Video communication over lossy packet networks such as the Internet or wireless links, is hampered by packet loss. Indeed, video quality severely degrades in presence of lost packets. This paper describes a technique based on Unbalanced Multiple Description Coding (UMD) to improve the robustness of video transmission. The proposed system relies on two descriptions, HR (High-Resolution) and LR (Low-Resolution) where LR description is primarily used as redundancy. HR and LR are produced by using different encoding parameters. The novelty of our approach, compared to other techniques based on UMD, is the use of different intra refresh periods for the produced descriptions. In particular we use shorter intra refresh period for LR description (in order to improve its resilience to bursts of packet losses), and higher intra refresh period for HR description (in order to improve coding efficiency). Moreover, a novel packetization scheme has been introduced in order to optimize network performance. This technique is able to produce acceptable quality even if redundancy percentage is less than packet loss rate. Therefore our UMD approach is suitable for multicast video distribution over WLAN (e.g. in "hotspots") where estimating packet loss can be a difficult task because different receivers experience different loss patterns.

two stations in the network, without traversing the AP.The DLS must be negotiated between the two peers This paper presents a novel architecture, called through a specific protocol that directly involves the Flex-WiFi, specifically designedfor IEEE 802.11 home AP (Figure 1); steps la/lb/2b/2a involve four different networks. Objective of the new approach is to improve frames. legacy network capacity in such home scenarios. Network capacity is increased by allowing setting up multiple contemporary IEEE 802.11 connections using a single WLAN card. All connections share the same la lb data link and physical layers but use different b XX channels; the MAC is responsible to handle the S S channel switching as well as to allocate/de-allocate the QSTAI QSTA2 direct link sessions. In particular we aim implementing a solution where stations can be associated to an Figure 1. Four steps 802.lle direct link setup. access point and can have ad-hoc connections on a diferet pysialchanelat he am tie. he deais In this paper we propose an enhancement of the 802.1 le Direct Link Session that introduces three to maximize the overall network capacity by features: the DLS negotiation protocol does not rely on transferring some traffic load from the infrastructure AP; the DLS may exploit a dedicated and negotiated to a direct link session. Results have been provided by PHY channel; stations in direct link may go in power implementing Flex-WiFi in the Madwifi open source s driverof the Aheros chipsets.saving (in 802.11le DLS stations in DLS cannot go in driver of the Atheros chipsets.poesaig power saving)

In this paper we present a novel approach to video telephony where we are able to exploit the benefits of the Universal Plug and Play (UPnP) protocol: self-configuration, discovery and control of available devices connected to the network. At the time being, UPnP does not deal with Video Voice over IP (VVoIP) applications. Integrating a signaling protocol like the Session Initiation Protocol (SIP) with UPnP allows interaction between the videophone and other UPnP compliant devices, like a TV set or a media server. This interaction, for example, makes it feasible to display the caller's image on the television screen, thus allowing the user to relax on the sofa and naturally converse. Another interesting scenario is the one where the user sends to the conversation partner a set of still pictures or short video clips acquired from a UPnP media server already available in the home premises. An advantage of this distributed approach is its cost effectiveness, since it allows to reuse existing UPnP devices also in the context of video telephony. The integration between SIP and UPnP has been achieved introducing a new UPnP device, the VVoIP device, which is a SIP User Agent able to interoperate with standard UPnP MediaServers and MediaRenderers.

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