eMSC给中兴MME返回“Mandatory IE incorrect”-

【问题现象】

中兴MME与爱立信eMSC配合时，eSRVCC切换失败。

【原因定位】

中兴MME在Sv接口上携带的STN-SR如下

Length: 6 (Bytes)
0000 …. = Spare: 0x00
…. 0000 = Instance Value: 0x00 NANPI: 0x11
STN-SR Value: 8613445243

TS 29.280：6.2中定义的STN-SR号码类型NANPI为addressstring。

STN-SR is defined in 3GPP TS 23.003 [4]. STN-SR is transferred via GTP tunnels. The sending entity copies the value part of the STN-SR into the Value field of the STN-SR IE. The STN-SR IE is coded as depicted in Figure 6.2-1. Octet 5 contains the Nature of Address and Numbering Plan Indicator (NANPI) of the “AddressString” ASN.1 type (see 3GPP TS 29.002 [11]). Octets 6 to (n+4) contain the actual STN-SR (digits of an address encoded as a TBCD-STRING as in the “AddressString” ASN.1 type). For an odd number of STN-SR digits, bits 8 to 5 of the last octet are encoded with the filler “1111”.
TS 29.002 17.7.8 Common data types

It is composed of
— a) one octet for nature of address, and numbering plan
— indicator.
— b) digits of an address encoded as TBCD-String.
— a) The first octet includes a one bit extension indicator, a
— 3 bits nature of address indicator and a 4 bits numbering
— plan indicator, encoded as follows:
— bit 8: 1 (no extension)
— bits 765: nature of address indicator
— 000 unknown
— 001 international number
— 010 national significant number
— 011 network specific number
— 100 subscriber number
— 101 reserved
— 110 abbreviated number
— 111 reserved for extension
— bits 4321: numbering plan indicator
— 0000 unknown
— 0001 ISDN/Telephony Numbering Plan (Rec ITU-T E.164)
— 0010 spare
— 0011 data numbering plan (ITU-T Rec X.121)
— 0100 telex numbering plan (ITU-T Rec F.69)
— 0101 spare
— 0110 land mobile numbering plan (ITU-T Rec E.212)
— 0111 spare
— 1000 national numbering plan
— 1001 private numbering plan
— 1111 reserved for extension
— all other values are reserved.
— b) The following octets representing digits of an address
— encoded as a TBCD-STRING.
因此按照3GPP规范定义NANPI该字段bit8为1 ，而中兴MME的PS TO CS request 消息中STN-SR的NANPI bit8为0,导致爱立信eMSC不支持。
【解决方案】