Computer Networks (CN) PDF

Computer Networks (CN)  What is Computer Network ?  It is a digital telecommunications network which allows nodes to share resources.  Sharing resources:  Software  Files and Data  Storage devices  Printers, Scanners, Fax and Modem...

Computer Networks (CN)  What is Computer Network ?  It is a digital telecommunications network which allows nodes to share resources.  Sharing resources:  Software  Files and Data  Storage devices  Printers, Scanners, Fax and Modem 2 3  Course Objectives 1. To introduce the concept, terminologies, and technologies used in modern data communication and computer networking and the functions of different layers. 2. To explain the basics of connecting devices used and protocols used in data link layer. 3. To understand the basic concepts of addressing and to study the various routing protocols. 4. To learn how process to process delivery is carried out in transport layer and basic transport layer protocols, congestion control techniques and applications. 4  Course Outcomes 1.Understand the principles of data communication and networking. 2.Gain knowledge of data link control, which involves flow and error control. 3.Know two prominent wireless technologies for LANs: IEEE 802.11 Wireless LANs, and Bluetooth, a technology for small wireless LANs. 4.Have exposure to principles of addressing and routing. 5.Gain the knowledge of network, transport and application layer protocols. 6.Introduced to basics of cryptography and internet security. 5  Unit I : Physical Layer  Data Communications, Networks  Networks models: OSI model, Layers in OSI model, TCP / IP protocol suite, Addressing  Guided and Unguided Transmission media.  Switching: Circuit switched networks, Data gram Networks, Virtual circuit networks.  Cable networks for Data transmission: Dial- up modems, DSL, Cable TV, Cable TV for Data transfer. 6 7  Unit II: Data Link Layer  Data link control: Framing, Flow and error control, Protocols for Noiseless and Noisy Channels, HDLC.  Multiple access: Random access and Controlled access  Wired LANS: Ethernet:- IEEE standards, standard Ethernet, changes in the standard, Fast Ethernet, Gigabit Ethernet.  Introduction to Wireless LANS: IEEE 802.11, Bluetooth.  Connecting LANS: Connecting devices, Backbone networks, Virtual LANS 8  Unit III: Network and Transport Layer  Logical addressing: IPv4 and IPv6 addresses.  Internet Protocol: Internetworking, IPv4, IPv6  Address mapping: ARP, RARP, BOOTP, DHCP, ICMP, IGMP.  Delivery: Forwarding , Routing, Unicast, Multicast routing protocols.  TRANSPORT LAYER: Process-to- Process delivery, User Datagram Protocol (UDP), Transmission Control Protocol (TCP). 9  Unit IV: Application Layer and Network Security  APPLICATION LAYER: Domain Name System (DNS) , E-mail, FTP,  WWW and HTTP Multimedia.  Introduction to Network Security, Services, Mechanisms and Attacks, Symmetric Key Cryptography, Asymmetric Key Cryptography, Security in the Internet, Firewalls. 10  List of Experiments 1. Study of Windows Server Operating System & Implementation of LAN. 2. Installation and configuration of Web & FTP Services. 3. Study of Network Protocol Analyser. 4. Examine how networking packets are transferred and exchanged in a TCP/IP network. 5. Write a program for implementation of Shortest Path algorithm. 6. Study of wireless LANs. 7. Write a program for Encryption and Decryption. 11  Learning resources Text Books: 1. Behrouz A. Forouzan, “Data communication and Networking”, 4th edition, TMH, 2006 2. Andrew S. Tannenbaum, “Computer Networks”, Pearson Education, Fourth Edition, 2003 12 Reference Books: 1. Wayne Tomasi, “Introduction to Data Communication and Networking”, 1/e, Pearson Education 2. James.F. Kurouse& W. Rouse, “Computer Networking: A Topdown Approach Featuring”,3/e, Pearson Education. 3. William Stallings, “Cryptography and Network Security Principles and Practices”, PHI. 4. Greg Tomshon, Ed Tittel, David Johnson. “Guide to Networking Essentials”, fifth edition, Thomson India Learning, 2007. 5. William Stallings, “Data and Computer Communication”, Eighth Edition, Pearson Education, 2000. 13  Assessment Scheme Class Continuous Assessment (CCA): 50 Marks Assignments Mid term Test Quizzes A1 (10M):- U1 & 2 (U 1 & 2) (U 1 to 4) Each unit: 5M A2 (10M):- U3 & 4 20M 20 M 20 M Laboratory Continuous Assessment (LCA): 50 Marks File Practical exam 30 20 End Term Examination: 40 M (entire syllabus)  Chapter 1 Introduction: Telecommunication: Communication at a distance. Examples: Telephony, Telegraphy, and TV. Data communications : Exchange of data between two devices ( or Communication system)  Communication system: combination of hardware (physical equipment) and software (programs). Data: Information presented in whatever form is agreed upon by the parties creating and using the data. 1.15  Fundamental characteristics (Effective data communications)  Delivery: The system must deliver data to the correct destination.  Accuracy: The system must deliver the data accurately.  Timeliness: The system must deliver data in a timely manner. This kind of delivery is called real-time transmission.  Real-time: Audio and Video Blockage of channel is not acceptable  Non-real time: E-mail, SMS, WhatsApp Blockage of channel is acceptable  Jitter: It refers to the variation in the packet arrival time. 16 Five components of data communication  1. Message: The message is the information (data) to be communicated.  