The following are the unit 1 class notes for data communication. It lacks some of the diagrams to save on time used to convert it from hardcopy to softcopy. Accessing the original hardcopy is highly recommended. INTRODUCTION TO NETWORKING AND DATA COMMUNICATION The term telecommunication means communication at a distance. Data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are exchange of data between two devices via some form of transmission medium such as a wire cable. The effectiveness of a data communication system depends in the four characteristics; 1. 2. 3. 4. Delivery Accuracy Timeliness Jitter Components of data communication; a) Sender: is the device that sends the data message. b) Message: information to be communicated c) Transmission medium: the physical path by which a message travels from sender to receiver. d) Receiver: device that receives the message. e) Protocols: rules governing data communication. Ways through which data can flow; 1. Half duplex: each station can both transmit and receive, but not at the same time. 2. Full duplex: both station can transmit and receive simultaneously. 3. Simplex: Only one of the two devices on a link can transmit while the other can only receive. NETWORK It is a set of devices connected by communication links. A network should meet the following criteria’s; 1. Performance – measured by a. Transit time: the time required for a message to travel from one device to another. b. Response time; elapsed time between an inquiry and a response. 2. Reliability: measured by the frequency of failure 3. Security; refers to issues protecting data from unauthorised access and losses. Types of connections; a. Point to point: provides a dedicated link between two devices. b. Multi-point: connection is one in which more than two devices share a single link. NETWORK CATEGOREIS LAN Are designed to allow resources to be shared between personal computers. A LAN uses one type of transmission media. The topologies used are bus, ring and star. WAN provides a long-distance transmission of data over large geographical areas e.g. country, continent or the whole world. The switched WAN connects the end systems, which usually comprise a router that connects to another LAN or WAN. Point-to-point WAN is normally a ;line leased from a telephone or cable TV provider that connects a home computer or a small LAN to an internet Service Provider. This type of WAN is often used to provide internet access. MAN. Is a network with a size between a LAN and a WAN? IT COVERS the area inside a city. Designed for customers who need a high speed connectivity, normally to the internet, and have endpoints spread overs a city. Example of MAN is a part of the telephone accompany network that can provided a high speed DSL line to the customer. Another example is the cable TV network that originally was designed for cable TV, but today can also be used for high speed data connection to the internet. INTERNET Is a large, interconnection of computer network in which every computer connected to it can exchange data with any other connected computer? Significant of internet; It’s the first mass medium that involves computers and uses digitalized data It provides the potential foot media convergence, the unification of all media. It’s transforming how we communicate, obtain information, learn, seek jobs, and maintain professional growth. Business find it an indispeNpensable tool for their needs. The internet Service Providers (ISPs). Are used by the end users to access the internet. They can be arranged as; International Service providers National Service providers Regional Service providers Local Service providers: these alter the ones that provide services to the end users. PROTOCOLS AND STANDARDS Protocols are rules that govern communication. Elements of protocols; A. Syntax: the structure of the data and the order in which they are presented. B. Semantics: the meaning of each section of bits. How is a particular pattern to be interpreted, and what action is to be taken based on that interpretation? C. Timing: refers to when data should be sent and how fast they can be sent. Standards provide guidelines to manufactures, vendors, government agencies, and other service providers to ensure the kind of interconnection necessary in today’s marketplace and in international community. Standard creation committees are; International Organisation for Standardization (ISO): is active in developing cooperation in the realms of scientific, technological, and economical activities. International Telecommunication Union-Telecommunication Standards Sector (ITU-T): by the early 1970s, a number of countries were defining national standards for telecommunications example is the USA that formed the ITU-IT. American National standards institute (ANSI): despite its name, ANSI is a private, non-profit corporation. However. All ANSI activities are undertaken with the welfare of the US and its citizens occupying primary importance. Institute of Electrical and Electronics Engineers (IEEE): is the largest professional engineering society in the world. International in scope, it aims to advance theory, creativity, and product quality in the field of electrical engineering, electronics, and radio as well as in all related branches of engineering. Electronic Industries Association (EIA): is a non-profit organization devoted to the promotion of electronics