Telecommunications

1. Technology Guide 4 Telecommunications

2. Hardware Communications media Communications networks Communications processors Communications software Data communications providers Communication protocols Communications applications Telecommunication System Atelecommunication system is a collection of compatible hardware and software arranged to communicate information from one location to another. The major components include;

3. Telecommunication System (cont.)

4. Analog signals are continuous waves that “carry” information by altering the amplitudeand frequencyof the waves. Digital signals are discrete on-off pulses that convey information in terms of 1s and 0s, just like the central processing unit in computers. Electronic Signals Telecommunications media can carry two basic types of signals;

5. Communication Processors • Modulationrefers to the conversion from digital to analog and the reverse is demodulation. • The device that performs these two processes is called a modem. • Modems are always used in pairs. • The unit at the sending end converts digital information into analog signals for transmission over analog lines; • At the receiving end, another modem converts the analog signal back into digital signals for the receiving computer.

6. Communication Processors (cont.) • Two main alternatives to analog modems are: • Digital subscriber line (DSL) • Cable modem • A multiplexor is an electronic device that allows a single communications channel (e.g, a telephone circuit) to carry data transmissions simultaneously from many sources. • A front-end processoris a specialized computer that manages all routing communications with peripheral devices.

7. Communications Media • Communications media (channels) refer to the physical pathway or medium for which data is communicated from one location to another. • There are two categories: • Wireline • Wireless

8. Wireline Twisted pair wire Coaxial cable Fiber optic cable Wireless Cellular radio Microwave transmission Satellite transmission Global positioning system Radio & Infrared light Wireline vs. Wireless Media

9. Mobile computing refers to the use of portable computer devices in multiple locations. Personal communication service (PCS) uses lower-power, higher frequency radio waves than cellular technology. As a result, PCS cells are smaller, more numerous and closer together. Personal digital assistants (PDAs) are small, pen-based, hand-held computers capable of digital communications transmission. Bluetoothis a relatively new technology that allows wireless communication between mobile phones, laptops, and other portable devices. Wireless Technologies

10. Transmission Speed • Bandwidth refers to the range of frequencies that can be sent over a communications channel. • Abaud is a detectable change in a signal (i.e., a change from a positive to a negative voltage in a wire). • Baud rate refers to the rate at which signals can be transmitted through a communications channel. • Channel capacity is usually divided into three bandwidths: • Narrowband (e.g., telegraph lines) • Voiceband (e.g., telephone) • Broadband(e.g., microwave, cable, and fiber-optic media)

11. Transmission Direction • Simplex data transmission uses one circuit in one direction only—similar to a doorbell, a public announcement system, or broadcast television and radio. • Half-duplex transmission also uses only one circuit, but it is used in both directions—one direction at a time. • Full-duplex transmission uses two circuits for communications—one for each direction simultaneously. • e.g, a common telephone

12. Transmission Mode & Accuracy • Data transmissions may be either asynchronous or synchronous; • Asynchronous - only one character is transmitted or received at a time. • Synchronous - a group of characters is sent over a communications link in a continuous bit stream while data transfer is controlled by a timing signal initiated by the sending device. • Because the loss of even one bit could alter a character or control code, data transmission requires accuracy controls. • These controls consist of bits calledparity bits.

13. Protocol • Protocolrefers to the set of rules and procedures governing transmission across a network. • The simplest protocol ispolling, where a master device polls, or contacts, each node. • In the token passing approach, a small data packet, called a token, is sent around the network. • In another approach called contention a device that wants to send a message checks the communications medium to see if it is in use. • The Transmission Control Protocol/Internet Protocol (TCP/IP) is a protocol for sending information across sometimes-unreliable networks.

14. Communication Standards The major types of standards are; • Networking standards • Transmission standards • Software standards

15. Networking Standards • One or more protocols define precisely how software programs on different systems interact to accomplish the functions for each layer. • The Open Systems Interconnection (OSI)model has seven layers, each having its own well-defined function: Layer 1:Physical layerLayer 5: Session layer Layer 2: Data link layerLayer 6: Presentation layer Layer 3: Network layerLayer 7: Application layer Layer 4: Transport layer

16. Transmission Standards • A number of network bandwidth boosters address the need for greater bandwidth on networks for advanced computing applications. • These include: • FDDI (fiber distributed data interface) • ATM (asynchronous transfer mode) • LAN switches • ISDN (integrated services digital network)

17. An interface is a physical connection between two communications devices. Parallel data transfer Serial data transfer The topology of a network is the physical layout and connectivity of a network. Ring topology Bus topology Star network Interface & Topology

18. Local area networks (LAN) Gateway, bridge, router Network Interface Cards Private branch exchange (PBX) Wide area networks (WAN) Value-added Network (VAN) Packet Switching Frame relay Virtual private network (VPN) Network Size There are two general network sizes:

19. Centralized Architecture • Centralized computer systems are centered around a large computer, known as the host, that provides computational power and internal storage. • Several devices that lack self-contained computer processors, such as “dumb” terminals and printers, are connected to the host. • Although mainframes have represented the dominant centralized form of computing for over 30 years, minicomputers, workstations, and powerful PCs are challenging that dominance.

20. Non-centralized Computing • Non-centralized computing architectures are decentralized or distributed. • Decentralized computing breaks centralized computing into functionally equivalent parts, with each part essentially a smaller, centralized subsystem. • Distributed computing breaks centralized computing into many computers that may not be (and usually are not) functionally equivalent.

21. Client/Server Architecture • The basic structure of client/server architecture is a client device(s) and a server device(s) that are distinguishable, but interact with each other. • In a client/server approach, the components of an application are distributed over the enterprise rather than being centrally controlled. • There are three application components that can be distributed: • the presentation component • the applications (or processing) logic • the data management component

22. Client/Server Architecture (cont.) There are five models of client/server implementation; • Distributed presentation • Remote presentation • Distributed function • Remote data management • Distributed data management

23. Peer-to-Peer Network Architecture • A peer-to-peer network architecture allows two or more computers to pool their resources together. • There are several advantages of peer-to-peer architecture:: • There is no need for a network administrator. • The network is fast and inexpensive to set up and maintain. • Each computer can make backup copies of its files to other computers for security. • It is the easiest network to build.

24. Open Systems • Open systems provide flexibility in implementing IT solutions, optimization of computing effectiveness, and the ability to provide new levels of integrated functionality to meet user demands. • Connectivityis the ability of the various computer resources to communicate with each other through network devices without human intervention. • Open systems and connectivity have enabled networks to completely span organizations.

25. Enterprise Networking • Portability is the ability to move applications, data, and even people from one system to another with minimal adjustments. • Interoperability refers to the ability of systems to work together by sharing applications, data, and computer resources. • Scalability refers to the ability to run applications unchanged on any open system where the hardware can range from a laptop PC to a super computer.