Popular forms : Text, Numbers, Pictures, Audio, and Video.  2. Sender: The sender is the device that sends the data message. Examples: Computer, Workstation, Telephone handset, Video camera.  3. Receiver: The receiver is the device that receives the message.  Examples: Computer, Workstation, Telephone handset, TV. 17 Five components of data communication  4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver.  5. Protocol. A protocol is a set of rules that govern data communications.  It represents an agreement between the communicating devices.  Without a protocol, two devices may be connected but not communicating. 18 Cont.  Wireline:  Telephony: Coaxial cable, Optical fiber cable (OFC)  RF and Microwave : Waveguides Wireless (RF-link): Antenna at both ends  Radio and TV  Satellite Communication  RADAR  Mobile Communication 19  Data flow (Simplex, Half-duplex, and Full-duplex) 20 Simplex (One-way communication) 21 Half duplex (walkie-talkie) 22 Full duplex 23  NETWORKS  A network is a set of devices (or nodes) connected by communication links (wired or wireless) and capable of communication.  Examples of devices or nodes:  Large computer  Desktop  Laptop  Cellular phone  Router (which connects the network to other networks)  Switch (which connects devices together)  MODEM (which changes the form of data)  Most networks use distributed processing. It means dividing a task among multiple computers. 24  Network Criteria  A network must be able to meet a certain number of criteria. 1. Performance 2. Reliability 3. Security 25 1. Performance  It can be measured in many ways, including transit time and response time.  Factors:  Number of users  Type of transmission medium  Capabilities of the connected hardware  Efficiency of the software  It is often evaluated by two networking metrics: throughput and delay. Expected: more throughput and less delay. 26 Reliability : It is measured by the frequency of failure, the time it takes a link to recover from a failure. Security:  Protecting data from unauthorized access, damage and development.  Implementing policies and procedures for data recovery and losses. 27  Physical Structures 1. Point-to-Point:  Dedicated link between two devices.  The entire capacity of link is reserved between those two devices. 28  2. Multipoint (or Multidrop)  More than two specific devices share a single link  The capacity of a channel is shared either Spatially (simultaneously) or Temporally (turn by turn basis) 29  Physical Topology  Physical topology: Physical layout of the network (or geometrical representation of the links and nodes)  2 or more devices connect to a link.  2 or more links form a topology. 30  1. Mesh  Every device has a dedicated point-to- point link to every other device.  Dedicated: Link carries traffic only between the two devices it connects.  Physical links: n(n - 1)  Duplex-mode links: {n(n - 1)}/2  Input/output ports: n -1 Example: n = 5  Physical links: 20  Duplex-mode links: 10  Input/output ports: n -1: 4 31  Advantages  Eliminating the traffic problems (dedicated links).  Robust: If one link becomes unusable, it does not disable the entire system.  Privacy or Security: Intended recipient sees it and others can not have access (physical boundaries prevent).  Finally, point-to-point links make fault. Identification and Fault isolation is easy.  Traffic can be routed to avoid links with suspected problems.  This will handle by N/W manager. 32 Disadvantages  Amount of cabling and the number of I/O ports required.  First: Installation and reconnection are difficult.  Second: The wiring is larger than the available space (in walls, ceilings, or floors).  Finally: Expensive (I/O ports and cable)  Implemented in a limited fashion: acts as a backbone (several other topologies can be connected).  Practical example : Telephone regional offices. 33 2. Star  Each device has a dedicated point-to-point link only to a central controller, usually called a hub. The devices are not directly linked to one another.  Unlike a mesh topology, It does not allow direct traffic between devices.  Hub or controller is a exchange. 34  Advantages Less expensive than a mesh topology. Each device needs only one link and I/O port. Easy installation and reconfiguration. Less cabling is needed. Robustness: If one link fails, only that link is affected. All other links remain active. Easy fault identification and isolation. Hub working: used to monitor link problems and bypass defective links. 35  Disadvantages Dependent on hub, If the hub goes down, the whole system is dead. More cabling is required than Ring or Bus topology. Application: LANs 36  3. Bus  It is an example of multipoint connection.  One long cable acts as a backbone.  Nodes are connected to link by drop lines and taps.  Signal strength is a function of cable length which limits the number of taps. 37  Advantages Ease of installation. Backbone cable can be laid along the most efficient path. It uses less cabling than Mesh or Star topologies. 38 Disadvantages  Difficult reconnection and fault isolation.  It is usually designed optimally efficient at installation.  It can therefore be difficult to add new devices.  Signal reflection at the taps can cause degradation in quality (solution: limits the number and spacing of devices).  