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260 CHAPTER NINE
PRIVACY
We will discuss security and privacy shortly. The only reason to mention privacy here
is that shared communication channels carry an extra risk of eavesdropping. This is
especially true if all users have the option of seeing all the traffic. TCP/IP systems often
have this limitation.

SHARED ACCESS ENVIRONMENT

A system in which multiple entities share the communications link can be designed in
many ways. Sometimes the very nature of the communications environment dictates the
methods used. Here are a couple of considerations a robot designer should take into
account when picking a communications system that will support multiple entities that
share access to the channel.

Closed System

If access to the communications system is restricted, then the designer can generally
count on uniformity of response. The entire system should behave according to the
architecture and protocols envisioned. If the communication link must be shared with
unknown communication entities, then all sorts of problems can arise.

Load Limits

The total amount of communication traffic that a link will bear is often determined by
both the protocol and the users’ actions on the link. It is not unusual for a communica-
tion link to top out at a fraction of the raw bit speed of the link.

Cooperative Users

If the communication entities cooperate, then the usable bandwidth of the communica-
tion link can be increased. If the communication entities can be synchronized, then they
can time-share a communication link fairly efficiently.

TYPES OF SHARED ACCESS

As we mentioned before, cooperation between communication entities that share a com-
munication link is beneficial. Here are a couple of specific types of shared access