Communication and Networking

1. Communication and Networking

2. 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

3. 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

4. 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.

5. Communication Basics • 1. 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.

6. 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).

7. Communication Basics • 3. 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.

8. Communication Basics • 4. Method of 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

9. Communication Basics • 5. 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.

10. 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.

11. 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 = megabytes per second (millions Gbps=Gigabytes per second (billions)

12. 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

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

14. 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

15. 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

16. Types of LAN Topologies (Configurations) • Star topology • Centers around one node to which all others are connected and through which all messages are sent. • Everything depends on the central host; if it goes down the whole network goes down.

17. Types of LAN Topologies (Configurations) • Ring topology • Connects all nodes in a closed loop on which messages travel in one direction. • A message sent out from one node is passed along to each node in between until the target node received the message. • More reliable than star network since one machine going down does not affect all of the connections.

18. Types of LAN Topologies (Configurations) • Bus topology • All nodes are connected to a single communication line (bus) that carries messages in both directions • Most reliable type of network • The primary protocol used for bus networks is called Ethernet which has become the industry standard for local-area networks • Messages are broadcast across the bus and picked up by the recipient • If two nodes send messages at the same time, this results in “collision” in which case, the protocol forces the nodes to wait for a random period of time and then retransmit.

19. Types of LANs • Client/server LAN: • Clients - microcomputers that request data; and • Server - a powerful microcomputer that manages shared devices

20. Types of LANs • Peer-to-peer LAN • all microcomputers on the network communicate directly with one another without relying on a server

21. Components of LANs

22. 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.

23. 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

24. 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.

25. 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.

26. 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.

27. 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.