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How to change the size of bytes sent in a packet using z-stack

Javier Longares
Intellectual 300 points

Other Parts Discussed in Thread: Z-STACK, CC2430

Hello!

I'm using CC2430 with Z-Stack 1.4.3 and for my particular application I need sometimes send messages with a maximum size of 256 bytes, I read in the F8W-2005-1503 document about 802.15.4 MAC API that there is a constant called MAC_MAX_FRAME_SIZE with a value of 102.  My question is if this value can be changed as needed.

Best regards.

  • 0
    Intellectual 440 points

    Hi,

    afaik the theoretical maximum transfer unit is 128 bytes.  In practice you will get less than 100 bytes. If you want to send more than the mtu, than you have to fragment your data into pieces of mtu's. I think this could be a way to transmit 256 bytes.

    Look at this faq threat. Maybe it helps.

    http://e2e.ti.com/support/low_power_rf/f/160/p/18418/71036.aspx#71036

  • 0 in reply to Wishmaster_de
    Intellectual 300 points

    Hello Whishmaster,

    Thank you for your response, however what I want is to get a bigger data zize in the packet, not to know the maximum, because I know that the maximum in Z-stack 1.4.3 is 85 for data bytes but I need to send data packets which have between 128 and 256 bytes.  I can fragment the packet, but with this solution the network reaction is slower, the traffic in the network is increased and then the latency is worse.

     

    I think the better solution is to increase the maximum of bytes which could be sent through the MAC by the APP, but I don't know how this could be achieved.  If not, there is a serious restriction here in terms of network latency.

     

    Best regards.

  • 0 in reply to Javier Longares
    Intellectual 440 points

    Hi Javier,

    i think due to the limitation  of IEEE802.15.4 standard you "will be lost". There was also something with the buffer that is 128bytes big.

    If you find a solution i'am interested in it.

     

    Best regards

  • 0 in reply to Wishmaster_de
    Intellectual 300 points

    Hi Wishmaster,

    I've read this, the 802.15.4 and I've seen the limit is 127 bytes, from which the header occupies 25 and for security purposes there are 21 bytes, thus the maximum effective MTU is reduced to 86 data bytes.  There is no alternative to data fragmentation.

    Best regards.