Always Best Packet Switching: the Mobile VoIP Case Study

Currently, a mobile device equipped with multiple heterogeneous wireless Network Interface Cards (NICs), cannot take fully advantage of its capabilities as the conventional mobility management approach allows it to select and use only one of its NICs at a time. In contrast to this approach, we propose the so-called Always Best Packet Switching (ABPS) model that allows applications to use simultaneously all the available NICs, and switch each given IP datagram through the most suitable NIC, depending on the characteristics of the datagram itself. Specifically, we show that the ABPS model enables mobile applications to create policies for load balancing and recovery purposes in order to support effectively mobile multimedia services. In particular, in this paper we describe a cross-layer mechanism, termed Robust Wireless Multi-Path Channel (RWMPC) that adopts the ABPS model in order to meet effectively interactivity and low packet loss Quality of Service (QoS) requirements of Voice over IP (VoIP) applications, running on mobile hosts equipped with multiple WLAN NICs. By Exploiting the RWMPC services, VoIP applications can establish and maintain separate wireless links with different access points providing access to, possibly independently managed, wireless networks, and select for each UDP datagram the best link to be used for communication purposes. In essence, the RWMPC mechanism monitors each link in use, and notifies the application if detects that a datagram has been lost. In this case, the application retransmits the datagram using an alternative link, available through one of the interfaces homed in the mobile host. We have carried out an experimental evaluation of our mechanism in a real wireless scenario through the emulation of a VoIP application. The results we have obtained from this evaluation are discussed in this paper and confirm the effectiveness of our approach. Index Terms – Voice over IP (VoIP), Quality of Service (QoS), WiFi, cross-layer protocols, multi-homing, retransmission, Always Best Packet Switching (ABPS).