SIP 486 Busy Here is generated by a UA that is already engaged in a call and cannot accept a new one. It's one of the simpler SIP responses — but when it appears unexpectedly or triggers a loop, there's always a specific cause. Here's what to look for.
SIP 486 Busy Here is defined in RFC 3261 Section 21.4.23. The UAS generates it when the called endpoint is currently engaged in a call and cannot accept a new INVITE. The "Here" is significant — it means this specific UA is busy, but other registered contacts for the same AOR might not be.
The Contact header in the 486 identifies which specific UA is busy. If the AOR has multiple registered contacts (e.g. a desk phone and a softphone), only the one that sent the 486 is busy — other contacts might accept the call.
Call waiting in SIP works by sending a second INVITE to an endpoint that already has an active call. The endpoint signals it's ringing via 180 (or the existing call leg) and the user can switch. If the endpoint doesn't support call waiting or it's disabled, it responds with 486 to the second INVITE.
Asterisk: Control call waiting with call-limit in sip.conf or max_contacts in PJSIP. Set to 2 or higher to allow simultaneous calls.
FreeSWITCH: Set max-calls on the endpoint profile. Call waiting behavior is controlled by the dialplan — use bridge with originate_timeout and handle 486 in the !CHANNEL_DESTROY handler.
Enable call waiting: On Asterisk, increase call-limit or max_contacts. On IP phones, enable call waiting in the phone's call settings menu.
Handle 486 in dialplan: After a 486 response, your dialplan should try an alternate destination, queue the call, or play a busy message. Don't let 486 silently fail the call with no user feedback.
Configure overflow routing: For inbound queues, configure overflow behavior when all agents are busy. Route to voicemail, an announcement, or a different queue rather than returning 486 to the caller.
SIP 486 Busy Here means the called endpoint is currently on another call and cannot accept a new INVITE. It is generated by the specific UA that is busy, not by the registrar or proxy. Other registered contacts for the same user may still be available.
SIP 486 Busy Here means the endpoint is actively engaged in a call. SIP 480 Temporarily Unavailable means the endpoint is not available but not necessarily busy — it could be unregistered, in do-not-disturb mode, or simply not answering.
Unexpected 486 is usually caused by call waiting being disabled or a max-calls limit being reached. Enable call waiting on the endpoint, increase the max concurrent calls limit, and configure your dialplan to handle 486 by routing to an alternate destination or voicemail.
Paste your SIP trace into SIPSymposium. The analyzer identifies whether the 486 is from the endpoint or the PBX, checks call limit configuration, and identifies dialplan handling gaps.