Adding new devices: Requires modification or replacement of the backbone.  Fault of break in bus: Stops all transmission.  It was one of the first topologies used in the design of early LANs.  Application: Ethernet LANs 39 4. Ring Each device has a dedicated point-to-point connection with only the two devices on either side of it. A signal is passed along the ring in one direction. Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the bits and passes them along. 40 Advantages  Easy to install and reconfigure.  Each device is linked to only its immediate neighbors (either physically or logically).  To add or delete a device requires changing only two connections.  The only constraints are media and traffic considerations (maximum ring length and number of devices).  In addition, fault isolation is simplified. 41  Disadvantages  Unidirectional traffic can be a disadvantage. Break in the ring (disabled station) can disable the entire n/w.  Solution: Dual ring  Less popular. 42 Hybrid 43  Categories of Networks  Two primary categories: (based on its length and topology) 1. Local Area Networks (LANs) : < 2miles 2. Wide Area Networks (WANs) : worldwide 3. Metropolitan Area Networks (MANs): 10 miles  Order of sequence: LAN, MAN and WAN Limited MAN connects WAN connects MANs in a large geographical area LANs in city or geographic area. Internet is such as home or town world’s largest WAN office building 44  1. LAN  Where? Office, Building, or Campus.  Home office: Two PCs and a printer.  Currently, LAN size is limited to a few kilometers.  LANs are designed to share resources:  Hardware (e.g., a printer)  Software (e.g., an application program)  Data.  LAN topologies: Bus, Ring, and Star.  LAN : Size, Transmission media and Topology  Early LANs : 4 to 16 Mbps.  Today’s LANs: 100 or 1000 Mbps.  Wireless LANs : Newest evolution in LAN technology. 45  3. WAN  Long-distance transmission of information.  Where? Over large geographic areas (Country, a Continent, or even the whole world). WAN can be:  as complex as the backbones that connect the Internet  as simple as a dial-up line that connects a home computer to the Internet. 46 47  Early switched WAN : X.25 (Packet-switching)  X.25 is being gradually replaced by Frame relay (high-speed and more efficient network).  Example of switched WAN:  asynchronous transfer mode (ATM) network (fixed- size data unit packets called cells).  wireless WAN (more popular). 48  2. MAN  Size: LAN < MAN < WAN.  Where? Town or City.  High-speed connectivity.  Examples:  Telephone Company network ( high-speed DSL line to the customer).  Cable TV network (high-speed data connection to the Internet). 49 Heterogeneous Network 50  Internet Service Providers (ISPs)  It allow users access to networks to establish Internet connectivity.  Local  Regional  National  International 51  Protocols and Standards Protocols OR Rules Standards: Agreed upon rules 52  Protocols  Key elements of a protocols are: 1. Syntax: Structure or format of the data, meaning in which they are presented.  Example: Protocol (first 8 bits of the data - address of the sender, second 8 bits of the data - address of the receiver, and rest bits are data (or message). 2. Semantics: Meaning (or interpretation) of each section of bits. 3. Timing: When data to be sent and how they can be sent.  Example: Sender - 100 Mbps, Receiver - 1 Mbps. 53  Standards  These are essential in creating and maintaining an open competitive market for equipment manufactures and in guaranteeing National and International interoperability of data and telecommunications technology and processes.  It provide guidelines to manufactures, vendors, government agencies, and other service providers.  Data communication standards fall into two categories: 1. de facto ( meaning “by fact”) 2. de jure (meaning “ by law” or “by regulation”)  Standards Organizations: 1. International Organization for Standardization (ISO) 2. International Telecommunication Union – Telecommunication (ITU-T) 3. American National Standards Institute (ANSI) 4. Institute of Electrical and Electronics Engineers (IEEE) 5. Electronic Industries Association (EIA) 54  TRAI: Telecom Regularity Authority of India.  FCC: Federal Communications Commission, US govt. agency.  ITU: The International Telecommunication Union is an agency of the United Nations, coordinate telecommunication operations and services throughout the world. 55  Chapter 2: Network Models  Two models haven been devised to define CN operations. 1. The OSI model – 7 layer n/w (1.Never implemented in practice, 2. Reference model) 2. The Internet model (TCP/IP) - 5 layer n/w (1. Implemented in practice, 2. CN syllabus is framed) 56  Protocol Layering Simple communication: Only one simple protocol Complex communication: Divide the task between different layers and we need a protocol at each layer, or protocol layering. 57  Advantages:  It allows us to separate the services from the implementation.  Internet: Communication does not always use only two end systems: there are intermediate systems that need only some layers, but not all layers.  Principles of Protocol Layering: 1. Bi-directional communication at each layer. 2. The two objects under each layer at both sites should be identical. 