就是通过Attach Type字段判断啊。依据是23060和24008。如下:
参考23060的6.5.3联合附着的信令流程第8a步:
“If Attach Type in step 1 indicated GPRS Attach while already IMSI attached, or combined GPRS / IMSI attached, then the VLR shall be updated if the Gs interface is installed. ”
SGSN只有收到了MS发送的attach type是联合附着的请求指示,才会在第8a步向MSC发送Location Update Request。
参考TS24008中关于attach type字段的取值如下:
"Type of attach (octet 1, bit 1 to 3)
Bits
3 2 1
0 0 1 GPRS attach
0 1 0 Not used. This value was allocated in earlier versions of the protocol (Note1)
0 1 1 Combined GPRS/IMSI attach
1 0 0 Emergency attach"。
Type of identity (octet 3) Bits | |||
3 | 2 | 1 |
|
0 | 0 | 1 | IMSI |
0 | 1 | 0 | IMEI |
0 | 1 | 1 | IMEISV |
1 | 0 | 0 | TMSI/P-TMSI/M-TMSI |
1 | 0 | 1 | TMGI and optional MBMS Session Identity |
0 | 0 | 0 | No Identity (note 1) |
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