearly any kind of information.
• Bluetooth: a technology that allows wide variety of nearby devices to communicate with one other without any physical connection.

Communications systems

• Communications systems are electronic systems that transmit data from one location to another. It has four basic elements:

Sending and receiving devices

• Often a computer or specialized communications device. They send as well as accept messages in form of data, information, and/or instructions.

Communication channel (aka transmission medium)

• The actual connection that carries the message
• Can be a physical wire, or cable or a wireless connection

Connection device (aka communications device)

• Act as an interface between the sending and receiving devices and the communication channel.  They convert outgoing messages into a form and format (digital) so that they can travel across the communication channel, and back again at the receiving (incoming) end.

Data transmission specifications

• The rules and procedures that coordinate the sending and receiving devices by precisely defining how the message will be sent across the communication channel.

 

Check Figure 7-3 page # 171.

Communication Channels

Communication channels actually carry the data from one computer to another. There are two categories: Physical connections and Wireless connections.

Physical Connections: use a solid medium to connect sending and receiving devices. They include:

Telephone lines

• Typically use twisted pair cables, made up of hundreds of copper wires covered with an insulating jacket
• Relatively inexpensive way to connect devices
• Now being phased out by more technically advanced and reliable media

Coaxial cable

• A high frequency transmission cable, replacing multiple lines of twisted pair cable with one single, solid copper core.
• Can carry 80 times the capacity of one twisted pair cable.
• Used to carry television signals as well as connect computers in a network.

Fiber-optic cable

• Transmit data as a pulse of light through tiny tubes of glass
• Has over 26,000 times the capacity as one twisted pair cable and faster than copper cable
• Fiber optic cables are rapidly replacing twisted pair telephone wires
• They are very thin (almost half the diameter of human hair) and have limited distance to carry information.
• They are more secure as they are immune to electrical interference, are lighter and less expensive than coaxial cable and more reliable.

Wireless Connections: do not use a solid medium to connect sending and receiving devices and rather use air itself. They include:

Microwave

• Use high-frequency radio waves to communicate
• Known as a “line of sight communication” as radio waves travel in straight line.
• As the rays cannot bend with earth’s curvature, they can be transmitted only short distances like between buildings in a city.
• For long distances, the waves must be relayed by means of “dishes” or antennas installed on towers, high buildings.
• Bluetooth uses microwaves to transmit data over short distances of up to 33 feet approximately.

Satellite

• Uses satellites orbiting up to 22,000 miles above the earth as microwave relay stations.
• Satellite’s rotates at precise point and speeds above the earth making them appear stationary so they can amplify and relay signals between transmitters on earth.
• Uplink is sending data to a satellite
• Downlink is receiving data from a satellite
• They can send large volumes of data but bad weather can sometimes interrupt flow of data.

Connection Devices

• A great deal of communication takes place over telephone lines
• Since telephone was used for voice, the technology typically used analog signals to transmit calls
• Computers use digital signals or on/off binary signals
• To connect computers via telephone lines, a system was needed to transmit data from digital to analog to digital again.  Modems were created to do this.

Modems

• Modem is an acronym meaning “modulator – demodulator”
• Modulation converts a digital signal to an analog signal
• Demodulation converts an analog signal back to digital
• Speed at which modems communicate is measured in bits per second (bps).
• Typically modem speeds are 33.6 and 56 kbps (kilo bits per second)

External modem

• Modem circuitry housed in a separate case outside the computer
• Connected to computer using a serial port, and to telephone using a phone wire and an RJ-11 jack

Internal modem

• Consist of a plug-in circuit board inside the computer
• Connects to telephone wall jack using a phone wire

PC Card modem

• Serves as an “external modem” for a portable computer (laptop)
• Credit card sized expansion board to connect a laptop computer to a telephone line

Wireless modem

• Very similar to external modem connecting to the computers serial port. But unlike external modem it does not connect with a cable.

