Data and Computer Communications

Ninth Editionby William Stallings

Chapter 1 – Data Communications, Data Networks, and the Internet

Data and Computer Communications, Ninth Edition by William Stallings, (c) Pearson

Education - Prentice Hall, 2011

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”

Data communications deals with the transmission of signals in a reliable and efficient manner.

- The Mathematical Theory of Communication,

Claude Shannon Message

Message

Technological AdvancementDriving Forces

Three different forces have consistently driven the architecture and evolution of data communications and networking facilities:

• Development of new services

• Advances in technology

Traffic growth at a high & steady

rate

Changes in Networking Technology

changes in the way organizations do business

* Emergence of high-speed LANs

* Digital electronics

* Corporate WAN needs

Convergence Convergence refers to The merger of

previously distinct telephony and information technologies and markets.

Convergence can be thought in terms of three 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

Efficiency

• better use of existing resources, and implementation of centralized capacity planning, asset and policy management

Effectiveness

• 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

Convergence benefits include:

Communications Modelthe transmission of signals in a reliable and efficient manner.

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

key tasks that must be performed in a data communications system

Data Communications Modelthe transmission of signals in a reliable and efficient manner.

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.

Capacity

Reliability

Cost

TransmissionLine

Transmission Lines

Transmission MediumsTwo mediums currently driving the evolution of data communications transmission are:

Fiber optic transmissions

and

Wireless transmissions

Networking

Voice Data

Image

Video

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

LANs and WANs

Local Area Networks (LAN)

Wide Area Networks (WAN)

There are two broad categories of networks:

Wide Area Networks (WANs)

Span a large geographical area

Require the crossing of public right-of-ways

Rely in part on common carrier circuits

Typically consist of a number of interconnected switching nodes

Wide Area Networks

Circuit switching Packet switchingRecently the following have assumed major roles. Frame relay Asynchronous Transfer Mode (ATM)

WANs have been implemented using one of two technologies :

Circuit Switching Uses a dedicated communications path Connected sequence of physical links

between nodes Logical channel dedicated on each link Rapid transmission The most common example of circuit

switching is the telephone network

Packet Switching Data are sent out in a sequence of small

chunks called packets Packets are passed from node to node

along a path leading from source to destination

Packet-switching networks are commonly used for terminal-to-terminal computer and computer-to-computer communications

Packet Switching Packet switching systems have large overheads

to compensate for errors Modern systems are more reliable Errors can be caught in end system Frame Relay provides higher speedsoriginal packet-switching networks were designed with a data rate to

the end user of about 64 kbps, frame relay networks are designed to operate efficiently at user data rates of up to 2 Mbps.

Frame Relay

Developed to take advantage of high data rates and low error rates

Operates at data rates of up to 2 Mbps Rate of errors dramatically lowered thus

reducing overhead of packet-switching

Asynchronous Transfer Mode (ATM)

Referred to as cell relay Culmination of circuit switching and packet

switching Uses fixed-length packets called cells Works in range of 10’s and 100’s of Mbps

and in the Gbps range 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

Internal data rates greater than WANs

Most common configurations are

switched LANs and wireless LANs

LAN

A LAN is a communications network that interconnects a variety of devices and provides a means for information exchange among those devices.

Metropolitan Area Networks (MAN)

Covers a geographic area such as a town,

city or suburb

Middle ground between LAN and

WAN

Supports both data and voice

Private or public network

MAN

typically spanning a city / metro area with higher speed connections.

The Internet

Internet evolved from ARPANETdeveloped in 1969 by the Advanced Research Projects Agency (ARPA) of the U.S. Department of Defense. Developed to solve the dilemma of

communicating across arbitrary, multiple, packet-switched network

TCP/IP provides the foundation

Internet Key Elementskey elements that comprise the Internet, whose purpose is to interconnect end systems, called hosts; including PCs, workstations, servers, mainframes, and so on. Most hosts that use the Internet are connected to a network, such as a local area network (LAN) or a wide area network (WAN). These networks are in turn connected by routers.

Internet Architecturehosts grouped into LANs, linked to an Internet service provider (ISP) through a point of presence (POP). The connection is made in a series of steps starting with the customer premises equipment (CPE). ISPs can be classified as regional or backbone, with peering links between.

Internet Terminology

A Networking Configurationtypical communications and network elements in use today

The Internet consists of a number of interconnected routers that span the globe.

The routers forward packets of data from source to destination through the Internet

Summary Trends challenging data communications:

• traffic growth• development of new services• advances in technology

Transmission mediums• fiber optic• wireless

Network categories:• WAN• LAN

Internet• evolved from the ARPANET• TCP/IP foundation