Chapter 3

• Telecommunications


  Electronic transmission of signals for communications
• Telecommunications medium


  Any material substance that carries an electronic signal to support communications between a sending and receiving device
• Networking protocol


  Set of rules, algorithms, messages, and other mechanisms that enable software and hardware in networked devices to communicate effectively
• Synchronous communications


  Receiver gets message instantaneously (Phone calls)
• Asynchronous communications


  Receiver gets message after some delay (walkie-talkie, email, sms)
• Simplex channel


  Transmits data in only one direction (radio)
• Half-duplex channel


  Transmits data in either direction, but not simultaneously
• Full-duplex channel


  Permits data transmission in both directions at the same time
• Channel bandwidth


  Rate at which data is exchanged
• Circuit switching network


  Sets up a circuit between the sender and receiver before any communications can occur (initially developed for voice communications)

  Connection oriented
• Packet switching network


  No fixed path is created between the communicating devices (initially developed for data communications)

  Connectionless

  Routes data packets from source to destination
• Telecommunications media categories

  • Guided transmission media
  • Wireless
• Guided transmission media types

  • Twisted-pair wire
  • Coaxial cable
  • Fiber-optic cable
• Twisted-pair wire


  Classified by category: category 2, 3, 5, 5E, and 6
• Coaxial cable


  Offers cleaner and crisper data transmission (less noise) than twisted-pair wire
• Fiber-optic cable


  Transmits signals with light beams
• Wireless communications options

  • Radio(WIFI)
  • Microwave
  • Infrared frequencies
• Near field communication (NFC)


  Newer than RFID, short-range wireless connectivity technology designed for cell phones and credit cards(such as Visa PayWave)
• Bluetooth


  Wireless communications specification that describes how cell phones, computers, personal digital assistants, etc., can be interconnected
• Ultra wideband (UWB)


  Short-range communications that employs extremely short electromagnetic pulses lasting just 50 to 1,000 picoseconds(ground probing radar, automotive radar, sensors)
• Infrared transmission


  Sends signals at a frequency of 300 GHz and above
• Zigbee


  Form of wireless communications frequently used in security systems and heating and cooling control systems
• Wi-Fi

  Wireless telecommunications technology brand owned by the Wi-Fi Alliance
• Wireless access point


  Consists of a transmitter with an antenna

  receives the signal and decodes it
• Wi-Fi access points


  Have maximum range of about 300 feet outdoors and 100 feet within a dry-walled building
• Microwave transmission


  High-frequency (300 MHz–300 GHz) signal sent through the air
• Common forms of satellite communications

  • Geostationary satellite
  • Low-earth orbit (LEO) satellite
  • Very small aperture terminal (VSAT)
• Wireless mesh


  Uses multiple Wi-Fi access points to link a series of interconnected local area networks
• 3G wireless communications


  Support wireless voice and broadband speed data communications in a mobile environment
• 4G wireless communications


  Will provide increased data transmission rates in the 20–40 Mbps range
• Worldwide Interoperability for Microwave Access (WiMAX)


  Set of IEEE 802.16 wireless metropolitan area network standards
• Computer network


  Consists of communications media, devices, and software needed to connect two or more computer systems or deviceC

  can transmit and receive information to improve organizational effectiveness and efficiency
• Network types

  • Personal area networks
  • Local area networks
  • Metropolitan area networks
  • Wide area networks
• Centralized processing


  All processing occurs in a single location or facility
• Decentralized processing


  Processing devices are placed at various remote locations (independent)
• Distributed processing


  Processing devices are placed at remote locations but are connected to each other via a network (a decision maker decides where to process)
• File server systems


  Users can share data through file server computing
• Client/server architecture


  Multiple computer platforms are dedicated to special functions
• Client


  Any computer that sends messages requesting services from the servers on the network
• Database server


  Sends only the data that satisfies a specific query, not the entire file