MINIPORT_CO_ACTIVATE_VC callback function

The MiniportCoActivateVc function is required for connection-oriented miniports. MiniportCoActivateVc is called by NDIS to indicate to the miniport driver that a virtual connection is being activated.

Note  You must declare the function by using the MINIPORT_CO_ACTIVATE_VC type. For more information, see the following Examples section.



NDIS_STATUS MiniportCoActivateVc(
  NDIS_HANDLE MiniportVcContext,



Specifies the handle to a miniport driver-allocated context area in which the miniport driver maintains its per-VC state. The miniport driver supplied this handle to NDIS from its MiniportCoCreateVc function.


Specifies the call parameters, as specified by the call manager, to be established for this VC. On output, the miniport driver returns altered call parameters if certain flags are set in the CO_CALL_PARAMETERS structure.

Return Value

Return code Description
Indicates that the VC was activated successfully.
Indicates that the miniport driver will complete the request to activate a VC asynchronously. When the miniport driver has finished with its operations, it must call NdisMCoActivateVcComplete.
Indicates that the call parameters specified at CallParameters are invalid or illegal for the media type that this miniport driver supports.
Indicates that the miniport driver could not activate the VC because it could not allocate all of the required resources that the miniport driver needs to maintain state information about the active VC.


The miniport driver must validate the call parameters for this VC, as specified in CallParameters, to verify that the adapter can support the requested call. If the requested call parameters cannot be satisfied, the miniport driver should fail the request with NDIS_STATUS_INVALID_DATA.

MiniportCoActivateVc can be called many times for a single VC in order to change the call parameters for an already active call. At every call, the miniport driver should validate the parameters and perform any processing as required by its adapter in order to satisfy the request. However, if it cannot set the given call parameters, MiniportCoActivateVc must leave the VC in a usable state, because the connection-oriented client or a call manager can continue to send or receive data using the older call parameters.

If the ROUND_UP_FLOW or ROUND_DOWN_FLOW flags are set in the call parameters structure at CallParameters->MediaParameters->Flags, the miniport driver has been requested to return the actual flow rate of the VC after the flow rate has been rounded according to the appropriate flag that has been set. If the miniport driver does change any of the call parameters because these flags have been set, it must return the actual call parameters in use for the VC at CallParameters.

If the call parameters are acceptable, MiniportCoActivateVc communicates with its adapter as necessary to prepare the adapter to receive or transmit data across the virtual connection (in other words, programming receive buffers).


To define a MiniportCoActivateVc function, you must first provide a function declaration that identifies the type of function you're defining. Windows provides a set of function types for drivers. Declaring a function using the function types helps Code Analysis for Drivers, Static Driver Verifier (SDV), and other verification tools find errors, and it's a requirement for writing drivers for the Windows operating system.

For example, to define a MiniportCoActivateVc function that is named "MyCoActivateVc", use the MINIPORT_CO_ACTIVATE_VC type as shown in this code example:

Then, implement your function as follows:
    NDIS_HANDLE  MiniportVcContext,
    PCO_CALL_PARAMETERS  CallParameters
The MINIPORT_CO_ACTIVATE_VC function type is defined in the Ndis.h header file. To more accurately identify errors when you run the code analysis tools, be sure to add the _Use_decl_annotations_ annotation to your function definition. The _Use_decl_annotations_ annotation ensures that the annotations that are applied to the MINIPORT_CO_ACTIVATE_VC function type in the header file are used. For more information about the requirements for function declarations, see Declaring Functions by Using Function Role Types for NDIS Drivers.

For information about Use_decl_annotations, see Annotating Function Behavior.


Minimum supported client Supported for NDIS 6.0 and NDIS 5.1 drivers (see MiniportCoActivateVc (NDIS 5.1)) in Windows Vista. Supported for NDIS 5.1 drivers (see MiniportCoActivateVc (NDIS 5.1)) in Windows XP.
Target Platform Windows
Header ndis.h (include Ndis.h)

See Also