3GPP TS 44.060
Network Assisted Cell Change
The mobile station shall support the Network Assisted Cell Change procedures. The Network Assisted Cell Change consists of two independent procedures:
-One procedure that can assist a mobile station in packet transfer mode or MAC-Shared state with neighbour cell system information for a GSM neighbouring cell required for initial packet access after a cell change;
-one procedure in which the mobile station notifies the network when it has determined to reselect to another GSM, to a 3G, or to an E-UTRAN cell and delays the cell re-selection (CCN mode procedures) to let the network e.g. in the case of reselection to a GSM cell, respond with neighbour cell system information.
The Network Assisted Cell Change procedures are part of the GERAN Feature Package 1. A mobile station indicating support of the GERAN Feature Package 1 in the Mobile Station Classmark 3 IE, the MS Radio Access Capability IE and the MS Radio Access Capability 2 IE supports the Network Assisted Cell Change procedures (see 3GPP TS 24.008).

Abnormal cases
In the following cases, the mobile station shall determine that the network controlled cell reselection procedure has failed:
-The PACKET CELL CHANGE ORDER message commands the mobile station to a frequency in a frequency band not supported by the mobile station. Cause: "frequency not implemented";
-The PACKET CELL CHANGE ORDER message is received while the mobile station is not in dual transfer mode but a circuit switched connection is on going. Cause: "on-going CS connection";
-In A/Gb mode, the PACKET CELL CHANGE ORDER message is received and the GMM READY timer (see 3GPP TS 24.008) is not running (i.e., mobile station in GMM STAND-BY state). Cause, if the GMM READY timer has a negotiated value equal to zero: "Forced to the Standby State". Cause, if the GMM READY timer has a negotiated value greater than zero: "MS in GMM Standby state";
-Access is denied in the new cell (i.e., the mobile station receives an IMMEDIATE ASSIGNMENT REJECT, a PACKET ASSIGNMENT REJECT or, in a UTRAN cell, an RRC CONNECTION REJECT message or fails to establish an RRC connection in an E-UTRAN cell as specified in 3GPP TS 36.331). Cause: "Immediate Assign Reject or Packet Access Reject on target cell";
-The mobile station is unable to synchronise to the new cell (see 3GPP TS 45.008) or the timer T3174 expires before a successful completion of the network controlled cell reselection procedure. Cause: "No response on target cell";
-Due to any other reason (e.g. unknown or unsupported target cell information). In this case the MS shall set the ARFCN and BSIC fields to the value zero and set the cause to value "frequency not implemented".