Indicating availability of RF resources at a peer base station in a two-way peer-to-peer communication system

A method for indicating availability of outbound RF resources (ORFRs) of peer base stations in a communication system enabling group communications between a plurality of interconnected peer base stations including a first peer base station at a first site and a plurality of first wireless communication devices (WCDs) registered with the first peer base station including a first wireless communication device (WCD) affiliated with a first communication group of WCDs having a first communication group identifier, the method comprising:

• receiving, at the first peer base station from the first WCD, a first group packet destined for WCDs belonging to the first communication group of WCDs and allocating a last remaining ORFR at the first peer base station for communications of the first communication group of WCDs;
• transmitting, from the first peer base station, a first peer busy indicator (PBI) to each of the other peer base stations in the plurality that supports at least one WCD that is affiliated with a same communication group of WCDs as at least one WCD supported by the first peer base station, wherein the first PBI indicates all ORFRs of the first peer base station are currently in use;
• and
• transmitting, from each of the other peer base stations that receive the first PBI, an inbound channel busy indictor (ICBI) that prevents registered WCDs from transmitting inbound communications unless the registered WCDs belong to a communication group of WCDs that has already been allocated an inbound RF resource (IRFR).