If a circuit connection has to be set up (for example for a Mobile Originated or Mobile Terminated Call Establishment) after an Inter-3G_MSC relocation without circuit connection, 3G_MSC-A shall request a Handover Number using a MAP-PREPARE-HANDOVER request, containing the IU-RAB-ASSIGNMENT-REQUEST, on the established MAP connection. For speech calls, 3G_MSC-A shall include the Iu Supported Codecs List in the MAP-PREPARE-HANDOVER request. 3G_MSC-A shall configure the RANAP RAB parameters according to the appropriate default speech codec. If 3G_MSC-A supports A interface over IP, then for speech calls 3G_MSC-A may include the AoIP-Supported Codecs List (Anchor) in the MAP-PREPARE-HANDOVER request to be used by 3G_MSC-B for subsequent intra-3G_MSC-B intersystem handover to an A over IP capable BSS. For a detailed description of the handling of this codec list by 3G_MSC-A and 3G_MSC-B see TS 23.153. Alternatively, if 3G_MSC-B is known to support the use of the Iu Supported Codecs List, 3G_MSC-A may configure the RANAP RAB parameters according to the preferred codec and indicate this to 3G_MSC-B by including the RAB configuration indicator in the MAP-PREPARE-HANDOVER request. The decision to use this option is based on internal configuration information in 3G_MSC-A. For an assignment in UTRAN Iu mode, 3G_MSC-A shall also include the NAS Synch Indicator in the Iu-RAB-ASSIGNMENT-REQUEST. If 3G_MSC-B indicates to 3G_MSC-B and to 3G_MSC-A that at least one of two procedures (RAB) assignment or Handover Number allocation can not be completed, then 3G_MSC-A shall terminate the circuit establishment attempt. The existing connection to the UE shall be maintained, if possible. Upon receipt of the MAP-PREPARE-HANDOVER request, 3G_MSC-B shall perform the requested RAB assignment operation towards the RNS. In addition it shall retrieve a Handover Number from VLR-B. For speech calls, if 3G_MSC-B supports the selection of codec based on the Iu-Supported Codecs List, 3G_MSC-B shall select an Iu Selected codec from the Iu Supported Codecs List and connect a transcoder. If the Iu Supported Codecs List was not received or 3G_MSC-B does not support the selection of codec based on the Iu-Supported Codecs List, 3G_MSC-B shall select the appropriate default speech codec. 3G_MSC-B shall reconfigure the RANAP RAB parameters according to the Iu Selected codec:

• if the RAB configuration indicator is included in the MAP-PREPARE-HANDOVER request and the codec selected by 3G_MSC-B is different from the preferred codec; or
• if the RAB configuration indicator is not included in the MAP-PREPARE-HANDOVER request and the codec selected by 3G_MSC-B is different from the appropriate default speech codec.

Additionally, for an assignment in UTRAN Iu mode, 3G_MSC-B shall include the NAS Synch Indicator for the Iu Selected codec in the Iu-RAB-ASSIGNMENT-REQUEST. If the Iu Supported Codecs List was received by 3G_MSC-B and 3G_MSC-B supports the selection of codec based on the Iu-Supported Codecs List, then the Iu Selected codec shall be indicated in the MAP-PREPARE-HANDOVER response, sent from 3G_MSC-B to 3G_MSC-A. If a failure occurs in the RAB assignment or Handover Number allocation then it shall be reflected in the MAP-PREPARE-HANDOVER response that at least one of these two procedures has not been completed (i.e. either by a MAP-PREPARE-HANDOVER result with the RAB assignment procedure outcome and the Handover Number allocation outcome or by a MAP-PREPARE-HANDOVER error). When 3G_MSC-A receives a successful MAP-PREPARE-HANDOVER response, it shall establish a circuit connection to 3G_MSC-B by using the appropriate network supported procedures. In figure 39 this is indicated by the IAM (Initial Address Message) and ACM (Address Complete Message). 3G_MSC-B shall also send the Answer message if appropriate to the signalling system. Upon receipt of the Answer 3G_MSC-A shall consider the circuit connection establishment phase complete. If a failure occurs during the circuit establishment phase then the existing connection to the UE shall be maintained, if possible.

If 3G_MSC-A and 3G_MSC-B support the optional supplementary service Multicall (See TS 23.135), 3G_MSC-A and 3G_MSC-B shall have the following functionality additionally to the description in subclause 13.4.1. A new circuit connection shall be able to set up (for example for a new Mobile Originated or a new Mobile Terminated Call Establishment) after an Inter-3G_MSC relocation with one or several circuit connections. The procedures for the establishment of the additional circuit connection in 3G_MSC-A and 3G_MSC-B are the same as that described in subclause 13.4.1.