58 Logical ( or Imaginary) Connections between Peer layers 59  The OSI Model  OSI: Open Systems Interconnection ( introduced in the late 1970s)  International Standards Organization (ISO: 1947) is a multinational body dedicated to worldwide agreement on international standards.  ISO standard covers: all aspects of n/w communications.  The OSI model is not a protocol.  It is a model for understanding and designing a network architecture that is flexible, robust, and interoperable. ISO is the organization. OSI is the model. 60 7- layers of the OSI model 61 Headers and Trailers 62 Interaction between layers  Software layers: 7, 6, and 5  Hardware + Software layers: 4, 3, and 2  Hardware layer: 1 63 Summary of layers 64  1. Physical Layer  It is responsible for movements of individual bits from one hop (node) to the next. 65  Physical characteristics of interfaces and medium: type of transmission medium Representation of bits: Define type of encoding or data formats ( digital data into digital signal conversion). Date (or Transmission) rates: Number of bits sent per second (fb) and Tb (bit duration). Tb = 1/fb Synchronization of bits: To sync sender and receiver clock. Line configuration: Point-to-Point OR Point-to-multipoint. Physical topology: Mesh, Star, Ring, Bus, or Hybrid. Transmission mode: Simplex, Half-duplex, or Full-duplex. 66 2. Data Link Layer It is responsible for moving frames from one node to the next. 67  Framing: It divides the stream of bits into data units called frames. Physical addressing: If the frames are to be distributed to different systems on the network, It adds a header to the frame to define the sender/or receiver of the frames. Flow control: If Date rate (Tx) > Date rate (Rx), the data link layer imposes a flow control mechanism to avoid overwhelming the receiver.  Error control: It adds reliability to the physical layer by adding mechanism to detect & retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames. It is normally achieved through a trailer added to the end of the frame. Access control: When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time. Hop – to - hop (node - to - node) delivery 70 3. Network Layer It is responsible for the delivery of the individual packets from the source host to the destination host. 71  Logical addressing: It adds a header includes logical address of the sender and receiver. Routing: When independent networks or links are connected to create internetworks (networks of network) or a large network, the connecting devices (called routers or switches) route the packets to their final destination. 72 Source-to-destination delivery 73 4. Transport Layer It is responsible for the delivery of a message from one process to another. 74  Service-point address: Computers often run several programs (specific process) at the same time. Transport layer header must contain source-point address (or port address). Segmentation and reassembly: A message is divided into segments, with each segment containing a sequence number. These numbers are used to reassemble the message and to identify and replace packets that were lost in transmission. 75  Connection control: The transport layer can be either connectionless or connection oriented. A connection – oriented:- Prior connection must be established. A connectionless:- No prior connection is established. Flow control: Similar to the data link layer. However, flow control at this layer is performed end to end rather than across a single link. Error control: Similar to the data link layer. However, error control at this layer is performed process to process rather than across a single link. Error correction is usually achieved through retransmission for damage, loss, or duplicate frames. 76  5. Session Layer It is responsible for dialog control and synchronization. 77  Dialog control: It allows the communication between two process to take place in either half-duplex or full-duplex. Synchronization: It allows a process to add checkpoints, or synchronization points to a stream of data. 78  6. Presentation Layer It is responsible for translation, compression, and encrytion. 79  Presentation layer is concerned with the syntax and semantics of the information exchanged between two. Translation: The process (running programs) in two systems are usually exchanging information in the form of character strings, numbers, and so on. The presentation layer at the sender changes the information from its sender-dependent format into a common format. The presentation layer at the receiving machine changes the common format into its receiver-dependent format. Encryption: To carry sensitive information, a system must be able to ensure privacy. Cryptography (Encryption and Decryption). Compression: Data compression reduces number of bits contained in the information. Data compression becomes particularly important in the transmission of multimedia such as text, audio, and video. 80  7. Application Layer It is responsible for providing services to the user.  X.500: (Directory service; Electronic directory of people)  FTAM: File Transfer and Access Management  X.400: Messaging standard specified by ITU-T 81  It enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e- mail, remote file access and transfer, shared database management, and other types of distributed information services. 