COMPUTER NETWORKING:NETWORKING IN PRACTICE

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NETWORKING IN PRACTICE

The following subsections go into some detail about the practical issues of networking. A brief overview is provided of the suggested way of starting activities devoted to advance analysis of the environment, planning the applications and their prerequisites, designing the network itself, and im- plementing the appropriate hardware and software. Classification of networking solutions and imple- mentation of network technology are investigated separately. As in the other parts of this chapter, the reader should look for a more detailed discussion in the specialized literature, some of which is listed in the References.

Methodology

Designing a good network is a complex task. It is essential that the planning and implementation phase be preceded by a thorough survey in which the following questions, at least, have to be answered:

• What is the principal goal of building the network?

• What is the appropriate type and category of the network?

• Is there a need for integration with existing networks?

• What kinds of computers and other hardware equipment are to be connected?

• What kinds of applications are to be implemented over the network?

• What kind of protocols should be supported?

• How much traffic should be carried by the network? What is the required bandwidth and throughput of the network? What is the highest expected peak load of the network?

• What is the maximum acceptable delay (latency) on the network?

• What level of reliability should be guaranteed?

• What level of security has to be reached?

• What kinds of enhancements and improvements are expected in the future? What level of scalability is desirable?

• What kinds of physical constraints (distance, trace, etc.) should be taken into consideration?

The actual process of implementation depends on the answers to these questions. The result (the adequacy and quality of the network) will greatly depend on how consistently the rules have been followed about building networks.

Designing the most appropriate topology is one of the key issues. Many other things depend on the actual topology. If the topology is not designed carefully, the network may be far from having optimum adequacy, quality, and cost / performance.

Choosing the right physical solutions and low-level protocols is also very important. Low-level protocols (TCP / IP, etc.) have a strong impact on the functionality of the network. Building a mul- tiprotocol network is advisable only if there is an explicit need for such a selection; this may increase the costs and make the management and maintenance tasks difficult and complicated.

Classification

Classification of networks by type may help significantly in selecting the solution for a specific application. Obviously, different types of networks are designed to serve different types of application needs.

Networks can be classified by a number of attributes. Important classification factors include:

• Purpose (general, industrial, process control, etc.)

• Size (local area network, metropolitan area network, wide area network)

• Technology (ethernet, fast ethernet, token ring, fiber digital data interface [FDDI], asynchronous transfer mode [ATM], etc.)

• Applied low-level protocols (TCP / IP, IPX / SPX, Decnet, AppleTalk, etc.)

• Speed (low, medium, high, ultrahigh)

• Mode of operation (open, private, intranet, extranet, etc.)

Often more than one kind of technology and / or protocol has to be used in the same network. Especially if the size of the network is large, different segments can be built up by using different technologies and / or protocols. Fortunately, modern network equipment allows the use of different technologies and protocols at the same time within the same network. This equipment takes care of the necessary translations when routing the information traffic.

Implementation Issues

Like the design process, implementation is a complex task that can involve difficult problems. The design team should understand the available technological solutions well in order to select the most appropriate ones for each part of the system.

As an example, ethernet technology is a widespread, efficiently functioning solution in most cases, but because it does not guarantee appropriate response times, it cannot be used in certain real-time environments. Ethernet is a reliable, effective, inexpensive, and very good technology, but the applied CSMA / CD algorithm is not real time. In practice, the process to be controlled by the network may be much slower than the ethernet technology. Therefore, especially if oversized network capacity is implemented, there will be no problem in such cases. But theoretically it is not the best choice. Of course, the choice and the means of implementation are also a financial question, and all the important factors should be taken into consideration in looking for a good compromise.

Decisions about what and how to implement have a serious impact on the reliability and security of the network, too. For building a high-reliability, high-availability network, redundant components must be used. Communication lines and passive and active network components all have to be multiplied in a well-designed way to get a partly or fully fault-tolerant system. Of course, this may result in significant extra costs. Similarly, if extra-high levels of security must be guaranteed, a number of additional hardware and software components may be needed. Again, a good compromise can be found by taking into account all the reliability and security aspects and cost considerations.

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