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Electronic - II Data communications Lecture- 1 Dr. Eng. Samy Elmokadem Chapter 1 References : Data Communications and Networking , 4 edition , Behrouz,Forouzan . Table of Contents Data communications * Components * Data Representation * Data Flow Networks * Distribution processing * Network Criteria * physical structure * Network Models * Category of Networks * Interconnection of Networks Table of Contents ( CONTINUE ) The Internet * Brief History * The Internet Today Protocols and standards * protocols * Standards Organizations * Internet Standards 1- Data communications Data communication : Is the exchange of data between devices via some form of transmission medium such as a wire cable . For data communication to occur , the communicating devices must be part of communication system made up of a combination of 1- Hardware ( physical equipment ) 2- Software (programs) 1- Data communications The effectiveness of data communications system depend on four fundamental characteristics : 1- Delivery 2- Accuracy 3- Timelines 4- Jitter 1- Data communications 1- Delivery : the system must deliver data to the correct destination 2- Accuracy : the system must deliver data accurately . 3- Timelines : the system must deliver data in a timely manner . Data delivered late are useless . 4- Jitter : refers to the variation of the packet arrival time it is the uneven delay in the delivery of data . Component of Data communications system Data communications system has five components: 1- Message : is the information (data) to be communicated such as ( text – picture – audio – video) . 2- Sender : the device that sends the data massage such as ( computer – workstation – telephone – video camera ) 3-Receiver : is the device that receives the massage such as ( computer – workstation – telephone – video camera ) 4- Transmission medium : is the physical path by which a massage travels from sender to receiver such as ( Twisted pair wire – Coaxial cable – fiber optic cable - Radio waves) 5- Protocol : is a set of rules that govern data communications. It represents an agreement between the communicating devices . Without a Protocol , Tow devices may be connected but not communicating . Just as a person speaking French can not be understood by a person who speaks only Japanese . Block diagram of data communication system Protocol Protocol Rule 1 Rule 2 Rule 3 Rule 1 Rule 2 Rule 3 Massage Receiver Sender Medium Five Components of Data Communication 1. 2. Message Sender 3. Receiver 4. Medium 5. Protocol Data Representation Information has a different forms such as : 1- Text 2- Numbers 3- Images 4- audio 5- video Data Flow Communication between two devices can be : 1- Simplex : in simplex mode the communication is unidirectional , as on a one way street .only one of the two devices on a link can transmit ; the other can only receive . • Example of simplex devices . The keyboard can only introduce input & the Monitor can only accept output . • * the simplex mode can only the entire capacity of the channel to send data in one direction . Data Flow 2- Half - Duplex : Each station can both transmit and receive , but not at the same time . When one device is sending the other can only receive and vice versa In half-Duplex transmission , the entire of channel is taken over by whichever of the two devices is transmitting at the time . Example on Half Duplex is walkie-talkies. Data Flow 3- Full-Duplex : In the full-Duplex mode , both station can transmit and receive simultaneously. - Signal going in one direction share the capacity of the link with signals going in the other direction . This share can occur in two ways : - Either the link must contain two physically separate transmission paths one for sending and the other for receiving or The capacity of the channel is divided between signals traveling in both direction • The full -Duplex mode is used when communication in both directions is required all the time. The capacity of the channel must be divided between the tow directions. • EX: The Telephone Network. 1-Simplex Data Flow Direction of data Monitor Mainframe 2-Half duplex Direction of data at time 1 station Direction of data at time 2 station 3-Full-Duplex Direction of data all the time station station Networks A network is a set of devices (nodes ) connected by communication links , A node can be a computer, printer , or any other device capable of sending or receiving data generated by other nodes on the network Distributed processing : Task is divided among multiple computers instead of single large machine. Network Criteria : A network must be able to meet a certain number of criteria , the most important of this are : 1-performance 2- reliability 3-security . 1- Performance : can be measured in many ways , including transit time and response time . - Transit time : is the amount of time required for a message to travel from one device to another . - Response time : is the elapsed time between an inquiry and a response . - the performance of a network depends on a number of factors , including: 1- the number of users 2- the type of transmission medium 3- the capabilities of the connected hardware 4- the efficiency of the software - performance is often evaluated by two network matrices : throughput and delay. 2- Reliability: The network reliability is measured by the frequency of failure, (the time it takes a link to recover from of failure). In addition to accuracy of delivery, network reliability is measured by : Frequency of failure Recovery time of a network after a failure Catastrophe. 3- Security : network security include protecting data from unauthorized access , protecting data from damage development , and implementing policies procedures for recovery from preaches and data losses Physical Structures We need to define some network attributes : type of connection : there are two possible type of connections: 1- Point to Point . 