  This paper considers a multichannel preemptive-resume priority queueing
system with a Poisson input and an arbitrary service time distribution
depending on the priority of job. Jobs of the same priority are serviced
according to the LIFO rule. If, at moment of job arrival, all servers are busy,
and at least one server is busy with the service of a job of a not higher than
the priority of arriving job, then the service of a job is preempted such that
the priority of preempted job is lowest from the priorities of the jobs in
service. The service of a preempted job is resumed later. The paper proposes
approximate formulas for the sojourn time of a prescribed priority job and some
other characteristics of the system.
