considers a queue with common exponential arrival and a finite number () of distinguishable and ordered servers (). As a client arrives, it will be served by the
first
available server, i.e., if is available,
the
client is served by it, otherwise if is available
the client
is served by it, and so on. This queue behavior is not monotonic, so
there
is no, at the authors best knowledge, product-form solution for this
model.
The SAN model describing this queue is presented in Figure. The
basic technique to model this queue
is to consider each server as an automaton (). The arrival
in
each server is expressed by a local event (called )
with
a functional rate that will be nonzero, e.g., ,
if all precedent servers are busy, and zero otherwise. At a given
moment,
only one server, the first available, has a nonzero arrival rate. The
end
of service at each server is simply a local event ()
with
a constant rate, e.g., .