The separates the 512 bits of generated MSK into four
equal portions of 128 bits each, i.e., four Sub-MSKs.
The UE shall use each Sub-MSK to generate the four PMKs.
PMK1 = HMAC-SHA-256(Sub-MSK, pmk@xxxxxxxxxx,0x01),[0:127]

Kindly let me know the reason for specifically using the
"pmk@xxxxxxxxxx" in HMAC-SHA-256 in CDMA2000 HRPD.
Why not another kind of string ?

Thx in advans,
Karthik Balaguru