SIP Error Codes & Troubleshooting Guide

12 min

This table lists SIP response codes you may encounter, what they usually mean in real deployments, where the issue most likely lies, and what to check next.

1) Provisional Responses (1xx – Informational)

SIP Code	Meaning	What It Means	What to Check
100	Trying	SIP request received and being processed	Normal behavior
180	Ringing	Destination endpoint is ringing	Normal behavior
183	Session Progress	Early media (IVR / announcements)	If audio missing → RTP ports

2) Successful Responses (2xx)

SIP Code	Meaning	What It Means	What to Check
200	OK	Call successfully connected	If no audio → RTP / NAT

3) Client Errors (4xx – Most Common)

SIP Code	Meaning	Likely Root Cause	What to Check
400	Bad Request	Malformed SIP headers or SDP	SIP logs for invalid headers
401	Unauthorized	Authentication required	Credentials (if applicable)
403	Forbidden	IP not allowed	ACL / whitelisted IP
404	Not Found	Invalid DID or routing	Phone number mapping
408	Request Timeout	No SIP response	Firewall / reachability
410	Gone	Number inactive or removed	DID status
415	Unsupported Media	Codec not supported	Ensure G.711 A-law enabled
480	Temporarily Unavailable	Endpoint unreachable	PBX availability
484	Address Incomplete	Invalid number format	E.164 format
486	Busy Here	Destination busy	Normal behavior
488	Not Acceptable Here	SDP / codec mismatch	G.711 A-law only

4) Server Errors (5xx)

SIP Code	Meaning	Likely Root Cause	What to Check
500	Server Error	Internal processing failure	Retry call
502	Bad Gateway	Upstream routing issue	Retry
503	Service Unavailable	Destination unreachable	Network / routing
504	Gateway Timeout	No upstream response	Firewall / latency
580	Precondition Failure	Media negotiation failed	RTP / NAT

5) Global Failures (6xx)

SIP Code	Meaning	Likely Root Cause	What to Check
600	Busy Everywhere	All endpoints busy	Retry
603	Decline	Call rejected by endpoint	PBX dialplan
604	Does Not Exist Anywhere	Invalid number	DID correctness
606	Not Acceptable	Media policy failure	Codec / SDP

6) Media (Audio) Issues – No SIP Error Shown

These are the most common issues and do not always show SIP error codes.

Symptom	Likely Cause	What to Check
No audio both ways	RTP blocked	UDP 10000–40000 open
One-way audio	NAT / firewall	Public IP in SDP
Audio drops after answer	RTP timeout	Firewall idle timeout
IVR audio but no agent audio	Asymmetric RTP	Symmetric RTP enabled

7) Codec Requirements (India)

Item	Requirement
Supported codec	G.711 A-law
Other codecs	Not supported
Common failure	415 / 488 errors

Ensure:

G.711 A-law is enabled

No other codec is forced ahead of it

Transcoding is disabled (recommended)

8) API-Level Errors (Exotel)

API Error Code	HTTP Status	Meaning	What It Indicates	Common Endpoints	What the Customer Should Do

1000	404	Not Found	Resource does not exist	POST /trunks/{trunk_sid}/phone-numbers POST /trunks/{trunk_sid}/whitelisted-ips POST /trunks/{trunk_sid}/destination-uris PUT /trunks/{trunk_sid}/phone-numbers/{id}	Verify trunk_sid, phone number ID, or API path

1001	400	Mandatory parameter missing	Required field not sent in request	POST /trunks POST /phone-numbers PUT /phone-numbers/{id}	Ensure all mandatory fields are present

1002	400	Invalid parameter	Field value is invalid or not allowed	POST /trunks POST /destination-uris POST /whitelisted-ips	Validate parameter format (IP, FQDN, E.164 number)

1007	400	Invalid request body	JSON is malformed or not parsable	All POST / PUT APIs	Fix JSON syntax, remove trailing commas, ensure valid JSON

1008	409	Duplicate resource	Resource already exists	POST /trunks POST /phone-numbers POST /whitelisted-ips	Safe to ignore if config already exists

1011	415	Unsupported content type	Incorrect Content-Type header	All POST / PUT APIs	Use Content-Type: application/json

9) Before Contacting Exotel Support

Please verify:

SIP signaling port (443 / 5070) reachable

UDP 10000–40000 open

Correct Exotel IPs allowed

Correct trunk domain used

Correct mode (pstn or flow)

Correct destination URI configured

G.711 A-law enabled

10) When to Contact Exotel Support

Raise a ticket at support.exotel.com([email protected]) only after verification.

Please share:

Trunk SID

CallSID

Call direction (Inbound / Outbound)

SIP response code (if any)

Timestamp (with timezone)

PBX SIP logs or PCAP (if available)