82 Reliable process-to-process delivery of a message 83  TCP/IP Protocol Suite  The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. It is a protocol suite (a set of protocols organized in different layers) used in the Internet today. Upper level protocol is supported by the 1 or 2 lower level protocols. Original TCP/IP: 4 layers Updated TCP/IP: 5 layers 84 Layered Architecture 85 Communication through an internet 86  Logical connections between layers of the TCP/IP protocol suite  Duty of application, transport, and network layers : End-to-End (internet).  Duty of data-link and physical layers: Hop-to-Hop (link).  Top 3 layers: The data units should not be changed by any router or switch.  Bottom 2 layers: The data units can be changed only by the routers, not by the switches. 87 Identical objects in the TCP/IP protocol suite 88 TCP/IP and OSI model 89  Physical and Data Link Layers:  TCP/IP does not define any specific protocol but it supports all the standard and proprietary protocols.  A network in a TCT/IP internetwork can be a LAN or a WAN.  Network Layer (or internetwork layer): TCP/IP supports the Internetworking Protocol (IP). In turn, uses 4 supporting protocols: ARP, RARP, ICMP, and IGMP IP: It is an unreliable and connectionless protocol – best effort delivery service. IP transports data in packets called datagrams. 1. Address Resolution Protocol (ARP): It obtains the physical address from the logical address. 2. Reverse ARP: It obtains the logical address from the physical address. 3. Internet Control Message Protocol (ICMP): It gives notification of datagram problems back to the sender. It also sends query and error reporting messages. 4. Internet Group Message Protocol (IGMP): It is used to facilitate the simultaneous transmission of a message to a group of recipients.  Transport Layer: Two main protocols - TCP and UDP IP :- Host – to – host protocol (delivery of a packet from one physical device to another). UDP and TCP:- Delivery of a message from one process (running program) to another process. 1. User Datagram Protocol (UDP):  It is the simpler of the two standard TCP/IP transport protocols.  It is a process – to – process to protocols that adds only port address, checksum error control, and length information to the data. 2. Transmission Control Protocol (TCP):  It provides full transport – layer services to applications.  It is a reliable stream (or connection – oriented) transport protocol. 3. Stream Control Transmission Protocol (SCTP):  It provides support for voice over the Internet.  It combines the best features of UDP and TCP. 91  Application Layer:  SMTP : Simple Mail Transfer Protocol  FTP : File Transfer Protocol  HTTP : Hyper Text Transfer Protocol  DNS : Domain Name System  SNMP : Simple Network Management Protocol.  TELNET : Terminal Network. 92 Encapsulation/Decapsulation 93  Addressing  Four levels of addresses are used in an internet employing the TCP/IP protocols. 94  1. Physical addresses  Also known as Link address  It is the address of a node as defined by its LAN and WAN  It is included in the frame used by the data link layer  It is lowest-level address.  Size and Format vary depending on the network.  Example: Ethernet uses a 6-byte (or 48-bit or 12 hexadecimal digits) physical address (imprinted on the NIC) 07:01:02:01:2C:4B 95  IMSI = MAC (NIC)  Mobile Number = IP address 96 2. Logical Addresses 97  Logical Addresses The physical addresses will change from hop to hop, but the logical addresses usually remain the same. 98  3.Port Addresses The physical addresses change from hop to hop, but the logical and port addresses usually remain the same. 99 4.Specific Addresses 100 Chapter 7: Transmission Media 101 Classes of transmission media 102  Twisted-Pair Cable  Wire carries signal.  It also carries: Interference (noise) and Crosstalk and create unwanted signals.  If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relative to the noise or crosstalk sources (e,g., one is closer and the other is farther).  This results in a difference at the receiver.  By twisting the pairs, a balance is maintained.  The unwanted (noise or cross talk) signals are mostly canceled out. 103  UTP and STP cables  The most common twisted-pair cable is unshielded twisted- pair (UTP).  IBM has also produced a version of twisted-pair cable for its use called shielded twisted-pair (STP).  Metal shield improves the quality of cable by preventing the penetration of noise.  It is bulkier and more expensive. 104  Categories of UTP cables The Electronic Industries Association (EIA) has developed standards to classify UTP cables. 105  UTP connector RJ 45 (Ethernet 802.3) 106  1000Base T: (Gigabit Ethernet)  It need all 8 pins.  It use 4 pairs (each transmits 250Mbps duplex) of wires.  Parallel transmissions. 107 UTP performance 108  Applications  Telephone lines to provide voice and data channels.  The local loop line: Subscribers to the central telephone office.  The DSL lines: Used by telephone companies to provide high-data-rate (or high-bandwidth) connections.  LANs : 10Base-T and 100Base-T. 109  Coaxial cable  It carries HF signals than UTP cables.  Larger BW is available. 110  Categories of coaxial cables  Each RG number denotes a unique set of physical specifications:  Wire gauge of the inner conductor  Thickness and type of the inner insulator  Construction of the shield  Size and Type of the outer casing 111 10Base2/5 112  BNC connectors (Bayonet Neill–Concelman) 113  Coaxial cable performance  Attenuation is much higher in coaxial cables than in UTP cable.  