Section: New Results
Low speed links
Participants : Laurent Guillo, Louis-Marie Le Ny, Cécile Marc, Elizabeth Martinez, Julio Orozco, David Ros, Gerardo Rubino, Bruno Sericola, Laurent Toutain.
If most of the QoS-related problems in the core network can be solved by overprovisioning, congestion may continue to arise in some specific cases: when the bandwidth is either physically limited, like in UMTS networks, or if traffic rerouting due to link failure may lead to an overload. Specific research themes and contributions of ARMOR in this context are the following:
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Header compression techniques (ROHC protocol) in IPv6. The performance of IPv6 in the radio link can be improved using header compression algorithms. The 3GPP (3rd Generation Partnership Project) consortium has adopted the ROHC (Robust Header Compression) algorithm of the IETF (Internet Engineering Task Force) [113] standard track for the real-time applications using RTP/UDP/IPv6 and UDP/IPv6. We have developed one of the first IPv6 implementations of this protocol. This allowed us to propose several enhancements in order to support more efficiently IPv6 [132] or to study parameters impact on performances. Collaborative works with the TEMICS project-team lead us to study a new ROHC profile dedicated to UDP-lite. Always in collaboration with the INRIA project TEMICS, we will study the impact of the residual transmission error on multimedia flows, in order to evaluate the QoS perceived by the user.
As a first result of these efforts, we present in [25] the analysis of the proposed standard ROHC deployed in an UMTS radio link and discuss different schemes to increase compression performance. The results are based on our IPv6 implementation of the ROHC header compression algorithm and on a simple and accurate analytical model used to evaluate the packet loss probability.
We have worked on interaction between ROHC Unidirectional flows and multicast. We have studied the behaviour between these two layers and propose a solution to reduce delays when a receiver subscribes to a multicast flow [82] . We are also studying the behavior of ROHC on IEEE 802.x network to also services such as Voice over Wi-Fi. We have studied the behaviour of tunnelled flows [108] , especially in NEMO context. Finally, with the INRIA ARES team we are using this proposal to work on ad-hoc architectures.
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Active queue management for diffserv. In the context of the diffserv architecture, active queue management (AQM) algorithms are used for the differentiated forwarding of packets. We have proposed a new active queue management algorithm, which we call Adaptive RIO (A-RIO), aimed at both easing the configuration of diffserv routers and building services with loose delay guarantees (thesis of Julio Orozco [14] ). Some issues regarding the performance of A-RIO (like fairness among flows) have been explored in [35] .
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Multimedia tagging for diffservWhen multimedia flows are transported on an IP network, congestion may lead to a severe degradation of the perceived quality if important information of the multimedia stream is lost. We have worked on the sequel of Octavio Medinas PhD thesis [131] , focusing in new video coding schemes like H.264, which are designed with network error resilience in mind and allow for more flexible tagging strategies [135] . We have also explored how to quantify the relative merits of different tagging strategies, in terms of the resulting subjective quality, by means of neural networks and the PSQA approach [14] .
