1 California State University, Fullerton Chapter 6 Information System Networks and the Internet

2 California State University, Fullerton Communications Hardware Two main types of communications hardware Communications channel – the link over which data is transmitted Communications processors – provide processing capabilities between the computer and the communications channel

3 California State University, Fullerton Communications Hardware Communications channel characteristics Data is transmitted over the channel as bits. Each bit is sent one after the other. Bits are grouped to form bytes that represent characters using ASCII, EBCDIC, Unicode or some other code.

4 California State University, Fullerton Communications Hardware (cont’d.) The way in which bits are sent determines two main characteristics of the channel Signal type Data rate

5 California State University, Fullerton Signal Type Bits can be sent either as An Analog signal – data is transmitted by a wave pattern that varies continuously A Digital signal – data is transmitted as a series of high and low pulses The human voice is analog Telephones are analog Computers are digital

6 California State University, Fullerton Data Rate Data rate is measured as bits per second (bps). Bandwidth also describes how much data can be transmitted over a channel in a given period of time.

7 California State University, Fullerton Data Rate (cont’d.) Baud rate refers to the maximum number of changes that can occur per second in the state of a communication channel (changes in a communication signal). The data transmition rate for a communication channel is equal to the baud rate for that channel times the number of bits that can be sent with each change in the state of that communication channel.

8 California State University, Fullerton Data Rate Broadband: refers to an analog communications method that splits an analog communication channel in to multiple communication channels.

9 California State University, Fullerton Data Rate Broadband ISDN (B-ISDN): Refers to a digital communication method that split a digital phone line in to multiple communication channel. Basic Rate ISDN (BRI) provide 2 channels each with capacity. Primary Rate ISDN (PRI): provide 23 channels with bps capacity. ISDN: Is an acronym for Integrated Services Digital Network.

10 California State University, Fullerton Types of Communications Channel Media Wire cables – sometimes called “copper cables” have been used since the 1800s. Two main forms Twisted-pair wiring Coaxial cable

11 California State University, Fullerton Communications Channel Media (cont’d.) Twisted-pair wiring Two insulated copper wires twisted together Most telephone lines are twisted-pair Can also be used for data Data transmission rate is slow compared to other media

12 California State University, Fullerton Communications Channel Media (cont’d.) Coaxial cable Copper wire insulated with rubber and plastic. Used with cable television systems. Data transmission rate is faster than twisted-pair, and more expensive, but slower than other media.

13 California State University, Fullerton Communications Channel Media (cont’d.) Fiber-optic cables Bundles of glass or plastic fibers. Each fiber is 1/2000 inch thick – about the size of a human hair. Data is transmitted by a laser that pulses light through the fiber. Data transmission rate is very fast.

14 California State University, Fullerton Communications Channel Media (cont’d.) Microwave (wireless) Special types of radio signals sent from one microwave antenna to another. Transmission is line-of-sight, i.e, one antenna must be able to “see” the other. Two types Land based – antenna approximately 30 miles apart. Satellite – positioned 22,300 miles in space – geosynchronous orbit.

15 California State University, Fullerton Communications Channel Media (cont’d.) Other wireless media Infrared spectrum Very short distances Relatively slow

16 California State University, Fullerton Communications Processors I. Channel interface devices II. Communications control units III. Protocols converter devices IV. Communications security devices

17 California State University, Fullerton I. Channel Interface Devices Modems – convert digital signals to analog signals at the origin and reverse the process at the destination of the signal. Digital to analog is MOdulation. Analog to digital is DEModulation. Modems may be either internal or external to the computer.

18 California State University, Fullerton I. Channel Interface Devices (cont’d.) Modem data rates are typically 33 Kbps to 56 Kbps. Cable modems (cable Adaptors) – are devices to provide the interface between a computer and a cable system’s data transmission capability. For ISDN or Digital Subscriber Line (DSL) digital modems (terminal adapters) is required.

19 California State University, Fullerton II. Communication Control Units Multiplexer – combines signals from several slow-speed devices to transmit over a high speed channel. Front-End Processor – is a computer that sits between the channel and the main computer (host computer) and is dedicated to performing communication functions.

20 California State University, Fullerton III. Communications Protocols Protocols, settings, standards, or parameters are the rules that must be followed when computers communicate with one another to avoid errors. Computers that wish to communicate and have different protocols must use a code converter and protocol converter to standardize their communication. Code conversion (conversion among ASCII, EBCIDIC, & unicode) Protocol conversion

21 California State University, Fullerton IV. Communications Security A problem with data communications is the lack of security over a communications channel. One way of solving this problem is to use data encryption to convert the data to an unintelligible form for transmission and to return it to an intelligible form at the destination. Decryption (decoding) requires a key. Asymmetric key cryptolography: Public key (for encription) & private key (for decription)

22 California State University, Fullerton Communications Software Communications software is required to control communications between computers. It receives data from communications processors connected to the channel and passes the data to other software in the computer for processing.

23 California State University, Fullerton Communications Software (cont’d.) Types of communications software Multi-user processing environment Terminal emulators Telecommunications monitor

24 California State University, Fullerton Communications Software (cont’d.) Client server processing environment requires Network Operationg System (NOS) which establishes and maintains the communication between the nodes (workstations and the file server) File server software Client software (workstation software) – as used in client/server computing Light client (Web browser) Heavy client (Traditional client programs that where proprietary, expensive to maintain)

25 California State University, Fullerton Network Topologies Star network – each node is connected to a central node. Hierarchical network – organized like a family tree. Each computer communicate with other computers through a common node. Bus network – each node is connected to a single communication channel. Ring network – each node is connected to a common channel forming a loop.

26 California State University, Fullerton Types of Networks Local Area Network (LAN) Wide Area Network (WAN) Metropolitan Area Network (MAN) Internetwork – connected networks

27 California State University, Fullerton Local Area Networks Local Area Network Structure Connection Topology Star, ring, Hierarchical, Bus, Hybrid Communications channel wired and Wire less Require Network Interface Cards (NIC) in each device on the network Permits sharing of resources Protocol is Usually either Ethernet (carrier sense multiple access with collision detection (CSM,CD)), Token Ring (token passing) or Polling.

28 California State University, Fullerton Wide Area Networks Connection Topology. Star, Hierarchical, or hybrid Communications channel. Any Type of media because of they use common carriers or telecommunications companies (packet switching, circuit switching, and frame relay). Permits sharing of resources. Can include a Virtual Private Network (VPN).

29 California State University, Fullerton Internet It is a public international network Grew slowly at first and “exploded” in 1993 with the adoption of the Hyper Text Markup Language (HTML) standards for the World Wide Web (WWW). Two protocols Transmission Control Protocol (TCP) Internet Protocol (IP) Most users require a relationship with an Internet Service Provider (ISP).

30 California State University, Fullerton Intranets and Extranets An Intranet is an Internet like network but access is restricted to within a business or organization. Firewalls are used to control access to an Intranet. An Extranet permits controlled outside access to an Intranet like network.

31 California State University, Fullerton Hardware and Software Requires the business have a web site. The web software runs on a web server which has special e-commerce software.