Types of Communication Services

Let s look at various types of applications a platform should support.

Private Network Services

Many network-aware applications never attempt to communicate to systems outside of some internal network. For example, many corporate applications communicate solely with one or more internal servers on the corporate network. In this tightly controlled environment, a developer can typically assume a common network protocol, security domain, authentication and authorization scheme, and often, development platform. Interoperability with foreign platforms is not a requirement. The number of users is often relatively small ”at least when compared to the number of users on the Internet as a whole.

Private Network to Private Network Services

When an application on one private network needs to communicate with an application on a different private network, complications arise. A business-to- business (B2B) application is a typical example of such an application. Company A s purchasing system would like to place an order with Company B s order entry system. In this situation, the purchasing application would typically run on one private network, the order entry application would run on a different private network, and the companies would use the Internet as the bridge between the two private networks.

This introduces a few complications in the connectivity. Because the communication occurs over the public Internet, data security becomes an issue. To establish secure communications between the applications, the two companies will typically need to implement authentication, authorization, and possibly, encryption services. These requirements aren t trivial, even when both companies use the same platform. However, the more common scenario is that the two companies do not use the same platforms and operating systems, meaning that the applications will very likely not have a common security infrastructure.

Of course, neither company has any control of the public portion of the network connection. The Internet is well known for its high latencies, but it s not quite as well known that certain types of messages can be dropped entirely. A robust application might need to handle these scenarios. In addition, limitations in transports and encodings might exist if there is a different platform on each side of a conversation.

Protocol Bridges

Over time, companies often want to connect existing applications to each other and to new applications. Existing systems often use disparate protocols, platforms, and data interchange formats. New applications must interoperate with existing deployed systems. This scenario has many similar requirements as the previous business-to-business scenario. In addition, interoperability to existing applications often requires support for protocols other than Transmission Control Protocol/Internet Protocol (TCP/IP), the standard protocol used on the Internet.

End User Communication Applications

The previously described, communication-based applications typically run within a corporate environment ”from server to server, within a company, or across companies. However, end user systems also run communications applications. A traditional client-server application runs on the client and initiates communication with a server. A server can communicate back to its clients only after the client has connected to it. A server cannot arbitrarily establish a connection to a client. A new, but growing area of communications applications is a client-to-client application , also known as a peer-to-peer application. Many games , instant messengers, and file-sharing applications support direct communication from one client application to another client application. Collaboration applications also typically share data by using peer-to-peer communications. Some applications combine client-server and peer-to-peer applications. Instant messenger applications typically contact a central server to receive presence notifications about a person, but they connect directly to the person s instant messenger application to send a file to that person.