Data Communications PDF

Data Communications I. Introduction to Data Communications 1ST Semester, A.Y 2024-2025  Data Communications I. Introduction to Data Communications...

Data Communications I. Introduction to Data Communications 1ST Semester, A.Y 2024-2025  Data Communications I. Introduction to Data Communications 1ST Semester, A.Y 2024-2025 Notes from previous slide: The term “Data Communication” comprises two words: Data and Communication. Data can be any text, image, audio, video, and multimedia files. Communication is an act of sending or receiving data. Thus, data communication refers to the exchange of data between two or more networked or connected devices. These devices must be capable of sending and receiving data over a communication medium. Examples of such devices include personal computers, mobile phones, laptops, etc. ------Picture: Figure: A simple network of computing devices. four different types of devices — computer, printer, server and switch are connected to form the network. These devices are connected through a media to the network, which carry information from one end to other end. Effective and efficient data communication and networking facilities are vital to any enterprise. Three different forces have consistently driven the architecture and evolution of data communications and networking facilities: traffic growth, development of new services, and advances in technology. Outline Topic Introduction to Data Communications Data Communications Network Architecture, Protocols, and Standards I. Networks II. Circuit Switching III. Packet Switching IV. Protocols V. Internet Standards Organizations for Data Communications Intended Learning Outcome Define the following terms: data, data communications, data communications circuit, and data communications network Give a brief description of the evolution of data communications Define data communications network architecture Describe data communications protocols Describe the basic concepts of connection-oriented and connectionless protocols Describe syntax and semantics and how they relate to data communications Define data communications standards and explain why they are necessary  DATA Refers to information presented in whatever form in agreed upon by the parties creating and using the data. INTRODUCTION DATA COMMUNICATIONS Are the exchange of data between two devices via some form of transmission medium such as wire cable. Notes from previous slide: Data can be any text, image, audio, video, and multimedia files. Data communications deals with the transmission of signals in a reliable and efficient manner. Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices. Data Communications”, deals with the most fundamental aspects of the communications function, focusing on the transmission of signals in a reliable and efficient manner. Consider this example: a sequence of numbers “100, 150, 200” is just data. However, if you put it into context: “The sales of a product over the past three months were 100, 150, and 200 units, The fundamental purpose of a communications system is the exchange of data between two parties. This section introduces a simple model of communication. Source - generates data to be transmitted Transmitter - converts data into transmittable signals Transmission System - carries data from source to destination Receiver - converts received signal into data Destination - takes incoming data  Enables an information system to deliver information DATA Improves the flexibility of data collection and transmission COMMUNICATIONS DO Basis of virtual organizations Provides e-collaboration  BASIC CONCEPT OF DATA COMMUNCATION ❑ Bandwidth: Amount of data that can be transferred from one point to another in a certain time period. ❑ Attenuation: Loss of power in a signal as it travels from the sending device to the receiving device. ❑ Broadband: Multiple pieces of data, sent simultaneously to increase transmission rate. ❑ Narrowband: Voice-grade transmission channel capable of transmitting a maximum of 56,000 bps, so only a limited amount of information can be transferred. ❑ Protocols: Rules that govern data communication - Error detection, message length, and transmission speed. 5 Components of Data TRANSMITTER RECEIVER MEDIUM MESSAGE PROTOCOL Communication Notes from previous slide: Transmitter: The transmitter is the device that sends the message. It can be a computer, workstation, telephone handset, video camera, and so on. Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. Medium: The transmission medium is the physical path by which a message travels from sender to receiver. It can consist of twisted pair wire, coaxial cable, fiber-optic cable, laser or radio waves (terrestrial or satellite microwave). Message: The message is the transmission (data) to be communicated. It can consist of text, number, pictures, sound, or video or any combination of these. Protocol: A protocol is a set of rules that governs data communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking German cannot be understood by a person who speaks only Japanese. In communication, Protocol is a set of standard rules that the communicating parties — the sender, the receiver, and all other intermediate devices need to follow. We know that the sender and receiver can be parts of different networks, placed at different geographic locations. Besides, the data transfer rates in different networks can vary, requiring data to be sent in different formats. 11.8.1 Need for Protocols We need protocols for different reasons such as flow control, access control, addressing, etc. Flow control is required when the sender and receiver have different speeds of sending and receiving the data Protocol – Agreement between the communicating devices. HTTP stands for HyperText Transfer Protocol. It is the primary protocol used to access the World Wide Web,  DATA Representation ❑ Text: ASCII: 7-bit pattern (128 different symbols) Extended ASCII: 8-bit pattern (with an extra 0 at left from 00000000 to 0111111 Unicode: 32 bits pattern (65,536,216) symbols, which is definitely enough to represent any symbol in the world. ❑ Numbers: represented by bit pattern (binary number) ❑ Images : represented by matrix of pixels (picture element), small dot. The size of pixel represent the resolution. ❑ Audio: represent sound by continuous (analog) signal ❑ Video: can be analog or digital signal DATA FLOW Notes from previous slide: Date Flow/ Type of Data Communication: As we know that data communication is communication in which we can send or receive data from one device to another. The data communication is divided into three types: 1. Simplex Communication: It is one-way communication or we can say that unidirectional communication in which one device only receives and another device only sends data and devices uses their entire capacity in transmission. For example, IoT, entering data using a keyboard, listing music using a speaker, etc. 2. Half Duplex communication: It is a two-way communication, or we can say that it is a bidirectional communication in which both the devices can send and receive data but not at the same time. When one device is sending data then another device is only receiving and vice-versa. For example, walkie-talkie. 3. Full-duplex communication: It is a two-way communication or we can say that it is a bidirectional communication in which both the devices can send and receive data at the same time. For example, mobile phones, landlines, etc. The main types are simplex (one-way communication), half-duplex (two-way communication, but not simultaneously), and full-duplex (two-way communication simultaneously).  