More number of repeaters are needed. 114  Applications  Telephone networks:  Analog: carry 10,000 voice signals simultaneously.  Digital: support 600 Mbps data rate.  Coaxial cables are replaced by fiber-optic cable.  Cable TV networks :  RG - 59.  Coaxial cables are replaced by fiber-optic cable.  Ethernet LAN:  10Base2 or Thin Ethernet (RG -58).  10Base5 or Thick Ethernet (RG -11). 115  Fiber-Optic Cable  It carries the signal in terms of light.  It is made of glass or plastic.  It has huge bandwidth (30 THz)  Broadband communication system (BCS):  Optical fiber communication (backbone of the telecommunication technology)  Satellite communication. 116  Principle of light ray  Light travels in a straight line: moving through a single uniform substance.  Light changes direction: moving from a more dense to a less dense substance. 117 Construction  Core (glass or plastic) is more dense than Cladding (plastic).  Dcore (50 μm) < Dcladding  Plastic buffer coating: to cushion the fiber.  Inside jacket: Kevlar (strong material used in the fabrication of bulletproof vests ) to strengthen the cable.  Outer jacket: made of either PVC or Teflon. 118  Operating principle  It uses total internal reflection principle to guide light.  Refractive index of the core (n1) > the cladding (n2). 119 Types 120  Multimode: Support multiple beams  Step-index : Density of the core remains constant from the center to the edges.  Graded-index: Varying densities (Density is highest at the center of the core and decreases gradually to its lowest at the edge).  Single-mode: It uses step-index fiber and carries a highly focused source of light. 121 Fiber types 122  FOC connectors  SC (Subscriber channel): used for cable TV. It uses a push/pull locking system.  ST (Straight-tip): used for connecting cable to networking devices.  MT-RJ: similar in size to RJ45. 123  Optical fiber performance  Attenuation is flatter than in the case of UTP and coaxial cable.  Need 10 times less repeaters. 124  Applications  Backbone networks: wide BW  WDM: wavelength-division multiplexing (WDM) -1600Gbps.  SONET n/w: (Synchronous Optical Network)  Hybrid n/w: Cable TV companies use a combination of optical fiber (backbone structure) and coaxial cable (connections to users: Narrow BW).  LAN:  100Base-FX network (Fast Ethernet)  1000Base-X (use FOC). 125  Advantages  Higher BW ( or higher data rates) than UTP and coaxial cable.  BW utilization are limited by the signal generation and reception technology available.  Less signal attenuation:  FOC: 50 km without repeater.  UTP or coaxial cable: need repeaters every 5 km.  Immunity to EM interference: EM noise cannot affect FOC.  Resistance to corrosive materials. Glass is more resistant to corrosive materials than copper.  Light weight:  Greater immunity to tapping:  Signal tapping is difficult in FOC than copper cables.  Copper cables create antenna effects that can easily be tapped.126  Disadvantages  Installation and maintenance:  FOC is a relatively new technology.  Installation and maintenance require expertise that is not yet available everywhere.  Unidirectional light propagation: Two fibers are needed for bidirectional communication.  Cost: The cable and the interfaces are more expensive. 127  Unguided media: Wireless  Transmission of EM waves without using a physical conductor.  Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. 128 RF wave propagation 129 Propagation methods 130 Frequency Bands 7.131 Wireless transmission waves 7.132  RF waves: Omnidirectional antenna (360˚ coverage)  Applications: Multicasting:  AM and FM radio  TV  Cordless phones. 7.133  Microwaves: Unidirectional antennas  Applications  Point-to-point link or Microwave link (LoS)  Cellular phones  Satellite networks  Wireless LANs 7.134  Infrared (Ir) signals These can be used for short-range communication in a closed area using line-of-sight propagation. The Infrared Data Association (IrDA): provides specifications for a complete set of protocols for wireless infrared communications. 135 136 137 138 Chapter 8: Switching  A network is a set of connected devices.  How to connect multiple devices?  Solution 1: Point-to-Point connection between each pair of devices (a Mesh topology) or between a central device and every other device(a Star topology).  Drawbacks:  Impractical and wasteful when applied to very large networks.  The number and length of links require too much infrastructure to be cost-efficient.  The majority of those links would be idle most of the time. 139  Solution 2: Multiconnections (a Bus topology)  Drawback:  Distance between devices and the total number of devices increase beyond the capacity of the media and equipment. 140  Better solution: Switching 141 Taxonomy of switched networks 142 A small circuit-switched network 8.143  Important points:  Circuit switching takes place at the physical layer.  Before starting communication, the station must make a reservation for the resources to be used during the communication:  Channels (Bandwidth in FDM and Time slots in TDM)  Switch buffers  Switch processing time  Switch input/output ports  Data transfer between two devices are not packetized.  