Q. If the callee is busy, what SIP code is returned?
a) 603 Decline
b) 486 Busy Here
c) 202 Accepted
d) 404 Not Found
Check 🔎
Correct answer: Letter b.
In a VoLTE call, SIP signaling handles session setup via the IP Multimedia Subsystem (IMS). When the callee (called UE) is busy (already in a call and can’t accept another one), the terminating UE or its P-CSCF/S-CSCF will respond with the SIP code 486 Busy Here.
This code is a 4xx class response, meaning it’s a client-side rejection — the UE is reachable, but temporarily unable to complete the call due to being engaged.
Q. If the callee is busy, what SIP code is returned?
a) 603 Decline
→ Incorrect. 603 Decline is a global rejection, often used when the user intentionally refuses the call — not necessarily because they’re busy.
b) 486 Busy Here
→ Correct. This is the standard SIP response when the callee is busy, and the rejection comes from the UE or its IMS node.
c) 202 Accepted
→ Incorrect. Indicates that the request has been accepted for processing — not related to busy conditions.
d) 404 Not Found
→ Incorrect. Returned when the callee doesn’t exist or the IMS cannot resolve the target URI.
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