NETWORKS NETWORK NODE LINK growth of number & power of computers is driving need for interconnection also seeing rapid integration of voice, data, image & video technologies two broad categories of communications networks: Local Area Network (LAN) Wide Area Network (WAN) Notes from previous slide: A set of processing nodes connected by communication links. 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. The number of computers in use worldwide is in the hundreds of millions, with pressure from users of these systems for ways to communicate among all these machines being irresistible. Advances in technology have led to greatly increased capacity and the concept of integration, allowing equipment and networks to deal simultaneously with voice, data, image, and even video. Have two broad categories of networks: Local Area Networks (LAN) and Wide Area Networks (WAN).  COMMUNICATION MEDIA Selection is a basic choice internal use entirely up to business long-distance links made by carrier Rapid technology advances change mix fiber optic wireless Transmission costs still high Hence interest in efficiency improvements Notes from previous slide: A simple recall: The basic building block of any communications facility is the transmission line. One of the basic choices facing a business user is the transmission medium. For use within the business premises, this choice is generally completely up to the business. For long-distance communications, the choice is generally but not always made by the long-distance carrier. In either case, changes in technology are rapidly changing the mix of media used. The ever-increasing capacity of fiber optic channels is making channel capacity a virtually free resource. However, switching is now becoming the bottleneck. The growing use of wireless transmission, is a result of the trend toward universal personal telecommunications and universal access to communications. Despite the growth in the capacity and the drop in cost of transmission facilities, transmission services remain the most costly component of a communications budget for most businesses. Thus, the manager needs to be aware of techniques that increase the efficiency of the use of these facilities, such as multiplexing and compression. Many types of communication media: twisted (copper) pair coaxial (copper) cable radio infrared fiber optic cable satellites  PHYSICAL STRUCTURE ❑ Type of Connection Point to Point - single transmitter and receiver Multipoint - multiple recipients of single transmission ❑ Physical Topology Connection of devices Type of transmission - unicast, mulitcast, broadcast  TYPE OF CONNECTION ❑ Point to Point - single transmitter and receiver Point-to-Point protocol (PPP) defines how two devices will authenticate each other and establish a direct link between them to exchange data. Point to Point Protocol (PPP) This protocol defines how two devices will authenticate each other and establish a direct link between them to exchange data. For example, two routers with direct connection communicate using PPP. The Internet users who connect their home computers to the server of an Internet Service Provider (ISP) through a modem also use PPP. The communicating devices should have duplex modes for using this protocol. This protocol maintains Notes 2024-25 Data Communication 219 data integrity ensuring that the packets arrive in order. It intimates the sender  TYPE OF CONNECTION ❑ Multipoint (multidrop) connection: TYPE OF TOPOLOGIES BUS TOPOLOGY Notes from previous slide: Bus topology In a Bus topology, one long cable acts as a single communication channel, and all the nodes or computers are connected to this cable. The cable that uses in bus topology is RJ-45 cable or coaxial cable. Advantages of Bus topology Easy to add or remove computer systems in a network. Required only cable to form the whole network. It is less expensive. It broadcast the message to all the devices that are connected through the Cable. It is easy to maintain. In case of any computer failure, there will be no effect on any other nodes. Disadvantages of Bus topology The entire network will be failed in case of cable failure. We can’t send private messages in bus topology. It takes more time to pass messages from one node to another node. The length of the cable is limited data transmission is done in only one direction. RING TOPOLOGY Notes from previous slide: Ring topology It is called Ring topology because it forms a ring, and in a ring topology each node is strongly connected with its adjacent node. Advantages of Ring topology It forms a strong network. Each and every node can share data with other nodes connected through a ring topology Transmission rate of data is very high. The data sent through this topology will be broadcast. Disadvantages of Ring topology It is a very difficult task to add new nodes. If we want to send data from a source to a destination machine then data will be unnecessarily passed to all the nodes. A single point of failure, that means if a single node goes down then the entire network goes down. It is very difficult to recover this topology if any particular machine is not working properly. We can’t send private messages. STAR TOPOLOGY Notes from previous slide: Star topology In Star topology all the computer systems are connected with a central device called HUB and the sharing of data is only possible through HUB. Advantages of Star topology It broadcast the messages. It is less expensive due to less cable. easy to connect a new computer system without affecting the rest of the network. If one system is failed, then it would not be a failure of the entire network. Disadvantages of Star topology In Star topology, we must require a network device like HUB, Switch, etc. If two systems want to share the data, then sharing is only possible through HUB. We should not send private messages (HUB will broadcast the message). If HUB is failed then the entire network will be failed. MESH TOPOLOGY Notes from previous slide: Mesh Topology In this topology every node is directly connected with each other, so we can directly send the data to the destination machine without going to the intermediate machine. Advantages of Mesh topology mesh topology is a very good topology to send private messages. All nodes are directly associated with another node. So, it provides point to point connection. Unlike ring topology, if a particular machine is failed then the entire network will not fail. multiple devices can send or receive data simultaneously. Disadvantages of Mesh topology It is very difficult to add some new nodes because each and every computer is directly connected to another. If a particular machine not working then we can’t send or receive data from the failed machine. HYBRID TOPOLOGY Notes from previous slide: Hybrid topology A combination of various different topologies such as Bus, Star, Ring, etc is called Hybrid topology. Advantages of Hybrid topology It is very flexible. We can easily add or remove new nodes without affecting the rest of the network. Hybrid topology is used to create large networks. We can modify it as per requirement. Disadvantages of Hybrid topology It is very expensive. Design of a Hybrid topology is very complex. Installation process is very difficult. TREE TOPOLOGY Notes from previous slide: Tree topology In this topology, all the nodes are connected like branches of a tree. the combination of Bus and Star topology is called Tree topology. Advantages of Tree topology We can easily add or remove new nodes without affecting the rest of the network. Tree topology is used to create large networks. It is easy to maintain. We can easily identify faults in tree topology. It is a combination of Bus and Star topology. Disadvantages of Tree topology Design of a Tree topology is very complex as compared to any other topology. If the first level of a node is not working properly then the next level of nodes also faces the same problem. It is very expensive as compared to any other topology.  