Wk1 Introduction To Data Communications PDF

Chapter 1 INTRODUCTION TO DATA COMMUNICATIONS Course : ECE144 (Data Communications) Prepared by : Engr. Jess David A. Doria, MBA, CISSP, CC Contents ▪ Networks and Network Types ▪ Protocol Layering ▪ TCP/IP Protocol Suite ▪ OSI Model Overview ▪ The word data refers to information...

Chapter 1 INTRODUCTION TO DATA COMMUNICATIONS Course : ECE144 (Data Communications) Prepared by : Engr. Jess David A. Doria, MBA, CISSP, CC Contents ▪ Networks and Network Types ▪ Protocol Layering ▪ TCP/IP Protocol Suite ▪ OSI Model Overview ▪ The word data refers to information presented in whatever form is agreed upon by the parties creating and using it. ▪ Data communications is the exchange of data between two devices via some form of transmission medium such as a wire cable. ▪ For data communications to occur, the communicating devices must be part of a communications system made up of a combination of hardware (physical equipment) and software (programs). Data Communications System ▪ The effectiveness of a data communications system depends on four fundamental characteristics: 1. Delivery – ensures data reaches the intended recipient, not someone else. 2. Accuracy – guarantees data arrives without any errors or corruption. 3. Timeliness – delivers data promptly, especially crucial for real-time applications like video calls. This kind of delivery is called real-time transmission. 4. Jitter – minimizes fluctuations in packet arrival times, preventing choppy audio or video playback. Data Communications System A data communications system has five components 1. Message – the information (data) to be communicated. 2. Sender – the device that sends the data message 3. Receiver – the device that receives the message 4. Transmission medium – the physical path by which a message travels from sender to receiver. 5. Protocol – set of rules that govern data communications. It represents an agreement between the communicating devices Forms of Message 1. Text – in data communications, this is represented as a bit pattern, a sequence of bits (0s or 1s). o Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the process of representing symbols is coding. o Today, the prevalent coding system is Unicode, which uses 32 bits to represent a symbol or character used in any language in the world 2. Numbers - also represented by bit patterns. However, a code such as Unicode is not used to represent numbers; a number is directly converted to a binary number to simplify mathematical operations Forms of Message 3. Images – also represented by bit patterns, and its simplest form, is composed of a matrix of picture elements (pixels), where each pixel is a small dot. The number of pixels depends on the resolution. 4. Audio – refers to the recording or broadcasting of sound or music. It is different from text, numbers, or images. Audio is continuous, not discrete. 5. Video – refers to the recording or broadcasting of a picture or movie. It can either be produced as a continuous entity (e.g., by a TV camera), or it can be a combination of images. Data Flow Communication between two devices can be: 1. Simplex – communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. Examples are keyboards, monitors 2. Half-Duplex – each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. Examples are walkie-talkies and CB radios. 3. Full-Duplex – both stations can transmit and receive simultaneously. This mode is like a two-way street with traffic flowing in both directions at the same time. Example is the telephone network. Data Flow Chapter 1 : Introduction to Data Communications NETWORKS Overview ▪ A network is the interconnection of a set of devices capable of communication. ▪ A device can be a host, such as a large computer, desktop, laptop, workstation, ▪ cellular phone, or security system. ▪ A device in this definition can also be a connecting device such as a router that connects the network to other networks, a switch that connects devices together, or a modem (modulator-demodulator) that changes the form of data. ▪ A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. Network Criteria 1. Performance – depends on several factors, including the number of users, the type of transmission medium, the capabilities of the connected hardware, and the efficiency of the software. It can be measured based on: ▪ Transit time is the amount of time required for a message to travel from one device to another. ▪ Response time is the elapsed time between an inquiry and a response. 2. Reliability – measured by the frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness in a catastrophe. 3. Security – include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses. Connection Types ▪ A network is two or more devices connected through links. ▪ A link is a communications pathway that transfers data from one device to another. ▪ For communication to occur, two devices must be connected in some way to the same link at the same time. ▪ There are two possible types of connections: 1. Point-to-point – provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. 