A Lesson in Scaling 6LoWPAN -- Minimal Fragment Forwarding in Lossy Networks

TL;DR

This paper compares hop-wise reassembly and minimal fragment forwarding strategies in 6LoWPAN IoT networks, revealing that direct forwarding can reduce latency but may decrease reliability under high transmission rates.

Contribution

It provides an extensive experimental evaluation of fragment forwarding strategies in lossy 6LoWPAN networks, challenging previous assumptions and highlighting conditions affecting reliability and latency.

Findings

Direct fragment forwarding can reduce end-to-end latency.

Higher link-layer transmission rates can decrease reliability.

Reliability issues are exacerbated by increased link-layer retransmissions.

Abstract

This paper evaluates two forwarding strategies for fragmented datagrams in the IoT: hop-wise reassembly and a minimal approach to directly forward fragments. Minimal fragment forwarding is challenged by the lack of forwarding information at subsequent fragments in 6LoWPAN and thus requires additional data at nodes. We compared the two approaches in extensive experiments evaluating reliability, end-to-end latency, and memory consumption. In contrast to previous work and due to our alternate setup, we obtained different results and conclusions. Our findings indicate that direct fragment forwarding should be deployed only with care, since higher packet transmission rates on the link-layer can significantly reduce its reliability, which in turn can even further reduce end-to-end latency because of highly increased link-layer retransmissions.