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Global Call IP Technology Guide — November 2007 587
Dialogic Corporation
IP-Specific Event Cause Codes
description of media capabilities may be present in the response, which is formatted according
to the Accept header field in the INVITE (or application/SDP if not present), the same as a
message body in a 200 (OK) response to an OPTIONS request.
IPEC_SIPReasonStatus491RequestPending (0x1573, 5491 decimal)
SIP Request Failure Response 491 - Request Pending - The request was received by a User
Agent Server (UAS) that had a pending request within the same dialog.
IPEC_SIPReasonStatus493Undecipherable (0x1575, 5493 decimal)
SIP Request Failure Response 493 - Undecipherable - The request was received by a User
Agent Server (UAS) that contained an encrypted MIME body for which the recipient does not
possess or will not provide an appropriate decryption key. This response may have a single
body containing an appropriate public key that should be used to encrypt MIME bodies sent to
this User Agent (UA).
Server Failure Response Codes (5xx)
IPEC_SIPReasonStatus500ServerInternalError (0x157c, 5500 decimal)
Server Failure Response 500 - Server Internal Error - The server encountered an unexpected
condition that prevented it from fulfilling the request. The client may display the specific error
condition and may retry the request after several seconds. If the condition is temporary, the
server may indicate when the client may retry the request using the Retry-After header field.
IPEC_SIPReasonStatus501NotImplemented (0x157d, 5501 decimal)
Server Failure Response 501 - Not Implemented - The server does not support the
functionality required to fulfill the request. This is the appropriate response when a User Agent
Server (UAS) does not recognize the request method and is not capable of supporting it for any
user. Proxies forward all requests regardless of method. Note that a 405 (Method Not Allowed)
is sent when the server recognizes the request method, but that method is not allowed or
supported.
IPEC_SIPReasonStatus502BadGateway (0x157e, 5502 decimal)
Server Failure Response 502 - Bad Gateway - The server, while acting as a gateway or proxy,
received an invalid response from the downstream server it accessed in attempting to fulfill the
request.
IPEC_SIPReasonStatus503ServiceUnavailable (0x157f, 5503 decimal)
Server Failure Response 503 - Service Unavailable - The server is temporarily unable to
process the request due to a temporary overloading or maintenance of the server or the use of
an unsupported transport protocol (for example, TCP). The server may indicate when the
client should retry the request in a Retry-After header field. If no Retry-After is given, the
client must act as if it had received a 500 (Server Internal Error) response. A client (proxy or
User Agent Client) receiving a 503 (Service Unavailable) should attempt to forward the
request to an alternate server. It should not forward any other requests to that server for the
duration specified in the Retry-After header field, if present. Servers may refuse the
connection or drop the request instead of responding with 503 (Service Unavailable).
IPEC_SIPReasonStatus504ServerTimeout (0x1580, 5504 decimal)
Server Failure Response 504 - Server Time-out - The server did not receive a timely response
from an external server it accessed in attempting to process the request. 408 (Request Timeout)
should be used instead if there was no response within the period specified in the Expires
header field from the upstream server.