Chapter One: Data Communication and Computer Networking Basics PDF

Chapter One Data Communication and Computer Networking Basics 1.1 Objectives At the end of this Chapter Students should be able to: Understand the concept of Network, Data communication Know the components of data communication Identify the various...

Chapter One Data Communication and Computer Networking Basics 1.1 Objectives At the end of this Chapter Students should be able to: Understand the concept of Network, Data communication Know the components of data communication Identify the various application of Networks Understand the classification of Network 2  Cont’d… Discuss the different shape of a network with their respective cons and prons. Describe the use of Network protocol and their significance Know the Network reference model both OSI as well as TCP/IP models 1.3  Introduction  Old paradigm: a single powerful computer serving all the needs of an organization  New paradigm† - Computer networks: a large number of separate (autonomous) but internetworked (being able to exchange information) computers doing the job  Merging of computer and communications technologies – no geographical barrier  Connection: copper wire, fiber optics, microwaves, infrared, communication satellites, … † Plus new applications: distributed processing (grid and cluster computing, pervasive computing, …), WWW, … 4 Introduction Introduction 1.1 Data Communications Communication: Means sharing information Local (face to face) or remote (over distance) Telecommunication Telephone, telegraph and television Means communication at a distance Tele is Greek for far Data Communications Data: Refers to information Presented in any form Agreed upon by the parties ( creating & using) Data communication : is the exchange of data between two devices via some form of transmission medium (wire cable). Data Communications Communication system made up of a combination of hardware and software Effectiveness of data communication system depends on: 1. Delivery : The system must deliver data to correct destination. Data received by the indented user only 2. Accuracy: The system must deliver data accurately (no change). Data changed & uncorrected is unusable Data Communications 3. Timeliness: The system must deliver data in timely manner Data arrived late are useless In the same order (video and audio) & without delay (Real time transmission) 4. Jitter: Variation in the packet arrival time (uneven quality in the video is the result) Data Communications  1-1 DATA COMMUNICATIONS Definition: The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Topics discussed in this section:  Components of a data communications system  Data Flow 1.12  Figure 1.1 Components of a data communication system A data communication system is made up of five components 1.13 Components 1. Message: the information (data) to be communicated – Consist of text, numbers, pictures, audio, or video 2. Sender: the device that sends the data message – Computer, workstation, telephone handset, video camera, … 3. Receiver: the device that receives the message – Computer, workstation, telephone handset, television, …. Components 4. Medium: The physical path by which a message travels from sender to receiver – twisted pair, coaxial cable, fiber-optic, radio waves Components 5. Protocol: a set of rules that govern data communications – An agreement between the communicating devices – Devices may be connected but not communicating (no protocol) – Arabic speaker with Japanese speaker Data Representation Text Numbers Images Audio Video Data Representation Unicode (4,294,967,296) Data Representation Data Representation pixels Data Representation Data Flow Data Flow Data Data Flow Data Data Data Flow Data Data Exercise Data Data  Figure 1.2 Data flow (simplex, half-duplex, and full-duplex) 1.27 Networks Network : A set of devices (nodes) connected by communication links Node : computer, printer, … - Distributed Processing : - Most networks used it - Task is divided among multiple computers instead of one single large computer Networks Network Criteria – Network must meet a certain number of criteria – The most important of the network criterions are: – Performance – Reliability – Security Networks Networks Networks Networks Networks Networks Networks Networks Networks  Digital Transmission of Digital Data 3 - 39  TRANSMISSION IMPAIRMENT Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received. Three causes of impairment are attenuation, distortion, and noise. 