Page 1079 - The Mechatronics Handbook

make a telephone call or send a telegraphic message. After a few years, static allocation of res-ources was
adopted, when users were allocated their own dedicated communication channels and these were not
shared among others. In the late 1960s, the era of computer networks dawned with dynamic allocation of
resources and all communication and computer networks have continued with this tradition to date.
With the advent of optical fiber, it was felt that the transmission resources are abundant and can satisfy
any demand at any time. Many researchers and manufacturers were in favor of going back to the static
allocation of resources, but a decision to continue with dynamic resource allocation was made and that
is here to stay for many years to come [10].

38.5 Challenges and Issues

Many challenges and issues are related to communications and computer networks that are still to be
overcome. Only the most important ones will be described in this section.
High data rates provided by optical fibers and high-speed processing available at the switching nodes
has resulted in lower delay for transferring information from one point to another. However, the propagation
delay (the time for a signal to propagate from one end to another) has essentially remained unchanged.
This delay depends only on the distance and not on the data rate or the type of transmission medium.
This issue is referred to as latency vs. delay issue [11]. In this situation, traditional feedback-based reactive
traffic management techniques become ineffective. New preventive techniques for effective traffic man-
agement and control are essential for achieving the full potential of these communication and computer
networks [22].
Integration of different services in the same networks has also posed new challenges. Each type of
service has its own requirements for achieving a desired level of quality of service (QoS). Within the
networks any attempt to satisfy QoS for a particular service will jeopardize the QoS requirements for
other services. Therefore, any attempt to achieve a desired level of quality of service must be uniformly
applied to the traffic inside a communication and computer network and should not be intended for any
specific service or user. That is another challenge that needs to be carefully addressed and its solutions
achieved [13].
Maintaining security and integrity of information is another continuing challenge. The threat of sensitive
information passively or actively falling into unauthorized hands is very real. In addition, proactive and
unauthorized attempts to gain access to secure databases are also very real. These issues need to be resolved
to gain the confidence of consumers so that they may use the innovations in communications and computer
networking technologies to their fullest [13].

38.6 Summary and Conclusions

This chapter discussed the fundamentals of communications and computer networks and the latest
developments related to these fields. Communications and computer networks have witnessed tremen-
dous growth and sophisticated improvements over the last several decades.
Computer networks are essentially resource sharing systems in which users share the transmission media
and the switching nodes. These are used for exchanging information among users that are not necessarily
connected directly. There has been a manifold increase in transmission rates of transmission media and the
processing power of the switching nodes (which are essentially computers) has also been multiplied. The
emerging computer networks are supporting communication of different types of services in an integrated
fashion. All types of information, irrespective of type and source, are being transported in the form of
packets (e.g., ATM cells). Resources are being allocated to users on a dynamic basis for better utilization.
Wireless communication networks are emerging to provide worldwide connectivity and exchange of infor-
mation at any time.
These developments have also posed some challenges. Effective traffic management techniques, meet-
ing QoS requirements, and information security are the major challenges that need to be surmounted
in order to win the confidence of users.

©2002 CRC Press LLC