IX15 compatibility with S2C XBee devices

Digi has updated and ported our XBee firmware from the XBee/XBee-PRO (S2C) hardware based on the SiLabs EM357 SoC, to the Digi XBee 3 hardware based on the SiLabs EFR32 SoC.

The Digi IX15 Gateway includes an XBee 3 device that can be configured to work with Zigbee, DigiMesh, or 802.15.4 networks.

This section assists you with configuring your Digi IX15 Gateway to work within a network of XBee/XBee-PRO S2C devices. While the basic functionality and communication are similar and compatible, there are some limitations to consider. The main limitations are:

  1. Zigbee
    1. The Digi IX15 Gateway should enable LQI compatibility mode—C8—so that all nodes in the network have the same priority when determining route costs.
    2. The Digi IX15 Gateway does not open the join window persistently.
    3. An XBee S2C OTA firmware update from an IX15 is possible when S2C devices are within range of another S2C device:
      • S2C end devices must have an S2C node as their parent.
      • S2C routers must have at least another S2C router node in range.
  2. DigiMesh
    1. The channel—CH—on the IX15 should be within 0x0C and 0x17 to guarantee communication with XBee S2C devices.
    2. If using encryption, the IX15 should enable 128-bit key for AES Encryption—C8—to be over-the-air compatible with S2C devices.
    3. Synchronous sleep mode is not supported in XBee S2C.
    4. XBee S2C OTA firmware update from an IX15 is possible when S2C devices are within range of another S2C device.
  3. 802.15.4
    1. The channel—CH—on the IX15 should be within 0x0C and 0x17 to guarantee communication with XBee S2C devices.
    2. An IX15 configured as the indirect messaging coordinator will not hold messages for longer than 65 seconds.
    3. XBee S2C OTA firmware update from an IX15 is not supported.

Zigbee

  1. Power cap on channel 26

    On the XBee S2C, output power on channel 26 is capped to +3 dBm for all device roles. Additionally, including channel 26 in the scan channel mask—SC—of the coordinator would reduce the output power on all channels to +3 dBm.

    The power cap on IEEE 802.15.4 channel 26 has been increased on XBee 3 and restrictions on the coordinator have been alleviated.

    The power cap on channel 26 of the XBee 3 is increased to +8 dBm. Including channel 26 in the scan channel mask has no impact to other channels. The default value for SC is 0x7FFF—Channels 11 through 25.

  2. LQI calculations

    On the S2C, the LQI curve is more flat and trends towards the top of the scale; where the LQI curve on the XBee 3 is linear and lower scale. As a result, if operating in a network with a mixture of XBee 3 and S2C modules, the S2C devices will have higher priority when determining route costs.

    An LQI compatibility mode was introduced in XBee 3 Zigbee version 1009, which can optionally have the XBee 3 operate with a similar LQI curve as the S2C. C8 bit 4—C8 | 0x10—on XBee 3 enables the LQI compatibility mode. The Digi IX15 Gateway should enable LQI compatibility mode.

  3. End Device timeout

    On the S2C, the parent node determines how long an end device exists in the child timeout table. The timeout value was based on the SP and SN parameters on the parent node.

    With XBee 3, the end device controls this timeout value. A new ET command—which is only set on an End Device—sets the child table timeout when it joins its parent. The timeout is a minimum of two minutes, but can be set as long as 273 hours.

  4. Join window is not persistently open

    Zigbee 3.0 does not support an open joining model. To meet this requirement, the NJ command has a new default setting of NJ = 0xFE. This generous joining window still allows other devices to join to the network, but the join window will close after 254s. The join window can be reopened again at any time by pressing the commissioning button twice, or issuing a CB2 AT command.

    To keep the join window open indefinitely, you must explicitly set NJ = FF.

  5. Join window indicators

    If the device is operating in API mode—AP = 1 or 2—Modem Statuses are emitted when the join window opens and closes:

    • 0x43 - Open Join Window
    • 0x44 - Closed Join Window

  6. OTA firmware update process

    The radio serving up the firmware image can be either a Digi XBee 3 Zigbee 3.0 or XBee/XBee-PRO ZB (S2C). However, since the XBee/XBee-PRO ZB (S2C) requires that another XBee/XBee-PRO ZB (S2C) be a nearest neighbor to act as the updater node, there is some limitation as to how nodes can be updated in a mixed network.

