ISOM 617

Distributed Information Systems

A Brief History of Information Systems

1950s: batch processing mainframes1960s: data communications over phone lines became common and mainframes became multi-user systems1970s: online real-time, transaction-oriented systems replaced batch processing. DBMSs become common1980s: the PC revolution1990s: PC LANs become common2000: networking everywhere

Host-based Architectures

The first application architecture to be developed was the host-basedThe ‘server’ in host-based architectures, usually a mainframe, performs all four application program functionsThe client, usually a terminal or a PC running a terminal emulation program captures key strokes which are sent to the mainframe and displays information according to the server’s instructions

Host-based Architectures

There are two main problems with host-based architectures: Since all processing is by the host, the

host becomes a bottleneck which can severely limit network performance

Upgrades are typically expensive and “lumpy”, meaning available upgrades require big jumps in processing and memory. Network demand grows more incrementally, so this often means a poor fit (too much or too little) between host performance and network demand.

Client-Based Architectures

Client-based architectures became important in the late 1980s with the widespread use of PCs, local area networks, and low-cost PC-based application programs such as spreadsheets and word processorsIn client-based architectures, application programs on the clients are responsible for the data access, application, and presentation logicThe server is responsible for data storage only

Client-Based Architectures

The main problem with client-based architectures is the need for all of the data to travel back and forth between server and clientFor example, if the client program is making a database query, the entire database must travel to the client before the query can be processedThe result can be poor network performance due to the bottleneck created by constantly sending large files back and forth over the network

Client-Server Architectures

In client-server architectures the application program functions are divided up between clients and serversThe client takes care of the presentation logicThe server handles data storage and data access logicApplication logic may reside on the client, server or be split up between the twoMost networks today use a client-server architecture

Client-Server Architectures

Client-server architectures are more efficient since they distribute processing between client and serverAnother strength is that they allow hardware and software from different servers to be used togetherThis is also a weakness, since it is sometimes difficult to get software from different vendors to work together smoothly For this reason, a third category of software, called middleware was developed

The Telephone: from Invention to Regulation

Invented in 1876, by 1900, there were millions of telephone lines in the USBy 1910, Bell Telephone was a de facto monopolyTelephone regulation began in 1892 in Canada and in 1910 when the Interstate Commerce Commission began to regulate long distance trafficIn 1934, the FCC was established to regulate interstate the telephone business

Deregulating the Telephone Industry

1970: MCI wins court case; begins providing some long distance services1984: Results of consent decree by US federal court: Divestiture: AT&T broken up into a long

distance company (AT&T) & 8 Regional Bell Operating Companies (RBOCs)

Deregulation: long distance market becomes competitive. MCI and Sprint enter market (among others)

Local exchange service markets remain monopolies for RBOCs

1996: US Telecom Competition and Deregulation Act

Act replaces all current laws, FCC regulations, 1984 consent decree and overrules state lawsMain goal was to open local markets to competition. To date, local competition has been slow to take hold Large IXCs were expected to move into

local markets, but this has not yet happened

Likewise, RBOCs were expected to move into long distance markets, but they are prohibited from doing so before competition begins in local markets

Telephony

LANs use traditional telephone building wiringTelephone technology is basis for much wide area networkingTelephone regulation and carriers affect wide area networkingDesire for converged services: integrated management of voice and data networks

Equipment Room (Usually in Basement)

ToTelcos

PBXInternal Telephone

Switch

WireBundle

(Many Pairs)

VerticalRiserSpace

TerminationEquipment

Internal Telephone Network

Horizontal DistributionOne 4-Pair UTP Cord

Final DistributionAlong

Patch Cord

LocalLoop

(Analog)

ResidentialTelephone(Analog)

Switch(Analog)

Switch(Analog)

Switch(Analog)

LocalLoop

(Analog)

BusinessTelephone(Analog)

Trunk Line(Analog)

Original Telephone Network: All Analog

Today’s Telephone Network: Predominantly Digital

LocalLoop

(Analog)

ResidentialTelephone(Analog)

Switch(Digital)

Switch(Digital)

Switch(Digital)

LocalLoop

(Digital)

PBX(Digital)

Trunk Line(Digital)

Subscriber access line is analog

Switch is digital

Codec converts between them

Codec

DigitalInternalSignal

DigitalSwitch

Local LoopAccess Line

End Office

AnalogSubscriber

Signal ADC

DAC

LAN Building Wiring

Equipment Room

ToWAN

CoreSwitch

(Chassis) Router

Single optical fiber pair or UTP cord from workgroup switch to core switch

LAN Building Wiring

Horizontal and Final Distributionare the Same as in Telephony

WorkgroupSwitch

Horizontal DistributionOne 4-Pair UTP Cord

Summary

Information systems architecturesDistributed systemsTelecommunications, telephony and networking