manufacturing concerns. Its activities include public awareness education and lobbying efforts in addition to standards development. LAYERED TASKS: OSI MODEL (OPEN SYSTEM FOR INTERCONNECTION) Term open denotes the ability to connect any two systems which conform to the reference model and associated standards. The purpose of the OSI Mode is: To facilitate communication between different systems with ought to requiring changes to the logic of the underlying hardware and software. Describes how information or data makes its way from application programmes (spreadsheets) through a network medium (such as a wire) to another application programme located on another network. The OSI reference model divides the problem of moving information between computer over a network medium into seven smaller and more manageable problems... this separation into smaller more PHYSICAL LAYER Provides physical interface for transmission of information Defines rules by which by which bits are passed from one system to another on a physical communication medium Covers all- mechanical, electrical, functional and procedural-aspects for physical communication Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications. Concerned with line configuration, physical topology and transmission mode. DATA LINK LAYER Data link layer attempts to provide reliable communication over the physical layer interface. Breaks the outgoing data into frames and reassemble the received frames. Create and detect frame boundaries. Handle errors by implementing an acknowledgement and retransmission scheme. Implement flow control Responsible for error control. Supports point- to -point as well as broadcast communication Supports simplex, half-duplex or full-duplex communication. NETWORK LAYER Implements routing of frames (packets) through the network Define she most optimum path the packet should take from the source to the destination. Defines logical addressing so that any endpoint can be identified. Handle congestion in the network The network layer also defines how to fragment a packet into smaller packets to accommodate different media. TRASPORT LAYER Purpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers Ensures that the data units are delivered error free Ensures that data units are delivered in sequence Ensures that there is no loss or duplication of data units Provides connectionless or connection oriented service Provides for the connection management Multiplex multiple a connection over a single channel SESSION LAYER Session layer provides mechanisms for controlling the dialogue between the end systems It defines how to start, control and end conversations (called sessions) between applications This layer requests for a logical connection to be established on an end-users request Any necessary log-on or password validation is also handled by this layer Session layer is also responsible for terminating the connection This layer provides services like dialogue discipline which can be full duplex or half duplex Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint PRESENTATION LAYER Presentation layer defines the format in which the data is to be exchanged between the two communicating entities Also handles data compression and data encryption (cryptography) APPLICATION LAYER Application layer interacts with application programs and is the highest level of OSI model Application layer contains management functions to support distributed applications Examples of application layer are applications such as file transfer, electronic mail, remote login etc. Fig.1.6 below shows summary of all layers of OSI model TCP/IP MODEL :( TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL) The layers in the TCP/IP protocol suite do not exactly match those in the OSI model .the original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: data link, network, and transport, and application, fig 1.7 below shows TCP/IP layers in comparison to OSI model: APPLICATION LAYER o o o o o o Application layer protocols define the rules when implementing specific network applications.it relies on the underlying layers to provide accurate and delivery. Typical protocols are: FTP-File Transfer Protocol: For file transfer Telnet-remote terminal protocol: for remote login on any other computer On the network SMTP-Simple Mail Transfer Protocol: for mail transfer HTTP-Hypertext Transfer Protocol: for web browsing TRANSPORT LAYER o o o Transport layer protocols define the rules of diving a chunk of data into segments and then reassemble into segments into the original chunk. Typical protocols are :TCP –Transmission Control Protocol: provide functions such as reordering and data resend UDP-User Datagram Service: Use when the message tube sent fit exactly into a datagram and use also when a more simplified data format is required SCTP- Scream Control Transmission Protocol: The stream control transmission protocol (SCTP) provides support for newer applications such as voice over the internet NETWORK LAYER o o o o o o o Network layer protocols define the rules of how to fin the routes for a packet to the destination It only gives the best effort delivery. Packets can be delayed, corrupted, lost, duplicated, outof-order. IP-Internet Protocol: Provide packet delivery ARP-Addresses Protocols define the procedures of network address or MAC address translation i.e. it is used to associate a logical address with a