The mechanism for the transfer of the RANAP messages on the E interface is defined in TS 29.002
. The operation of the relocation procedures between 3G_MSCs and the use of the RANAP messages for those procedures is described in TS 23.009
and TS 29.010
RANAP is defined to connect the RNS to both, the cs and ps domain of an UMTS CN. Procedures, messages and IEs, only defined for communication between the RNS and the ps domain of an UMTS CN will, of course, never appear on the E-interface.
In the same way as a the connection oriented service of SCCP is used for the messages relating to one UE on the 3G_MSC RNS interface a TCAP dialogue is used on the E interface for messages relating to one UE. As no correspondence to the connectionless service on the 3G_MSC RNS interface is used on the E interface none of the global procedures are applicable.
The management of the terrestrial circuits between the 3G_MSCs is outside the scope of the E interface (see TS 23.009
), therefore all procedures, messages and information elements relating to terrestrial circuits are also excluded from the RANAP procedures and messages used on the E interface.
The RANAP data which on the 3G_MSC RNS interface is contained in the user data field of the exchanged SCCP frames is on the E interface transferred as the contents of the access network signalling info in the AN APDU parameter as described in TS 29.002
, indicating the access network protocol identification "ts3G-25413".
For the description in the present document, the 3G_MSC's functionality related to the relocation between 3G_MSCs has been split into three logical parts, 3G_MSC A, 3G_MSC T and 3G_MSC I. The different roles need not necessarily be performed by different 3G_MSCs.
3G_MSC A is the call/connection controlling part of the 3G_MSC where the call/connection was originally established and the switching point for relocation between 3G_MSCs. (This corresponds to 3G_MSC A as defined in TS 23.009
and TS 29.002
). The 3G_MSC that is the 3G_MSC A will not be changed during the duration of a call/connection.
3G_MSC T is the part relating to the transitory state during the relocation for the 3G_MSC controlling the RNS the serving RNS functionality is relocated to, when basic relocation or subsequent relocation (see TS 23.009
) take place. (This corresponds, depending on the type of relocation to 3G_MSC A, 3G_MSC B or 3G_MSC B' in TS 23.009
and TS 29.002
3G_MSC I is the part of a 3G_MSC through which the 3G_MSC A, via an E interface (or an internal interface) is in contact with the UE. (This corresponds, depending on the type of relocation to 3G_MSC A, 3G_MSC B or 3G_MSC B' in TS 23.009
and TS 29.002
The 3G_MSC that is the 3G_MSC A can also have the role of either the 3G_MSC I or the 3G_MSC T during a period of the call/connection.
The following is applicable for the involved 3G_MSCs concerning the exchange of RANAP data on an E interface before and after a successful inter 3G_MSC relocation:
At basic relocation, two 3G_MSCs are involved, one 3G_MSC being 3G_MSC A and one being 3G_MSC T. When this relocation has been performed, the two 3G_MSCs interworking on the E interface have the roles of 3G_MSC A and 3G_MSC I respectively, i.e. the 3G_MSC that is the 3G_MSC T during the relocation is now the 3G_MSC I.
At subsequent relocation back to 3G_MSC A, two 3G_MSCs are involved. The 3G_MSC having the role of 3G_MSC A has also the role of 3G_MSC T. The other 3G_MSC involved has the role of 3G_MSC I. When this relocation has been completed, there is no exchange of RANAP data on the E interface, i.e. the 3G_MSC being the 3G_MSC I before and during the relocation is now no longer taking part.
At subsequent relocation of SRNS to an 3G_MSC not being 3G_MSC A, three 3G_MSCs are involved. The roles of these 3G_MSCs are 3G_MSC A, 3G_MSC I, and 3G_MSC T respectively. When this relocation has been performed, the two 3G_MSCs interworking on an E interface have the roles of 3G_MSC A and 3G_MSC I respectively, i.e. the 3G_MSC that is the 3G_MSC T during the relocation is now the 3G_MSC I and the 3G_MSC being 3G_MSC I during the relocation is now no longer taking part.