CHAPTER 11 MY NOTES
How application layer functions are spread among computers to deliver service to users
Thanks layering ability to separate function at different layers most application architecture can run over
TCP/IP, IPX/SPX and other standards below the application layer
Note: if you use TCP it does not care what application architecture you are using.
Important networked applications
world wide web
The only layer whose functionality users see directly
TRADTIONAL APPLICATION ARCHITECTURES
Terminal-host systems, client/server architectures (both file server program access and client/server processing.
Hosts with Dump terminals
The first step beyond stand-alone machines still place the processing power on a single host computer but distributed input/output (I/O) functions out to user sites.
It placed these functions in dumb terminals which sent user keystrokes to the host an painted host information on the terminal screen but did little else
Computer was often overloaded by the need to process both applications and terminal communication
And this resulted in slow response times
Resulted in high transmission cost. All keystrokes had to be sent to the host computer for processing
Generated a great deal of traffic.
To reduce transmission costs, most terminals limited the information they could display to monochrome text (one color against a contrasting background) graphics were seldom available
Uses a more complex design for their terminal-host systems that added other pieces of equipment beyond terminals and hosts.
This extra equipment reduced cost and improved response time. In addition, IBM terminals-host systems had higher speeds that traditional terminals and so were able to offer limited color graphics.
These advances extended the life of terminal-host systems, even these advanced IBM systems were less satisfactory than subsequent developments, including the client/serve systems described next.
After terminal hosts systems
A big breakthrough came in form of client/server systems
They placed some power on the client computer
This was made possible by the emerge of personal computers in the 1980
File Server Program Access
The server's only role is to store programs and data files.
For processing the program is copied across the network the to the client PC along with data files
The client PC does the actual processing of the program and data files
Many client Pc's are operatively underpowered
Even the faster are usually fairly slow compared to servers
File server program access is only sufficient for word processing, email and other small application
It is not useful for large database applications.