One E1 has 32 devices of which the first one is used for synchronisation . In case we are using ss7 then we have another 31 ckts for speech, and 30 in case of R2(where the signalling for teh E1 will be in the same E1). Consider a blocking factor of .8 to .9 for the BH and you have 26.35 Erlang traffic capacity for the E1 for an SS7 route and 25.5 Erlang for an R2 route.