XK-Z11-M Digi International, XK-Z11-M Datasheet - Page 65

• Manufacturer Part Number: XK-Z11-M
• Description: ZIGBEE MODULE DEVELOPMENT KIT
• Manufacturer: Digi International
• Series: XBee™r
• Type: Transceiver, 802.15.4/ZigBeer

Specifications of XK-Z11-M

• Frequency: 2.4GHz
• For Use With/related Products: XBee Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 602-1184

© 2010 Digi International, Inc.
XBee®/XBee‐PRO® ZB RF Modules
Encrypted Transmissions
Maximum RF Payload Size
Throughput
Encrypted transmissions are routed similar to non-encrypted transmissions with one exception. As an encrypted
packet propagates from one device to another, each device decrypts the packet using the network key, and
authenticates the packet by verifying packet integrity. It then re-encrypts the packet with its own source address
and frame counter values, and sends the message to the next hop. This process adds some overhead latency to
unicast transmissions, but it helps prevent replay attacks. See chapter 5 for details.
XBee ZB firmware includes a command (ATNP) that returns the maximum number of RF payload bytes that can be
sent in a unicast transmission. Querying the NP command, like most other commands, returns a HEXADECIMAL
value. This number will change based on whether security is enabled or not. If security is enabled (EE command),
the maximum number of RF payload bytes decreases since security requires additional overhead.
After reading the NP value, the following conditions can affect the maximum number of data bytes in a single RF
transmission:
Throughput in a ZigBee network can vary by a number of variables, including: number of hops, encryption enabled/
disabled, sleeping end devices, failures/route discoveries. Our empirical testing showed the following throughput
performance in a robust operating environment (low interference).
Data Throughput*
Retries and Acknowledgments
•Broadcast transmissions can support 8 bytes more than unicast transmissions.
•If source routing is used, the 16-bit addresses in the source route are inserted into the RF payload space. For
example, if NP returns 84 bytes, and a source route must traverse 3 intermediate hops (3 16-bit addresses),
the total number of bytes that can be sent in one RF packet is 78.
•Enabling APS encryption (API tx option bit set) will reduce the number of payload bytes by 4.
provide it with a new source route. This requires that remote devices periodically send data transmissions
into the data collector. See the earlier "Acquiring Source Routes" section for details.
ZigBee includes acknowledgment packets at both the Mac and Application Support (APS) layers. When data
is transmitted to a remote device, it may traverse multiple hops to reach the destination. As data is
transmitted from one node to its neighbor, an acknowledgment packet (Ack) is transmitted in the opposite
direction to indicate that the transmission was successfully received. If the Ack is not received, the
transmitting device will retransmit the data, up to 4 times. This Ack is called the Mac layer
acknowledgment.
In addition, the device that originated the transmission expects to receive an acknowledgment packet (Ack)
from the destination device. This Ack will traverse the same path that the data traversed, but in the
opposite direction. If the originator fails to receive this Ack, it will retransmit the data, up to 2 times until an
Ack is received. This Ack is called the ZigBee APS layer acknowledgment.
Refer to the ZigBee specification for more details.
Configuration
1 hop, RR, SD
1 hop, RR, SE
1 hop, RE, SD
1 hop, RE, SE
1 hop, ER, SD
Data Throughput
35kbps
19kbps
25kbps
16kbps
21kbps
64