[mle] implement alternate RLOC16 usage during role transition (openthread#10006)

This commit introduces a mechanism for a device transitioning from
child to router role to keep receiving frames addressed to its
previous short address for a brief period.

A new radio platform API, `otPlatRadioSetAlternateShortAddress()`, is
introduced. This allows the OT stack to configure an alternate short
address. Radio platform support for this function is indicated by the
`OT_RADIO_CAPS_ALT_SHORT_ADDR` capability in `otPlatRadioGetCaps()`
The same function can be used with `OT_RADIO_INVALID_SHORT_ADDR`
(`0xfffe`) to clear a previously set alternate short address. Support
for the new API is implemented in RCP and `RadioSpinel`, ensuring
backward compatibility by dynamically checking supported radio
capabilities.

MLE code is updated to instruct the radio to use the old child RLOC16
as an alternate address upon role transition. The MLE layer will
automatically clear the alternate address after eight seconds, or if
other state/mode changes occur. This eight-second window ensures the
new router can transmit four MLE Advertisement messages.

Author: abtink

examples/platforms/simulation/radio.c

@@ -382,6 +382,15 @@ void otPlatRadioSetShortAddress(otInstance *aInstance, otShortAddress aShortAddr
     sRadioContext.mShortAddress = aShortAddress;
 }
 
+void otPlatRadioSetAlternateShortAddress(otInstance *aInstance, otShortAddress aShortAddress)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+
+    assert(aInstance != NULL);
+
+    sRadioContext.mAlternateShortAddress = aShortAddress;
+}
+
 void otPlatRadioSetPromiscuous(otInstance *aInstance, bool aEnable)
 {
     OT_UNUSED_VARIABLE(aInstance);
@@ -849,9 +858,9 @@ void radioProcessFrame(otInstance *aInstance)
 
     otEXPECT(sPromiscuous == false);
 
-    otEXPECT_ACTION(
-        otMacFrameDoesAddrMatch(&sReceiveFrame, sPanid, sRadioContext.mShortAddress, &sRadioContext.mExtAddress),
-        error = OT_ERROR_ABORT);
+    otEXPECT_ACTION(otMacFrameDoesAddrMatchAny(&sReceiveFrame, sPanid, sRadioContext.mShortAddress,
+                                               sRadioContext.mAlternateShortAddress, &sRadioContext.mExtAddress),
+                    error = OT_ERROR_ABORT);
 
 #if OPENTHREAD_CONFIG_MLE_LINK_METRICS_SUBJECT_ENABLE
     otEXPECT_ACTION(otMacFrameGetSrcAddr(&sReceiveFrame, &macAddress) == OT_ERROR_NONE, error = OT_ERROR_PARSE);

examples/platforms/utils/mac_frame.cpp

@@ -41,6 +41,15 @@ bool otMacFrameDoesAddrMatch(const otRadioFrame *aFrame,
                              otPanId             aPanId,
                              otShortAddress      aShortAddress,
                              const otExtAddress *aExtAddress)
+{
+    return otMacFrameDoesAddrMatchAny(aFrame, aPanId, aShortAddress, Mac::kShortAddrInvalid, aExtAddress);
+}
+
+bool otMacFrameDoesAddrMatchAny(const otRadioFrame *aFrame,
+                                otPanId             aPanId,
+                                otShortAddress      aShortAddress,
+                                otShortAddress      aAltShortAddress,
+                                const otExtAddress *aExtAddress)
 {
     const Mac::Frame &frame = *static_cast<const Mac::Frame *>(aFrame);
     bool              rval  = true;
@@ -52,7 +61,9 @@ bool otMacFrameDoesAddrMatch(const otRadioFrame *aFrame,
     switch (dst.GetType())
     {
     case Mac::Address::kTypeShort:
-        VerifyOrExit(dst.GetShort() == Mac::kShortAddrBroadcast || dst.GetShort() == aShortAddress, rval = false);
+        VerifyOrExit(dst.GetShort() == Mac::kShortAddrBroadcast || dst.GetShort() == aShortAddress ||
+                         (aAltShortAddress != Mac::kShortAddrInvalid && dst.GetShort() == aAltShortAddress),
+                     rval = false);
         break;
 
     case Mac::Address::kTypeExtended:

examples/platforms/utils/mac_frame.h

@@ -132,6 +132,25 @@ bool otMacFrameDoesAddrMatch(const otRadioFrame *aFrame,
                              otShortAddress      aShortAddress,
                              const otExtAddress *aExtAddress);
 
