System Architecture Issues CSC 426

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 . . .

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

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.

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

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

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

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

Next: The Internet’s Effect on System Architecture

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.

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.

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

Network Topologies Hierarchical Star Bus Ring

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.

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

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

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

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

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

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