CATEGORIES OF NETWORKS ❑ Local Area Networks (LANs) Short distances Designed to provide local interconnectivity ❑ Metropolitan Area Networks (MANs) Provide connectivity over areas such as a city, a campus ❑ Wide Area Networks (WANs) Long distances Provide connectivity over large areas  SWITCHING TECHNIQUES 1 Circuit Switching 2 Packet Switching  CIRCUIT SWITCHING Uses a dedicated communications path established for duration of conversation Comprising a sequence of physical links With a dedicated logical channel Notes from previous slide: 11.5.1 Circuit Switching In circuit switching, before a communication starts, a dedicated path is identified between the sender and the receiver. This path is a connected sequence of links between network nodes. All packets follow the same path established during the connection. In earlier days, when we placed a telephone call, the switching equipment within the telephone system finds out a physical path or channel all the way from our telephone at home to the receiver’s telephone. This is an example of circuit switching. All resources (e.g. communication links) needed by a “call” are dedicated to that call for its duration. In a circuit-switching network, a dedicated communications path is established between two stations through the nodes of the network. That path is a connected sequence of physical links between nodes, with a logical channel dedicated to the connection. Data generated by the source station are transmitted along the dedicated path as rapidly as possible. The most common example of circuit switching is the telephone network. eg. telephone network/ A voice telephone call See illustration above. Call from A to F blocks calling from B to E. Resource reservation: resources are always available when needed by a call, providing a guaranteed quality of service.  PACKET SWITCHING Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications Notes from previous slide: Data entering network is divided into small chunks called “packets”. A packet-switching network uses a quite different approach, without need to dedicate transmission capacity along a path through the network. Rather, data is sent in a sequence of small chunks, called packets. Each packet is passed through the network from node to node along some path leading from source to destination. At each node, the entire packet is received, stored briefly, and then transmitted to the next node. Packet-switching networks are commonly used for terminal-to-computer and computer-to-computer communications. See illustration above: Packets traversing the network share network resources with other packets. Demand for resources may exceed resources available: Contention: two packets arrive simultaneously at D destined for E or F Queuing (waiting) for resources. Statistical sharing of resources.  WHY RESOURCE SHARING? To save/make money! Circuit switching: give each caller 100 Kbits/sec capacity. 10 callers can be supported. Packet switching: with 35 calls in progress, the probability that 10 or more callers are simultaneously active is less than 0.0004. Many more callers can be supported with only a small probability of contention. If users are “bursty”, then packet switching is advantageous.  PROTOCOLS Rules by which active network elements communicate with each other is a protocol Protocols define the formats and timing of messages exchanged, and actions taken on receipt of messages for peer entities  STANDARD BODIES Industry Canada National Research Council (Canada) (NRC-CNRC) National Canadian Standards Association (CSA) Standard Bodies American National Standards Institute (ANSI) US National Institute of Standards and Technology (NIST)  STANDARD BODIES International Organization for Standardization (ISO) International International Telecommunications Union (ITU) Standard Bodies Non- governmental Organizations  STANDARD BODIES ISO (www.iso.ch) Non-treaty agency of the United Nations. Collaborates standards development for information technology. ITU (www.itu.int) ITU-T: telecom sector of ITU UN treaty agency that sets telecommunications standards. ANSI (www.ansi.org) The US national standards body. Coordinates and accredits standards development across the US. IEEE (www.ieee.org) US based international professional organization. Develops standards and submits to ANSI for approval.  STANDARD BODIES Telcordia (www.telcordia.com) Coordinates and develops standards for US telephone service ETSI (www.etsi.org) European Telecommunications Standards Institute Similar to Telcordia, but for Europe IAB / IETF / IRTF Internet Architecture Board (www.iab.org) Internet Engineering Task Force (www.ietf.org) Internet Research Task Force (www.irtf.org) Object Management Group (OMG) (www.omg.org) Consists of many companies Develops/co-ordinates CORBA/IDL, UML standards WWW consortium (www.w3.org) Develops/co-ordinates standards such as HTTP, HTML, XML, …  THE INTERNET Internet evolved from ARPANET first operational packet network applied to tactical radio & satellite nets also had a need for interoperability led to standardized TCP/IP protocols Four “classic” (1980s) Internet applications: Electronic mail Usenet news Remote login File transfer  Networking Today Networks in Our Past and Daily Lives Interconnecting Our Lives Networking Impacts in Our Daily Lives ❑ Networks support the way we learn. ❑ Networks support the way we communicate. ❑ Networks support the way we work. ❑ Networks support the way we play.  The concept of any device, to any content, in anyway is a The Changing major global trend that requires significant changes to the way devices are used. This trend is known as Bring Your Own Environment Device (BYOD).  Network Trends Online Collaboration | Cloud Computing Cloud computing offers the following potential benefits: Organizational flexibility Agility and rapid deployment Reduced cost of infrastructure Refocus of IT resources Creation of new business models THANK YOU!  Data Communications and Computer Networking I ( ECE 112) II. Open System Interconnection 1st Semester, A.Y 2024-2025 Outline Topic Open System Interconnection in a Network OSI Layer Physical Layer Data Link Layer Network Layer Intended Learning Outcome Conceptualize open systems interconnection Identify and explain the functions of each of the layers of the seven-layer OSI model Open System Interconnection (1984) Open systems interconnection (OSI) is the name for a set of standards for communicating among computers. The primary purpose of OSI standards is to serve as a structural guideline for exchanging information between computers, workstations, and networks. The OSI is endorsed by both the ISO and ITU-T, which have worked together to establish a set of ISO standards and ITU-T recommendations that are essentially identical  OSI Layers It is used for data network design, operation specifications, and troubleshooting. The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. This hierarchy was developed to facilitate the intercommunications of data processing equipment by separating network responsibilities into seven distinct layers. In fact, if all seven levels of the OSI model are addressed, as little as 15% of the transmitted message is actually source information, and the rest is overhead. The result of adding headers to each layer is illustrated in Figure above.  