SIP 600 Busy Everywhere
What SIP 600 means
The person you called is busy on every device they have. Unlike a 486, which refuses at one handset, this ends the attempt everywhere, so there is no point in the call ringing elsewhere.
What SIP 600 Busy Everywhere actually means
The callee was contacted successfully but is busy and does not wish to take the call, and the answer is given for the user rather than for one device. That global scope is the entire distinction from a 486.
What causes SIP 600 on a business phone system
- The user is busy across all their devicesWhere desk phone, softphone and mobile app all count as one user, being busy on any of them can refuse the lot.
- A busy policy is applied at account levelSome platforms express a busy condition globally rather than per device, so the same situation that yields a 486 elsewhere yields a 600 here.
How to fix SIP 600
- Set a busy destination for the userSend calls arriving while they are engaged to voicemail or a colleague rather than returning busy.
- Use a hunt group for shared numbersA number the business depends on should not resolve to a single user who can be busy.
Fixing the underlying problem
This page explains the code. These guides walk through the fix in detail.
Questions about SIP 600
What is the difference between SIP 600 and SIP 486?
A 486 says this particular device is busy, so the call could still be answered on another of the user devices. A 600 says the user is busy everywhere and ends the attempt outright.
Related SIP response codes
Source. SIP 600 Busy Everywhere is defined in RFC 3261 section 21.6.1 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.