PROTOCOL_CM_MODIFY_QOS_CALL callback function (ndis.h)

The ProtocolCmModifyCallQoS function is required. ProtocolCmModifyCallQoS is called by NDIS when a connection-oriented client requests that the call parameters be changed for an existing virtual connection (VC). If the underlying network medium does not support QoS, ProtocolCmModifyQoS should simply return NDIS_STATUS_NOT_SUPPORTED.

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



NDIS_STATUS ProtocolCmModifyQosCall(
  [in] NDIS_HANDLE CallMgrVcContext,
  [in] PCO_CALL_PARAMETERS CallParameters


[in] CallMgrVcContext

Specifies the handle to a call manager-allocated context area in which the call manager maintains its per-VC state. The call manager supplied this handle to NDIS for its ProtocolCoCreateVc function.

[in] CallParameters

Pointer to a CO_CALL_PARAMETERS structure that contains the new call parameters, as specified by a connection-oriented client, for the VC.

Return value

ProtocolCmModifyQoS returns the status of its operation(s) as one of the following values:

Return code Description
Indicates that the call manager successfully changed the parameters of the call with the network to the call parameters specified at CallParameters .
Indicates that the call manager will complete the request to modify the call parameters asynchronously. When the call manager has completed all operations necessary to modify the call parameters, it must call NdisCmModifyCallQoSComplete.
Indicates that the call manager could not change the call parameters of the VC because dynamically allocated resources were not available.
Indicates that the call manager was unable to change the call parameters of the VC because the call parameters provided at CallParameters were illegal or invalid.
Indicates that the call parameters could not be set to the call parameters provided because of a failure in the network or in another connection-oriented network component.


ProtocolCmModifyQoS communicates with network control devices or other media-specific agents, as necessitated by its media, to modify the media-specific call parameters for an established virtual connection. If the call manager is required to communicate with network control agents (in other words, a networking switch) it should use a virtual connection to the network control agents that it established in its ProtocolBindAdapterEx function. Stand-alone call managers communicated to the network agents by calling NdisCoSendNetBufferLists. Miniport drivers with integrated call-management support never call NdisCoSendNetBufferLists. Instead, such a driver simply transfers the data over the network to the target network agent.

After communicating with the network and if the changes were successful, the call manager must then call NdisCmActivateVc with the new call parameters. This notifies NDIS and/or the connection-oriented miniport driver that the call parameters have changed and provides the miniport driver with an opportunity to validate those parameters.

If either the network cannot accept the new call parameters or the underlying miniport driver cannot accept the parameters, the call manager must restore the virtual connection to the state that existed before any modifications were attempted, and return NDIS_STATUS_FAILURE.


To define a ProtocolCmModifyCallQoS 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 ProtocolCmModifyCallQoS function that is named "MyCmModifyCallQoS", use the PROTOCOL_CM_MODIFY_QOS_CALL type as shown in this code example:


Then, implement your function as follows:

    NDIS_HANDLE  CallMgrVcContext,
    PCO_CALL_PARAMETERS  CallParameters

The PROTOCOL_CM_MODIFY_QOS_CALL 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 PROTOCOL_CM_MODIFY_QOS_CALL 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 ProtocolCmModifyCallQoS (NDIS 5.1)) in Windows Vista. Supported for NDIS 5.1 drivers (see ProtocolCmModifyCallQoS (NDIS 5.1)) in Windows XP.
Target Platform Windows
Header ndis.h (include Ndis.h)
DDI compliance rules SpinLockBalanced(ndis), SpinLockDpr(ndis)

See also