Benefits of using Layered Model Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below. Fosters competition because products from different vendors can work together. Prevents technology or capability changes in one layer from affecting other layers above and below. Provides a common language to describe networking functions and capabilities. OSI Layer and Function The OSI seven-layer protocol hierarchy. In recent years, the OSI seven-layer model has become more academic than standard, as the hierarchy does not coincide with the Internet’s four-layer protocol model. However, the basic functions of the layers are still performed, so the seven-layer model continues to serve as a reference model when describing network functions. Levels 4 to 7 address the applications aspects of the network that allow for two host computers to communicate directly. The three bottom layers are concerned with the actual mechanics of moving data (at the bit level) from one machine to another. A brief summary of the services provided by each layer is given here.  1. PHYSICAL LAYER 2nd Semester, A.Y 2020-2021  OSI Layer Controls how data is placed on the communication media. The role of the OSI Physical layer is to encode the binary digits Physical that represent Data Link layer frames into signals and to Layer transmit and receive these signals across the physical media o copper wires, o optical fiber, and o wireless - that connect network devices.  OSI Layer Physical Layer  OSI Layer The Physical Layer interconnects our data networks. The OSI Physical layer provides the means to transport across the network media the bits that make up a Data Link layer frame. This layer accepts a complete frame from the Data Link layer and encodes it as a series of signals that are transmitted onto the local media. Physical The encoded bits that comprise a frame are received by either an end device or an intermediate device. Layer The delivery of frames across the local media requires the following Physical layer elements: The physical media and associated connectors A representation of bits on the media Encoding of data and control information Transmitter and receiver circuitry on the network devices The purpose of the Physical layer is to create the electrical, optical, or microwave signal that represents the bits in each frame.  OSI Layer The Physical layer technologies are defined by organizations such as: o The International Organization for Standardization (ISO) Physical o The Institute of Electrical and Electronics Engineers (IEEE) Layer o The American National Standards Institute (ANSI) o The International Telecommunication Union (ITU) o The Electronics Industry Alliance/Telecommunications Industry Association (EIA/TIA) o National telecommunications authorities such as the Federal Communication Commission (FCC) in the USA.  OSI Layer Three Fundamentals Functions The physical Data components Signaling Encoding  OSI Layer Three Fundamentals Functions The 3 Fundamental Functions of Physical Layer: The physical elements are the electronic hardware devices, media and connectors other that transmit and carry the signals to represent the bits. Encoding: Encoding is a method of converting a stream of data bits into a predefined "code. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the received. In addition to creating codes for data, encoding methods at the Physical layer may also provide codes for control purposes such as identifying the beginning and end of a frame. Signaling: The Physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing the bits is called the signaling method. The Physical layer standards must define what type of signal represents a "1" and a "0". This can be as simple as a change in the level of an electrical signal or optical pulse or a more complex signaling method. Many signaling methods use predictable transitions in the signal to provide synchronization between the clocks of the transmitting and the receiving devices. Characteristics & Uses of Network Media  Characteristics & Uses of Network Media Cables have different specifications and expectations pertaining to performance. Coaxial Cable: Requires fewer repeaters than twisted pair Less expensive than fiber More expensive and more difficult to install than twisted pair Shielded twisted-pair cable (STP) Screened UTP (ScTP), also known as Foil Twisted Pair (FTP) Unshielded twisted-pair cable (UTP) is a four-pair wire medium used in a variety of networks. TIA/EIA-568-A contains specifications governing cable performance. RJ-45 connector When communication occurs, the signal that is transmitted by the source needs to be understood by the destination. The transmitted signal needs to be properly received by the circuit connection designed to receive signals. The transmit pin of the source needs to ultimately connect to the receiving pin of the destination.  Unshielded Twisted Pair (UTP) A. Straight-through B. Cross-Over C. Rollover  Unshielded Twisted Pair (UTP) Hub or Switch Host or Router  Unshielded Twisted Pair (UTP) A. Straight-through - The cable that connects from the switch port to the computer NIC port is called a straight- through cable. B. Cross-Over - The cable that connects from one switch port to another switch port is called a crossover cable. SAFETY ISSUES: Electrical Hazards A potential problem with copper media is that the copper wires could conduct electricity in undesirable ways. This could subject personnel and equipment to a range of electrical hazards. A defective network device could conduct currents to the chassis of other network devices. Additionally, network cabling could present undesirable voltage levels when used to connect devices that have power sources with different ground potentials. copper cabling may conduct voltages caused by lightning strikes to network devices. Fire Hazards Cable insulation and sheaths may be flammable or produce toxic fumes when heated or burned. Building authorities or organizations may stipulate related safety standards for cabling and hardware installations.  2. DATA LINK LAYER The data-link layer is responsible for providing error-free communications across the physical link connecting primary and secondary stations (nodes) within a network (sometimes referred to as hop-to-hop delivery). The data-link layer packages data from the physical layer into groups called blocks, frames, or packet provides a means to activate, maintain, and deactivate the data communications link between nodes. The data-link layer provides the final framing of the information signal, provides synchronization, facilitates the orderly flow of data between nodes, outlines procedures for error detection and correction, and provides the physical addressing information. 