What is “GP” timeslots ? (sorry, I’m not working with Siemens, but I can try to help)
Do you mean “Gb” ?
The best KPI to calculate EGPRS traffic is the data volume, why do you need Erlang ?
I assume that you are trying to compute the traffic on the interfaces, and see if the interfaces are congested or not? In this case, the best KPI would be the interface load, if you have t 🙂
For instance, in alcatel, each interface (Abis or Ater) can be divided in “nibbles” (= 16kb/s = one quarter of a timeslot). And there are indicators that say how much nibbles are used at BH, and how many are available.
So it’s really simple to check the load (busy / available)
On the Gb interface, we are using a frame relay interface, which capacity is counted in kb/s, so it’s ok to work with data volume or data throughput.
I’m sorry again not to answer your question precisely, but perhaps it can give you some ideas.