SIP 486 Busy Here

What SIP 486 means

The person you called is busy on this device. It is a healthy response rather than a fault, and if you would rather callers did not hear engaged the answer is call waiting, extra call appearances, or a busy-forward destination.

Client error (4xx)
Sent by The called handset or its PBX
Common

What SIP 486 Busy Here actually means

The called party was contacted successfully but is not able to take another call on this particular device. Because it is specific to one device, a call forked to several destinations can still be answered elsewhere, which is what separates it from a 600 Busy Everywhere.

What causes SIP 486 on a business phone system

The extension is genuinely on a callWith call waiting switched off, a second call to a handset already in conversation is refused rather than queued. This is the expected behaviour, not a fault.
Every call appearance is in useHandsets allow a fixed number of simultaneous call legs. Once they are all occupied, including calls on hold, further calls are refused even though the user may feel they are only on one call.
A concurrent call limit has been reachedWhere an extension or trunk is licensed for a set number of simultaneous calls, hitting that ceiling produces a busy response. Worth checking on small trunk bundles at peak times.

How to fix SIP 486

Turn on call waiting if a second call should be able to arriveThis is the direct fix where users want to be interrupted. Consider whether they actually do, since a second call arriving mid-conversation is not always welcome.
Set a busy-forward destinationSend calls that arrive while the extension is engaged to voicemail, a colleague or a hunt group, so nobody hears an engaged tone.
Use a hunt group or queue for shared numbersFor a main business number, a queue or hunt group is the right structure rather than a single extension, so a busy person never blocks the number.
Check the concurrent call allowanceIf busy responses appear at busy times across several extensions, the trunk capacity is the constraint rather than any individual phone.

Fixing the underlying problem

This page explains the code. These guides walk through the fix in detail.

Questions about SIP 486

Is SIP 486 Busy Here a fault?

No. It is the correct response when someone is already on a call and cannot take another on that device. It only becomes a problem worth solving if callers to a main number are hearing engaged, in which case you want a queue or a busy-forward rather than a fix.

What is the difference between 486 Busy Here and 600 Busy Everywhere?

A 486 is about one device, so a call ringing several destinations can still be answered on another. A 600 says the person is busy on every device they have, and it ends the call attempt everywhere.

Call hangup causes that become SIP 486

If the call crossed a gateway between SIP and ISDN or SS7, this status may have started life as one of these Q.850 cause values. The mapping is defined in RFC 3398 section 7.2.4.1.

Q.850 cause 17User busy

Related SIP response codes

Source. SIP 486 Busy Here is defined in RFC 3261 section 21.4.24 and registered in the IANA SIP Parameters — Response Codes. The causes and fixes above are drawn from our own experience supporting UK business phone systems.

All VoIP & SIP codes