1st Semester, A.Y 2024-2025  OSI Layer Data Link The Data Link layer provides a means for exchanging data over Layer a common local media. The service of the Data Link Layer provides as it prepares communication for transmission on specific media. The Data Link layer performs two basic services: Allows the upper layers to access the media using techniques such as framing Controls how data is placed onto the media and is received from the media using techniques such as media access control and error detection  OSI Layer A block diagram of a network showing data transferred between two computers (A and E) at the datalink level is illustrated in Figure above. Note that the hubs are transparent but that the switch passes the transmission on to only the hub serving the intended destination.  3. NETWORK LAYER The network layer provides details that enable data to be routed between devices in an environment using multiple networks, subnetworks, or both. Networking components that operate at the network layer include routers and their software. 1st Semester, A.Y 2024-2025  OSI Layer The Network layer determines which network configuration is most appropriate for the function provided by the network and addresses and routes data within networks by establishing, maintaining, and terminating connections between them. Network Layer The network layer provides the upper layers of the hierarchy independence from the data transmission and switching technologies used to interconnect systems. The network layer also typically provides the source and destination network addresses (logical addresses), subnet information, and source and destination node addresses. Figure  OSI Layer Network Layer Figure above illustrates the network layer of the OSI protocol hierarchy. Note that the network is subdivided into subnetworks that are separated by routers.  ANNOUNCEMENT Next Topic 4. Transport Layer 5. Session Layer 6. Presentation Layer 7. Application Layer THANK YOU!  Data Communications and Computer Networking I ( ECE 112) II. Open System Interconnection 1st Semester, A.Y 2024-2025 Outline Topic OSI Layer TRANSPORT LAYER SESSION LAYER PRESENTATION LAYER APPLICATION LAYER  4. TRANSPORT LAYER The transport layer controls and ensures the end-to-end integrity of the data message propagated through the network between two devices, which provides for the reliable, transparent transfer of data between two endpoints. Transport layer responsibilities includes message routing, segmenting, error recovery, and two types of basic services to an upper-layer protocol: connectionless oriented and connectionless. The transport layer is the highest layer in the OSI hierarchy in terms of communications and may provide data tracking, connection flow control, sequencing of data, error checking, and application addressing and identification 1st Semester, A.Y 2024-2025  Transport Layer OSI Layer Figure above depicts data transmission at the transport layer. The Transport layer prepares application data for transport over the network and processes network data for use by applications.  OSI Layer Transport Layer Major functions of the transport layer and the role it plays in data networks.  5. SESSION LAYER The session layer is responsible for network availability (i.e., data storage and processor capacity). Session layer protocols provide the logical connection entities at the application layer. These applications include file transfer protocols and sending e-mail. Session responsibilities include network log-on and log-off procedures and user authentication. 1st Semester, A.Y 2024-2025  OSI Layer A session is a temporary condition that exists when data are actually in the process of being transferred Session and does not include procedures such as call Layer establishment, setup, or disconnect. The session layer determines the type of dialogue available Simplex Half duplex Full duplex  OSI Layer Session Layer Session layer characteristics include virtual connections between applications entities, synchronization of data flow for recovery purposes, creation of dialogue units and activity units, connection parameter negotiation, and partitioning services into functional groups. Figure above illustrates the establishment of a session on a data network.  6. PRESENTATION LAYER The presentation layer provides independence to the application processes by addressing any code or syntax conversion necessary to present the data to the network in a common communications format. 1st Semester, A.Y 2024-2025  OSI Layer The presentation layer specifies how end-user Presentat applications should format the data. This layer ion Layer provides for translation between local representations of data and the representation of data that will be used for transfer between end users. The results of encryption, data compression, and virtual terminals are examples of the translation service.  OSI Layer Presentat ion Layer Figure above shows an illustration of the presentation layer. The presentation layer translates between different data formats and protocols. Presentation functions include data file formatting, encoding, encryption and decryption of data messages, dialogue procedures, data compression algorithms, synchronization, interruption, and termination. The presentation layer performs code and character set translation (including ASCII and EBCDIC) and formatting information and determines the display mechanism for messages.  7. APPLICATION LAYER The application layer is the highest layer in the hierarchy and is analogous to the general manager of the network by providing access to the OSI environment. 2nd Semester, A.Y 2020-2021  OSI Layer The applications layer provides distributed Application information services and controls the sequence Layer of activities within an application and also the sequence of events between the computer application and the user of another application.  OSI Layer Application Layer  OSI Layer The application layer (shown in Figure above) communicates directly with the user’s application program. Application User application processes require application layer service elements to access the networking environment. There are two types of service elements: CASEs (common Layer application service elements), which are generally useful to a variety of application processes and SASEs (specific application service elements), which generally satisfy particular needs of application processes. CASE examples include association control that establishes, maintains, and terminates connections with a peer application entity and commitment, concurrence, and recovery that ensure the integrity of distributed transactions. SASE examples involve the TCP/IP protocol stack and include FTP (file transfer protocol), SNMP (simple network management protocol), Telnet (virtual terminal protocol), and SMTP (simple mail transfer protocol). OSI Layer in General  ANNOUNCEMENT Next Topic Data Communications Circuit THANK YOU! ECE 110 Communications 3: Data Communications Configurations and Network Topology Prepared by: Engr. Lovely Mae Dagsa, MSc., ECT Course Instructor  NETWORK Uses communication equipment to connect LAN – shares data and WAN – shares data two or more PC based resources among users among users who are computers and their in close proximity geographically distant resources  BASIC COMPONENTS o Sending device o Communications link o Receiving device  NETWORK DESIGN Transmission Media Topology – Physical layout of components Protocol – Rules governing communication - LAN Distance - WAN - Peer-to-peer Technology - File server - Client/server  DATA TRANSMISSION o Digital lines o Sends data as distinct pulses o Need digital line o Analog lines o Sends a continuous electrical signal in the form of a wave o Conversion from digital to analog needed o Telephone lines, coaxial cables, microwave circuits  ANALOG TRANSMISSION o Alter the carrier wave o Amplitude – height of the wave is increased to represent 1 o Frequency – number of times wave repeats during a specific time interval can be increased to represent a 1  MODEM o Modulate - Convert from digital to analog o Demodulate - Convert from analog to digital o Speeds up to 56,000 bps (56K)  MODEM Transmission process o Modulation – Computer digital signals converted to analog. o Sent over analog phone line. o Demodulation – Analog signal converted back to digital.  