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How long it takes for 126 byte packet to be delivered?

Leila Keyvani
Expert 1090 points
Other Parts Discussed in Thread: CC2520

Hi all,

I have a 99-byte data in a packet on Zigbee pro, one ED, one router and one gateway. I checked the packet length in packet sniffer, total length of packet with headers becomes 126 bytes. My application reads some analog data from sensors, puts them together and sends out. So, I need to know how long it takes for a packet to be delivered to destinaton, so that I can adjust my sampling rate. Does my calculation below seem correct? 

Zigbee rate is 250kbps so a 126-byte packet takes 126*8/250=4.032 msec to be sent from ED to router

ACK=5 bytes -> 5*8/250=0.16 msec

again same 126 from router to gateway = 4.032

ack=0.16

total=8.384 msec

How ever using packet sniffer I see it takes almost 16 msec for a packet to be delivered to gateway. Any idea about this?

Thanks in advance,

Leila

  • 0
    TI__Mastermind 19350 points

    I have posted results in another thread from using a scope to measure the time for sending one message, one hop, on a clean channel, by toggling a bit at the Application layer of each device - the cost is 10-12 msecs on the SOC and 4 msecs with the CC2520 and MSP430EXP5438. There is internal overhead and processing of messages as they are routed. You should search for these discussions on the forum and collaborate with others doing similar studies concurrently, like this one, for example:

    http://e2e.ti.com/support/low_power_rf/f/158/t/152431.aspx

     

  • 0 in reply to Dirty Harry
    Expert 1090 points

    Thanks for your post. I followed the other thread you have posted and I am kind of confused. as far as I understood from the other post, I can send a 100 byte packet every 10 msec (I have only one ED , router and gateway so I should be able to send even faster). but here you are mentioning that it takes 10-12 msecs for a message. could you please clarify it a little bit more?

    Thank you,

    Leila