When Microsoft Teams Phone Error Code 481 appears, the signaling layer is usually reporting a missing SIP dialog or transaction, not a random app failure. One side still sends a request, the other side no longer recognizes that call leg in its current state. In Direct Routing, that often means the call was already ended, replaced, transferred, parked, or rewritten by the SBC before the next SIP message arrived. [✅Source-1]
What this error usually tells you: the call state on Teams and the call state on the SBC or peer endpoint are no longer aligned.
- Transfer flow can fail when REFER, NOTIFY, INVITE, or BYE messages arrive out of order.
- Park and retrieve can fail when policy scope, timeout, or dialog continuity does not line up.
- Header rewriting can break the identity of the live dialog even when the call looks normal to the user for a few seconds.
Table of Contents
What Error Code 481 Means in Teams Phone
In Teams Direct Routing, reading 481 by itself is not enough. Teams pairs the SIP response with a Microsoft response code. When that Microsoft code starts with 560, the final SIP response came from the SBC side. If it does not start with 560, the call failure was generated by a Microsoft service. That split changes your first troubleshooting move straight away. [✅Source-2]
A short version, then: 481 means the next SIP message did not match the live call state. Clean signaling matters here. Late CANCEL, late INFO, wrong dialog identifiers, stale transfer state, or an SBC that normalized headers too aggressively can all produce the same visible code while the real reason sits one level deeper. Administrators often confirm the pattern by comparing it with other documented Microsoft Teams signaling error codes to determine whether the mismatch is tied to dialog identity, transfer flow timing, or header rewriting.
Where This Error Shows up Most Often
This error tends to appear when the call changes shape quickly. Small mismatch, big effect. The most common places are blind transfer, consult transfer, park and retrieve, and the short period after a call is replaced or released.
- Transfer in progress: Teams may use REFER, a new INVITE, or internal transfer handling depending on SBC capability and call path.
- Retrieving a parked call: the user or device retrieving the call may not match the policy scope or the parked dialog may already be outside the valid window.
- Late in-dialog message: a BYE, CANCEL, or INFO arrives after the other side already considers that dialog gone.
- Path or identity drift: Contact, Record-Route, DNS target, or SBC routing state no longer matches the call that is actually alive.
Transfers deserve extra attention because Teams expects a very specific flow. Calls that use SIP REFER must move through the Teams infrastructure, and the new INVITE must come back to the SIP proxy rather than going off to another destination directly. When that chain breaks, 481 can be one of the visible outcomes. [✅Source-3]
Parked-call scenarios are another place to look. Call park in Teams uses a generated pickup code, and retrieval depends on policy alignment and timing. A user can park on one client and retrieve on another, but the policy still has to line up cleanly. [✅Source-4]
What to Check First
Start with one failed call record, not with a general guess. Pull the exact call from the Teams admin center, note the time, direction, and whether the user transferred, parked, resumed, or hung up just before the failure. Then open the SIP call flow for that call if the feature is available in your tenant. [✅Source-5]
- Read the SIP response code and the Microsoft response code together.
- If the Microsoft code begins with 560, move to SBC logs first.
- If the call involved transfer, inspect the order of REFER, INVITE, NOTIFY, and BYE.
- If the call involved park and retrieve, check policy assignment, timeout, and retrieval path.
- If the problem is intermittent, compare a failed call and a successful call from the same route. The difference is often narrow.
A useful rule: when the error follows a single transfer or park event, inspect message order and dialog identity before you change policies, numbers, or licenses. That is where many 481 cases are found.
Root Causes Behind Error 481
Transfer Signaling Broke Mid-Flow
If the call is being transferred, Teams and the SBC must agree on the transfer method. Teams Direct Routing supports transfer through REFER or by an INVITE with a Replaces header depending on capability. When the SBC handles REFER, it must send the new INVITE back to the Teams SIP proxy, preserve the Refer-To and Referred-By values as they were received, and report progress with 202 Accepted and NOTIFY. A BYE that arrives too early can end the original call before the replacement path is stable. [✅Source-6]
Header Identity Changed During the Call
Teams expects the paired SBC FQDN in the Contact header for incoming SIP messages. Not an IP address. If the SBC inserts an IP into the Contact header, or if rewriting changes the live dialog identity across the route, later in-dialog requests may no longer match. The failure might first show as another code on connection setup, then surface later as 481 once the dialog state drifts. Clean headers matter. [✅Source-7]
SIP Options Health Drifted Across the Route
An SBC can look healthy for one path and still send live traffic to the wrong place later. Teams recommends TLS 1.2 or higher, correct FQDN handling in Contact or Record-Route, incoming access from all Microsoft signaling IP addresses, and use of all three SIP proxy FQDNs: sip.pstnhub.microsoft.com, sip2.pstnhub.microsoft.com, and sip3.pstnhub.microsoft.com. Sending OPTIONS to fixed resolved IP addresses instead of FQDNs can create stale routing after maintenance or failover. Old path, new request, broken match.
