1. mazharjaved2001@yahoo.com1 Types of computer networks LAN ( LOCAL AREA NETWORK ) WAN (WIDE AREA NETWROK )

2. mazharjaved2001@yahoo.com2 LAN (Local Area Network) It covers small area Most LANs are used to connect computer in a single building or group of buildings LANs can be found in industrial plants, office buildings,colleges or universities Capable of transmitting data at very fast rate It is much faster than data transmission over a telephone line LAN CHARACTERISTICS SizeTransmission TechnologyTopology Restricted in Size Single Cable 10 to 100 Mbps Low delay (ms) Very few Errors Megabits/Sec. (Unit) BUS (Ethernet) Ring (Token ring)

3. mazharjaved2001@yahoo.com3 Uses of LAN Sharing of one copy by all users System resources can be share like printer Easy to manage data store Data is more secure from being copied or destroyed It may be in form of Peer-to-peer Network Client Server Network

4. mazharjaved2001@yahoo.com4 WAN (Wide Area Network ) It covers the large area WAN connects computer in different cities and countries When devices are speared by more than a few hundred yards. Normally a WAN consists of two or more interconnected LANs Connected through telephone lines or satellites WAN is expensive than LAN Speed depends on the speed provided by the company Communication may be via microwave, satellite link or telephone line. Use in banks or in air ticketing system Alternative technologies –Circuit switching –Packet switching –Frame relay –Asynchronous transfer mode (ATM)

5. mazharjaved2001@yahoo.com5 Transmission Rate Baud rate: The speed at which data is transmitted serially is known as the baud rate. The 'Baud Rate' is the number of symbols transmitted per second. A 'symbol' is one chunk of information. Note that 'baud rate' is not the same as bit-rate. One symbol (a chunk of information) can be carried by many bits. Difference between Baud and bit rate The difference between the two is complicated and intertwining. They are dependent and inter-related. But the simplest explanation is that a Bit Rate is how many data bits are transmitted per second. A baud Rate is the measurement of the number of times per second a signal in a communications channel changes. Engineers use more than one bit per symbol because it helps detect errors.

6. mazharjaved2001@yahoo.com6 Modes of operation Baseband mode: One channel system – whole bandwidth dedicated to one data channel, e.g. Ethernet. Used for data communication over short distances for example, LAN’s. LANs typically operate in baseband mode, which means that a given cable is carrying a single data signal at any one time. Computers connected to this LAN must take turns using the medium.

7. mazharjaved2001@yahoo.com7 BroadBand Mode Multi-channel system - several channels are combined onto a carrier signal – the bandwidth is shared by several data channels. Used for long distance data communication. Using the analogy of SKY TV, all channels are broadcast to your receiver at once but on different frequencies. The receiver then decodes the channel you wish to watch and displays it on the TV. Long-distance communications media, on the other hand, are expensive to install and maintain. It would be wasteful if each media path could support only a single data stream. WANs, therefore tend to use broadband media. Broadband media allow two or more data streams to be carried at the same time.

8. mazharjaved2001@yahoo.com8 Network Topologies The physical layout or the way in which network connections connection are made is called topology It refers especially to the locations of the computer and how the cable runs between them It may be Bus or Line Topology Star Topology Ring Topology Tree Topology

9. mazharjaved2001@yahoo.com9 Bus or Line Topology All computers or network nodes are connected to a common communication medium In a local network this medium is often a central wire called bus Information can be transmitted in either direction from any PC to any other Working If a computer wants to send data to the other computer in the network,it sends the data via the bus The data and address move from one computer to other and checks the address if it matches then it goes to other computer

10. mazharjaved2001@yahoo.com10 Advantages Simple easy and suitable for small network Least amount of cable is required Easy to extend a bus Disadvantages Heavy network traffic can slow a network A cable breaks or loose connector will disconnect the entire network No of computer increase then speed of network will be slow Cable failure is difficult to isolate.

11. mazharjaved2001@yahoo.com11 Star Topology Is one in which all the cables run from the computers to a central location Connected with the device called hub Used in client server network Working If two computers want to share data the sender computer sends data to the hub and hub sends it to the receiving computer

12. mazharjaved2001@yahoo.com12 Advantages Hub can accommodate multiple cable types Easy to modify Reliable market proven system Finding faults becomes easy No problem with collisions of data since each stations has its own cable to the server. Single computer failure cannot break the network Message passing from one workstation to other is more secure Variable transmission rates are possible between the file server. Disadvantages If central hubs fails the entire network fails It is more expensive because all network cables must be pulled to a central point

13. mazharjaved2001@yahoo.com13 Ring Topology Each computer is connected to the next computer with the last one connected to the first Data flow around the circle from device to device in one direction only Working Each computer retransmits what it receives from the previous computer The message flow in one direction

14. mazharjaved2001@yahoo.com14 Advantages There is no signal loss problem Every computer has a equal access to the token Transmission of messages around the ring is relatively simple Transmission rate is higher. Disadvantages Failure of one computer on ring effect the whole network Difficult to troubleshoot Adding or removing computers disrupts the network

15. mazharjaved2001@yahoo.com15 Protocols Used for communications between entities in a system An agreed-upon format or set of rules for transmitting data between two devices. Must speak the same language Entities –User applications –E-mail facilities –Terminals Systems –Computer –Terminal –Remote sensor

16. mazharjaved2001@yahoo.com16 Design Issues Addressing. Data transfer. –Simplex communication. –Half-duplex communication. –Full-duplex communication. Number and priorities of the logical connection channels. Many networks provide at least two logical channels per connection, one for normal data and one for urgent data. Error control. –Error detecting code. –Error correcting code. How to receive data in order (sequence no.). How to keep a fast sender from swamping a slow receiver with data (flow control). Size of the message: disassembling >transmitting >reassembling messages. Routing: multiple paths between source and destination.

17. mazharjaved2001@yahoo.com17 Protocol Architecture Task of communication broken up into modules For example file transfer could use three modules –File transfer application –Communication service module –Network access module

18. mazharjaved2001@yahoo.com18 Standard Protocol Protocol stack: A list of protocol used by a certain system, one protocol per layer. Examples of Protocol: TCP/IP :Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. X25A: popular standard for packet-switching networks. The X.25 standard was approved by the CCITT (now the ITU) in 1976.

19. mazharjaved2001@yahoo.com19 Problems in protocols It is also possible to link equipment using a special translation device called a protocol converter to link then there is a compatibility problem for example PC to Mainframe communication Protocol Different types of transmission: PC may use asynchronous transmission, and the mainframe synchronous transmission. Different character representation: PC use ASCII whereas Mainframe use EBCDIC Different Error detection and Correction methods

20. mazharjaved2001@yahoo.com20 Handshaking Handshaking is the exchange of signals between devices to establish their readiness to send or receive data. E.g. Between Computer and Printer It is one method of ensuring that both the sender and receiver are ready before transmission begins. The conversation between the two devices is along the lines of following Device 1 Device 2 Are you ready to receive data Yes go ahead Sends data Message received thanks