RNDIS Concepts (Windows Embedded CE 6.0)
1/6/2010
RNDIS compliance places requirements on the communication channel and lower-layer drivers that are used to communicate between the host and the RNDIS device.
The following table provides a brief description of RNDIS requirements on the host.
| RNDIS concept | Description |
|---|---|
Control Channel |
The control channel must be reliable and ensure sequenced delivery. It is used for all communication except for the transmission of network data packets. All required control messages, except REMOTE_NDIS_HALT_MSG and REMOTE_NDIS_INDICATE_STATUS_MSG, are request and response exchanges initiated by the host. The device must respond within the timeout period as specified for each bus. |
Data Channel |
The data channel is used exclusively for the transmission of network data packets. It may consist of multiple sub channels as defined for the appropriate bus. |
Initialization and Teardown |
The control and data channels are initialized and set up as specified for the appropriate bus. The host sends a REMOTE_NDIS_INITIALIZE_MSG message to the RNDIS device. The RNDIS device provides information about its type, supported medium, and version in the response message REMOTE_NDIS_INITIALIZE_CMPLT. Either the host or the RNDIS device can tear down the communication channel through the REMOTE_NDIS_HALT_MSG message. All outstanding requests and packets are discarded on receipt of this message. |
Halt |
At any time that the device is in the rndis-initialized or rndis-data-initialized state, the host computer may terminate the RNDIS functionality of the device by sending REMOTE_NDIS_HALT_MSG to the device. |
Resetting the Communication Channel |
The communication channel is reset when an error, such as message timeout, occurs. The host may initiate a reset at any time when the device is in the rndis-initialized state by sending the message REMOTE_NDIS_RESET_MSG to the device. The device must send a response message when it has completed the reset. |
Flow Control |
The RNDIS device may need to exercise flow control to prevent the host from overflowing its data buffers with packets. Any flow control provisions or requirements are bus specific. |
Numeric Byte Ordering |
All numeric values in RNDIS messages must be coded in little-endian format (least significant byte first). |
NDIS Message Encapsulation |
There is no RNDIS specification for the way NDIS messages are encapsulated in native bus messages or primitives. |
In the sense that any handles continue to be valid after a reset, any reset is a soft reset. The RNDIS device discards all outstanding requests and packets as part of the reset process. The remote device might reset a portion of its hardware, but keeps the communication channel intact.
If the RNDIS device performs a reboot, this event is equivalent to "Remove" followed by "Add" plug-and-play events. The host NDIS miniport driver will be halted and removed, and a new instance will be added and started. All bus-level and RNDIS initialization will be re-executed. A RNDIS device may reboot itself in the event of a critical device failure.
The following table shows the device states possible for RNDIS devices.
| Device state | Description |
|---|---|
Rndis-uninitialized state |
Following bus-level initialization, the device is said to be in the rndis-uninitialized state. If the device receives a REMOTE_NDIS_HALT_MSG, a bus-level disconnects, or a hard-reset at any time, it forces the device to the rndis-uninitialized state. |
Rndis-initialized state |
After the device receives a REMOTE_NDIS_INITIALIZE_MSG and responds with a REMOTE_NDIS_INITIALIZE_CMPLT with a status of RNDIS_STATUS_SUCCESS, the device enters the rndis-initialized state. If the device is in the rndis-data-initialized state when it receives a REMOTE_NDIS_SET_MSG specifying a zero filter value for OID_GEN_CURRENT_PACKET_FILTER, this event forces the device back to the rndis-initialized state. |
Rndis-data-initialized state |
If the device receives a REMOTE_NDIS_SET_MSG that specifies a non-zero filter value for OID_GEN_CURRENT_PACKET_FILTER, the device enters the rndis-data-initialized state. |