There is no addressing involved during data transfer. Of course, there is end-to-end addressing used during the set-up phase. 144 Three phases 145  Delay:  Total delay: Connect + Data transfer+ Disconnect  Connect: 1. The propagation time of the source device A (slope of the first green box) 2. Request signal transfer time (Height of the first green box) 3. Propagation time of the acknowledgment (ACK) device B (slope of the second green box) 4. Signal transfer time of the ACK (height of the second green box)  Data transfer: 1. The propagation time (slope of the colored box) 2. Data transfer time (height of the colored box)  Disconnect: 1. Receiver requests discussion + signal transfer time 146  Efficiency:  Circuit-switched networks are not efficient as compared to other two types of networks because resources are allocated during the entire duration of the connection.  These resources are not available to the other connections. 147  2.Packet-switched Networks  Packet:  Obtained from input data  called Datagrams.  Size (fixed or variable): Network and the governing Protocol.  Operating at network layer.  The Internet has adopted the datagram approach.  It uses the universal addresses to route packets : S to D.  Two types: 1. Datagram Networks 2. Virtual-Circuit Networks 148  No resource allocation for a packet. It means  No reserved BW on the links.  No scheduled processing time for each packet.  Resources are allocated on demand basis (first come, first-served). Example: When a switch receives a packet, no matter what is the S or D, the packet must wait if there are other packets being processed. 149 Datagrams Networks  Switch is called a router.  Each packet treated independently.  Packets can take any practical route.  Packets may arrive out of order.  Packets may get lost or delayed.  In most protocols, it is the responsibility of an upper-layer protocol to reorder the datagrams or ask for lost datagrams before passing them on to the application. 8.150  The datagram networks : called connectionless networks.  Connectionless: the switch does not keep information about the connection state.  No setup or teardown phases. 151  Routing table  If there are no setup or teardown phases, how to route the packets?  Routing table :  It has a destination address with forwarding output ports (recorded form).  Dynamic and updated periodically.  The destination address (header of a packet) remains the same during the entire journey of the packet.  Circuit-switched network: Each entry is created (setup phase is completed) and deleted (teardown phase is over). 8.152  Efficiency  Better efficiency than the circuit-switched network.  Reason: Resources are allocated only when there are packets to be transferred. 153  Greater delay than the virtual- Delay circuit network.  Reasons:  Although there are no setup and teardown phases, each packet may experience a wait at a switch before it is forwarded.  Delay is not uniform for the packets of a message (different paths)  Delay calculation (2 switches): 3T + 3τ + WI + W2 T: Transmission time τ : Propagation delay (slopes 3τ of the lines) W1 and W2: Waiting times  Processing time in each switch is ignored. 8.154  2.2 Virtual-Circuit Network  It is a cross between a circuit-switched n/w and a datagram n/w. It has some characteristics of both. 1. Circuit-switched n/w: 3 phases ( setup, data transfer and teardown). 2. Allocation of Resources:  Circuit-switched n/w:- during the setup phase  Datagram n/w: on demand basis 3. Datagram network: data are packetized and each packet carries an address in the header. 4. Circuit-switched n/w: all packets follow the same path established during the connection. 5. Circuit-switched n/w: Physical layer Datagram n/w: Network layer Virtual-circuit n/w: Data link layer 155  Virtual-circuit n/w Switches: allow traffic from S to D.  Examples of S or D: Computer, Packet switch or Bridge. 8.156  Addressing  Two types of addressing are involved: 1. Global 2. Local VCI (virtual-circuit identifier). 157  Global Addressing A source or a destination needs to have a global address - an address that can be unique over world wide.  Used only to create a VCI. 158  Virtual-circuit identifier (VCI)  It is used for data transfer.  When a frame arrives at a switch, it has a VCI; when it leaves, it has a different VCI. 8.159  Three Phases 1. Setup phase: The S and D use their global addresses to help switches make table entries for the connection. 2. Data transfer 3. Teardown phase: The S and D inform the switches to delete the corresponding entry. 160 2.Source-to-destination data transfer 8.161  3.Setup acknowledgment 1.Setup request 8.162 Teardown Phase: In this phase, source A, after sending all frames to B, sends a special frame called a teardown request. Destination B responds with a teardown confirmation frame. All switches delete the corresponding entry from their tables. 163  Efficiency  Resource reservation can be made: 1. During the setup: Delay for each packet is the same. 2. On demand during the data transfer phase: each packet may have different delays.  Big advantage: Resource allocation is on demand.  The source can check the availability of the resources, without actually reserving it. 164  Delay  Total delay is 3T+ 3τ + setup delay + teardown delay T: Transmission time τ : Propagation delay 8.165  Ch.9: Using Telephone and Cable Networks for Data Transmission Telephone networks (late 1800s) : Based on circuit switching  First: analog voice communication.  