  A single server retrial queueing system with two-classes of orbiting
customers, and general class dependent service times is considered. If an
arriving customer finds the server unavailable, it enters a virtual queue,
called the orbit, according to its type. The customers from the orbits retry
independently to access the server according to the constant retrial policy. We
derive the generating function of the stationary distribution of the number of
orbiting customers at service completion epochs in terms of the solution of a
Riemann boundary value problem. For the symmetrical system we also derived
explicit expressions for the expected delay in an orbit without solving a
boundary value problem. A simple numerical example is obtained to illustrate
the system's performance.
