If the Bearer capability information element is coded as circuit-mode, and the network cannot interpret octets 5b, 5c, 5d, 6 and 7, the network may accept these octets without declaring a protocol error and pass these octets on without change.
When a message other than SETUP, DISCONNECT, RELEASE, or RELEASE COMPLETE is received which has one or more mandatory information elements with invalid content, no action should be taken on the message and no state change should occur. A STATUS message is then returned with cause No. 100, "invalid information element contents".
When a SETUP or RELEASE message is received which has one or more mandatory information elements with invalid content, a RELEASE COMPLETE message with cause No. 100, "invalid information element contents" shall be returned.
When a DISCONNECT message is received with invalid content of the Cause information element, the actions shall be the same as if a DISCONNECT message with cause No. 31, "normal, unspecified" was received (see 5.3), with the exception that the RELEASE message sent on the local interface contains cause No. 100, "invalid information element contents".
When a RELEASE COMPLETE message is received with invalid content of the Cause information element, it will be assumed that a RELEASE COMPLETE message was received with cause No. 31, "normal,unspecified".
Information elements with a length exceeding the maximum length (given in 3) shall be treated as an information element with content error.
Note - As an option of the user equipment (e.g.NT2), cause values, location codes, and diagnostics which are not understood by the NT2 may be passed on to another entity (e.g. user or NT2) instead of treating the cause value as if it were cause No. 31, normal,unspecified and sending cause No. 100, invalid information element contents with the RELEASE message. This option is intended to aid user equipment to be compatible with future additions of cause values, location codes and diagnostics to the Recommendation.