UPC/i2CAT UPC/i2CAT University of Cambridge RFC 4944 specifies 6LoWPAN fragmentation, in order to support the IPv6 MTU requirement over IEEE 802.15.4-2003 networks. The 6LoWPAN fragmentation header format comprises a 4-byte format for the first fragment, and a 5-byte format for subsequent fragments. This specification defines a more efficient 3-byte, optimized 6LoWPAN fragmentation header for all fragments.