physical address. ARP is used to find the physical address of the node when its internet address is known. RARP – reserves address resolution protocol: tallows a host to discover its internet address when it knows only its physical address. ICMP-Internet Control Message Protocol: is a mechanism used by hosts and gateways to send notification of datagram problems back to the sender. IGMP – Internet Control Message Protocol: is used to facilitate the simultaneous transmission of a message to a group pf recipients. PHYSICAL AND DARA LINK LAYER At this layer TCP/IP does not defines any specific protocol. Rather it supports all the transfer protocols. ADDRESSING A. Physical addressing Is the address of a node as defined by its LAN or WAN. It is included in the frame used by the data link layer. It is the lowest-level address. The size and format of these addresses vary depending on the network. E.g. of Physical Addressing: anode with physical address 10 sends a frame to anode with physical address 87. The tow nodes are connected by a link 9 bus topology LAN). B. Logical Addressing Necessary for universal communication that are independent of underlying physical networks. Physical address are not adequate in an internetwork environment here different networks can have different address formats. A universal addressing system is needed in which each host can be designed for this purpose. A logical address in the internet is currently a 32 bit address that can uniquely define a host connected to the internet. No two publicly addressed and visible hosts on the internet can have the same IP address. Example of logical addressing: C. PRT addressing: The ip address and the physical address are necessary a quantity of data travel from a source to other destination host. However arrival at the destination host is not the final objective of data communications on the internet a system that sends nothing but data from one computer to another is not complete. Today, computers are devices that can run multiple processes at the same time. The end objective of the internet communication is a process communicating with another process. For example, computers communicates with computer C by using TELNET. At the same time, Computer communicates with computer B by using the file transfer Protocol (FTP). For others processes to receive data simultaneously we need a method to label the different processes. In other words they need address in TCPIP architecture, the label assigned to a process is called a port address. A port address in TCPIP is 16 bits in length. Example of port addressing. D. Specific addressing Some applications have user friendly addresses that are address Designed for that specific address. Examples include the email address (for example, forouzan@fhda.edu): defines the recipient of an email and the universal resource allocation (URL). (For example, www.mhhe.com):usedto find a document on the World Web. These addresses, however, get changed to the corresponding port and logical addresses by the sending computer. E. LINE CODING REVIEW The process of converting digital data to digital signals.Line coding converts a sequence of bits to a digital signal. At the sender, the digital data are encoded into a digital signal: at the receiver, the digital data are recreated by decoding the digital signal. a. Unipolar Scheme: all the signal levels are on one side of the time axis, either above or below. It is a NonReturn to Zero (NRZ) scheme in which rte positive voltage defines bit 1 b. c. d. e. and the zero voltage defines bit O. It is called NRZ becaouse the signal does not return to zero at the middle of the bit. Polaar schemes: the voltage are on the both sides of the time axis. Eg the voltage level for 0 can be positive and the voltage level for 1 can be negative. Biphase: in Manchester encording, the duration of the bit is divided into two halves. The voltage remains at one level during the first half and moves ro tohe other level in the second half. The transition at the middle of the bit provides synchronizaiton. Differential Manchester, on the other hand, combines the ideas of RZ and NRZ-I. there is always a transition at the middle of the bit, but the bit values are determined at eh beginning of the bit. Bipolar schemes: there are three voltage levels : positive negative and zero. The voltage level for one data element is at zero. While the voltage level for the other element alternates between positive and negatifve. Multilevel Schemes: the desire to increase the data speed or decfrease the required bandwidth has resulted in the creation of many schemes. The goal is to increase the number of bits per banund by encording a partern of m data elements into a pattern of n signal elements. We only have two types of dat elements (0 and1), which means that agroup of m data elemcets can produce a combination of 2 to power m data patterns Summary of the coding schemes Category Unipolar Scheme NRZ Unipolar NRZ-L Bandwidth Characteristics B=N/2 Costly, no self-synchronization if long 0s or 1s. DC B=N/2 No self-synchronization for long 0s or 1s. DC B=N/2 No self-synchronization for long 0s or 1s. DC B=N self-synchronization, no DC. High bandwidth B=N/2 no self-synchronization for long 0s, DC B=N/4 no self-synchronization for long same double bits B=3N/4 self-synchronization, no DC B=N/8 self-synchronization, no DC B=N/3 no self-synchronization for long 0s