[CST-2] CSM 1994p7q3

[Tim Harris]

> Someone kindly confirm whether part A of 94/7/3 is correct or not !

I'd draw it as

  http://www.cl.cam.ac.uk/~tlh20/csm-94-7-3.gif

where the servers are A,B and the customers are x,y.  The state

  A: x,y
  B:

represents the system when both customers are at server A with
x at the head of the queue, currently being served.

As usual it's a big hint that the solution is on the right
track if the states can be laid out in a nice symmetric arrangement!

The full answer would also need the state transitions to be labelled,
but these are just p_{klm}\mu_{kl} where p_{klm} is the probability
that customer "k" will move "l->m" when completing service at "l"
and \mu_{kl} is the service rate for customer "k" at server "l".
(The memoryless property means I've omitted the transitions 
from one start back to itself!).

It becomes simpler if the service rates are either customer-
independent or device-independent, and also if (e.g.) customers
always move to the other server.

Tim