+/**
+ * Check if @p aFrame matches the @p aPandId and @p aShortAddress, or @p aAltShortAddress or @p aExtAddress.
+ *
+ * @param[in]   aFrame            A pointer to the frame.
+ * @param[in]   aPanId            The PAN id to match with.
+ * @param[in]   aShortAddress     The short address to match with.
+ * @param[in]   aAltShortAddress  The alternate short address to match with. Can be `OT_RADIO_INVALID_SHORT_ADDR` if
+ *                                there is no alternate address.
+ * @param[in]   aExtAddress       The extended address to match with.
+ *
+ * @retval  true    It is a broadcast or matches with the PAN id and one of the addresses.
+ * @retval  false   It doesn't match.
+ */
+bool otMacFrameDoesAddrMatchAny(const otRadioFrame *aFrame,
+                                otPanId             aPanId,
+                                otShortAddress      aShortAddress,
+                                otShortAddress      aAltShortAddress,
+                                const otExtAddress *aExtAddress);
+
 /**
  * Get source MAC address.
  *
@@ -319,6 +338,7 @@ typedef struct otRadioContext
     uint32_t         mCslSampleTime; ///< The sample time based on the microsecond timer.
     uint16_t         mCslPeriod;     ///< In unit of 10 symbols.
     otShortAddress   mShortAddress;
+    otShortAddress   mAlternateShortAddress;
     otRadioKeyType   mKeyType;
     uint8_t          mKeyId;
     otMacKeyMaterial mPrevKey;

include/openthread/instance.h

@@ -52,7 +52,7 @@ extern "C" {
  *
  * @note This number versions both OpenThread platform and user APIs.
  */
-#define OPENTHREAD_API_VERSION (460)
+#define OPENTHREAD_API_VERSION (461)
 
 /**
  * @addtogroup api-instance

include/openthread/link.h

@@ -588,10 +588,19 @@ otError otLinkSetPollPeriod(otInstance *aInstance, uint32_t aPollPeriod);
  *
  * @param[in]  aInstance A pointer to an OpenThread instance.
  *
- * @returns A pointer to the IEEE 802.15.4 Short Address.
+ * @returns The IEEE 802.15.4 Short Address.
  */
 otShortAddress otLinkGetShortAddress(otInstance *aInstance);
 
+/**
+ * Get the IEEE 802.15.4 alternate short address.
+ *
+ * @param[in]  aInstance A pointer to an OpenThread instance.
+ *
+ * @returns The alternate short address, or `OT_RADIO_INVALID_SHORT_ADDR` (0xfffe) if there is no alternate address.
+ */
+otShortAddress otLinkGetAlternateShortAddress(otInstance *aInstance);
+
 /**
  * Returns the maximum number of frame retries during direct transmission.
  *

include/openthread/link_raw.h

@@ -115,6 +115,26 @@ otError otLinkRawSetPromiscuous(otInstance *aInstance, bool aEnable);
  */
 otError otLinkRawSetShortAddress(otInstance *aInstance, uint16_t aShortAddress);
 
+/**
+ * Set the alternate short address.
+ *
+ * This is an optional API. Support for this is indicated by including the capability `OT_RADIO_CAPS_ALT_SHORT_ADDR` in
+ * `otLinkRawGetCaps()`.
+ *
+ * When supported, the radio will accept received frames destined to the specified alternate short address in addition
+ * to the short address provided in `otLinkRawSetShortAddress()`.
+ *
+ * The @p aShortAddress can be set to `OT_RADIO_INVALID_SHORT_ADDR` (0xfffe) to clear any previously set alternate
+ * short address.
+ *
+ * @param[in] aInstance      The OpenThread instance structure.
+ * @param[in] aShortAddress  The alternate short address. `OT_RADIO_INVALID_SHORT_ADDR` to clear.
+ *
+ * @retval OT_ERROR_NONE             Successfully set the alternate short address.
+ * @retval OT_ERROR_INVALID_STATE    The raw link-layer is not enabled.
+ */
+otError otLinkRawSetAlternateShortAddress(otInstance *aInstance, otShortAddress aShortAddress);
+
 /**
  * Transition the radio from Receive to Sleep.
  * Turn off the radio.

