Which SIP request method enables reliability of SIP 1xx response types?
A.
ACK
B.
PRACK
C.
OPTIONS
D.
CANCEL
E.
REGISTER
Explanation:
In order to achieve reliability for provisional responses, we do nearly the same thing. Reliable
provisional responses are retransmitted by the TU with an exponentialbackoff. Those
retransmissions cease when a PRACK message is received. The PRACK request plays the same
role as ACK, but for provisional responses. There is an important difference, however. PRACK is a
normal SIP message, like BYE. As such, its own