OCSI Environments as IT Infrastructure

Client Server Basics

Object-Oriented Client-Server Internet (OCSI) environments provide the IT infrastructure for supporting OCSI applications. For our purposes, infrastructure refers to operating systems, networks, middleware, and hardware. OCSI are distributed applications with three core technologies: Client-Server, in which parts of the application behave as clients (or service consumers) and others behave as servers (or service providers); object-oriented programming, which allows applications to be easily created, modified, reused and; the Internet, which provides access to application components, like business logic or databases, through web browsers.

The IT infrastructure platform begins with operating systems and hardware. Above this layer exist two side by side modules, the network services and the local services. On top of that is middleware and the final, top layer is the application itself. These are the building blocks. They can come from multiple vendors. Clients-server models contain functional modules with defined interfaces. Client-Server relationships exist between two functional modules, one is the ‘client’ and the other is the ‘server’.

However, thinking of them as modules neutralizes confusion, since one server can become a client for another server depending on the original request and the processing it requires. In other words, clients may make requests of servers that generate other requests making the server occupy the client position in the newly initiated communication. However, it will always remain a server to the original client. The ‘client’ requests a service from the ‘server’ who then processes the request and returns a response. Information exchange between clients and servers is performed through messages. Messaging is a crucial feature of Client-Server models. These messages are interactive.

Features like message queuing allow clients to store messages and pick them up asynchronously by servers later. Because in our discussion clients and servers are located on different machines, real-time messages pass between them over a network. This improves flexibility and scalability, but creates problems regarding interoperability, portability, performance, and security. Middleware addresses these technical issues.

Middleware is the software that provides the “glue” between separate programs, allowing them to understand and work for each other. Conceptually, it is located above the network and below the application. It provides business un-aware services (more technical than computing), where as the top application software is business aware. Middleware services are made available to applications through APIs (Application Programming Interfaces). They are accessible to humans through GUIs (Graphical User Interfaces).

Client-Server models are only one example of DCS (Distributed Computing System). Other examples of DCS are file transfer models and peer-to-peer models. These systems do not share memory with other nodes on the network and communication between the nodes only occurs through messaging.

Internet

The Internet, as a Client-Server system, has made all the information and services on the World Wide Web a household tool. It has accomplished this by making the system so user friendly. The Internet uses GUI clients also known as web browsers to search, navigate and share information on the web regardless of location. Documents and information is connected through hypermedia links.

A layered technical view of the Internet and the World Wide Web begins with the physical network and the machines on that network. Above that is the IP (Internet Protocol) stack. This includes an IP layer that contains the protocol or language of rules and formatting for delivering data over networks. On the layer above that located side by side are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). Working with IP, TCP is a protocol to send packets of data over networks.

While IP actually delivers the data, TCP keeps track of the data packets in a message to make sure they are routed correctly. TCP/IP is the backbone of the Internet. UDP works with IP as well. UDP/IP is protocol that is also primarily used to broadcast messages over networks. It sends and receives datagrams directly over IP networks. Datagrams are units that are transmitted between Internet modules. At the top of the IP stack are application protocols like File Transfer Protocol (FTP), Network File System Protocol, Simple Mail Transfer Protocol (SMTP), and Remote Procedure Call (RPC).

World Wide Web applications are the top layer. They interact directly with the IP stack or with middleware specific to the World Wide Web. This middleware is made up of different components like web browsers, web servers, and web gateways. It also contains all the necessary technology for the creation of dynamic web content, such as HTML and HTTP (Hypertext Transfer Protocol). World Wide Web applications communicate with the web middleware, which then communicates downward to the IP stack.