CST(28)-Distributed Time and Security services

Distributed time services:

Maintaining a single notion of time is important for ordering events that occur on distributed clients and servers. Typically the NOS addresses the problem of distributed time using two complementary techniques;

1. It periodically synchronizes the clocks on every machine on the network.- The NOS typically has an agent on each machine. DCE calls is a Time Clerk tha asks Time Servers for the correct time and adjust the local time accordingly. The agents may consult one or more Time Servers and then calculate the probable correct time and its accuracy based on responses it receives.
2.  It introduces an inaccuracy component to compensate for unequal clock drifts that occur between synchronizations:

The local time agents are configured to know the limits of their local clock. They maintain a count of the inaccuracy factor and return it to an API call that asks for time. The time agent requests a synchronization after the local clock drifts past an inaccuracy threshold.

Distributed Security Services:

The client/server environment introduces new security threats beyond those found in traditional time-shared systems. In a client/server system, even if the client machines are highly secure, the network itself is highly accessible. Sniffer devices can easily record traffic between machines and introduce forgeries and Trojan Horses into the system