CLIENT/SERVER TECHNOLOGY:FEATURES OF C / S SYSTEMS

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1. FEATURES OF C / S SYSTEMS
Advantages

The advantages of C / S systems derive from their distributed processing structure, which C / S systems adopt, where processing is handled by two or more cooperating geographically distinct processors.

1. Performance tuning: In a distributed processing environment, the service requests from a client are not concentrated on a single server but can be distributed among several servers. Therefore, it becomes possible to distribute required workload among processing resources and improve the performance, such as response time to the client. Furthermore, adopting an efficient al- gorithm of request distribution such as an adaptive algorithm taking account of current loads of all servers makes it possible to improve the throughput (the amount of work processed per unit time) of the system.

2. Availability improvement: Clients are sensitive to performance of the system, but they do not perceive the physical structure of the distribution for requests. In other words, the group of networked servers seems to the client like one server. In a distributed processing environment, even if one server breaks, other servers can substitute for the broken server and continue to process its tasks. This can guarantee the high availability of services to the client compared to a host-centric processing environment.

3. Scalability and cost-efficiency: Scalability is the capacity of the system to perform more total work in the same elapsed time when its processing power is increased. With a distributed system, the processing capacity of the system can be scaled incrementally by adding new computers or network elements as the need arises, and excessive investment in a system can be avoided at the introduction stage of the C / S system. On the other hand, with a host-centric system, if the load level is going to saturate the system, the current system will be replaced by a more powerful computer. If further growth is planned, redundant computer capacity will need to be built into the current system to cope with future growth in requirements.

Disadvantages

1. Strong dependence on the network infrastructure: Because a distributed environment is largely based on a networking infrastructure, the performance and availability of the distributed system are strongly influenced by the state of the network. For example, if a network failure, such as of the router or transmission line, occurs, performance and availability for services may seri- ously deteriorate. The system designer and manager should design the fault-tolerant system and plan the disaster recovery taking account of the networking infrastructure.

2. Security: From the viewpoint of security, the possibility exists that confidential information stored on the database may leak out through the network. The system manager should take security measures such as authentication, access control, and cryptographic control according to the security level of information.

3. Complexity of system configuration: C / S systems are composed of several components from multiple vendors. Distributed applications often have more complex functionality than cen-

tralized applications, and they are built from diverse components. Multitier architectures, which will be explained in the next section, provide a nearly limitless set of choices for where to locate processing functions and data. In addition to choices about locations, there are also more hardware and software choices, and more data sharing occurs. These cause the difficulty in developing a C / S system and the complexity of managing it.

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