2. Multipoint – also called multidrop connection; one in which more than two devices share a single link. In a multipoint environment, the capacity of the channel is shared, either spatially or temporally. Connection Types Physical Topology ▪ Refers to the way in which a network is laid out physically. ▪ Two or more devices connect to a link; two or more links form a topology. ▪ The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. ▪ There are four basic topologies possible: 1. Mesh Topology (point-to-point) o Every device has a dedicated point-to-point link to every other device. Dedicated means that the link carries traffic only between the two devices it connects. o This topology needs n(n − 1) physical links to connect all devices. Physical Topology 2. Star Topology (point-to-point) o Each device has a dedicated point-to-point link only to a central controller, usually called a hub. o Does not allow direct traffic between devices because they are not directly linked to one another 3. Bus Topology (multipoint) o One long cable acts as a backbone to link all the devices in a network o Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. Physical Topology 4. Ring Topology (point-to-point) o Each device has a dedicated point-to-point connection with only the two devices on either side of it. o A signal is passed along the ring in one direction, from device to device, until it reaches its destination. o Each device in the ring incorporates a repeater, which regenerates the bits and passes them along. Chapter 1 : Introduction to Data Communications NETWORK TYPES Local Area Network (LAN) ▪ Usually privately owned and connects some hosts in a single office, building, or campus. ▪ Each host in a LAN has an identifier, which is an address that uniquely defines the host in the LAN. A packet sent by a host to another host carries both the source host’s and the destination host’s addresses. ▪ When LANs were used in isolation (which is rare today), they were designed to allow resources to be shared between the hosts. As we will see shortly, LANs today are connected to each other and to WANs (discussed next) to create communication at a wider level. Local Area Network (LAN) Wide Area Network (WAN) ▪ WAN is also an interconnection of devices capable of communication. ▪ However, it has a wider geographical span, spanning a town, a state, a country, or even the world. ▪ It interconnects connecting devices such as switches, routers, or modems. ▪ There are two distinct examples of WANs today: 1. Point-to-point WAN – a network that connects two communicating devices through a transmission medium (cable or air). 2. Switched WAN – a network with more than two ends. It is used in the backbone of a global communications network today. Wide Area Network (WAN) (1) Point-to-point WAN (2) Switched WAN Wide Area Network (WAN) Internetwork ▪ In today’s practice, it is very rare to see a LAN or a WAN in isolation; they are connected to one another. When two or more networks are connected, they make an internetwork, or internet (note the lowercase i). ▪ Image below shows another internet with several LANs and WANs connected. One of the WANs is a switched WAN with four switches. The Internet ▪ The most notable internet is called the Internet (uppercase I ) and is composed of thousands of interconnected networks. ▪ Image below shows a conceptual (not geographical) view of the Internet. A heterogeneous internetwork made of four WANs and two LANs The Internet The Internet today The Internet ▪ The Internet is composed of the following: 1. At the top level, the backbones are large networks owned by some communication companies. They are connected through some complex switching systems, called peering points. They are often referred to as international ISPs. 2. At the second level, there are smaller networks, called provider networks, that use the services of the backbones for a fee. They are connected to backbones and sometimes to other provider networks. They are often referred to as national or regional ISPs. 3. The customer networks are networks at the edge of the Internet that use the services provided by the Internet. They pay fees to provider networks for receiving services. Chapter 1 : Introduction to Data Communications PROTOCOL LAYERING Overview ▪ As discussed previously, a protocol defines the rules that both the sender and receiver and all intermediate devices need to follow to be able to communicate effectively. ▪ When communication is simple, we may need only one simple protocol; when the communication is complex, we may need to divide the task between different layers, in which case we need a protocol at each layer, or protocol layering. ▪ Modularity means independent layers. A layer (module) can be defined as a black box with inputs and