Q.850 cause 63 Service or option not available, unspecified

• Service or option unavailable class
• Sent by The equipment handling service authorisation for the call
• Rare

What Q.850 cause 63 Service or option not available, unspecified actually means

The value of a catch-all lies in the company it keeps. Cause 63 closes the class that contains not subscribed, not authorised and not presently available, so the equipment has told you it was refusing on service grounds while admitting it could not say which ground. That still rules a great deal out, and it points your first question at provisioning rather than at the network. Because RFC 3398 lists no mapping, the SIP status you see is whatever the gateway chose; the RFC's general guidance is that unlisted causes default to 500 Server Internal Error, which is a fallback rather than a meaning.

This cause is used to report a service or option not available event only when no other cause in the service or option not available class applies.

— ITU-T Q.850 section 6.2.7.3.8

The SIP equivalent of Q.850 cause 63

RFC 3398 publishes no recommended SIP status for this cause. It maps a subset of cause values only, and states that a cause outside that subset should default to 500 Server Internal Error. Seeing this cause reach a SIP leg unchanged usually means something in the path passed it through without translating it.

What causes Q.850 cause 63 on a business phone system

• A service refusal the switch could not classifySome platforms distinguish only a handful of service failures internally and use the class catch-all for the rest. The refusal is real and deliberate even though the code carries no detail.
• Detail lost when the cause crossed a network boundaryA precise service cause from one network can arrive as the generic one after interworking. The original reason still exists upstream, which is why the carrier can often answer a question your own logs cannot.
• A half-completed provisioning orderServices delivered in stages can leave a line partly configured, with the capability present but its enabling record missing. This tends to appear within days of an order rather than out of nowhere.
• A vendor default for unrecognised feature requestsWhere an implementation returns this for anything it declines, the number tells you nothing on its own. Be honest about that when raising a ticket, and ask for the internal reason rather than the Q.850 value.

How to fix Q.850 cause 63

1. Establish exactly what the call was asking forIdentify the destination, the feature in use and whether anything unusual was requested. A catch-all cause is only interpretable in the light of what triggered it.
2. Compare a working line with the failing oneWhere one extension or trunk succeeds and another does not, the difference in their provisioning is the answer. This is faster than any amount of protocol analysis on a cause that carries no detail.
3. Ask the carrier what the code means on their platformVendors use catch-alls differently, and the carrier can often map it to a specific internal reason. Phrase the question as what did your platform actually refuse rather than what does cause 63 mean.
4. Review recent orders and changesLook at anything provisioned in the fortnight before the first failure. Partly applied changes are the single most common explanation when this cause appears on a service that used to work.

Questions about Q.850 cause 63

Related Q.850 cause values

• Q.850 cause 50Requested facility not subscribed
• Q.850 cause 57Bearer capability not authorized
• Q.850 cause 58Bearer capability not presently available

Source. Q.850 cause 63 Service or option not available, unspecified is defined in ITU-T Q.850 section 6.2.7.3.8 and registered in the ITU-T Recommendation Q.850 (10/2018). The causes and fixes above are drawn from our own experience supporting UK business phone systems.

All Call hangup causes (Q.850) codes