Types of Connections

• Standard telephone lines and modems are called dial-up services which is very slow
• Large organizations use higher speed connections such as T1, T2, T3, and T4 lines.
• These all support digital communications, so they don’t use modems but do require special equipment.
• They tend to be expensive, but can transmit data at high speeds, e.g. 1.5 Mbps (1,500 kbps) almost 26 times faster than standard dial up service

Digital Subscriber Line (DSL)

• Uses existing telephone lines to provide high speed connections

Cable modems

• Uses existing telephone lines to provide high speed connections as fast as T1 or DSL at lower cost.

Satellite/air connection services

• Uses satellite and air to download and upload data at rate seven times faster than dial-up connections
• Another competitor for high speed Internet services, often offered in areas where Cable or DSL is not available

Data Transmission

• Several factors affect how data is transmitted across a communication medium, including:

Bandwidth: measurement of the capacity of the communication channel – how much information can move across the communication channel in a given amount of time. To transmit text documents, a slow bandwidth is acceptable but for video and audio a wider bandwidth is required.

Voice band (aka low bandwidth)

• Used for standard telephone connections
• Microcomputers with standard modems and dial-up service use this bandwidth.
• Typical speed is 56 to 96 kbps
• Good for transmitting text documents but too slow for other types like high-quality video.

Medium band

• Bandwidth used in special leased lines to connect minicomputers and main frames as well as transmitting data over long distances
• Typically used by businesses and not individuals

Broadband

• Used for high-capacity transmissions
• Microcomputers with DSL, cable, or satellite connections use this
• Speeds are typically 1.5 Mbps, but can go higher

Protocols: for data transmission to be successful, sender and receiver must follow a set of communication rules for exchange of information.

• Protocols are the rules for exchanging data across a network
• A standard for the Internet is the TCP/IP protocol – Transmission Control Protocol / Internet Protocol
• Essential features of TCP/IP is for identifying the sending and receiving devices, and reformatting the data so it can be sent via the Internet

Identification

• Every computer on the Internet has an IP address (Internet Protocol address).  This is a numeric address such as 198.45.19.151 which is difficult for people to remember and use.
• A Domain Name Server (DNS) converts a text based address, e.g. http://www.McGraw-Hill.com into the IP address 198.45.19.151

Reformatting

• Information sent or transmitted across the Internet usually travels through numerous interconnected networks.
• The data is broken into a series of “packets” and sent separately over the Internet.
• At the receiving end, these packets are reassembled into the correct order, and the transmission is complete

Networks

• A computer network is a communication system that connects two or more computers in different arrangements so that they can exchange information and share resources.

Terms

Node

• Any device connected to a network; a printer, a PC, storage device, etc.

Client

• A node that requests and uses resources available from other nodes

Server

• A node that shares resources with other nodes
• Dedicated servers include application servers, communication servers, database servers, file servers, printer servers or web servers

Hub

• The center or central node for other nodes
• It may be a server or a central connection point

Network Interface Card (NIC)

• An adapter card for connecting a node to a network

Network Operating System (NOS)

• Controls and coordinates the activities of all computers and other devices on a network

Distributed Processing

• A system in which computing power is located and shared at different locations

Host Computer

• A large, centralized computer, usually a minicomputer or a main frame

Network Manager

• A computer specialist, also known as a network administrator, responsible for maintaining the network operations

Network Types

Communication networks differ in geographical size.

Local Area Networks (LANs)

• Networks with nodes that are in a close physical proximity
• Linked by cable – telephone, coaxial, or fiber-optic – LANS often use a bus form of organization.
• Typically LANs span distances less than a mile and are owned and operated by individual organizations
• LANs offer two primary benefits: economy and flexibility – users can share key resources such as printers and data storage
• Network gateways allow users on a LAN to connect to other networks with different configurations
• Network bridges allow users on a LAN to connect to other users on a different LAN, e.g.
• The most common standard for connecting nodes is the Ethernet standard.

Metropolitan Area Networks (MANs)

• The next step up from a LAN
• Span distances of up to 100 miles
• Frequently used as links between office buildings located throughout a city

Wide Area Networks (WANs)

• Country wide and world wide networks
• Span distances greater than 100 miles
• Use microwave relays and satellites to reach users over long distances
• Internet is the widest of all WANs

Network Architecture

• Network architecture describes how a network is arranged and how resources are coordinated and shared.

