Data and Computer Communications Chapter 1 Data Communications

Data and Computer Communications Chapter 1 – Data Communications, Data Networks, and the Internet Ninth Edition by William Stallings

Data Communications, Data Networks, and the Internet “The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point” - The Mathematical Theory of Communication, Message Claude Shannon

1 -1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. 1. 3

Figure 1. 1 Five components of data communication 1. 4

Figure 1. 2 Data flow (simplex, half-duplex, and full-duplex) 1. 5

1 -2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. 1. 6

Figure 1. 3 Types of connections: point-to-point and multipoint 1. 7

Technological Advancement Driving Forces Traffic growth at a high & steady rate • Development of new services • Advances in technology

Changes in Networking Technology * Emergence of high-speed LANs * Corporate WAN needs * Digital electronics

Convergence Ø The merger of previously distinct telephony and information technologies and markets Ø Layers: • applications • these are seen by the end users • enterprise services • services the information network supplies to support applications • infrastructure • communication links available to the enterprise

Convergence Layers

Benefits Convergence benefits include: Effectiveness Efficiency • better use of existing resources, and implementation of centralized capacity planning, asset and policy management • the converged environment provides users with flexibility, rapid standardized service deployment and enhanced remote connectivity and mobility Transformation • enables the enterprise-wide adoption of global standards and associated service levels

Communications Model

Communications Tasks Transmission system utilization Addressing Interfacing Routing Signal generation Recovery Synchronization Message formatting Exchange management Security Error detection and correction Network management Flow control

Transmission Lines Capacity The basic building block of any communications facility is the transmission line. The business manager is concerned with a facility providing the required capacity, with acceptable reliability, at minimum cost. Reliability Cost Transmission Line

Transmission Mediums Two mediums currently driving the evolution of data communications transmission are: Fiber optic transmissions and Wireless transmissions

Networking Advances in technology have led to greatly increased capacity and the concept of integration, allowing equipment and networks to work simultaneously. Voice Data Image Video

Network Hardware Classifying networks based on their scale: Ø Local Area Networks Ø Metropolitan Area Networks Ø Wide Area Networks Ø Wireless Networks Ø Home Networks Ø Internetworks 18

Network Hardware 19

LANs and WANs There are two broad categories of networks: Local Area Networks (LAN) Wide Area Networks (WAN)

Wide Area Networks (WANs) Ø Span a large geographical area Ø Require the crossing of public right-of-ways Ø Rely in part on common carrier circuits Ø Typically consist of a number of interconnected switching nodes

Wide Area Networks Alternative technologies used include: l l Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)

Circuit Switching Ø Uses a dedicated communications path Ø Connected sequence of physical links between nodes Ø Logical channel dedicated on each link Ø Rapid transmission Ø The most common example of circuit switching is the telephone network

Network Hardware Wide Area Networks 24

Packet Switching Ø Data are sent out in a sequence of small chunks called packets Ø Packets are passed from node to node along a path leading from source to destination Ø Packet-switching networks are commonly used for terminal-to-terminal computer and computer-to-computer communications

Asynchronous Transfer Mode (ATM) Ø Referred to as cell relay Ø Culmination of circuit switching and packet switching Ø Uses fixed-length packets called cells Ø Works in range of 10’s and 100’s of Mbps and in the Gbps range Ø Data rate on each channel dynamically set on demand

Local Area Networks (LAN) Smaller scope, typically a single building LANs are usually owned by the same organization that owns attached devices LAN Internal data rates greater than WANs Most common configurations are switched LANs and wireless LANs

Metropolitan Area Networks (MAN) Covers a geographic area such as a town, city or suburb Middle ground between LAN and WAN MAN Supports both data and voice Private or public network

Network Hardware Wireless Networks Categories of wireless networks: Ø System interconnection Ø Wireless LANs Ø Wireless WANs 29

Network Hardware Wireless Networks Ø System interconnection l Bluetooth a short-range wireless network. Allows system components together, digital cameras, headsets, scanners, and other devices to connect to a computer by merely being brought within range. Ø Wireless LANs l l Every computer has a radio modem and antenna with which it can communicate with other systems. Standard for wireless LANs: IEEE 802. 11, which most systems implement and which is becoming very widespread. 30

Network Hardware Wireless Networks ØWireless WANs (cont. ) l l Wireless LANs an operate at rates up to about 50 Mbps over distances of tens of meters. While cellular systems (Wireless WANs) operate below 1 Mbps, but the distance between the base station and the computer or telephone is measured in kilometers rather than in meters. High-bandwidth wide area wireless networks are also being developed (IEEE 802. 16). 31

The Internet Ø Internet evolved from ARPANET Ø Developed to solve the dilemma of communicating across arbitrary, multiple, packet-switched network Ø TCP/IP provides the foundation

Internet Key Elements

Internet Architecture

Figure 1. 11 WANs: a switched WAN and a point-to-point WAN 1. 35

Figure 1. 12 A heterogeneous network made of four WANs and two LANs 1. 36

Figure 1. 13 Hierarchical organization of the Internet 1. 37