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603
6xx Global failure, RFC 3261

SIP 603 Decline

SIP 603 Decline means the call was refused on purpose: the person rejected it, or a call-blocking service declined it for them. Trying the same call again elsewhere will not help.

Who sends it
The called side
When
Ringing, before answer
Retry?
No. The refusal is deliberate.
The caller hears
A busy tone or a message that the call was declined, sometimes after a ring.
PBXYour phone or PBX
SIPThe SIP trunk
☎The called sidesends 603
FIX

What causes 603, and how to fix it

603 is a deliberate refusal. The called person rejected the call, or a network or spam filter declined it on their behalf.

  1. 1
    Most common

    The person rejected the call.

    Nothing to fix. Try another time or another channel.

  2. 2
    Most common

    A call-blocking or spam-protection service declined it.

    Send a valid caller ID you are allowed to use; calls with no or invalid caller ID are more often blocked.

  3. 3
    Sometimes

    Many short calls from your number look like automated dialling.

    If many destinations decline, slow down repeated calls and check that your calling pattern looks like normal use.

  4. 4
    Rare

    The destination network does not accept calls from your number range.

    Try a different caller ID you own, such as your virtual number, and see if the result changes.

LOG

What 603 looks like in a SIP log

SIP/2.0 603 Decline

Capturing one: reading the SIP log.

SIP response
SIP/2.0 603 Decline
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK-74bf9
Call-ID: [email protected]
≠

Not to be confused with

603, 486, 607 or 608?

486

Busy Here

The person is busy. Some phones send 486 instead of 603 for a reject.

607

Unwanted

The person marked the call as unwanted, for example spam.

608

Rejected

An analytics or anti-fraud service in the network rejected the call.

FAQ

SIP 603 questions

Why do some numbers always decline my calls?
The person may reject unknown callers, or their network blocks calls it sees as spam. A valid caller ID you are allowed to use helps; repeated short calls make blocking more likely.
Am I charged for a declined call?
No. A declined call is not answered, and on LinkedSIP only answered calls are charged.
What is SIP 603+?
A 603 with an added reason saying the network blocked the call on analytics (ATIS-1000099). Since 25 March 2026, US providers that block calls on analytics must answer with 603+ instead of 607 or 608.

Not 603? Look up another code.

The full list: SIP response codes. 603 again and again? Check your SIP trunk configuration.

All SIP codesFind a fault by symptom