Configurations

• Topology: the arrangement of a network – four principal network topologies include the star, bus, ring, and hierarchical topology
• Star Network:
• a number of small computers or peripherals are linked to a central unit.  Central unit is called a network hub and it can be a file server or host computer. 
• Communication control is maintained by polling in which each connecting device is asked whether it has a message to send and allowed to send its message in turn.
• It provides a time-sharing system where several users can share resources on a central computer.
• It is common to link several microcomputers to a mainframe in an organization to access its database.
• Bus Network:
• also known as Ethernet
• each device on the network handles its own communications control.  There is no host computer. 
• All communications travel along a connecting cable called a bus or backbone and as the information passes along the bus, it is examined by each device to see if that is intended for it.
• Typically used when only a few computers are to be linked together
• Bus network is not as efficient as star network for sharing resources but it is less expensive.
• Ring Network:
• each device is connected to two other devices, forming a ring.  There is no central server. 
• Messages are passed around the ring until they reach the correct destination.
• It’s used to link mainframe computers rather than microcomputers.
• Often used in distributed data processing systems since the computers can perform processing tasks at their own locations and also share data and other resources (tape drives, printers, etc.)
• Hierarchical network (aka hybrid network)
• consists of several computers linked to a central host, just like star network, but they also might serve as smaller hubs to other computers.
• Often used in centralized office systems, where departmental microcomputers share a server, and these servers are tied to a mainframe.

Strategies

• A network strategy is the way of coordinating the sharing of information and resources.
• Common network strategies are terminal, client server, and peer-to-peer systems
• Terminal network system:
• processing power is centralized on one large computer usually a mainframe. 
• Nodes are typically terminals (dumb terminals with just input – keyboard and output – monitor but no processing capabilities) or microcomputers with terminal emulators (allowing them to act like a terminal). 
• Star and hierarchical networks are typical configurations with UNIX as the operating system.
• Many airline reservations systems use this approach. 
• An advantage is the centralized control of the system.  The disadvantage is the lack of control and flexibility for the end user.  These are slowly being phased out.
• Client server network systems:
• Use one computer to coordinate and supply services to other nodes on the network.
• the server coordinates and supplies the specialized services, the clients will request the services. 
• Commonly used network operating systems are Novell’s Netware, Microsoft’s Windows NT.
• One advantage of this system is its ability to handle very large networks efficiently. This strategy is used very much on Internet and when you connect to a Website, your computer is a client and the Web site’s computer is the server.
• Another advantage is the powerful network management software that monitor’s and controls the network’s activities.
• The major disadvantage is the cost of installation and maintenance.
• Peer-to-peer network system:
• nodes have equal authority to act as both clients and servers. 
• A typical configuration is the bus network.
• Commonly used network operating systems are Novell’s Netware, Microsoft’s Windows NT.
• The advantages are the network is easy to install and inexpensive and work well for smaller systems with fewer than 10 nodes.
• The disadvantage is that the performance of network declines as the number of nodes increases.
• Another disadvantage is the lack of powerful management software to effectively monitor network’s activities.
• Gnutella is a widely used peer-to-peer network for Internet music sharing.  These are easy to install, but can have performance problems in very large networks.

Organizational Internets: Intranets and Extranets

• Networks have grown in complexity over time.
• One approach to managing them is to apply Internet technologies to support communications between organizations using intranets and extranets.

Intranets

• An intranet is a private network that resembles the Internet
• Intranets use browsers, web sites, and web pages, but the access is restricted to those users within the organization
• They are commonly used to provide information to the employees, such as job openings, human resource information, etc.

Extranets

• An extranet is a private network that resembles the Internet, but it connects more than one organization
• A company may set one up to link key suppliers and customers of the organization

Firewalls

• A firewall is a security system that is designed to protect the organizations network against external threats.
• Firewalls consist of both hardware and software to block access to those people who shouldn’t connect with an Intranet or Extranet.
• Proxy servers act as a gateway to block IP traffic between the organizations network and the Internet.  The proxy server looks at the addresses of all messages, and decides whether to let them pass or not.