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Fragmentation In 6lowpan Networks

Discussion in '6LowPAN Networks' started by Homaei, Nov 3, 2013.

  1. Homaei

    Homaei Administrator Staff Member

    If an entire payload data-gram fits within a single 802.15.4 frame, it is unfragmented and the LoWPAN encapsulation should not contain a fragmentation header. If the data-gram does not fit within a single IEEE 802.15.4, it shall be broken into link fragments.
    As the fragment offset can only express multiples of eight bytes, all link fragments except the last one must be multiples of eight bytes in length.
    The first link fragment header should follow the structure shown in the next figure:
    9.jpg
    Fig1. First fragment
    The second and subsequent link fragments should conform the next format:
    10.jpg
    Fig2. Subsequent fragment​


    • Datagram_size (11 bits): size of the entire IP packet before link-layer fragmentation. This value must be the same for all fragments.
    • Datagram_tag (16 bits): the sender should increment the data gram tag for successive fragmented datagrams. This value must be the same for all fragments of a payload.
    • Datagram_offset (8 bits): only in the second and subsequent fragments and in increments on 8 octets.

    The next figure is a graphical view of the different headers that can have a UDP packet sent over a 6LoWPAN network.

    upload_2013-11-3_10-17-7.png

    Fig3. 6LoWPAN - UDP compressed

    Referenced by: http://www.wsnlab.org
    Author: Mohammah Hossein Homaei
    Wireless Sensor Networks Laboratory of Iran
    www.wsnlab.org

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