Data Communications 1

The Basic Communication Model Sender Coder Channel Decoder Receiver 2

The Basic Communication Model Send Sender Coder Coder Channel Decoder Receiver The Basic Communication Model 3

Computer-based Data Communications Data communications definition: The movement of coded data and information from one point to another by means of electrical or electromagnetic devices, fiber-optical cables, or microwave signals. Also called teleprocessing, telecommunications, telecom, and datacom. 4

The Basic Data Communications Schematic Terminal Modem Channel Modem Computer 5

Basic Data Communications Schematic Terminal to Modem to Channel to Computer A modem is always required between a telephone and a digital computer. 6

Types of Networks (interconnected datacom devices) WAN (wide area network) Covers a large geographic area Includes a wide variety of circuits Usually includes host computers LAN (local area network) Limited area but could include 100 or so micros Facilitates office automation MAN (metropolitan area networks) spans one city/metropolitan area 7

Communications Network An Expanded Data Communications Network Visual display terminals Multiplexer Cluster control unit Modem Hard copy terminals Other types of terminals Channel Multiplexer Front-end processor Host computer Modem 8

Terminal Types Keyboard CRT - Cathode Ray Tube VDT - Video Display Terminal Hardcopy terminal Teleprinter terminal 9

Terminal Types (continued) Keyboard terminals Push-button telephone Point-of-Sale (POS) Data collection Special purpose 10

Other Data Communications Hardware Cluster control unit -- controls multiple terminals in an area Modem -- rated speed of bits per second determines transmission speed. Like a pipe determines water flow. Multiplexer -- allows multiple terminals to share a single channel. 11

Channel WAN channel components Local loop IXC circuit (interexchange) Typical circuitry Twisted pair (4 wires) Coax (buried) IXC circuit (interexchange) Microwave Fiber-optical cable 12

The Channel of a Wide Area Network Earth Satellite Local Earth loop User’s modem IXC circuit Local loop Earth station (interexchange channel) Earth station Telephone company central office Microwave tower IXC circuit (interexchange channel) Microwave tower Local loop Telephone company central office User’s modem Telephone company central office Telephone company central office 13

Front-end Processor Ports Serial versus parallel transmission Message switching, store and forward Host 14

The Front-end Processor Software Channel Interface Units Host Computer Interface Parallel transmission Serial To host transmission Secondary storage 15

Data Communications Software Host (telecommunications monitor or TCM) Front-end processor (network control program) 16

Telecommunications Monitor (TCM) Host Prioritize message 3 4 Security log 1 2 Maintain security log Interface with DBMS DBMS Primary storage status Backup and restart 17

Network Control Program (NCP) Poll terminals such as roll call polling Maintain a record of activity; date and time stamps Convert codes Editing such as error checking and reformatting Add and delete routing codes Maintain a history file of messages Maintain statistics on network use

Data Communications Links the General Systems Model Elements T = terminal Standards Information processor T Environment T Management T Input T Transformation T Output T

Basic Network Approaches Timesharing Distributed processing Client/server computing Clients are users, typically using workstations networked to form LANs Server is a mainframe, mini, or even a micro 20

Basic Network Approaches (continued) Complex software permits resource sharing Combines central computing (MIS, DP) with end-user computing 21

A Timesharing Network Legend: Computer Terminal 22

A Distributed Processing Network Legend: Central Distributed Computer Computer 23

Common Carriers Services Integrated services digital network (ISDN) Public-measured Private (a.k.a. leased or dedicated line) Integrated services digital network (ISDN) 24

ISDN- Integrated Services Digital Network Simultaneous multimedia transmissions Two types of channels B channel carries data D channel carries signals Data Signals 25

Two Standard Structures Basic access (typically residential) 2 B channels @ 64 kbps ea. 1 D channel @ 16 kbps Primary access (typically business) 23 B channels @ 64 kbps ea. 1 D channel @ 64 kbps 26

Local Area Networks File server, network server Peripherals Circuitry Owned by using firm Twisted pair is least expensive Coax handles videoconferencing Fiber-optics is most secure 27

LAN Software Novell (NetWare) and Microsoft (Windows NT) are leading vendors of LAN software Software allows servers and peer-to-peer connections

A Local Area Network Users Workstation 1 Manager 1 Letter Quality Printer Workstation 2 Network Server Secretary 1 Users Workstation 3 Plotter Secretary 2 Hard Disk Workstation 4 Manager 2 A Local Area Network 29

LAN Control Methodologies Contention-based (Ethernet) First-come, first-served Collisions occur when load is heavy Token-passing (IBMs Token Ring Network) Token -- set of data bits required to send a message 30

Highlights in MIS Mobile computing Wireless networks cellular wireless Lans wide-area wireless paging networks

A Network with Mobility Capability MU MU MU MU MU MU Fixed host MSS MSS Fixed network Fixed host Fixed host MSS MSS Fixed host MU MU MSS = mobile support station MU = mobile units MU MU MU MU

Network Management 1. Network planning 2. Network control Capacity planning Staff planning Performance monitoring 2. Network control 3. Network manager Staff Network analysts (a type of systems analyst) Software analysts (specialize in datacom software) Datacom technicians (specialize in hardware) LAN managers 33

The Intranet Intranet applications policy and procedure manuals Product and pricing information Employee information Job openings Documents needing signatures Schedules and calendars Access to databases Access to groupware

The Intranet (continued) Steps to a successful Intranet 1. Determine information needs 2. Establish Intranet policy 3. Build an Intranet staff 4. Provide for end user document preparation 5. Determine whether to outsource the Intranet service 6. Select the Intranet outsourcer 7. Provide datacom services 8. Build in Intranet security 9. Monitor system performance

Intranet Implementation Steps Yes No 1. Determine information needs 5. Outsource? 2. Establish Intranet policy 6. Select the Intra- net outsourcer 7. Provide datacom resources 3. Build an Intranet staff 8. Build in Intra- net security 4. Provide for end user document preparation 9. Monitor system performance