3.40  PROTOCOLS A protocol is synonymous with rule. It consists of a set of rules that govern data communications. It determines what is communicated, how it is communicated and when it is communicated. The key elements of a protocol are syntax, semantics and timing 1.41  Elements of a Protocol Syntax Structure or format of the data Indicates how to read the bits - field delineation Semantics Interprets the meaning of the bits Knows which fields define what action Timing When data should be sent and what Speed at which data should be sent or speed at which it is being received. 1.42  Standards 1 - 43  Standardization Processes 1 - 44  Major Standards Bodies 1 - 45  Major Standards Bodies (Cont.) 1 - 46  Some Data Comm. Standards Layer Common Standards HTTP, HTML (Web) 5. Application layer MPEG, H.323 (audio/video) IMAP, POP (e-mail) 4. Transport layer TCP (Internet) SPX (Novell LANs) 3. Network layer IP (Internet) IPX (Novell LANs) Ethernet (LAN) 2. Data link layer Frame Relay (WAN) PPP (dial-up via modem for MAN) RS-232c cable (LAN) 1. Physical layer Category 5 twisted pair (LAN) V.92 (56 kbps modem) 1 - 47 Switching Networks Nodes Simple Switched Network Circuit Switching Circuit Switching - Applications Packet Switching Principles Basic Operation Use of Packets Advantages Switching Technique Datagram Virtual Circuit Virtual Circuits v Datagram Circuit v Packet Switching  1-2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. A link can be a cable, air, optical fiber, or any medium which can transport a signal carrying information. Topics discussed in this section:  Network Criteria  Physical Structures  Categories of Networks 1.62  Network Criteria Performance Depends on Network Elements Measured in terms of Delay and Throughput Reliability Failure rate of network components Measured in terms of availability/robustness Security Data protection against corruption/loss of data due to: Errors Malicious users 1.63  The Uses of a Network 9A-64  The Uses of a Network 9A-65  Sharing Data File server contains documents used by other computers. 9A-66  The Uses of a Network 9A-67  Voice Over IP 9A-68  The Uses of a Network 9A-69 Categories of Networks Local Area Network (LAN) Local Area Network (LAN) An isolated LAN connecting 12 computers to a hub in a closet Local Area Network (LAN) Wide Area Networks (WAN) Wide Area Networks (WAN) Wide Area Networks (WAN) Metropolitan Area Networks (MAN) Interconnection of Networks: Internetworks The Internet The Internet The Internet Data rate The Internet Hierarchical organization of the Internet  Common Network Types 9A-83  Common Network Types 9A-84  Hybrid Network Types 9A-85  Hybrid Network Types 9A-86  Hybrid Network Types 9A-87  Hybrid Network Types 9A-88  How Networks Are Structured 9A-89  How Networks Are Structured 9A-90  How Networks Are Structured 9A-91 Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology Physical Topology  Network Topologies 9A-107  Network Topologies 9A-108  Network Topologies 9A-109  Network Topologies 9A-110  Star Topology 9A-111  Network Topologies 9A-112  Network Topologies 9A-113  Mesh Topology 9A-114  Network Media 9A-115  Wire Based Media n Twisted-pair cabling Most common LAN cable Called Cat5 or 100BaseT Four pairs of copper cable twisted May be shielded from interference Speeds range from 1 Mbps to 1,000 9A-116 Mbps  Wire Based Media 9A-117  Wire Based Media n Fiber-optic cable Data is transmitted with light pulses Glass strand instead of cable Immune to interference Very secure Hard to work with Speeds up to 100 Gbps 9A-118  Wireless Media 9A-119  Network Hardware 9A-120  Network Hardware 9A-121  Network Hardware 9A-122  Network Hardware 9A-123  Network Hardware 9A-124  Network Hardware 9A-125  Network Hardware 9A-126  Network Cabling 9A-127  Network Cabling 9A-128  Network Cabling 9A-129  Network Cabling 9A-130  Network Cabling 9A-131  Network Protocols 9A-132  Network Protocols 9A-133  Network Protocols 9A-134  Network Protocols 9A-135  Network Protocols 9A-136  Network Models We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Topics discussed in this section: Sender, Receiver, and Carrier Hierarchy 2.137  Figure 2.1 Tasks involved in sending a letter 2.138  2-2 THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. Topics discussed in this section: Layered Architecture Peer-to-Peer Processes Encapsulation 2.139  Note ISO is the organization. OSI is the model. 