SESI X

 Network ◦ An interconnected chain, group or system  Number of possible connections on a network is N * (N-1) ◦ Where N = number of nodes (points of connections on the network) ◦ Example, if there are 10 computers on a network, there are 10 * 9 = 90 possible connections

 The usefulness of a network equals the square of the number of users  On a small network, a change in technology affects technology only  On a large network like the Internet, a change in technology affects social, political and economic systems

 Telecommunications ◦ Exchange of information in any form (voice, data, text, images, audio, video) over networks

 Information systems that use common standards for hardware, software, applications and networks  Internet networking technologies are a common standard for open systems  Connectivity: ◦ Ability of networked computers to easily access and communicate with each other and share information  Interoperability: ◦ The ability of an open system to enable end user applications to be accomplished using different varieties of computer systems, software packages, and databases provided by a variety of interconnected networks

 Any programming that serves to “glue together” two separate programs

 Rapid change from analog to digital network technologies  Analog: voice-oriented transmission, sound waves  Digital: discrete pulse transmission  Digital allows: ◦ Higher transmission speed ◦ Larger amounts of information ◦ Greater economy ◦ Lower error rates ◦ Multiple forms of communications on same circuit

 Next generation of the Internet  High-performance network  In use at 200 universities, scientific institutions, communications corporations

 Over 46 million servers (2004)  710 – 945 million users (2004)  No central computer system  No governing body  No one owns it

 ISP ◦ A company that specializes in providing easy access to the Internet ◦ For a monthly fee, you get software, user name, password and access  ISPs are connect to one another through network access points

 A network inside an organization ◦ That uses Internet technologies (such as Web browsers and servers, TCP/IP protocols, HTML, etc.) ◦ To provide an Internet-like environment within the organization ◦ For information sharing, communications, collaboration and support of business processes ◦ Protected by security measures ◦ Can be accessed by authorized users through the Internet

 Network links that use Internet technologies ◦ To connect the Intranet of a business ◦ With the Intranets of its customers, suppliers or other business partners

 Any arrangement where a sender transmits a message to a receiver over a channel consisting of some type of medium

 Terminals: any input/output device that uses networks to transmit or receive data  Telecommunications Processors: devices that support data transmission and reception  Telecommunications Channels: media over which data are transmitted and received  Computers: all sizes and types  Telecommunications Control Software: programs that control telecommunications activities

 Telecommunications network that covers a large geographic area Source: Courtesy of Cisco Systems Inc.

 Connect computers within a limited physical area such as an office, classroom, or building

 A secure network that uses the Internet as its backbone but relies on firewalls, encryption and other security  A pipe traveling through the Internet

 Clients: End user personal computers or networked computers  Interconnected by LANs  Servers: manage networks  Processing shared between clients and servers

 Networks are the central computing resource of the organization  Thin clients: network computers and other clients provide a browser-based user interface

 Networks that connect from one PC to another PC  Common use is the downloading and trading of files

 Twisted-pair wire: ◦ Ordinary telephone wire ◦ Copper wire twisted into pairs Source: Phil Degginger/Getty Images.

 Coaxial cable: ◦ Sturdy copper or aluminum wire wrapped with spacers to insulate and protect it Source: Ryan McVay/Getty Images.

 Fiber-optic cable: ◦ One or more hair-thin filaments of glass fiber wrapped in a protective jacket Source: CMCD/Getty Images.

 Network providers use fiber optic to provide backbone  But houses are connected to the backbone via twisted-pair  Cannot get the benefit of the faster, better technology

 Terrestrial microwave ◦ Earthbound microwave systems that transmit high- speed radio signals in a line-of-sight path ◦ Between relay systems spaced approximately 30- miles apart  Communications satellites ◦ Satellite serves as relay stations for communications signals ◦ Uses microwave radio signals

 Cellular and PCS telephone and pager systems ◦ Divide the geographic area into small areas or cells ◦ Each cell has transmitter or radio relay antenna to send message from one cell to another  Wireless LANs ◦ Radio signals within an office or building ◦ Connect PCs to networks  Bluetooth ◦ Short-range wireless technology ◦ To connect PC to peripherals such as printer

 Connect portable communications devices to the Internet

 Modems ◦ Convert digital signals from a computer into ◦ Analog frequencies that can be transmitted over ordinary telephone lines

 Switch – makes connections between telecommunications circuits in a network  Router – intelligent communications processor that interconnects networks based on different protocols  Hub – a port switching communications processor  Gateway – connects networks using different communications architectures

 Multiplexer ◦ Allows a single communications channel to carry simultaneous data transmissions from many terminals

 Used by servers and other computers to manage network performance  Network Operating Systems  Middleware

 Traffic Management – manage network resources and traffic to avoid congestion and optimize service levels to users  Security – provide authentication, encryption, firewall, auditing and enforcement  Network Monitoring – troubleshoot and watch over the network, informing network administrators of potential problems before they occur  Capacity Planning – survey network resources and traffic patterns and users’ needs to determine how best to accommodate the needs of the network as it grows and changes

Network Topologies  Topology: structure of a network  Star: ties end user computers to a central computer  Ring: ties local computer processors together in a ring on a relatively equal basis  Bus: local processors share the same communications channel

 Protocol: standard set of rules and procedures for the control of communications in a network  Network Architecture: ◦ Master plan of standard protocols, hardware, software and interfaces between end users and computer systems ◦ Goal of promoting an open, simple, flexible, and efficient telecommunications environment

 Open Systems Interconnection (OSI) Model ◦ A seven-layer model that serves as a standard model for network architectures ◦ Model for how messages should be transmitted between two points in a network ◦ Each layer adds functions  Transmission Control Protocol / Internet Protocol (TCP/IP) ◦ A five layer telecommunications protocol used by the Internet

 Using an Internet connection to pass voice data using IP  Voice over IP (VoIP)  Skips standard long-distance phone charges

 Bandwidth ◦ Frequency range of a telecommunications channel ◦ Determines transmission rate ◦ Classified in bits per second (bps)  Transmission Rates: ◦ Narrow-band – low-speed ◦ Broadband – high-speed

 Circuit Switching ◦ Switch opens a circuit to establish a link between a sender and receiver ◦ it remains open until the communication session is completed  Packet Switching ◦ Break messages into groups called packets ◦ Transmit packets separately

 Ensure that anyone anywhere on one network  Can communicate  With anyone anywhere on another network  Telecommunications as discussed in this chapter wouldn’t be possible without interoperability