Second: Digital-voice (using PCM)  Third: Digital data using dial-up modem (existing but slow)  Fourth: Digital subscriber line (DSL): High-speed downloading and uploading. Cable networks:  First: TV programs.  Second: Internet with high-speed. 9.166  A telephone system  PSTN: Public Switched Telephone Network  Local-loop: Twisted-pair cable with BW of 4 kHz.  Trunks: Optical fiber or Satellite link (supports large number of voice conversations simultaneously) 9.167  Functionalities 1. Signaling: Dial tone, Ringing tone, and Busy tone 2. Transferring telephone numbers between offices 3. Maintaining and monitoring the call 4. Keeping billing information 5. Maintaining and monitoring the status of the telephone network equipment 6. Providing other functions such as caller ID, voice mail, and so on 168  Data signals require a higher degree of 1. Dial-up modems accuracy to ensure integrity. For safety’s sake, therefore, the edges of this range are not used for data communications 169  MODEM Standards (ITU-T)  The modem uses a combined modulation and encoding technique called trellis coded modulation (TCM).  Trellis is essentially QAM plus a redundant bit (used for error detection).  Basic data rate: 2.4 kbps  V.32:- 32-QAM (5-bits):  4 - bits for date and 1 bit for error detection  Resulting data rate= 4 x 2.4 = 9.6 kbps  V.32 bis:- First ITU-T standard: 128 - QAM (7 bits)  6 bits for data and 1 bit for error detection  Resulting data rate= 6 x 2.4 = 14.4 kbps 170 V.34bis:  28.8 kbps with 960 - point constellation.  33.6 kbps with 1664 - point constellation. V.90 : 56 k modems: (world-wide telephone companies)  fs = 8000 sps  n = 8 bits per sample.  7 bits for data and 1 bit for control purpose.  Total bit rate: 8000 x 7 = 56 kbps. 171 Uploading and downloading in 56K modems 9.172  2.Digital Subscriber Line (DSL) It provides higher-speed than exiting local lines (Modems) to access the Internet.  DSL technologies: ADSL, VDSL, HDSL, and SDSL.  called: xDSL (where x can be replaced by A, V, H, or S)  ADSL: Asymmetric DSL  HDL: High-bit-rate DSL  VDSL: Very high-bit-rate DSL  SDSL: Symmetric DSL 173  ADSL Asymmetric DSL. Different uploading and downloading speed. Designed for residential users and not for businesses. The existing local loops can handle bandwidths up to 1.1 MHz 174  Adaptive Technology  Theoretical bandwidth of the local loop is 1.1 MHz.  Factors affecting the bandwidth:  Distance between residence and the switching office  The size of the cable  The signalling used  Date rate of ADSL is not fixed, it changes based on the condition and type of the local loop cable 175 Discrete Multitone Technique (DMT) (QAM and FDM) 9.176  Channel 0: Voice channel  Idle channels: 1 to 5 are not used and provide a gap between voice and data communication.  Upstream data and control:  Channels: 6 to 30 (25 channels)  24 for data + 1 for control  Total bit rate: 24 x 4 KHz x 15 = 1.44 Mbps  Actual: below 500 kbps  Downstream data and control:  Channels: 31 to 255 (225 channels)  224 for data + 1 for control  Total bit rate: 224 x 4 KHz x 15= 13.4 Mbps.  Actual : below 8 Mbps 177 Customer site: ADSL modem Telephone company site: DSL access multiplexer 9.178 Summary of DSL technologies 9.179  3. Cable TV network Communication in the traditional cable TV network is unidirectional. 180  Hybrid fiber-coaxial (HFC) network Communication in an HFC cable TV network can be bidirectional. 9.181  4.Cable TV for Data transfer Cable companies are now competing with telephone companies for the residential customer who wants high-speed data transfer. DSL (high-data-rate connections) for residential subscribers using UTP cable, which is very susceptible to interference.  Solution: Cable TV network. 182  Bandwidth  Video band:  RF band: 54 to 550 MHz.  Each TV signal has BW of 6 MHz.  RF BW = (550 - 54) MHz= 490 MHz.  Number of TV channels = 490 MHz/6 MHz = 80. 9.183  Bandwidth  Downstream Data Band  RF band: 550 to 750 MHz. This band is divided into 6-MHz channels.  Modulation: 64-QAM (N = 6 bits/symbol) or possibly 256-QAM.  5 bits for data and one bit for FEC.  Data rate:  30 Mbps (5 bits/Hz × 6 MHz).  With 1OBase-T cable, this limits the data rate to 10 Mbps. 9.184  Upstream Data Band  5 to 42 MHz. This band is also divided into 6-MHz channels.  Modulation:  LF are more susceptible to noise and interference. For this reason, the QAM technique is not suitable for this band.  A better solution is QPSK.  Data Rate:  2 bits/symbol in QPSK.  12 Mbps (2 bits/Hz × 6 MHz)  However, actual data rate is less than 12 Mbps. 185  Sharing  Upstream:  RF BW = (42 – 5) MHz = 37 MHz  Channels = 37 MHz/6MHz = 6.  How 1000, 2000, or even 100,000 subscribers can be served with 6 channels.  Solution: FDM/TDM sharing.  Downstream:  RF BW = (750 – 550) MHz = 200 MHz  Channels = 200 MHz/6 MHz = 33 channels  Solution: FDM/TDM sharing. 186  CM and CMTS CM : Cable Modem CMTS: CM Transmission system 187  Data Transmission Schemes: DOCSIS  Several schemes have been designed to create a standard for data transmission over an HFC network.  Multimedia Cable Network Systems (MCNS), called Data Over Cable System Interface Specification (DOCSIS). It defines all the protocols necessary to transport data from a CMTS to a CM. 188