The modify GTP operation is used to add or delete CTPs to/from a GTP. For a given request, the NMS can only add or delete CTPs, not both. It should not be possible to add a CTP that is already involved in a cross connection or SNC, or that is part of another GTP.
Attempts to modify a GTP that is involved in a cross connection or SNC should be rejected by the EMS.
The operation is best-effort, i.e., the EMS will add or delete as many of the identified CTPs as possible.
If the operation is called with the name of a non-existent GTP or CTP, it will fail.

Note: If the NMS created a GTP with gtpEffort equal to EFFORT_SAME, this also implies that the EMS will not modify on its own, i.e., the EMS will only modify the GTP if requested by the NMS via the modifyGTP operation.

Operation Exceptions:
1. NOT_IMPLEMENTED - Raised when EMS does not support modification of GTPs via this interface.
2. INTERNAL_ERROR - Raised in case of non-specific EMS internal failure.
3. UNABLE_TO_COMPLY - Raised when the EMS cannot reply to the GTP modification request.
3. INVALID_INPUT - Raised when input parameter is syntactically incorrect.
4. ENTITY_NOT_FOUND - Raised when the GTP to be modified or TPs to be added do not exist.
5. OBJECT_IN_USE - Raised when the GTP is part of a cross connection or SNC.
6. NE_COMM_LOSS - Raised when communication to managed element is lost and this prevents modification of the GTP.
