3/20: Telecommunications & Networking

• What is telecommunications?

• The hardware: physical components of telecommunications, inc. channels

• Standards: agreements on how to connect & communicate

• Network Topologies

Defining Telecommunications• Communicating information via electronic

means over some distance

• Information Superhighway:– National / worldwide high

speed digital telecommunications accessible by general public

Elements of Telecommunications• Computers

• Terminals (input / output devices)

• Communications channels

• Processors (modems; Multiplexers; Front-end processors)

• Communications software

Communication Channels

The means by which data are transmitted.

• Twisted wires (copper wires)

• Coaxial cable: (insulated copper wires)

• Fiber-optic cable

• Wireless channels– Microwaves– Pagers, cell phones,

mobile data networks

Channels: Fiber-Optics• Super clear glass strands• Fast, light, durable• Billions of bits per second• Expensive, harder to install• Often used as backbone of networks

Channels: Microwaves• Building-to-building

• Earth-to-satellite

UPLINKUPLINK

MICROWAVE MICROWAVE TRANSMISSIONTRANSMISSION

DOWNLINKDOWNLINK

Channels: Other Wireless Channels• PAGING SYSTEM: Pager receives short

messages

• CELLULAR TELEPHONE: Uses radio waves to reach antennas within areas called cells

• MOBILE DATA NETWORKS: Radio-based data network using hand-held computers; cheap, efficient

Channels: Other Wireless Channels• PERSONAL COMMUNICATION SERVICE:

Cellular; lower power; higher frequency. Smaller phones not shielded by buildings, tunnels

• PERSONAL DIGITAL ASSISTANT: Handheld digital communicator

• SMART PHONE: Wireless, voice, text, Internet

Comparing Channels• Transmission speed: bits/second (BPS) or baud

• Bandwidth: capacity of channel; Difference between highest & lowest frequencies

MediumMedium SpeedSpeed CostCost Twisted wireTwisted wire 300 bps - 10 mbps300 bps - 10 mbps LowLow

Land MicrowaveLand Microwave 256 kbps - 100 mbps256 kbps - 100 mbps

SatelliteSatellite 256 kbps - 100 mbps256 kbps - 100 mbps

Coaxial cableCoaxial cable 56 kbps - 200 mbps56 kbps - 200 mbps

Fiber opticsFiber optics 500 kbps - 10 gbps500 kbps - 10 gbps HighHigh

Standards: Protocols

• Rules & procedures to govern transmission between components in a network

• Analog vs. Digital

• TCP/IP

Standards: Analog vs. DigitalRecall:• Analog signals

– Continuous waveform– Passes thru system– Voice communications

• Digital signals– Discrete waveform– Two discrete states: on / off pulse– Data communication– Uses modem to translate analog to digital, digital to

analog

Standards: TCP/IP• Transmission Control Protocol / Internet

Protocol

• Developed by Department of Defense in 1972

1. TRANSMISSION CONTROL PROTOCOL (TCP): Breaks data into datagrams

2. INTERNET PROTOCOL (IP): Breaks, sends datagrams as smaller IP packets; can repeat transmission to increase reliability

Standards: OSI

• Open System Interconnect

• International reference model for linking different types of computers & networks

Standards: Connectivity• Measure of ability of computing devices to pass

& share information without human intervention

• OPEN SYSTEMS: Software able to function on different computer platforms. Nonproprietary operating systems, applications, protocols

Network Topologies: Star• Topology: Layout

HOSTHOST

USERUSER

USERUSER

USERUSER USERUSER

Network Topologies: Bus

USERUSER

USERUSER

USERUSER

USERUSER

USERUSER

USERUSER

Network Topologies: Token Ring

USERUSER

USERUSER

USERUSER

USERUSER

Local Networks• PRIVATE BRANCH EXCHANGE (PBX)

– firm’s central switching system

• LOCAL AREA NETWORK (LAN) – dedicated channels– limited distance (less than 2000 foot radius)– higher capacity than PBX– Can share expensive

hardware & software

Local Networks: LAN• GATEWAY: Connection to other networks

• ROUTER: Forwards data to other networks

• NETWORK OPERATING SYSTEM (NOS): Manages file server; routes communications on network

• PEER - TO - PEER: In some small networks all computers have equal power

Wide-Area Networks: WANs• A LAN that spans large geographic distances.

• Can include cable, satellite, microwave

• SWITCHED LINES: Route determined by current traffic

• DEDICATED LINES: Constantly available for high-volume traffic

Next Time: More on Telecom• VANs

• Network Services– DSL, ISDN, Cable Modems, T1 lines, etc.– Which to use?

• X.25 and ATM

• E-Commerce & E-Business technologies

• EDI: Electronic Data Interchange

• Email – available services, etiquette