ISOM 617 Distributed Information Systems

A Brief History of Information Systems 1950s: batch processing mainframes 1960s: data communications over phone lines became common and mainframes became multi-user systems 1970s: online real-time, transaction-oriented systems replaced batch processing. DBMSs become common 1980s: the PC revolution 1990s: PC LANs become common 2000: networking everywhere

Host-based Architectures The first application architecture to be developed was the host-based The ‘server’ in host-based architectures, usually a mainframe, performs all four application program functions The 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 processors In client-based architectures, application programs on the clients are responsible for the data access, application, and presentation logic The 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 client For example, if the client program is making a database query, the entire database must travel to the client before the query can be processed The 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 servers The client takes care of the presentation logic The server handles data storage and data access logic Application logic may reside on the client, server or be split up between the two Most networks today use a client-server architecture

Client-Server Architectures Client-server architectures are more efficient since they distribute processing between client and server Another strength is that they allow hardware and software from different servers to be used together This 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 US By 1910, Bell Telephone was a de facto monopoly Telephone regulation began in 1892 in Canada and in 1910 when the Interstate Commerce Commission began to regulate long distance traffic In 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 services 1984: 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 laws Main 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 wiring Telephone technology is basis for much wide area networking Telephone regulation and carriers affect wide area networking Desire for converged services: integrated management of voice and data networks

Equipment Room (Usually in Basement) To Telcos PBX Internal Telephone Switch Wire Bundle (Many Pairs) Vertical Riser Space Termination Equipment

Internal Telephone Network Horizontal Distribution One 4-Pair UTP Cord Final Distribution Along Patch Cord

Local Loop (Analog) Residential Telephone (Analog) Switch (Analog) Switch (Analog) Switch (Analog) Local Loop (Analog) Business Telephone (Analog) Trunk Line (Analog) Original Telephone Network: All Analog

Today’s Telephone Network: Predominantly Digital Local Loop (Analog) Residential Telephone (Analog) Switch (Digital) Switch (Digital) Switch (Digital) Local Loop (Digital) PBX (Digital) Trunk Line (Digital)

Subscriber access line is analog Switch is digital Codec converts between them Codec Digital Internal Signal Digital Switch Local Loop Access Line End Office Analog Subscriber Signal ADC DAC

LAN Building Wiring Equipment Room To WAN Core Switch (Chassis) Router Single optical fiber pair or UTP cord from workgroup switch to core switch

LAN Building Wiring Horizontal and Final Distribution are the Same as in Telephony Workgroup Switch Horizontal Distribution One 4-Pair UTP Cord

Summary Information systems architectures Distributed systems Telecommunications, telephony and networking