2.140 Figure 2.2 Seven layers of the OSI model 2.141 Figure 2.3 The interaction between layers in the OSI model 2.142 Figure 2.4 An exchange using the OSI model 2.143  2-3 LAYERS IN THE OSI MODEL In this section we briefly describe the functions of each layer in the OSI model. Topics discussed in this section: Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer 2.144  Figure 2.5 Physical layer 2.145  Note The physical layer is responsible for movements of individual bits from one hop (node) to the next. 2.146  Figure 2.6 Data link layer 2.147  Note The data link layer is responsible for moving frames from one hop (node) to the next. 2.148 Figure 2.7 Hop-to-hop delivery 2.149  Figure 2.8 Network layer 2.150  Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. 2.151 Figure 2.9 Source-to-destination delivery 2.152  Figure 2.10 Transport layer 2.153  Note The transport layer is responsible for the delivery of a message from one process to another. 2.154 Figure 2.11 Reliable process-to-process delivery of a message 2.155 Figure 2.12 Session layer 2.156  Note The session layer is responsible for dialog control and synchronization. 2.157 Figure 2.13 Presentation layer 2.158  Note The presentation layer is responsible for translation, compression, and encryption. 2.159 Figure 2.14 Application layer 2.160  Note The application layer is responsible for providing services to the user. 2.161 Figure 2.15 Summary of layers 2.162  2-4 TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Topics discussed in this section: Physical and Data Link Layers Network Layer Transport Layer Application Layer 2.163 Figure 2.16 TCP/IP and OSI model 2.164  2-5 ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. Topics discussed in this section: Physical Addresses Logical Addresses Port Addresses Specific Addresses 2.165 Figure 2.17 Addresses in TCP/IP 2.166 Figure 2.18 Relationship of layers and addresses in TCP/IP 2.167  Example 2.1 In Figure 2.19 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver. 2.168 Figure 2.19 Physical addresses 2.169  Example 2.2 Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address. 2.170  Example 2.3 Figure 2.20 shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection. 2.171 Figure 2.20 IP addresses 2.172  Example 2.4 Figure 2.21 shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination. 2.173 Figure 2.21 Port addresses 2.174  Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same. 2.175  Example 2.5 A port address is a 16-bit address represented by one decimal number as shown. 753 A 16-bit port address represented as one single number. 2.176 Transmission Media n The transmission medium is the physical path by which a message travels from sender to receiver. n Computers and telecommunication devices use signals to represent data. n These signals are transmitted from a device to another in the form of electromagnetic energy. n Examples of Electromagnetic energy include power, radio waves, infrared light, visible light, ultraviolet light, and X and gamma rays. n All these electromagnetic signals constitute the electromagnetic spectrum  Not all portion of the spectrum are currently usable for telecommunications Each portion of the spectrum requires a particular transmission medium  Signals of low frequency (like voice signals) are generally transmitted as current over metal cables. It is not possible to transmit visible light over metal cables, for this class of signals is necessary to use a different media, for example fiber-optic cable. Classes of transmission media Transmission Media n Guided media, which are those that provide a conduit from one device to another. n Examples: twisted-pair, coaxial cable, optical fiber. n Unguided media (or wireless communication) transport electromagnetic waves without using a physical conductor. Instead, signals are broadcast through air (or, in a few cases, water), and thus are available to anyone who has a device capable of receiving  Guided Media There are three categories of guided media: 1. Twisted-pair cable 2. Coaxial cable 3. Fiber-optic cable Twisted-pair cable n Twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. n Twisted-pair cable comes in two forms: unshielded and shielded n The twisting helps to reduce the interference (noise) and crosstalk. UTP and STP Frequency range for twisted-pair cable Unshielded Twisted-pair (UTP) n cable Any medium can transmit only a fixed range of frequencies! n UTP cable is the most common type of telecommunication medium in use today. n The range is suitable for transmitting both data and video. n Advantages of UTP are its cost and ease of use. UTP is cheap, flexible, and easy to install. The Electronic Industries Association (EIA) has developed standards to grade UTP. 1. Category 1. The basic twisted-pair cabling used in telephone systems. This level of quality is fine for voice but inadequate for data transmission. 