DSL o Uses conventional telephone lines o Uses multiple frequencies to simulate many modems transmitting at once o No industry standard - Cost - Speed o Phone line shared between computer and voice  CABLE MODEM o Coaxial cables o Does not interfere with cable TV reception o Up to 10 million bps o Always on o Shared capacity o Security problem  CELLULAR MODEM o Uses cellular telephone system o Slow speed  ISDN Integrated Services Digital Network o Digital transmission o Speeds of 128,000 bps o Connect and talk at same time o Need - Adapter - Upgraded phone service o Initial costs high o Ongoing monthly fees may be high o Not available in all areas  Transmission Asynchronous and Synchronous Sending and receiving devices must work together to communicate ASYNCHRONOUS TRANSMISSION o Start/stop transmission o Start signal o Group – generally one character o Stop signal o Low-speed communications  SYNCHRONOUS TRANSMISSION o Blocks of data transmitted at a time o Send bit pattern o Align internal clock of sending / receiving devices o Send data o Send error-check bits o More complex o More expensive o Faster transmission  NETWORK CABLE o Twisted pair o Coaxial cable o Fiber optic cable o Wireless o Uses infrared or low-power radio wave transmissions o No cables o Easy to set up and reconfigure o Slower transmission rates o Small distance between nodes  TWISTED PAIR WIRE PAIR o Inexpensive o Susceptible to electrical interference (noise) o Telephone systems o Physical characteristics o Requires two conductors o Twisted around each other to reduce electrical interference o Plastic sheath o Shielded twisted pair o Metallic protective sheath o Reduces noise o Increases speed  COAXIAL CABLE o Higher bandwidth o Less susceptible to noise o Used in cable TC systems o Physical characteristics o Center conductor wire o Surrounded by a layer of insulation o Surrounded by a braided outer conductor o Encased in a protective sheath  FIBER OPTICS o Transmits using light o Higher bandwidth o Less expensive o Immune to electrical noise o More secure – easy to notice an attempt to intercept signal o Physical characterizes o Glass or plastic fibers o Very thin (thinner than human hair) o Material is light  MICROWAVE TRANSMISSION o Line-of-site o High speed o Cost effective o Easy to implement o Weather can cause interference o Physical characteristics o Data signals sent through atmosphere o Signals cannot bend of follow curvature of earth o Relay stations required  SATELLITE TRANSMISSION o Microwave transmission with a satellite acting as a relay o Long distance o Components o Earth stations – send and receive signals o Transponder – satellite o Receives signal from earth station (uplink) o Amplifies signal o Changes the frequency o Retransmits the data to a receiving earth station (downlink) SATELLITE TRANSMISSION  NETWORK TOPOLOGY o Network topologies describe the ways in which the elements of a network are mapped. They describe the physical and logical arrangement of the network nodes. o The physical topology of a network refers to the configuration of cables, computers, and other peripherals Components of a Network Topology Diagrams  NETWORK TOPOLOGY o Physical layout o Bus Topology o Start Topology o Ring Topology o Mesh Topology o Tree Topology o Hybrid Topology o Node – any device connected to the network o Server o Computer o Printer o Other peripheral  BUS TOPOLOGY o All the nodes (file server, workstations, and peripherals) on a bus topology are connected by one single cable. o A bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable. o Popular on LANs because they are inexpensive and easy to install. BUS TOPOLOGY  BUS TOPOLOGY Advantages of Bus Topology o It is Cheap, easy to handle and implement. o Require less cable o It is best suited for small networks. Disadvantages of Bus Topology o The cable length is limited. This limits the number of stations that can be connected. o This network topology can perform well only for a limited number of nodes.  RING TOPOLOGY o In a ring network, every device has exactly two neighbours for communication purposes. o All messages travel through a ring in the same direction. o A failure in any cable or device breaks the loop and can take down the entire network. o To implement a ring network we use the Token Ring technology. o A token, or small data packet, is continuously passed around the network. When a device needs to transmit, it reserves the token for the next trip around, then attaches its data packet to it. RING TOPOLOGY  RING TOPOLOGY Advantage of Ring Topology o Very orderly network where every device has access to the token and the opportunity to transmit. o Easier to Mange than a Bus Network o Good Communication over long distances o Handles high volume of traffic Disadvantages of Ring Topology o The failure of a single node of the network can cause the entire network to fail. o The movement or changes made to network  STAR TOPOLOGY o In a star network, each node (file server, workstations, and peripherals) is connected to a central device called a hub. o The hub takes a signal that comes from any node and passes it along to all the other nodes in the network. o Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. o The hub, switch, or concentrator manages and controls all functions of the network. o The star topology reduces the chance of network failure by connecting all of the systems to a central node. STAR TOPOLOGY  STAR TOPOLOGY Advantages of Star Topology o Easy to manage o Easy to locate problems (cable/workstations) o Easier to expand than a bus or ring topology. o Easy to install and wire. o Easy to detect faults and to remove parts. Disadvantages of Star Topology o Requires more cable length than a linear topology. o If the hub or concentrator fails, nodes attached are disabled. o More expensive because of the cost of the concentrators.  TREE TOPOLOGY o A tree topology (hierarchical topology) can be viewed as a collection of star networks arranged in a hierarchy. o This tree has individual peripheral nodes which are required to transmit to and receive from one other only and are not required to act as repeaters or regenerators. o The tree topology arranges links and nodes into distinct hierarchies in order to allow greater control and easier troubleshooting. o This is particularly helpful for colleges, universities and schools so that each of the connect to the big network in some way. TREE TOPOLOGY  TREE TOPOLOGY Advantages of a Tree Topology o Point-to-point wiring for individual segments. o Supported by several hardware and software vendors. o All the computers have access to the larger and their immediate networks. Disadvantages of a Tree Topology o Overall length of each segment is limited by the type of cabling used. o If the backbone line breaks, the entire segment goes down. o More difficult to configure and wire than other topologies.  