Hi, 

I read some articles but still I am not able to find a conclusion. 

Do commercial ZigBee nodes or 802.15.4 PHY based nodes, have ACK mechanism enabled by default or is it optional ? 

By ACK means, the receiver will send an ACK signal to the transmitter whenever receiver decodes a frames successfully (CRC OK). 

If yes, is there any time bound for that. For example 802.11g has SIFS timing of 10 micro secs.

Regards

Sumit  

Hi cogwsn,

I will try to answer your question or at least give you some references.

As Zigbee standard is based on IEEE 802.15.4 protocol acknowledgment at the MAC layer is defined by IEEE 802.15.4 standard specification. I didn't found information that acknowledgment at MAC layer is mandatory, thus I can make assumption that it is optional for unicast messages and should be disabled for broadcast messages. However, from my experience of work with IEEE 802.15.4 (non-beacon networks) and Zigbee modules with different stacks from different vendors I can say that it is enabled by default. Furthermore, in case of Zigbee modules configuration at MAC layer is not available usually.

Time for acknowledgment is defined by attribute macAckWaitDuration, which in turns depends on a number of other parameters. Please, refer to standard specification document IEEE Std 802.15.4 - 2011 for more details. From different sources in the Internet and from my tests I see that typically macAckWaitDuration can be up to 1-2 ms.

Talking about ZigBee protocol, its stack has multiple layers and there is additional optional acknowledgment mechanism is available at Application Support (APS) Sub-Layer. This acknowledgment is defined by attribute apscAckWaitDuration. According to paragraph 2.2.7 of ZigBee Specification (Document 053474r20) its maximum value is 100 ms.