An Adaptive Optimized RTO Algorithm for Multi-homed Wireless Environments

As a transport layer protocol SCTP uses end to end metrics, such as Retransmission Time Out (RTO), to manage mobility handover. Our investigation illustrates that Wireless LAN (WLAN) mobility causes continuously increased Round Trip Times (RTT) resulting from 802.11 MAC retransmissions, regardless of the service specified by upper layers. We present scenarios where the current understanding of SCTP switchover aggressiveness is invalid; spurious failovers together with excessive RTO result in new forms of receiver buffer blocking communication failure. Given wireless mobility performance issues, together with the ambiguity of end to end metrics, we propose an Adaptive Optimized RTO algorithm for wireless Access Networks (AORAN) which uses local as well as end to end metrics to manage mobility. AORAN measures RTT between the mobile node and Access Point (AP) to calculate wireless and Internet RTO subcomponents. We also show binary exponential backoff has negative effects on SCTP with increased wireless RTT; AORAN introduces a decision mechanism which implements backoff on RTO subcomponents only when appropriate.