outputs, without concern about how inputs are changed to outputs. ▪ If two machines provide the same outputs when given the same inputs, they can replace each other. Overview ▪ Some of the advantages: o It allows us to separate the services from the implementation o Communication does not always use only two end systems; there are intermediate systems that need only some layers, but not all layers. o If protocol layering is not used, intermediate systems need to be created as complex as the end systems, which makes the whole system more expensive. Principles ▪ First Principle: If bidirectional communication is desired, each layer must be created such that it is able to perform two opposite tasks, one in each direction. ▪ Second Principle: Two objects under each layer at both sites should be identical. Chapter 1 : Introduction to Data Communications TCP/IP PROTOCOL SUITE TCP/IP Protocol Suite ▪ Transmission Control Protocol / Internet Protocol (TCP/IP) is a protocol suite (a set of protocols organized in different layers) used on the Internet today. ▪ A hierarchical protocol made up of interactive modules, each of which provides a specific functionality. The term hierarchical means that each upper-level protocol is supported by the services provided by one or more lower-level protocols. ▪ The TCP/IP protocol suite is defined as five layers: Internet Layer Network Access Layer TCP/IP Protocol Suite Communication through the Internet TCP/IP Protocol Suite Logical connections between layers of the TCP/IP protocol suite TCP/IP Protocol Suite ▪ The duty of the application, transport, and network layers is end-to-end. ▪ However, the duty of the data-link and physical layers is hop-to-hop, in which a hop is a host or router. ▪ In other words, the domain of duty of the top three layers is the internet, and the domain of duty of the two lower layers is the link. ▪ Another way of thinking about the logical connections is to think about the data unit created from each layer. Using the second principle discussed previously for protocol layering, image in the next slide shows the identical objects below each layer related to each device. TCP/IP Protocol Suite Identical objects in the TCP/IP protocol suite Layers 1. Physical Layer – responsible for carrying individual bits in a frame across the link. The lowest level in the TCP/IP protocol suite. 2. Data-Link Layer – when the next link to travel is determined by the router, this layer is responsible for taking the datagram and moving it across the link. 3. Network Layer – responsible for creating a connection between the source computer and the destination computer. The communication at the network layer is host-to-host. 4. Transport Layer – responsible for giving services to the application layer: to get a message from an application program running on the source host and deliver it to the corresponding application program on the destination host. 5. Application Layer – handles process-to-process communication Chapter 1 : Introduction to Data Communications OSI MODEL Open Systems Interconnection (OSI) Model ▪ A standard developed by the International Organization for Standardization (ISO) that covers all aspects of network communications and was first introduced in the late 1970s ▪ An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture. ▪ The purpose of the OSI model is to show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software. ▪ OSI is not a protocol; it is a model for understanding and designing a network architecture that is flexible, robust, and interoperable. ▪ The OSI model was intended to be the basis for the creation of the protocols in the OSI stack. Open Systems Interconnection (OSI) Model ▪ The OSI model is a layered framework for the design of network systems that allows communication between all types of computer systems. ▪ It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network OSI versus TCP/IP Two reasons were mentioned for this decision: ▪ First, TCP/IP has more than one transport-layer protocol. Some of the functionalities of the session layer are available in some of the transport-layer protocols. ▪ Second, the application layer is not only one piece of software. Many applications can be developed at this layer. Lack of OSI Model’s Success 1. OSI was completed when TCP/IP was fully in place and a lot of time and money had been spent on the suite; changing it would cost a lot. 2. Some layers in the OSI model were never fully defined. For example, although the services provided by the presentation and the session layers were listed in the document, actual protocols for these two layers were not fully defined, nor were they fully described, and the corresponding software was not fully developed. 3. When OSI was implemented by an organization in a different application, it did not show a high enough level of performance to entice the Internet authority to switch from the TCP/IP protocol suite to the OSI model. FIN