Signaling Plane

Figure 5-4 shows the signaling plane from MS
to SGSN. At the lower layers, it is identical to the transmission plane. However,
at the higher layers, we find the GPRS Mobility Management and Session
Management (GMM/SM) protocol instead of the SNDCP. This is the
protocol that is used for routing area updates, security functions (such as
authentication), session (that is, the PDP context) establishment, modification,
and deactivation.