MESH TOPOLOGY o In this topology, each node is connected to every other node in the network. o Implementing the mesh topology is expensive and difficult. o In this type of network, each node may send message to destination through multiple paths. o While the data is travelling on the Mesh Network it is automatically configured to reach the destination by taking the shortest route which means the least number of hops. MESH TOPOLOGY  MESH TOPOLOGY Advantage of Mesh Topology o No traffic problem as there are dedicated links. o It has multiple links, so if one route is blocked then other routes can be used for data communication. o Points to point links make fault identification easy. Disadvantage of Mesh Topology o There is mesh of wiring which can be difficult to manage. o Installation is complex as each node is connected to every node. o Cabling cost is high.  HYBRID TOPOLOGY o A combination of any two or more network topologies. o A hybrid topology always accrues when two different basic network topologies are connected. o It is a mixture of above mentioned topologies. Usually, a central computer is attached with sub-controllers which in turn participate in a variety of topologies HYBRID TOPOLOGY  HYBRID TOPOLOGY Advantages of a Hybrid Topology o It is extremely flexible. o It is very reliable. Disadvantages of a Hybrid Topology o Expensive  ORIENTATION AND CLASS POLICIES The End. Next Topic: “Transmission Media”  ECE 110 Communications 3: Data Communications Transmission Media Prepared by: Engr. Lovely Mae Dagsa, MSc., ECT Course Instructor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Figure 7.1 Transmission medium and physical layer 7.2  Figure 7.2 Classes of transmission media 7.3  7-1 GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable 7.4  Figure 7.3 Twisted-pair cable 7.5  Figure 7.4 UTP and STP cables 7.6  Table 7.1 Categories of unshielded twisted-pair cables 7.7  Figure 7.5 UTP connector 7.8  Figure 7.6 UTP performance 7.9  Figure 7.7 Coaxial cable 7.10  Table 7.2 Categories of coaxial cables 7.11  Figure 7.8 BNC connectors 7.12  Figure 7.9 Coaxial cable performance 7.13  Figure 7.10 Fiber optics: Bending of light ray 7.14  Figure 7.11 Optical fiber 7.15  Figure 7.12 Propagation modes 7.16  Figure 7.13 Modes 7.17  Table 7.3 Fiber types 7.18  Figure 7.14 Fiber construction 7.19  Figure 7.15 Fiber-optic cable connectors 7.20  Figure 7.16 Optical fiber performance 7.21  7-2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Topics discussed in this section: Radio Waves Microwaves Infrared 7.22  Figure 7.17 Electromagnetic spectrum for wireless communication 7.23  Figure 7.18 Propagation methods 7.24  Table 7.4 Bands 7.25  Figure 7.19 Wireless transmission waves 7.26  Note Radio waves are used for multicast communications, such as radio and television, and paging systems. They can penetrate through walls. Highly regulated. Use omni directional antennas 7.27  Figure 7.20 Omnidirectional antenna 7.28  Note Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Higher frequency ranges cannot penetrate walls. Use directional antennas - point to point line of sight communications. 7.29  Figure 7.21 Unidirectional antennas 7.30  Note Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation. 7.31  Wireless Channels ◼ Are subject to a lot more errors than guided media channels. ◼ Interference is one cause for errors, can be circumvented with high SNR. ◼ The higher the SNR the less capacity is available for transmission due to the broadcast nature of the channel. ◼ Channel also subject to fading and no coverage holes. 7.32 ECE 110 Data Communications and Networking I TRANSMISSION MODES TWO-WIRE and FOUR-WIRE CIRCUITS Prepared by: Engr. Lovely Mae Dagsa, ECT Course Instructor  INTRODUCTION ❑Data communications circuits can be configured in a multitude of arrangements depending on the specifics of the circuit, such as how many stations are on the circuit, type of transmission facility, distance between stations, and how many users are at each station. ❑A data communications circuit can be described in terms of circuit configuration and transmission mode.  DATA COMMUNICATION NETWORKS Categorized as either two point or multipoint. ❑ Two-point configuration - involves only two locations or stations. This involves the transfer of digital information between a mainframe computer and a personal computer, two mainframe computers, two personal computers, or two data communications networks. ❑ Multipoint configuration - involves three or more stations. Regardless of the configuration, each station can have one or more computers, computer terminals, or workstations. A multipoint network is generally used to interconnect a single mainframe computer (host) to many personal computers or to interconnect many personal computers.  TRANSMISSION MODES There are four modes of transmission for data communications circuits: Four Modes: ❑ SIMPLES ❑ HALF DUPLEX ❑ FULL DUPLEX ❑ FULL/FULL DUPLEX  SIMPLEX SIMPLEX (SX) Mode ❑ Data Transmission is unidirectional. Only one of the two devices on a link can transmit, the other can only receive ❑ Called (Receive-only, transmit-only, or one-way-only lines.  SIMPLEX ❑ A Communication between a computer and a keyboard involves simplex duplex transmission. A television broadcast is an example of simplex duplex transmission. ❑ Another example of simplex transmission is loudspeaker system. An announcer speaks into a microphone and his/her voice is sent through an amplifier and then to all the speakers. ❑ Many fire alarm systems work the same way  HALF DUPLEX HALF DUPLEX (HDX) Mode ❑ Data Transmission is possible in both directions but not at the same time. ❑ Called (two-way-alternate or either-way lines).  HALF DUPLEX ❑ Walkie- talkie in which message is sent one at a time and messages are sent in both the directions. ❑ Citizens Band (CB) radio is an example of half duplex transmission because to send a message, the push-to-talk (PTT) switch must be depressed, which turns on the transmitter and shuts off the receiver. To receive a message, the PTT switch must be off, which shuts off the transmitter and turns on the receiver.  FULL DUPLEX FULL DUPLEX (FDX) Mode ❑ Data Transmission are possible in both directions simultaneously, but they must be between the same two stations. ❑ Called (two-way simultaneous, duplex, or both-way lines).  FULL DUPLEX In full duplex mode, signals going in one direction share the capacity of the link with signals going in other direction, this sharing can occur in two ways: Either the link must contain two physically separate transmission paths, one for sending and other for receiving. Or the capacity is divided between signals travelling in both directions. ❑A Local Telephone call is an example of full-duplex transmission.  FULL/FULL DUPLEX FULL/FULL DUPLEX (F/FDX) Mode ❑ Data Transmission is possible in both directions at the same time but not between the same two stations. ❑ Possible only on multipoint circuits. o The U.S. postal system is an example of full/full duplex transmission because a person can send a letter to one address and receiver a letter from another address at the same time.  