LAUSR

In 2005, IPv6 over Low Power WPAN (6LoWPAN), the first Working Group (WG) on the Internet of Things (IoT), was established in the Internet Engineering Task Force (IETF) to standardize mechanisms to transmit IPv6 datagrams over IEEE 802.15.4 technology. Since IPv6 may contain datagram sizes much larger than the IEEE 802.15.4 maximum frame size, a new adaptation layer was specified by standardizing several documents such RFC 4944, RFC 6282, and RFC 6775 in the 6LoWPAN WG. In 2007, RFC 4944 was published, and it defines the frame format for transmission of IPv6 datagrams. Moreover, it specifies techniques for header compression, fragmentation, and reassembly, and two fragment forwarding modes, "mesh under" and "route over." In 2012, RFC 6282 was published to update RFC 4944; however, it does not update the fragment forwarding mechanism. Indeed, an IPv6 datagram larger than 1000 bytes could be fragmented to 10 fragments when considering IEEE 802.15.4 technology that comes with a maximum transmission unit of 127 bytes. Furthermore, under the 6LoWPAN route-over mode, the fragmented 6LoWPAN datagram must be reassembled and fragmented again at every hop, which will negatively affect the network reliability and latency. In this article, we first introduce the main operations of RFC 4944, and then we present the potential fragment forwarding issues when the route over mode is employed. We then give an overview of the ongoing proposed works at the IETF to solve the undesired issues of RFC 4944.