Validity period specifies the time when SM expires. If SM is't delivered before that moment, it is discarded by SC. Validity-Period can be in three different format; Relative, Absolute and Enhanced.
Relative:The TP-Validity-Period comprises 1 octet in integer representation, giving the length of the validity period, counted from when the SMS-SUBMIT is received by the SC. The representation of time is as follows:
TP-VP value Validity period value 0 to 143 (TP-VP + 1) * 5 minutes (i.e. 5 minutes intervals up to 12 hours) 144 to 167 12 hours + ((TP-VP - 143) * 30 minutes) 168 to 196 (TP-VP - 166) * 1 day 197 to 255 (TP-VP - 192) * 1 week
AbsoluteTP-VP field is 7 octets long, containing TP-SCTS formatted time when SM expires. See ETSI 03.40 for more information.
EnhancedSee ETSI 03.40