Chapter Preview  In this chapter, we will study:  The basic components of a telecomm system  The technologies used in telecomm systems  Various ways to configure networks  Various ways that businesses use networks today

Telecommunications  The transmission of different forms of data (such as text, audio, video, images, graphics) from one set of electronic devices over media to another set of geographically separated electronic devices.

The Telecommunications System  The hardware and software that transmits information from one location to another  Components include:  Hardware  Media  Networks  Software  Data comm providers  Protocols  Applications

Telecommunication Signals  Analog signals  Continuous waves  Information conveyed by changing wave characteristics (amplitude and frequency)  Digital signals  Discrete pulses  Information conveyed in binary form (on or off pulses)  Easily understood by computer

Communication Processors  Hardware devices utilized in data transmission and reception  Modem - device that converts analog signals to digital (and vice versa); enables signal transmission over telephone system  Multiplexor - device that transmits multiple signals over single medium  Front-end processor – specialized computer dedicated to managing communication tasks

The Five Characteristics of Channels Characteristics Description Transmission rate Rate at which channel carries data from one computer to another. Volume or capacity of data that a channel can carry. Ways by which data are transmitted. Two ways include asynchronous (one byte at a time) and synchronous (blocks of bytes). Three directions for transmitting data include simplex, half duplex, and full duplex. Information travels as analog or digital signals. Bandwidth Transmission mode Transmission direction Transmission signals

Wire-based Communication Channels  Twisted-pair wire (telephone wire)  Cheap and easy to work with  Slow; subject to interference; low security  Coaxial cable  Carries more data; shielded from interference  More expensive; harder to work with; low security

Wire-based Communication Channels (continued)  Fiber-optic cable  Transmit information as light waves through glass fiber  Fast; high-capacity; secure; not subject to interference  Hard to work with

Wireless Communication Channels  Microwave  High capacity; inexpensive relative to wire  Requires line of sight transmission towers; subject to environmental interference  Satellite  Very high capacity; large coverage area  Expensive; propagation delay; requires encryption for security

Wireless Communication Channels (continued)  Radio  Suitable for short distance communication; inexpensive; easy to install; high speed  Interference problems; insecure  Cellular radio technology  Infrared

Understanding Communication Media  Transmission speed  Bandwidth – the range of frequencies available in a channel  More bandwidth, more channel capacity  Transmission mode  Character by character (asynchronous)  Streams of characters (synchronous)  Transmission accuracy  Accuracy controls added to messages  Error detection and correction required

Telecomm Carriers and Services  Telecomm carriers – provide telecomm technology and services for data communication  Common carriers – long-distance phone companies  Value-added carriers – provide private telecomm systems and services for a fee

Telecomm Carriers and Services (continued)  Telecomm services  Switched lines – transmission is routed along path to destination  Dedicated lines – continuous connection is established  Wide-area Telecomm Service (WATS) – lower cost long distance telephone service  Integrated Services Digital Network (ISDN) – high speed data transmission over existing phone lines  Digital Subscriber Lines (DSL) - high speed digital transmission over existing phone lines

Network Basics  Network – the communication devices, media, and software needed to connect two or more computer systems.  Local area networks (LANs) – a network that spans a relatively small geographic distance  Wide area networks (WANs) – network that spans a large geographic distance

Network Topology There are three popular network topologies: Bus topology Ring topology Star topology

Alternative LAN Topologies

Bus Topology  A network configuration in which all computers on the network are connected through a single circuit, such as twisted-pair cable. Messages are transmitted to all computers on the network, although only the targeted device responds to the message.

Ring Topology  A network configuration in which computers are arranged in the form of a ring using twisted-wire, coaxial cable, or fiber optics. Messages are transmitted in one direction to all devices between the sending node and the receiving node.

Star Topology  A topology in which a central host computer receives all messages and then forwards the message to the appropriate computer on the network.

Local Area Networks  Connect computers and other devices enabling resource sharing  Variety of topologies can be used, each with performance strengths and weaknesses  Several LANs can be connected via bridges  LANs can be connected to external networks via gateways