CIRCUIT ❑ Logical connection over a physical line: o path, link, line , and channel , although such usage can be specific to the underlying technology ❑Circuits also may be for purposes of either access (from the customer premises to the edge of the carrier network) or transport (circuits are employed in the core , or backbone , of the network for purposes of long - haul transmission) ❑ Simplex (one - way), half - duplex (two - way, but only one way at a time), or full - duplex (simultaneous two - way)  TYPES OF CIRCUITS Two wires vs Four wires Circuit: Comparison of Two wires and Four wires Circuits Two wires vs Four wires Circuit: Comparison of Two wires and Four wires Circuits  TYPES OF CIRCUITS Two-Wires Circuit o A two-wire circuit has two insulated electrical conductors. One wire is used for transmission of the information. The other wire acts as the return path to complete the electrical circuit. Two-wire circuits are generally deployed in the analog local loop, which is the last mile between the subscriber and the subscriber's first point of access into the network o Generally cover a short distance o Generally they are analog in nature; therefore, error performance (quality) is relatively poor  TYPES OF CIRCUITS Four-Wires Circuit A four-wire circuit has two pairs of conductors. That is, it has two sets of one-way transmission paths: one path for each direction and a complementary path to complete the electrical circuit. carry information signals in both directions over separate physical links or paths and in support of simultaneous, two - way transmission.  TYPES OF CIRCUITS Four-Wires Circuit Advantages: o Can accommodate multiple simultaneous communications in a full - duplex mode all multichannel circuits are four wire. o Multichannel capability greater bandwidth, or capacity digital, rather than analog – improve error performance  TYPES OF CIRCUITS Using Two-Wire and Four-Wire Circuits o Whenever you release energy into space, it loses power as it's traveling over a distance. So, because networks were designed to carry communications over a distance, we need tools to augment signals that have been losing power as they have traveled across the network, which are called attenuated signals. These tools are called amplifiers and repeaters. An amplifier boosts an attenuated signal back up to its original power level so it can continue to make its way across the network. The PSTN traditionally used copper wires. Based on how quickly the signals flow through the copper wires, there's a certain distance requirement between amplifiers. The distance requirement between amplifiers is relatively short on copper wires—generally about 6,000 feet (1,800 meters). As networks were built, these distance considerations were kept in mind. (Repeaters are discussed later in this chapter, in the section "Digital Transmission.")  TYPES OF CIRCUITS Using Two-Wire and Four-Wire Circuits Network builders had to give some thought to another aspect of amplifiers: First- generation amplifiers were unidirectional. They could only amplify a signal moving in one direction, so any time you needed to provision a circuit that was going to be crossing a distance, you had to literally provision two circuits—one to amplify the information in the transmit direction and a second to amplify the information in the receive direction. Therefore, whenever a network was crossing a distance, it needed to use a four-wire circuit. But in building out the millions of local loops for subscribers, it was seen as being cost-effective to have to pull only two wires into every home rather than four. Therefore, the local loops were intentionally engineered to be very short; some 70% to 80% of the local loops worldwide are less than 2 miles (3.2 kilometers) long. Because the local loops are short, they don't need amplifiers, and therefore the subscriber access service can be provisioned over a two-wire circuit. However, the local loop is increasingly being digitalized, so as we migrate to an end- to-end digital environment, everything becomes four-wire.  CIRCUIT Link: two - point segment of an end - to - end circuit (e.g., from terminal to switch or from switch to switch)Either single link or multiple links. Example: Between a host computer and a peripheral, such as a printer. Line: In a Private Branch eXchange (PBX) environment, a station line refers to the connection between the PBX switch and the station user ’ s terminal equipment, such as telephone, fax machine etc. Trunk: Trunks interconnect switches. Trunks are directional in nature, with the options being one - way outgoing (originating), one – way incoming (terminating), or two - way (combination).  DEDICATED CIRCUIT Physical circuits dedicated to directly connecting devices (e.g., PBXs and host computers) across a network Advantages: o Serve a single - user organization only, rather than serving multiple users o Ability to condition dedicated circuits to deliver specific levels of performance by adding amplification or other signal processing enhancements to the line to optimize its transmission characteristics. Disadvantages: o In terms of network efficiency because that circuit is taken out of shared public use and, therefore, is unavailable for use in support of the traffic of other users rather expensive. o Could be difficult and lengthy design and configuration process. – for huge connections  VIRTUAL CIRCUITS The virtual circuit is a connection between two devices that acts as though it's a direct connection, but it may, in fact, be composed of a variety of different routes. These connections are defined by table entries inside the switch. A connection is established after both devices exchange agreement on communications parameters that are important to establishing and maintaining the connection and on providing the proper performance for the application they are supporting. The types of communication parameters that could be included are message size, the path to be taken, how to deal with acknowledgements in the event of errors, flow-control procedures, and error-control procedures. The term virtual circuit is largely used to describe connections between two hosts in a packet-switching network, where the two hosts can communicate as though they have a dedicated connection, although the packets may be taking very different routes to arrive at their destination.  VIRTUAL CIRCUITS Example of circuit switched connections Switched Circuits. Example of circuit switched connections Switched Circuits: More flexible Virtual Circuits logical, rather than physical, circuits. are established through the network based on options and instructions defined in software routing tables Divided into two: - Permanent Virtual Circuits (PVCs) - Switched Virtual Circuits (SVCs)  VIRTUAL CIRCUITS o PVCs A PVC is a virtual circuit that is permanently available; that is, the connection always exists between the two locations or two devices in question. A PVC is manually configured by a network management system, and it remains in place until the user reconfigures the network. Its use is analogous to the use of a dedicated private line because it provides an always-on condition between two locations or two devices. o SVCs In contrast to PVCs, SVCs are set up on demand. They are provisioned dynamically by using signaling techniques. An SVC must be reestablished each time data is to be sent, and after the data has been sent, the SVC disappears. An SVC is therefore analogous to a dialup connection in the PSTN. The main benefit of an SVC is that you can use it to access the network from anyplace  ORIENTATION AND CLASS POLICIES The End. Next Topic: “Types of Synchronization, Network Components”