Here I write on How Inter-RAT Mobility performs in LTE, means Handover to LTE and Mobility from LTE.

Handover to LTE

Procedure for handover of LTE is largely the same as the handover procedure in LTE. The main difference is that the handover to LTE AS a whole-configuration must be signaled, and the LTE it is possible to use ‘ signaling delta “, according to which only the changes in the configuration are displayed.

If you like to offer subscribers a better handover had not yet been activated in previous INSTALLMENTS, E-UTRAN activates Ciphering, possibly using the NULL algorithm, as part of the procedure. E-UTRAN also establishes SRB1, SRB2 and one or more of the DRBs (i.e. at least DRB is associated with the default “bearer of EPS).

Mobility from LTE

Generally, the procedure for LTE mobility from another RAT supports both handover and Cell Change Order (CCO), possibly with Assistance Network (NACC – Network Assisted Cell Change). The procedure CCO / NACC is applicable only to GERAN mobility.

Mobility from LTE is performed only after security has been activated. When used for enhanced CSFB18 for CDMA2000, the handover procedure includes support for parallel (ie both 1XRTT and HRPD), surrendered to 1XRTT along with redirection to HRPD, and redirection to HRPD only.

Mobility-LTE

The procedure is shown in Figure.

1. The UE may send a Measurement Report message.

2. In the case of handover (unlike CCO), the source eNodeB requests the target radio access (RAN) node to prepare for handover. As part of the source of “the handover of preparing the query” eNodeB provides information on applicable between RAT UE capabilities, as well as information about the current set-carriers. In response to the target RAN generates a ‘handover command, and returns the source eNodeB.

3. Source eNodeB sends a message from the mobile team to EUTRA UE, which includes inter-RAT or message received from the target (in the case of transmission), or the target cell / frequency and inter-RAT several parameters (in the case of COC).

4. After receiving the message from the mobility team EUTRA, UE starts timer T304 and connect to the target node, or by using the radio to get the configuration (transfer) or by initiating a connection (CBS) in accordance with the specifications of the target RAT.
The upper layers of the UE reports to the AS the target RAT, that the carriers are installed. Consequently, UE may occur if some of the established carriers, were not admitted to the target RAN node.

For CDMA2000

For CDMA2000, additional procedures have been defined to support the transfer of information dedicated to the CDMA2000 upper layers, which are used to record the presence of the UE in the core network before performing the handover target (the preregistration). These procedures use SRB1.