include/openthread/platform/radio.h

@@ -82,6 +82,9 @@ enum
     OT_RADIO_LQI_NONE      = 0,   ///< LQI measurement not supported
     OT_RADIO_RSSI_INVALID  = 127, ///< Invalid or unknown RSSI value
     OT_RADIO_POWER_INVALID = 127, ///< Invalid or unknown power value
+
+    OT_RADIO_INVALID_SHORT_ADDR   = 0xfffe, ///< Invalid short address.
+    OT_RADIO_BROADCAST_SHORT_ADDR = 0xffff, ///< Broadcast short address.
 };
 
 /**
@@ -120,17 +123,18 @@ typedef uint16_t otRadioCaps;
  */
 enum
 {
-    OT_RADIO_CAPS_NONE                 = 0,      ///< Radio supports no capability.
-    OT_RADIO_CAPS_ACK_TIMEOUT          = 1 << 0, ///< Radio supports AckTime event.
-    OT_RADIO_CAPS_ENERGY_SCAN          = 1 << 1, ///< Radio supports Energy Scans.
-    OT_RADIO_CAPS_TRANSMIT_RETRIES     = 1 << 2, ///< Radio supports tx retry logic with collision avoidance (CSMA).
-    OT_RADIO_CAPS_CSMA_BACKOFF         = 1 << 3, ///< Radio supports CSMA backoff for frame transmission (but no retry).
-    OT_RADIO_CAPS_SLEEP_TO_TX          = 1 << 4, ///< Radio supports direct transition from sleep to TX with CSMA.
-    OT_RADIO_CAPS_TRANSMIT_SEC         = 1 << 5, ///< Radio supports tx security.
-    OT_RADIO_CAPS_TRANSMIT_TIMING      = 1 << 6, ///< Radio supports tx at specific time.
-    OT_RADIO_CAPS_RECEIVE_TIMING       = 1 << 7, ///< Radio supports rx at specific time.
-    OT_RADIO_CAPS_RX_ON_WHEN_IDLE      = 1 << 8, ///< Radio supports RxOnWhenIdle handling.
-    OT_RADIO_CAPS_TRANSMIT_FRAME_POWER = 1 << 9, ///< Radio supports setting per-frame transmit power.
+    OT_RADIO_CAPS_NONE                 = 0,       ///< Radio supports no capability.
+    OT_RADIO_CAPS_ACK_TIMEOUT          = 1 << 0,  ///< Radio supports AckTime event.
+    OT_RADIO_CAPS_ENERGY_SCAN          = 1 << 1,  ///< Radio supports Energy Scans.
+    OT_RADIO_CAPS_TRANSMIT_RETRIES     = 1 << 2,  ///< Radio supports tx retry logic with collision avoidance (CSMA).
+    OT_RADIO_CAPS_CSMA_BACKOFF         = 1 << 3,  ///< Radio supports CSMA backoff for frame tx (but no retry).
+    OT_RADIO_CAPS_SLEEP_TO_TX          = 1 << 4,  ///< Radio supports direct transition from sleep to TX with CSMA.
+    OT_RADIO_CAPS_TRANSMIT_SEC         = 1 << 5,  ///< Radio supports tx security.
+    OT_RADIO_CAPS_TRANSMIT_TIMING      = 1 << 6,  ///< Radio supports tx at specific time.
+    OT_RADIO_CAPS_RECEIVE_TIMING       = 1 << 7,  ///< Radio supports rx at specific time.
+    OT_RADIO_CAPS_RX_ON_WHEN_IDLE      = 1 << 8,  ///< Radio supports RxOnWhenIdle handling.
+    OT_RADIO_CAPS_TRANSMIT_FRAME_POWER = 1 << 9,  ///< Radio supports setting per-frame transmit power.
+    OT_RADIO_CAPS_ALT_SHORT_ADDR       = 1 << 10, ///< Radio supports setting alternate short address.
 };
 
