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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