Park Retrieval Context Did Not Match
Call park looks simple to the user, yet it has real state behind it. Users who park and retrieve calls must share the same call park policy. If they do not, retrieval fails. Teams also applies a pickup-code range and a timeout window, so a parked call that sits too long or is retrieved under the wrong policy context can fail even though the original call was fine moments earlier. Same feature, different state. That is enough.
A Late In-Dialog Request Arrived After the Dialog Closed
The SIP standard is direct here. For INFO, a server sends 481 when the request does not match an existing call leg. The same family of problem appears with other in-dialog signaling too: one endpoint still thinks the session is alive, the other side has already released or replaced it. That pattern shows up often after transfer, fast hang-up, or a retry from a stale call state. [✅Source-8]
Symptom Patterns and First Places to Look
| What You See | What It Usually Points to | Check First |
|---|---|---|
| 481 appears right after consult transfer or blind transfer | REFER handling, missing NOTIFY, early BYE, or broken replacement dialog | Teams SIP call flow and SBC transfer trace |
| 481 appears when a parked call is retrieved on another device | Call park policy mismatch, timeout expiry, or stale retrieval context | Call park policy assignment and park timeout |
| 481 shows only on one SBC or after SBC profile changes | Header normalization, Contact identity drift, or route-specific signaling behavior | SBC manipulation rules and Contact or Record-Route output |
| 481 appears after short pauses, retries, or fast hang-up | Late in-dialog request after the far end already closed the dialog | Order of INVITE, BYE, CANCEL, INFO, and NOTIFY |
| 481 is intermittent and follows path changes | OPTIONS health drift, FQDN versus IP targeting, or failover path mismatch | DNS, firewall rules, SIP OPTIONS behavior, and active route |
Fix It Step by Step
- Capture one failed call cleanly. Record the user, number, time, direction, and the exact action taken just before failure (transfer, park, resume, hang-up).
- Split Microsoft-side from SBC-side. Use the Microsoft response code. If it begins with 560, start at the SBC. If not, start in Teams call records and SIP call flow.
- Rebuild the message order. In failed transfer cases, compare the sequence of REFER, INVITE, 202 Accepted, NOTIFY, and BYE.
- Preserve header strings exactly. Do not rewrite Refer-To, Referred-By, or dialog identifiers unless the vendor documentation for your model requires a very specific change.
- Validate Contact identity. The Contact header should present the paired SBC FQDN, not an IP. Also review Record-Route when a proxy SBC stays in path.
- Check OPTIONS health and route reachability. Keep TLS at 1.2 or above, allow all Microsoft signaling IP addresses, and send to the Microsoft SIP proxy FQDNs rather than pinned IP addresses.
- Review park settings when retrieval is involved. Confirm both users or devices are under the same call park policy and that the parked call is still within the valid timeout window.
- Test one scenario after each change. Do not batch-edit everything at once. A single controlled retest shows which adjustment actually fixed the state mismatch.
A practical admin habit: compare one good call and one failed call from the same route. In many 481 cases, the difference is not broad. It is one header, one branch, one timing gap, one message too early.
Numbers That Matter
- SIP T1 default: 500 ms.
- INVITE timeout base: 64 × T1, which is 32 seconds when T1 stays at the default value.
- Default call park pickup range: 10-99.
- Allowed custom call park range: 10-9999.
- Allowed park timeout: 120-1800 seconds, with 300 seconds as the default.
- Microsoft SIP proxy FQDN count to configure for failover: 3.
Those values help narrow the problem. A call that fails after a transfer step is rarely fixed by changing user behavior alone. Timing, dialog identity, and route continuity are the areas that usually move the needle.
FAQ
Does Teams Phone Error Code 481 usually mean a licensing problem?
Usually no. It more often points to signaling state mismatch. Licensing and policy issues can block calling, but 481 itself usually appears when one side sends a request for a dialog or transaction the other side no longer matches.
Is Error Code 481 more common in Direct Routing than in Teams-only calling paths?
It is more visible in Direct Routing because the call crosses the Teams SIP proxy and an SBC, which adds another place where dialog identity, transfer handling, and header integrity must stay aligned.
Can call transfer trigger Error 481?
Yes. Transfer changes the call state quickly. If REFER handling, replacement INVITE creation, NOTIFY progress, or BYE timing breaks, the next request can land on a dialog the far end no longer treats as valid.
Can call park and retrieve be involved?
Yes. Park and retrieve depend on policy scope, pickup code validity, and timeout. If users do not share the same call park policy, or the parked session has already timed out, retrieval can fail.
Should I look at Teams admin data or SBC logs first?
Use the Microsoft response code to decide. If it starts with 560, begin with the SBC logs. If not, begin with the Teams admin center call record and SIP call flow.
Is using an IP address in the Contact header a good workaround?
No. Teams expects the paired SBC FQDN in the Contact header for incoming SIP messages. Using an IP can break identity matching and create a new signaling problem instead of solving the old one.