Point-to-point transmitter
==========================

The model implements a point-to-point connection (for example, a leased line
or a fiber optics cable).

The line itself is modelled by a connection with data rate assigned.
Transmissions on the link are controlled by PointToPointIF modules at both
ends of the connection. A PointToPointIF module monitors the state of the
link, and frames that arrive from the source while transmission is going on
are queued up.

While a bare connection with a data rate (and without PointToPointIF-style
modules) can fullfill the basic functionality of a point-to-point connection
(see the Manual for details on how it works), there are reasons for
introducing PointToPointIF: extensibility and additional flexibility.

The model can be easily extended to limit the length of the queue (i.e. discard
frames if queue is too long), to make it possible to query the queue length
from another module via a direct method call interface, to implement priority
queueing (let "expedited" frames go first), or to collect link statistics
(utilization, etc.)

In this model, link traffic is generated by a bursty source whose implementation
demonstrates the use of the FSM (Finite State Machine) macros.