Overview

SIP (Session Initiation Protocol) response codes are standardized three-digit codes defined in RFC 3261 that indicate the outcome of call setup attempts. These codes appear in Voice Call Action (VCA) and Voice Call Status (VCS) webhooks as sipCode and help diagnose call failures, network issues, and endpoint behavior.

Note: CDRs (Call Detail Records) are a separate feature available to SIP trunk customers and when a support ticket is created with 8x8 CPaaS Support. For CPaaS Voice products (Voice Messaging, IVR, Number Masking, Programmable SIP), call outcomes are available via Voice Session Summary webhooks and the Reporting API, while SIP response codes are exposed via Voice Call Action and Voice Call Status webhooks.

SIP Response Code Categories

1xx - Provisional Responses

Indicates the request has been received and is being processed.

Code	Reason Phrase	Description
100	Trying	Request received, processing continues
180	Ringing	Destination is being alerted (phone is ringing)
181	Call Is Being Forwarded	Call is being forwarded to another destination
182	Queued	Destination is temporarily unavailable, request queued
183	Session Progress	Conveys information about the progress of a call

2xx - Success Responses

Indicates the request was successful.

Code	Reason Phrase	Description
200	OK	Request successful (call answered)
202	Accepted	Request accepted for processing, but processing not complete

3xx - Redirection Responses

Further action is needed to complete the request (typically forwarding scenarios).

Code	Reason Phrase	Description
300	Multiple Choices	Multiple options available for the requested resource
301	Moved Permanently	User can no longer be found at the original address
302	Moved Temporarily	User temporarily moved to a different address
305	Use Proxy	Requested resource must be accessed through a proxy
380	Alternative Service	Call failed but alternative services are available

4xx - Client Error Responses

The request contains bad syntax or cannot be fulfilled by the server.

Code	Reason Phrase	Description	Common Cause
400	Bad Request	Malformed request syntax	Malformed number or SIP headers
401	Unauthorized	Authentication required	Invalid credentials
402	Payment Required	Reserved for future use (billing/prepaid scenarios)	-
403	Forbidden	Server refuses to authorize the request	Unauthorized Caller ID or restricted destination
404	Not Found	User does not exist at the domain specified	Invalid phone number
405	Method Not Allowed	Request method not supported for the target	-
406	Not Acceptable	Response doesn't match acceptable values in request headers	-
407	Proxy Authentication Required	Client must authenticate with a proxy	-
408	Request Timeout	Server did not receive a complete request in time	Network issues or destination unreachable
410	Gone	User previously existed but is no longer available	Number disconnected
413	Request Entity Too Large	Request body is larger than the server is willing to process	-
414	Request-URI Too Long	Request-URI is longer than the server can interpret	-
415	Unsupported Media Type	Message body format is not supported	Codec incompatibility
416	Unsupported URI Scheme	Request-URI scheme is not recognized	-
420	Bad Extension	Server did not understand a required protocol extension	-
421	Extension Required	Server requires a specific extension not listed in request	-
423	Interval Too Brief	Expiration time is too short	-
480	Temporarily Unavailable	Callee's endpoint is currently unavailable	Device offline or out of coverage
481	Call/Transaction Does Not Exist	Server received a request that doesn't match any dialog or transaction	-
482	Loop Detected	Server detected a loop in the request routing	-
483	Too Many Hops	Max-Forwards header reached zero	-
484	Address Incomplete	Request-URI is incomplete	-
485	Ambiguous	Request-URI is ambiguous	-
486	Busy Here	Callee's endpoint is busy (user declined or DND enabled)	Line in use
487	Request Terminated	Request cancelled before completion (caller hung up during ringing)	Caller hung up before answer
488	Not Acceptable Here	Some aspect of the session description is not acceptable	SDP/codec mismatch
491	Request Pending	Server has a pending request from the same dialog	-
493	Undecipherable	Request contains an encrypted body that cannot be decrypted	-

5xx - Server Error Responses

Indicates a server-side issue prevented call completion.

Code	Reason Phrase	Description	Common Cause
500	Server Internal Error	Unexpected server error	Temporary system issue
501	Not Implemented	Server does not support the functionality required	-
502	Bad Gateway	Invalid upstream response	Carrier connectivity issue
503	Service Unavailable	Service temporarily unavailable	System maintenance or capacity
504	Server Timeout	Upstream timeout	Carrier response delay
505	Version Not Supported	SIP protocol version is not supported	-
513	Message Too Large	Message length exceeds server capabilities	-

6xx - Global Failure Responses

Indicates the call cannot be completed anywhere.

Code	Reason Phrase	Description	Common Cause
600	Busy Everywhere	All destinations busy	No available endpoints
603	Decline	Call declined	Recipient rejected the call
604	Does Not Exist Anywhere	Destination invalid globally	Number does not exist
606	Not Acceptable	Call parameters rejected	Incompatible session requirements

Call Status in Voice Session Summary

The Voice Session Summary (VSS) webhook provides call outcome information via the sessionStatus field (for the overall session) and the callStatus field (for individual call legs).

Session Status Values (sessionStatus)

Status	Description
COMPLETED	Session was connected and completed successfully
NO_ANSWER	Call rang but was not answered
BUSY	Destination was busy
CANCELED	Call was cancelled before connection
FAILED	Call could not be completed
ERROR	An error occurred during the session

Call Leg Status Values (callStatus)

Status	Description
COMPLETED	Call leg was connected and completed successfully
NO_ANSWER	Call leg rang but was not answered
BUSY	Destination was busy
CANCELED	Call leg was cancelled before connection
FAILED	Call leg could not be completed

Note: The ERROR status only applies to sessionStatus and does not appear in callStatus for individual call legs.

SIP Code in Webhooks

The sipCode field is available in Voice Call Action (VCA) and Voice Call Status (VCS) webhooks. This field typically shows 200 for connected calls.

For call outcome information, use the callStatus and sessionStatus fields from Voice Session Summary webhooks rather than sipCode.

For detailed webhook payload structure, see:

• Voice Session Summary (Voice Messaging)
• Voice Session Summary (IVR)
• Voice Session Summary (Number Masking)

Best Practices

Number Formatting

• Use E.164 format for all phone numbers (e.g., +14155551234)
• Include the + prefix and country code

Caller ID (CLI)

• Use a verified 8x8 virtual number as your Caller ID
• Ensure CLI is authorized for the destination country

Error Handling

• Implement retry logic with exponential backoff for 5xx errors
• Do not retry 4xx errors without correcting the request
• Log SIP response codes for troubleshooting

Codec Support

8x8 CPaaS Voice supports the following codecs:

• G.711 µ-law (PCMU)
• G.711 A-law (PCMA)
• G.722
• Opus (coming soon)

Troubleshooting

Issue	Possible SIP Codes	Action
Call not connecting	480, 408, 487	Check destination availability and number validity
Call rejected immediately	403, 603	Verify caller ID, check if number is blocked
Invalid number format	404, 484	Validate E.164 format, ensure country code is correct
Network/routing issues	500, 502, 503, 504	Contact 8x8 CPaaS Support if persistent
Call drops during ringing	487	Normal user behavior (caller hung up)

References

• Voice Session Summary webhook
• Voice Error Codes
• Voice Status Codes and Status Messages
• RFC 3261 - SIP: Session Initiation Protocol

Support Channels

• Technical support: support@cpaas.8x8.com
• Sales inquiries: Contact your account manager or visit cpaas.8x8.com/en/contact-us
• Support Portal: https://support.cpaas.8x8.com/hc/en-us