GSM/GPRS coordination (RR/GRR)
If we go from a pure circuit-switched GSM to a combined GSM + GPRS MS, we need various coordination tasks between the CS and PS plane - mostly on the RR/GRR layer, but possibly also ranging into MM/GMM.
For example, while the MS has active TBFs, it cannot scan for CS neighbor cells, and it might receive CS paging via the PACCH.
Figure 5.3/3GPP TS 24.007 depicts a "GMM/MM Coord" SAP (though doesn't formally specify it afaict). We probably want to implement that SAP with our own messages as we see need them.
Also TS 24.008 6.6 "Registration Services for GPRS-Services" states:
It shall be noted, that the registration services for mobiles of class A or B may depend on the service states for GPRS
and non-GPRS services. Therefore the internal access points MMCOORD and the GMMCOORD (see figure 5.3) are
used by GMM and MM to inform each other about the relevant conditions. No service primitives between the entities
within the same sublayer, i.e. the MM sublayer, are defined in the present document. The Mobility Management for
class A and B mobiles is further specified in 3GPP TS 24.008 .