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E0 Mandatory IE missing. The equipment sending this cause receives a message is missing an
information element that is necessary for it to process the message. This problem usually
occurs due to a D channel error. Upgrade the Cisco IOS software on the router to resolve
this problem. Contact the Telco if the problem occurs systematically.
E1 Message type not implemented. The equipment sending this cause receives an
unrecognized message due to either the message type is invalid, or it does not support or
implement the message type. The problem usually occurs due to the D channel of the local
router or the configuration of the remote router.
E2 Message not compatible with call state or not implemented. The equipment sending this
cause receives a message that is not permissible in the call state according to the procedures,
or it receives a STATUS message which indicates an incompatible call state. This problem
usually occurs due to a D channel error. Contact the Telco if the problem occurs.
E3 IE not implemented. The equipment sending this cause receives a message that contains an
unrecognized information element which it does not support or implement. However, the
message does not need to contain the information element in order for the equipment
sending this cause to process the message. This problem usually occurs due to a D channel
error. Contact the Telco if the problem occurs.
E4 Invalid IE contents. The ISDN switch receives a message that contains invalid contents in
the information element – the information element is implemented, but one or more of the
fields in the information element are coded differently. This cause is usually followed by the
information element that is causing the problem.
E5 Message not compatible with call state. The ISDN switch receives a message that does not
correspond to the current call state for the call.
E6 Recovery on timer expired. Occurs when ISDN messages do not arrive in specified time
according to the Q.931 specification. This cause if sometimes followed by the expired timer.
Wait and try again later. Contact the Telco if the problem persists.
E7 Parameter not implemented. The equipment sending this cause receives a message which
contains an unrecognized parameter which it does not support or implement. Contact the
Telco if the problem occurs.
EE Message with unrecognized parameter discarded. The equipment sending this cause has
discarded a received message which contains an unrecognized parameter.
EF Protocol error, unspecified. This cause code is used to report a protocol error event only
when no other cause in the protocol error class applies. This problem usually occurs due to a
D channel error.
FF Interworking, unspecified. The ISDN network is interworking with another network which
does not provide the next course of action. The precise problem is unknown.
Note: Closed User Group (CUG) is a facility in X.25 and ISDN networks that allows a called
number to be available only to a limited number of users in a virtual private network.
IE – Information Element.
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