READ Free Dumps For Cisco- 400-051
| Question ID 12919 | Which SIP request method enables reliability of SIP 1xx response types?
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| Option A | ACK
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| Option B | PRACK
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| Option C | OPTIONS
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| Option D | CANCEL
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| Option E | REGISTER
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| Correct Answer | B |
Explanation 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
| Question ID 12920 | Which SIP reason phrase maps to SIP response reason code 181?
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| Option A | Ringing
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| Option B | Call is Being Forwarded
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| Option C | Session in Progress
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| Option D | Unknown Number
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| Option E | Call Does not Exist
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| Correct Answer | B |
Explanation Explanation: 1xxProvisional Responses 100 Trying Extended search being performed may take a significant time so a forking proxy must send a 100 Trying response. 180 Ringing Destination user agent received INVITE, and is alerting user of call. 181 Call is Being Forwarded Servers can optionally send this response to indicate a call is being forwarded.[1]:21.1.3 182 Queued Indicates that the destination was temporarily unavailable, so the server has queued the call until the destination is available. A server may send multiple 182 responses to update progress of the queue. 183 Session in Progress This response may be used to send extra information for a call which is still being set up. 199 Early Dialog Terminated Can be used by User Agent Server to indicate to upstream SIP entities (including the User Agent Client (UAC)) that an early dialog has been terminated. Reference: http://en.wikipedia.org/wiki/List_of_SIP_response_codes