MAC Layer Support for Delay Tolerant Video Transport in Disruptive MANETs

Abstract

The overall goal of this work is to improve video delivery in emergency and rescue scenarios using sparse MANETs that might be prone to frequent link breaks and network partitions. The core idea of our approach is to reduce the number of MAC layer retransmissions that are likely to fail. We do not drop packets that could not be sent after the final retransmission. Instead we handle them in an overlay for storecarry-forwarding. The design of the overlay protocol takes the instability of the network into account, in such a way that each overlay entity works autonomously and keeps a minimum amount of state. Our experimental results show that we reduce packet loss seen on broken links, while at the same time significantly reducing overhead in terms of the total amount of packets transmitted at the physical layer.

Message lost or message taken - on message ferry selection in DTNs -

“…Configuration C1 with cross-layer adaptations to lower layers as identified in [9]. These adaptations are (1) handing dropped packets at the MAC layer back to DtsOverlay, (2) reducing the MAC layer retransmission limit to three, (3) avoiding links with a high amount packets queued for retransmission at the MAC layer, and finally (4) avoiding links where ARP cannot resolve the IP address on the link receiver side.…”

“…For a fair and meaningful comparison of the four strategies, we evaluate them in a common system called Dts-Overlay [9], running on top of a set of standard MANET protocols. Otherwise, strategies would be strongly affected by lower layer protocols, mechanisms of store-carry-forwarding (like the rate of emptying buffers) and the way that ferry values are exchanged.…”

“…We attributed in [9] high packet loss to lower layers. This loss was eliminated through techniques of cross-layer adaptation.…”

“…The application workload consists of a single unicast stream of the video entitled Foreman 2 , resolution CIF (352x288) and 25 fps frame rate as in [9]. The video is pre-encoded with H.264 baseline profile and target bitrate 256 kb/s.…”

“…In all network scenarios we model IEEE 802.11b in ad-hoc mode. The devices simulate direct-sequence spread spectrum (DSSS) modulation, and a constant data transmission mode of 11 Mbps as in [9]. The wireless channel is modelled using the constant speed propagation delay model, and the Friis propagation loss model.…”