The main function of the ESM sublayer is to
support the EPS bearer context handling in the UE and in the MME.
The ESM comprises procedures for:
- the activation,
deactivation and modification of EPS bearer contexts;
- the
request for resources (IP connectivity to a PDN or dedicated bearer resources)
by the UE; and
- the transport
of user data via the control plane between the UE and the MME.
Each EPS
bearer context represents an EPS bearer between the UE and a PDN. EPS bearer
contexts can remain activated even if the radio and S1 bearers constituting the
corresponding EPS bearers between UE and MME are temporarily released.