1. System Architecture Issues
CSC 426

2. Factors to Consider Scalability Processing Modes Web Integration
Can it grow or shrink?
Web Integration
Web-centric?
Legacy Systems
Interfaces? Replace?
Processing Modes
Batch? Online? 24/7?
Security
Centralized vs distributed;
Web considerations;
Privacy; homeland security . . .

3. The Big Picture
Mainframe/centralized system
Stand-alone
LANs, WANs

4. Client/Server vs. Mainframe – Let’s Not Be Biased . . .
Mainframes:
Slow and stupid?
Inflexible?
The Good
Centralized control.
Single vendor (less finger-pointing).
The Bad
Constrains the user (is this always bad?).
Single vendor (less flexibility).
The Ugly
Less sophisticated user interface.

5. Variations on the Client/Server Theme
Database server
Transaction server
Object server
Web server

6. Thin versus FAT Low network traffic Fast Lower H/W cost
Most maintenance on central server
Harder – must place logic appropriately
High network traffic
Slow (lots of traffic)
High H/W cost
High maintenance cost (more code!)
Easier development

7. Client/Server Tiers Two-tier Three-tier N-tier
User interface – client
Data – server
Application logic – either or both
Three-tier
As above, except middle layer has logic
N-tier
Middleware – the “glue” that binds tiers, provides interfaces between dissimilar platforms

8. Client/Server Features
Flexibility of scale
Reduced network traffic compared to file servers
Potential performance shortfall
Network capacity can be a bottleneck.
Affected by data location

9. Next: The Internet’s Effect on System Architecture

10. The Web: A Different Environment
Internet
Allows even a small, local business to establish a world-wide presence.
Lots of bang for the buck.
Intranet
Facilitates internal systems and communications.

11. Choices in Internet Commerce
Site preparation and maintenance.
Build your own.
Purchase packaged solution.
Pay for service from e-commerce service provider.
Hosting.
Internal
External.

12. Networks Open System Interconnection (OSI) Model
Seven functional layers.
Logical model.

13. Network Topologies
Hierarchical
Star
Bus
Ring

14. Network Topologies Hierarchical
One computer controls computers at the next lower level.
At each lower level in the hierarchy, each computer on that level controls computers at the next level.

15. Network Topologies Star
A hub computer controls the network and all traffic flows through it.

16. Network Topologies Bus
All devices are attached to a single bus (communication channel).
Two-way traffic.

17. Network Topologies Ring
Devices are connected to the same communication channel.
One-way traffic.
A failed device stops traffic.

18. Network Protocols Protocol?
An agreed-upon method of controlling data transmission.
Popular type: TCP/IP (What does this mean?)

19. Wireless IEEE Protocols Security issues. Very flexible.
802.11b, g
Security issues.
Very flexible.
Relatively inexpensive to set up a network.

20. More Choices for the Designer!
Oh, for the simple mainframe world . . .
Systems analyst
More complex knowledge and skill sets required.
More flexibility in solutions.