2. Category 2. This category is suitable for voice and data transmission of up to 2Mbps. 3. Category 3.This category is suitable for data transmission of up to 10 Mbps. It is now the standard cable for most telephone systems. 4. Category 4. This category is suitable for data transmission of up to 20 Mbps. able 7.1 Categories of unshielded twisted-pair cables Category Bandwidth Data Rate Digital/Analog Use 1 very low < 100 kbps Analog Telephone 2 < 2 MHz 2 Mbps Analog/digital T-1 lines 3 16 MHz 10 Mbps Digital LANs 4 20 MHz 20 Mbps Digital LANs 5 100 MHz 100 Mbps Digital LANs 6 (draft) 200 MHz 200 Mbps Digital LANs 7 (draft) 600 MHz 600 Mbps Digital LANs  UTP connectors The most common UTP connector is RJ45 (RJ stands for Registered Jack). Shielded Twisted (STP) Cable n STP cable has a metal foil or braided-mesh covering that enhances each pair of insulated conductors. n The metal casing prevents the penetration of electromagnetic noise. n Materials and manufacturing requirements make STP more expensive than UTP but less susceptible to noise. Applications Coaxial Cable (or coax) n Coaxial cable carries signals of higher frequency ranges than twisted-pair cable. n Coaxial Cable standards: RG-8, RG-9, RG-11 are used in thick Ethernet RG-58 Used in thin Ethernet RG-59 Used for TV  BNC connectors To connect coaxial cable to devices, it is necessary to use coaxial connectors. The most common type of connector is the Bayone-Neill-Concelman, or BNC, connectors. There are three types: the BNC connector, the BNC T connector, the BNC terminator. Applications include cable TV networks, and some traditional Ethernet LANs like 10Base-2, or 10-Base5. Optical Fiber Metal cables transmit signals in the form of electric current. Optical fiber is made of glass or plastic and transmits signals in the form of light. Light, a form of electromagnetic energy, travels at 300,000 Kilometers/second ( 186,000 miles/second), in a vacuum. The speed of the light depends on the density of the medium through which it is traveling ( the higher density, the slower the speed). The Nature of the Light Refraction  Critical angle If the angle of incidence increases, so does the angle of refraction. The critical angle is defined to be an angle of incidence for which the angle of refraction is 90 degrees. Reflection n When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection. n Light no longer passes into the less dense medium at all. Critical Angle n Optical fibers use reflection to guide light through a channel. n A glass or core is surrounded by a cladding of less dense glass or plastic. The difference in density of the two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being into it. n Information is encoded onto a beam of light as a series of on-off flashes that represent 1 and 0 bits. Fiber construction Types of Optical Fiber n There are two basic types of fiber: multimode fiber and single-mode fiber. n Multimode fiber is best designed for short transmission distances, and is suited for use in LAN systems and video surveillance. n Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems. Propagation Modes (Types of Optical Fiber ) n Current technology supports two modes for propagating light along optical channels, each requiring fiber with different physical characteristics: Multimode and Single Mode. n Multimode, in turn, can be implemented in two forms: step-index or graded index. n Multimode: In this case multiple beams from a light source move through the core in different paths. n In multimode step-index fiber, the density of the core remains constant from the center to the edges. A beam of light moves through this constant density in a straight line until it reaches the interface of the core and cladding. At the interface there is an abrupt change to a lower density that alters the angle of the beam’s motion. n In a multimode graded-index fiber the density is highest at the center of the core and decreases gradually to its lowest Propagation Modes n Single mode uses step-index fiber and a highly Type Core Claddi Mode focused source of ng light that limits beams to a small 50/125 50 125 Multimode, range of angles, all graded-index close to the horizontal. Multimode, n Fiber Sizes 62.5/125 62.5 125 graded-index Optical fibers are defined by the Multimode, 100/125 100 125 ratio of the graded-index diameter of their core to the 7/125 7 125 Single-mode diameter of their cladding, both  Light sources for optical fibers The purpose of fiber-optic cable is to contain and direct a beam of light from source to target. The sending device must be equipped with a light source and the receiving device with photosensitive cell (called a photodiode) capable of translating the received light into an electrical signal. The light source can be either a light- emitting diode (LED) or an injection laser diode.  