Transmission Basics
Terminals and Workstations

Digital Transmission

•	Advantages over analog transmission
•	faster speeds
•	greater accuracy
•	improved error checking
•	more accurate storage and retrieval
•	Also -- merges telecommunications and computing

The Components of a Network

•	Terminals and workstations
•	Transmission links
•	Transmission methods -- protocols
•	Nodes and switches
•	Network architecture standards

Types of Networks

•	Two main distinctions:  geography and public v. private
•	Local Area Network (LAN)
•	Wide Area Private Network (WAN)
•	Public Voice Network
•	Public Data Networks (PDNs)
•	Value-added Networks (VANs)

Transmission Media

•	A wire, a fiber optic cable or a radio signal
•	Electromagnetic spectrum
•	Any message through any medium 

Bandwidth

•	Carrying capacity of a transmission link
•	Kilo, mega, giga and terahertz
•	Channels -- more than television
•	Satellites -- geosynchronous, geostationary, low-orbit, C-band, Ku-band, Ka-band, VSATs, footprints

Transmission Speeds

•	Usually stated as rates
•	Bits per second (bps) -- the standard measure
•	Kilobits per second (kbps) -- historically the most common
•	Megabits per second (mbps) -- T1s the industry standard for high speed, long distance data transmission
•	Gigabits per second (gbps) -- fiber optics:  SONET
•	Terabits per second (tbps) – coming soon to fiber near you

Terminals

•	Input/output devices
•	Single-purpose to multi-purpose
•	The PC: stand-alone processor to dumb terminal to intelligent workstation

Role of Terminals in a Network

•	Data Termination Equipment (DTE)
•	Data Circuit-terminating Equipment (DCE)
•	The Basis of Data Communications?
•	To Connect a DTE to a DCE

Examples of Terminals

•	Fax Machine
•	Personal Computer
•	Mini or Mainframe Computers
•	Automatic Teller Machine
•	Optical Character Reader
•	Telephone
•	Network Printer
•	Sensor/Alarm
•	Earth Station

Key Terminal Characteristics

•	Input Mode
•	Presentation Mode
•	Level of Intelligence
•	Data Rate/Speed of Operation
•	Communications Mode
•	Terminal Control Mechanism
•	Configuration in the Network
•	Degree of Mobility

Input Modes

•	Using a Mouse and/or Typing in Characters
•	Speaking or Pushing Buttons or a Touchscreen 
•	Scanning:
•	A barcode (point-of-sale register)
•	A document (facsimile or image storage)
•	Retinas or fingerprints

Presentation Modes

•	Video Display Terminal (VDT)
•	Scroll mode VDT
•	Page mode VDT
•	Forms mode VDT
•	Graphics mode VDT
•	Multiple Windows VDT
•	Teleprinter
•	Only if the printer is connected directly to the network
•	Connected to your computer doesn’t count

Terminal Intelligence

•	Dumb, smart, intelligent
•	Refers to the ability to 
•	Process or alter the information entered into the terminal or
•	Manipulate the information that is received by the terminal
•	Peer-to-Peer Processing vs. Slave/Host Processing

Communications Modes

•	Asynchronous Transmission
•	One character at a time with start/stop bits
•	Single parity check
•	Has the advantage of simplicity
•	Synchronous Transmission
•	Multiple characters in frames
•	Contains control and error detection info
•	More efficient for large amounts of info
•	Greater responsiveness at the same transmission rate

Control Mechanisms

•	Stand-alone Mode
•	More intelligence in the terminal
•	Faster response time
•	More expensive
•	Cluster-controlled Mode
•	Intelligence in the controller
•	Slower response time
•	Lower cost
•	Front-end Processors

Network Configurations

•	Point-to-Point Configuration
•	Terminal has direct link to the network
•	Better response time
•	More expensive
•	Multidrop Configuration
•	Terminals share a transmission line
•	Slower because of polling and contention
•	Lower cost

Mobility and Portability

•	Extend the Reach of a Network
•	Cellular Phones
•	Laptop computers
•	Personal Communications Devices
•	Low Earth Orbit Satellites

Trends in Terminals

•	Telephones -- more varied, more versatile, more services
•	VDTs -- more point of sale, more desktop issues
•	OCRs -- faxing is ubiquitous, barcode scanners dominating retail and freight
•	Teleprinters -- once common,now just for the hardcopy option
•	Mini and Mainframes -- regarded more and more as terminals due to enterprise networks

Terminal Selection Criteria

•	General vs. Special-purpose Features
•	Intelligence and Processing Capability
•	Type and Form of Output
•	User Capabilities and Limitations
•	Compatibility With Reach, Range and Responsiveness of the Platform
•	Cost

Terminal/Network Interfaces

•	Physical Connection Must Be Specified
•	Coding of Information and Data Flow Rules/Procedures Must Be Specified
•	Timing of the Information Flow Must Be Consistent and Coordinated

Telephone Interfaces

•	RJ-11 Jack Connector
•	Coding and Signaling Sequence
•	Produce ready signal (dial tone)
•	Dial destination number
•	Set up circuit path
•	Ring
•	Answer and complete connection
•	Exchange of information
•	Hang up
•	Disconnect circuit

Data Communications Interfaces

•	Parallel Transmission
•	Each bit in a byte sent simultaneously over its own wire -- 8, 16, or 32 bits
•	Advantage is speed
•	Limited distance -- 15 feet or less
•	Serial Transmission
•	Common interface for many years -- RS-232-C connector
•	Each of 25 pins had a specific function
•	Limited to a transmission rate of 20 kbps and a distance of about 15 meters
•	Universal Serial Bus (USB) has become standard on all computers
•	USB 1.0 – 1.5 Mbps, USB 1.1 – 12 Mbps
•	USB 2.0 – 480 Mbps maximum
•	Cable length about 15 ft.
•	IEEE 1394 – Apple Firewire, Sony iLink
•	1394a – 400 Mbps, 1394b – 800 Mbps
•	Has the potential to reach 3.2 Gbps
•	Ethernet – IEEE 802.3, RJ 45 connector
•	Transmission speeds – 10, 100 Mbps for LANs, Gbps for WANs

Types of DCEs

•	Modem -- Modulator/Demodulator
•	Converts digital to analog and vice versa
•	Channel Service Unit/Data Service Unit (CSU/DSU)
•	For use in end-to-end digital networks
•	Packet Assembler/Deassembler (PAD)
•	converts data and destination information into blocks called packets, reassembles data packets and strips destination and error checking bits

Virtual Terminal Service

•	Software Package is an Abstract Representation of a Terminal
•	Solves the Problem of Many Different Types of Terminals
•	Network Interface Unit (NIU)
•	Links a PC to a network
•	Accepts and buffers data from the PC
•	Addresses and transmits packets
•	Scans the network for packets
•	Transmits data from the PC to the network