NETWORK ARCHITECTURE AND COMPUTER NETWORKS

NETWORK ARCHITECTURE

In communications, data is transferred either in parallel or serial. Parallel communications is faster but requires more wires. Serial communications is much slower but requires fewer wires. Serial is more practical for communications with remote sites, and the existing telephone system can be used for the communications link to various locations by the use of modems. Most, if not all, computer networks use serial communications for linking computers. The network architecture defines the message and data formats as well as the protocols and other standards to which the hardware and
software must conform to in order to meet certain objectives. These objectives are listed below:

Connectivity

This objective specifies that the hardware and software, which are built in conformance to the standards, must be able to communicate with each other over the network.

Flexibility

Due to the constant enhancement in technology or due to the change in the user needs, the network may have to be modified. Flexibility specifies that this up-gradation must be possible without the need for costly new interfaces or software modification.

Modularity

Modularity specifies that the hardware and software modules must be capable of production in large quantities so that they can be used in variety of devices.

Reliability

Reliability deals with the issues, which concern error free communication over the network. Error free communication has to be realized by providing appropriate error detection and correction capabilities.

Simplicity

This aspect of architecture specifies that the network should permit its easy implementation, installation and re-configuration. Even the services that are provided by a network must be simple to implement and maintain.

Diversity

The network must provide a variety of services and at the same time, isolating the user from the network structure or implementation details. In our discussion, we will refer to each computer on the network as a node or station, and the facilities for linking the computers as a link. There are several different ways to organize structure these nodes and links to form a network. The structure is referred to as a topology which has been discussed in detail, later in the chapter.

COMPUTER NETWORKS

systems located at the same/different places. The interconnection
is done through a communication link also known as the physical
layer of the network and this link is such that it is totally transparent
to the users of the network. The transparency of the communication
link is brought about by interfacing software known as protocols
which enables a user in one location to freely access a computer
system/database/process/software in another location.
However if the computers in the network operate together as a
single unit, which to the user appears as a single computer, albeit
physically dispersed, then the complete system is more accurately
described as a distributed system. Therefore although any
interconnected set of computers is often conveniently referred to as
a computer network. The use of the term often implies an
interconnected set of independent computers and not a distributed
system. However, it may be useful when considering a distributed
system to be able to recognise the particular type of network on
which it is based.
The hierarchy of a typical network has terminals at the lowest level.
Terminals are connected to the terminal controllers which in turn
are linked to the host computer. Terminals are connected either
serially or in parallel. In a series connection, which is also called
a multidrop line, the terminals are wired to the same line which
connects to the terminal controller. Each terminal is connected
directly by a separate line to the terminal controller in a parallel
connection. Terminal controllers are also connected to each other
and the nodes in a similar fashion.