Fiber-optic cable connectors The subscriber channel (SC) connector is used in cable TV. It uses a push/pull locking system. The straight-tip (ST) connector is used for connecting cable to networking devices. MT-RJ is a new connector with the same size as RJ45. Advantages of Optical Fiber n The major advantages offered by fiber-optic cable over twisted-pair and coaxial cable are noise resistance, less signal attenuation, and higher bandwidth. n Noise Resistance: Because fiber- optic transmission uses light rather than electricity, noise is not a factor. External light, the only possible interference, is blocked from the channel by the outer jacket. Advantages of Optical Fiber Disadvantages of Optical Fiber Unguided Media Propagation of Radio Waves Radio technology considers the earth as surrounded by two layers of atmosphere: the troposphere and the ionosphere. The troposphere is the portion of the atmosphere extending outward approximately 30 miles from the earth's surface. The troposphere contains what we generally think of as air. Clouds, wind, temperature variations, and weather in general occur in the troposphere. The ionosphere is the layer of the atmosphere above the troposphere but below space. Propagation methods  Ground propagation. In ground propagation, radio waves travel through the lowest portion of the atmosphere, hugging the earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. The distance depends on the power in the signal. In Sky propagation, higher-frequency radio waves radiate upward into the ionosphere where they are reflected back to earth. This type of transmission allows for greater distances with lower power output. In Line-of-Sight Propagation, very high frequency signals are transmitted in straight lines directly from antenna to antenna.  Bands Band Range Propagation Application VLF 3–30 KHz Ground Long-range radio navigation Radio beacons and LF 30–300 KHz Ground navigational locators MF 300 KHz–3 MHz Sky AM radio Citizens band (CB), HF 3–30 MHz Sky ship/aircraft communication Sky and VHF TV, VHF 30–300 MHz line-of-sight FM radio UHF TV, cellular phones, UHF 300 MHz–3 GHz Line-of-sight paging, satellite SHF 3–30 GHz Line-of-sight Satellite communication EHF 30–300 GHz Line-of-sight Long-range radio navigation Propagation of Specific Signals n VLF Very Low Frequency waves are propagated as surface waves, usually through the air but some times through seawater. VLF waves do not suffer much attenuation in transmission but are susceptible to the high levels of atmospheric noise ( heat and electricity) active at low altitudes. n VLF waves are use mostly for long-range radio navigation and for submarine n LF low frequency waves are also propagated as surface waves. LF waves are used for long-range radio navigation and for radio beacons or navigational locators. n MF Middle frequency signals are propagated in the troposphere. Uses for MF transmissions include AM radio, maritime radio, and emergency n HF high frequency signals use ionospheric propagation. These frequencies move into the ionosphere, where they are reflected back to earth. Uses for HF signals include amateur radio, citizen’s band (CB) radio, military communication, long-distance aircraft and ship communication, telephone, n VHF Most very high frequency waves use line-of-sight propagation. Uses for VHF include VHF television, FM radio, and aircraft navigational aid. n UHF Ultrahigh frequency waves always use line-of- sight propagation. Uses for UHF includes UHF television, mobile telephone, cellular radio, and n SHF Superhigh frequency waves are transmitted using mostly line-of-sight and some space propagation. Uses for SHF include terrestrial and satellite microwave and radar communication. n EHF Extremely high frequency waves use space propagation. Uses for EHF are predominantly scientific and include radar, satellite and experimental communications.