Basics of Communication & Networking

Networking A computer network is a collection of computing devices that are connected in various ways in order to communicate and share resources Usually, the connections between computers in a network are made using physical wires or cables However, some connections are wireless, using radio waves or infrared signals The generic term node or host to refer to any device on a network A key issue related to computer networks is the data transfer rate, the speed with which data is moved from one place on a network to another

Networking Computer networks have opened up an entire frontier in the world of computing called the client/server model A file server is a computer that stores and manages files for multiple users on a network A Web server is a computer dedicated to responding to requests (from the browser client) for Web pages A mail server is a computer that stores email messages for multiple users and routes the messages to the email clients when a request is made. Network printers … Client/Server interaction

Communication Basics Properties of Transmission: Each link has common attributes 1. Type of signal communicated (analog or digital) 2. The speed at which the signal is transmitted. 3. The type of data movement allowed on the channel. 4. The method used to transport the data. 5. Single channel and multichannel transmission.

Communication Basics Type of signal communicated. Analog - A continuously changing signal similar to that found in voice transmission (e.g., phone lines). Digital - Signals consist of pulses of electrical energy that represent 0’s or 1’s.

Communication Basics MODEM - MOdulator DEModulator Outgoing: Converts binary data from computer (digital) into telephone compatible signals (analog). Incoming: Converts telephone signal (analog) into binary data for the computer (digital).

Communication Basics Type of data movement. Three types of data movement can occur on a channel: Simplex transmission - One way transmission. Half-duplex transmission - Can flow only one way at a time. Full-duplex transmission - Two-way transmission at the same time.

Communication Basics Method of transmission. Asynchronous transmission Two types of data transmission, each requiring a different modem. Asynchronous transmission data is sent one byte at a time, with each string of bits making up the byte bracketed with special control bits Synchronous transmission data is sent in blocks, with start and stop bit patterns (synch bytes) at the beginning and end of the blocks

Communication Basics Single channel versus multi-channel transmission Channel - A path of a signal. Single channel - Capable of only sending/receiving one signal at a time. Phone line - Single line = single phone call at a time. Multi-channel - Capable of more than one channel at a time. Fiber-optic cable, microwaves, Satellite transmissions.

Communication Basics How is it possible to measure the capacity of communications links? Bandwidth In Digital: Number of bits per second (bps) that can be sent over a link. Wider bandwidth, the more diverse kinds of information can be sent. Simplest is voice, most sophisticated is moving videos. In Analog: The difference between the highest and lowest frequencies that can be sent over an analog link (like phone lines). Measurement is given in hertz (Hz). For both: The wider the bandwidth, the more information can flow over the channel.

Communication Basics Typical cable bandwidths used in local area networks. Cable: Typical Bandwidth: Twisted Pair 10 to 100 Mbps Coaxial Cable 10 to 100 Mbps Fiber-optic cable 100 to 200 Mbps The bandwidths of different services offered by a telephone company: Service: Bandwidth ISDN 64 Kbps T1 1.544 Mbps T3 44.736 Mbps STS-1 51.840 Mbps STS-3 155.250 Mbps STS-12 622.080 Mbps STS-24 1.244160 Gbps STS-48 2.488320 Gbps Mbps = megabits per second (millions) Gbps=Gigabits per second (billions)

Types of Networks A local-area network (LAN) connects a relatively small number of machines in a relatively close geographical area A wide-area network (WAN) connects two or more local-area networks over a potentially large geographic distance Often one particular node on a LAN is set up to serve as a gateway to handle all communication going between that LAN and other networks Communication between networks is called internetworking The Internet, as we know it today, is essentially the ultimate wide-area network, spanning the entire globe

Types of Networks Local-area networks connected across a distance to create a wide-area network

Intranets and Extranets Intranet - an organization’s internal private network that uses the infrastructure and standards of the Internet and the WWW Extranets - private intranets that connect not only internal personnel but also selected suppliers and other strategic parties

Firewalls A firewall is a machine and its software that serve as a special gateway to a network, protecting it from inappropriate access Filters network traffic that comes in, checking the validity of the messages as much as possible and perhaps denying some messages altogether Enforces an organization’s access control policy

Types of LANs Client/server LAN: Clients - microcomputers that request data; and Server - a powerful microcomputer that manages shared devices File server - a computer that acts like a disk drive, storing the programs and data files shared by users on a LAN. Database server - a computer in a LAN that stores data but doesn’t store programs. Print server - controls one or more printers and stores the print-image output from all the microcomputers on the system. Web server - contains web pages that can be viewed using a browser. Mail server - manages e-mail.

Types of LANs Peer-to-peer LAN all microcomputers on the network communicate directly with one another without relying on a server Peer-to-peer networks are cheaper than client/server networks, but only work effectively for up to 25 computers.

Components of LANs Router - a special computer that directs communicating messages when several networks are connected together. Bridge - an interface used to connect the same types of networks. Gateway - an interface permitting communication between dissimilar networks.

Components of LANs Hub A device that repeats or broadcasts the network stream of information to individual nodes ( usually personal computers) Switch A device that receives packets from its input link, and then sorts them and transmits them over the proper link that connects to the node addressed. Bridge A link between two networks that have identical rules of communication. Gateway A link between two different networks that have different rules of communication. Router A node that sends network packets in one of many possible directions to get them to their destination.

Communication Channels Communications channel the path (physical medium) over which information travels in a telecommunications system from its source to its destination The physical media used to connect the networks are: Twisted pair coaxial cable fiber optic cable and Wireless channels

Communication Channels Twisted pair: Two wires twisted together. Less susceptible to acting like an antenna and picking up radio frequency information or appliance noise. Used by the telephone company.

Communication Channels Coaxial cable: One wire is formed into a tube which is electrically grounded. The other wire is placed down the center of this tube and the space between is filled with a special nonconducting material.

Communication Channels Fiber-optic cable: Optical cable allowing light to pass along the cable. Light is electromagnetic, and because of its higher frequencies, transmits a lot more information through a single strand.

Communication Channels Three types of wireless communication commonly used Infrared: Commonly used in TV and VCR remote controls. Use infrared frequencies of electromagnetic radiation that behave much like visible light. Must be in the line of sight. Often used to connect keyboards, mice, and printers. Radio frequency: Uses radio frequencies. Not commonly used because of the possible interference from other sources of electromagnetic radiation. Microwave: Often used to communicate with distant locations. Must be line of sight. Satellite communications use microwaves.