 #define OT_PANID_BROADCAST 0xffff ///< IEEE 802.15.4 Broadcast PAN ID
@@ -517,6 +521,26 @@ void otPlatRadioSetExtendedAddress(otInstance *aInstance, const otExtAddress *aE
  */
 void otPlatRadioSetShortAddress(otInstance *aInstance, otShortAddress aShortAddress);
 
+/**
+ * Set the alternate short address.
+ *
+ * This is an optional radio platform API. The radio platform MUST indicate support for this API by including the
+ * capability `OT_RADIO_CAPS_ALT_SHORT_ADDR` in `otPlatRadioGetCaps()`.
+ *
+ * When supported, the radio should accept received frames destined to the specified alternate short address in
+ * addition to the short address provided in `otPlatRadioSetShortAddress()`.
+ *
+ * The @p aShortAddress can be set to `OT_RADIO_INVALID_SHORT_ADDR` (0xfffe) to clear any previously set alternate
+ * short address.
+ *
+ * This function is used by OpenThread stack during child-to-router role transitions, allowing the device to continue
+ * receiving frames addressed to its previous short address for a short period.
+ *
+ * @param[in] aInstance      The OpenThread instance structure.
+ * @param[in] aShortAddress  The alternate IEEE 802.15.4 short address. `OT_RADIO_INVALID_SHORT_ADDR` to clear.
+ */
+void otPlatRadioSetAlternateShortAddress(otInstance *aInstance, otShortAddress aShortAddress);
+
 /**
  * Get the radio's transmit power in dBm.
  *

src/cli/README.md

@@ -70,7 +70,7 @@ Done
 - [linkmetricsmgr](#linkmetricsmgr-disable)
 - [locate](#locate)
 - [log](#log-filename-filename)
-- [mac](#mac-retries-direct)
+- [mac](#mac-altshortaddr)
 - [macfilter](#macfilter)
 - [meshdiag](#meshdiag-topology-ip6-addrs-children)
 - [mliid](#mliid-iid)
@@ -4196,6 +4196,16 @@ Print API version number.
 Done
 ```
 
+### mac altshortaddr
+
+Get the alternate short address used by MAC layer. Can be `0xfffe` if not set.
+
+```bash
+> mac altshortaddr
+0x4801
+Done
+```
+
 ### mac retries direct
 
 Get the number of direct TX retries on the MAC layer.

src/cli/cli.cpp

@@ -7306,7 +7306,21 @@ template <> otError Interpreter::Process<Cmd("mac")>(Arg aArgs[])
 {
     otError error = OT_ERROR_NONE;
 
-    if (aArgs[0] == "retries")
+    /**
+     * @cli mac altshortaddr
+     * @code
+     * mac altshortaddr
+     * 0x4802
+     * Done
+     * @endcode
+     * @par api_copy
+     * otLinkGetAlternateShortAddress
+     */
+    if (aArgs[0] == "altshortaddr")
+    {
+        OutputLine("0x%04x", otLinkGetAlternateShortAddress(GetInstancePtr()));
+    }
+    else if (aArgs[0] == "retries")
     {
         /**
          * @cli mac retries direct (get,set)

src/core/api/link_api.cpp

@@ -182,6 +182,11 @@ otShortAddress otLinkGetShortAddress(otInstance *aInstance)
     return AsCoreType(aInstance).Get<Mac::Mac>().GetShortAddress();
 }
 
+otShortAddress otLinkGetAlternateShortAddress(otInstance *aInstance)
+{
+    return AsCoreType(aInstance).Get<Mac::Mac>().GetAlternateShortAddress();
+}
+
 uint8_t otLinkGetMaxFrameRetriesDirect(otInstance *aInstance)
 {
     return AsCoreType(aInstance).Get<Mac::Mac>().GetMaxFrameRetriesDirect();