    The image below describes how it is determined whether nodes in a mixed network arrangement can be updated from a single firmware image server. The image server can be either Digi XBee 3 Zigbee 3.0 or XBee/XBee-PRO ZB (S2C). S2C devices must be within range of another S2C device to be updated:

    • S2C end devices must have an S2C node as their parent.
    • S2C routers must have at least another S2C router node in range.

Note For more information, see the Digi XBee 3 Zigbee Migration Guide.

DigiMesh

  1. Expanded channel selection

    The IEEE 802.15.4 standard allows for 16 channels to be used for communication: from 2.405 GHz—Channel 11—through 2.480 GHz—Channel 26. On the previous XBee-PRO S2C DigiMesh modules, the range of available channels—via the CH command—was restricted on the PRO variant. This restriction is alleviated on the XBee 3 and all 16 channels are available for use regardless of the variant.

    The CH parameter on the IX15 should be within 0x0C and 0x17 to guarantee communication.

  2. Synchronized cyclic sleep

    XBee S2C DigiMesh devices lacked the hardware necessary to keep the network in sync over long periods of time, so no support was included. This feature has now been reintroduced on XBee 3.

  3. Enhanced security

    On the previous XBee S2C DigiMesh modules, 128-bit AES encryption was used to secure RF traffic. The default security on the XBee 3, when enabled, is 256-bit AES with counter mode to protect against replay attacks. As a result, the KY parameter has been increased to a 256-bit value—64 ASCII characters—on the XBee 3.

    In order to provide compatibility with legacy DigiMesh networks, a bit in the C8 command has been created. Bit 2 of the C8 bitfield—C8 | 0x4—when set, reduces the security mode of the XBee 3 to 128-bit AES; this is over-the-air compatible with legacy 2.4 GHz DigiMesh devices.

    When this compatibility mode is enabled, only the last 32 ASCII chars—128 least significant bits—of the 256-bit KY parameter will be used. KY cannot be read and is write-only.

    Examples:

    • If EE = 1 and C8 = 0, then KY is a 256-bit Link key and will only communicate with other XBee 3 DigiMesh devices with the same C8 and KY values.
    • If EE = 1 and C8 = 4, then KY is a 128-bit Link key that is compatible with S1, S2C, and XB3 DigiMesh using with the same 128-bit KY value.

    If KY =11112222333344445555666677778888ZZZZYYYYXXXXWWWWVVVVUUUUTTTTSSSS, the underlined portion would be the 128-bit link key.

  4. OTA firmware update process

    The radio serving up the firmware image can be either a Digi XBee 3 DigiMesh or XBee/XBee-PRO DM(S2C). However, since the XBee/XBee-PRO DM (S2C) requires that another XBee/XBee-PRO DM(S2C) be a nearest neighbor to act as the updater node, there is some limitation as to how nodes can be updated in a mixed network.

    The image below describes how it is determined whether nodes in a mixed network arrangement can be updated from a single firmware image server. The image server can be either Digi XBee 3 DigiMesh or XBee/XBee-PRO DM(S2C). S2C modules must be within range of another S2C module to be updated.


Note For more information, see the Digi XBee 3 DigiMesh Migration Guide.

802.15.4

  1. Expanded channel selection

    The IEEE 802.15.4 standard allows for 16 channels to be used for communication: from 2.405 GHz—Channel 11—through 2.480 GHz—Channel 26. On the previous XBee-PRO S2C 802.15.4 modules, the range of available channels—via the CH command—was restricted on the PRO variant. This restriction is alleviated on the XBee 3 and all 16 channels are available for use regardless of the variant.

    The CH parameter on the IX15 needs to be within 0x0C and 0x17 to communicate.

  2. Indirect messaging limitation

    SP determines the asynchronous cyclic sleep period, the same as S2C 802.15.4. However, on the XBee 3, the indirect messaging coordinator will not hold messages for longer than 65 seconds, even if SP * 2.5 > 65 seconds.

  3. OTA firmware update process

    The OTA firmware update process for the XBee 3 802.15.4 is different than the process on the S2C. When performing an OTA firmware update, both the server and client nodes must be of the same type—XBee 3 to XBee 3, S2C to S2C. This means remote firmware update is not supported from the IX15 to remote XBee S2C 802.15.4 devices.

Note For more information, see the Digi XBee 3 802.15.4 Migration Guide.