2.2 Troubleshoot Elements of a SIP 350-801 Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A user reports that calls to a remote office connect but there is no audio in either direction. A packet capture on the calling phone shows the INVITE with an SDP offer containing `m=audio 49170 RTP/AVP 0 8 18` and `c=IN IP4 192.168.10.50`. The 200 OK from the remote phone contains `m=audio 5004 RTP/AVP 0 8` and `c=IN IP4 10.20.30.40`. The ACK is sent, but RTP packets never flow. What is the most likely cause?

   • AThe ACK was sent before the 200 OK was fully processed, causing the media session to be rejected.
   • BThe remote phone selected payload type 8, which is not valid for G.711 μ-law in an answer.
   • CThe remote phone rejected the G.729 codec because it was not in the 200 OK answer.
   • DThe SDP connection line in the offer points to a private address that the remote phone cannot reach.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A user reports that calls to a specific external number fail immediately with a fast busy tone. A SIP trace shows the INVITE is sent, and the proxy responds with `483 Too Many Hops`. What is the most likely cause?

   • AThe INVITE contains a Max-Forwards header that has been decremented to zero.
   • BThe destination phone is busy and rejected the call with a 486 Busy Here.
   • CThe proxy could not find a route to the destination and returned a 404 Not Found.
   • DThe INVITE was rejected because the caller's authentication credentials were invalid.
   Reveal Solution Discussion Select an answer first
4. 3application · medium

   Two SIP phones in the same office are configured with different codec lists. Phone A offers `m=audio 4000 RTP/AVP 0 8 18` and Phone B answers with `m=audio 5000 RTP/AVP 0`. The call connects and audio works. Later, a user reports that calls to a third phone (Phone C) have one-way audio. A trace shows Phone A offers `m=audio 4000 RTP/AVP 0 8 18` and Phone C answers with `m=audio 6000 RTP/AVP 8`. What is the most likely cause of the one-way audio?

   • APhone C selected a codec (G.711 μ-law) that Phone A did not offer.
   • BPhone A is sending RTP to Phone C's advertised port, but Phone C is sending RTP to a different port than Phone A expects.
   • CPhone A and Phone C negotiated different sample rates, causing the audio to be garbled.
   • DPhone C's answer omitted the `a=rtpmap` for payload type 8, so Phone A cannot decode the audio.
   Reveal Solution Discussion Select an answer first
5. 4foundation · easy

   Which SIP message pair is used to gracefully terminate an established SIP session?

   • AINVITE and ACK
   • BBYE and 200 OK
   • CCANCEL and 200 OK
   • DREFER and NOTIFY
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   A Cisco IP phone and a third-party softphone are on different subnets. The phone offers `m=audio 4000 RTP/AVP 0 8 18` and `c=IN IP4 192.168.1.50`. The softphone answers with `m=audio 5000 RTP/AVP 0` and `c=IN IP4 10.0.0.25`. The call connects, but there is one-way audio: the phone can hear the softphone, but the softphone cannot hear the phone. What is the most likely cause?

   • AThe softphone is sending RTP to the phone's advertised IP address, but the phone is sending RTP to a different address.
   • BThe phone's SDP advertises a private IP address (192.168.1.50) that the softphone cannot reach from its subnet.
   • CThe phone and softphone negotiated different codecs, causing the audio to be garbled.
   • DThe softphone's SDP advertises a private IP address (10.0.0.25) that the phone cannot reach.
   Reveal Solution Discussion Select an answer first