Cisco 400-051 Exam

Which SIP request method enables reliability of SIP 1xx response types?

  • A. ACK
  • B. PRACK
  • C. OPTIONS
  • D. CANCEL
  • E. REGISTER
Answer: Option B.
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 provisional responses. There is an important difference, however. PRACK is a normal SIP message, like BYE. As such, its own

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