2- point to Multipoint. Types of connections: point-to-point and multipoint Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network Wide Area Network (WAN) Local Area Network (LAN) Physical Topology Physical Topology refers to the way in which a network is laid out physical . The topology of a network : is the trigonometric representation of the relationship of all the links and linking devices Why Computer Network? To share information or receive a service via a network, group members must be able to communicate with each other. “ A computer network is a collection of computers and other devices (nodes) that use a common network protocol to share resources (Printer, Scanner, Memory, Information , Data Base, Network Bandwidth, Internet Services , etc ) with each other over a network medium such as a wire cable . Categories of Networks Computer networks can be classified according to their size to three categories : 1- Local Area Network (LAN) 2- Metropolitan Area Network (MAN) 3- Wide Area Network (WAN) LAN MAN WAN Network Classification Upon the scale (size) :1. 2. 3. 4. 5. PAN (Personal Area Network). LAN (Local Area Network). CAN (Campus Area Network). MAN (Metropolitan Area Network). WAN (Wide Area Network). 1-PAN (Personal Area Network) PAN is a short-distance network design to individual user (person). PAN may be contain:- printer, mobile, computer, wireless printers , PDA, etc. components of PAN connected together via Bluetooth , USB cable ,IrDA (infrared), etc. 26 2-LAN (Local Area Network) A LAN is a group of node connected together in a small specific area. LAN may be contain workstations, computers, scanner, printers, servers, etc. 3- CAN (Campus Area Network) A CAN is a group of interconnection LAN within limited geographical area. A CAN using in school campus, military base, university campus ,etc. 4- MAN (Metropolitan Area Network) A MAN is a large computer network uses to connect between LAN in different location (cities). Is a network with a size between a LAN and WAN . A MAN is a group of node connect together over city. 5- Wide Area Network (WAN ) Provides long distance transmission of data. It has no geographical limit . A WAN is made up of a number of interconnected LANs. Ex : Internet WAN (Wide Area Network) A WAN is a computer network that covers large geographical area. WANs are used to connect types of networks together. WAN MAN CAN LAN PAN 32 LAN Basics 1- Local Area Network ( LAN) • A LAN is a network that is used for communicating among computer devices, usually within an office building or home • LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users • Is limited in size, typically spanning a few hundred meters, and no more than a mile • Is fast, with speeds from 10 Mbps to 10 Gbps • Requires little wiring, typically a single cable connecting to each device • Has lower cost compared to MAN’s or WAN’s LAN Basics LAN’s can be either wired or wireless. Twisted pair, coaxial or fiber optic cable can be used in wired LAN’s Nodes in a LAN are linked together with a certain topology. These topologies include: Bus Ring Star Mesh Branching tree Network topologies 1- Bus 2- Ring 3- Star 4- Mesh 5- Branching tree Mostly used network topologies bus star Ring mesh Network Topologies 1- Bus Topology Each node is connected one after the other (like Christmas lights) Nodes communicate with each other along the same path called the backbone PC A bus topology connecting three stations Advantages of Bus Topology 1- Use of cable is economical 2- media is inexpensive and easy to work with it. 3- Easy to be extended 4- if any computer on the Bus stopped to work, that does not effect on the entire network Disadvantages of bus topology 1- Network can slow in heavy traffic. 2- Cable (backbone) break effect on the entire network. 3- Number of computers is limited. 2- Ring topology -The ring network is like a bus network, but the “end” of the network is connected to the first node. -Nodes in the network use tokens to communicate with each other. PC (NODE) Backbone A ring topology connecting six stations Ring Topology *Advantages - High performance ,despite many users. *Disadvantages - Failure of one computer can impact the rest of the network. - failure of one cable impact the entire network 3- Star Topology - Each node is connected to a device in the center of the network called a Hub - The hub simply passes the signal arriving from any node to the other nodes in the network - The hub does not route the data Hub A star topology connecting four stations Star Topology Advantages Adding new computers is easy. - centralized monitoring and management are possible . - failure of one computer does not affect the rest of the network. Disadvantages 1- If the centralized point fails the entire network will be got down also. 2- Many cables are used for connection. 4- Mesh topology PC FULLY CONNECTED Advantages System increased redundancy and reliability. Disadvantages system is expensive to install because it uses a lot of cabling. A fully connected mesh topology (five devices) 5-Branching tree Topology A hybrid topology: a star backbone with three bus networks 3- Wide Area Network (WAN ) Provides long distance transmission of data. It has no geographical limit . A WAN is made up of a number of interconnected LANs. Ex : Internet WANs : a switched WAN and a point-to-point WAN A heterogeneous network made of four WANs and two LANs THE INTERNET The Internet is the network of internetworking . The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. It has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. Hierarchical organization of the Internet PROTOCOLS AND STANDARDS protocols and standards. First, we define protocol, which is synonymous with rule. Then we discuss standards, which are agreed-upon rules. Protocols and Standards Protocol Protocol : is a set of rules that govern data communications. It represents an agreement between the communicating devices . Without a Protocol , Tow devices may be connected but not communicating. The key element of a Protocol are: 1- Syntax 2- Semantics 3-Timing Protocol ( CONTINUE ) Syntax : is the structure or format of data . - For example : a simple protocol might expect the first 8 bit of data to be the address of the sender , the second 8 bits to be the address of the receiver , and the rest of the stream to be the massage itself. Semantics : refers to the meaning of each section of bits Protocol ( CONTINUE ) Timing : refers to two characteristics 1- when data should be sent 2- how fast they can be sent Ex : if a sender produces data at 100 Mbps but the receiver can process data at 1 Mbps , the transmission will overload the receiver and some data will be lost Standards Standards : are necessary to ensure that products from different manufacturers can work together as expected . Examples on some organizations involved in standards creation are : 1- The International Standards Organization (ISO)) 2-Institute of Electrical and Electronic Engineers (IEEE) References 60