Section: 8.51.2 RNC ID
Content: The Target Type is RNC ID for SRNS relocation procedure, handover to UTRAN and RAN Information Relay towards UTRAN or GERAN operating in GERAN Iu mode, and 5G-SRVCC from NG-RAN to UTRAN procedure. In this case the "Target ID" field shall contain a non-transparent copy of the corresponding IEs (see clause 8.2.2) and be encoded as specified in Figure 8.51-1a below. The "Target RNC-ID" part of the "Target ID" parameter is specified in 3GPP TS 25.413[ UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling ]  [33] and 3GPP TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [84]. NOTE 1: The ASN.1 parameter "Target ID" is forwarded non-transparently in order to maintain backward compatibility. NOTE 2: The preamble of the "Target RNC-ID" (numerical value of e.g. 0x20) shall not be included into octets 6 to (n+4). Also, the optional "iE-Extensions" parameter shall not be included into the GTP IE. Figure 8.51-1a: Target ID for Type RNC ID If only two digits are included in the MNC, then bits 5 to 8 of octet 7 (MNC digit 3) shall be coded as "1111". The location area code (LAC) consists of 2 octets. Bit 8 of octet 9 is the most significant bit and bit 1 of octet 10 is the least significant bit. The coding of the location area code is the responsibility of each administration. Coding using full hexadecimal representation (binary, not ASCII encoding) shall be used. During a 5G-SRVCC Handover, the AMF does not receive the target RAC in the "Target RNC-ID" part of the "Target ID" IE of the Handover Required message (see clause 9.3.1.25 of 3GPP TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [84]). The AMF should set the RAC to a default value, e.g. hexadecimal value 'FF'. The MME_SRVCC shall ignore the received RAC value. The RNC-ID consists of 2 octets and contains 12 bits long value (see 3GPP TS 25.413[ UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling ]  [7]). Bit 4 of octet 12 is the most significant bit and bit 1 of octet 13 is the least significant bit (bits 8 to 5 of octet 12 are set to 0). The coding of the RNC-ID is the responsibility of each administration. Coding using full hexadecimal representation (binary, not ASCII encoding) shall be used. The Extended RNC-ID consists of 2 octets and contains 16 bits long value within the range 4096 to 65535. Bit 8 of octet a is the most significant bit and bit 1 of octet (a+1) is the least significant bit. The coding of the Extended RNC-ID is the responsibility of each administration. Coding using full hexadecimal representation (binary, not ASCII encoding) shall be used. If the optional Extended RNC-ID is included, then the receiver shall ignore the RNC-ID. If the optional Extended RNC-ID is not included, then the length variable 'n' = 8 and the overall length of the IE is 13 octets. Otherwise, 'n' = 10 and the overall length of the IE is 15 octets. NOTE 3: In the "TargetRNC-ID" ASN.1 type definition in 3GPP TS 25.413[ UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling ]  [7] the "RAC" parameter is marked as optional. RAC is however always available at an SGSN/MME when it sends the RAC in e.g. a GTPv2 Forward Relocation Request message.