SIP 486 Busy Here
The callee is reachable but busy at this location.
4xx Client failure · RFC 3261 · Answer to OPTIONS: Up. It rejected the request.
What SIP 486 means
A 486 says the callee's device was reached but is busy and can't take another call. It is specific to this location: the same user might be free on another device, and the server may include Retry-After to say when to try again. Under RFC 3398, Q.850 cause 17, user busy, maps to 486, and 486 maps back to cause 17.
On a call center line, 486 usually comes from a PBX or queue that has no free agent or line and signals busy instead of queuing the call. Callers hear a busy tone. RFC 3261 also says OPTIONS should get the same response an INVITE would have, so a busy user agent may answer OPTIONS with 486 too.
Example response
SIP/2.0 486 Busy Here
Via: SIP/2.0/UDP 198.51.100.27:5060;branch=z9hG4bK-486-u9
From: <sip:+[email protected]>;tag=6f2a
To: <sip:+[email protected]>;tag=bh-71
Call-ID: [email protected]
CSeq: 3 INVITE
Retry-After: 60
Reason: Q.850;cause=17;text="User busy"
Content-Length: 0Common causes of SIP 486
- The called phone is on another call and has no call waiting or second line.
- The hunt group or queue is full and is set to return busy rather than hold the call.
- The number has a limit on concurrent calls, and that limit has been reached.
- The phone network reported user busy, and the gateway passed it on as 486.
How to fix SIP 486
- Check whether the 486s line up with real load; if every agent is busy, the system is working as configured.
- Look at the concurrent-call limit on the number or the hunt group, and raise it if callers should queue instead.
- Send busy calls to voicemail or an overflow queue instead of returning busy to the caller.
- If 486 appears with no load at all, look for stuck calls holding lines that aren't really in use.
SIP 486 as an answer to OPTIONS
A 486 to OPTIONS means the server is up and the user agent behind the address is busy; it is the answer an INVITE would have got. It doesn't mean the SBC is faulty. A PingVo Route counts it as reachable by default.
Questions about SIP 486
What is the difference between SIP 486 and 600?
486 is busy at this location only, so a proxy can still try the user's other devices. 600 Busy Everywhere says every location is busy and there is no point trying elsewhere.
Why do callers get busy when agents are free?
Something thinks the lines are in use: a concurrent-call limit counting stuck calls, or a queue set to return busy. Compare the PBX's view of active calls with reality.