Opportunistic routing is a recent technique that achieves high throughput in the face of lossy wireless links. The current opportunistic routing protocol, ExOR, ties the MAC with routing, imposing a strict schedule on routers ’ access to the medium. Although the scheduler delivers opportunistic gains, it misses some of the inherent features of the 802.11 MAC. For example, it prevents spatial reuse and thus may underutilize the wireless medium. It also eliminates the layering abstraction, making the protocol less amenable to extensions to alternate traffic types such as multicast. This paper presents MORE, a MAC-independent opportunistic routing protocol. MORE randomly mixes packets before forwarding them. This randomness ensures that routers that hear the same transmission do not forward the same packets. Thus, MORE needs no special scheduler to coordinate routers and can run directly on top of 802.11. Experimental results from a 20-node wireless testbed show that MORE’s median unicast throughput is 22 % higher than ExOR, and the gains rise to 45 % over ExOR when there is a chance of spatial reuse. For multicast, MORE’s gains increase with the number of destinations, and are 35-200 % greater than ExOR.

This paper investigates the use of programming language constructs to realize adaptive behavior in support of collaboration among users of wearable and handheld computers. A prototype language, Adaptive Java, contains primitives that permit programs to modify their own operation in a principled manner. In a case study, Adaptive Java was used to construct MetaSocket components, whose composition and behavior can be adapted to changing conditions during execution. MetaSockets were then integrated into Pavilion, a web-based collaboration framework, and experiments were conducted on a mobile computing testbed containing wearable, handheld, and laptop computer systems. Performance results demonstrate the utility of MetaSockets to improving the quality of interactive audio streams and reliable data transfers among collaborating users.

Abstract—This paper investigates the TCP simultaneous-send problem which arises in infrastructure mode 802.11 wireless local area networks. In particular it has been observed that for file transfer traffic, 802.11 wireless nodes have a sustained supply of packets to send and hence experience a relatively high rate of MAC contention. For TCP, this results in competition among data and ACK packets for channel access which causes the simultaneous-send problem that deteriorates flow throughput. This simultaneous-send problem can be alleviated by skipping TCP ACKs. Detailed simulation results are presented to demonstrate the usefulness of ACK skipping in various network scenarios such as with MAC retries and multiple TCP flows. The largest improvement is seen for the case of a single TCP flow, and moderate gains are also achieved in cases with multiple streams. For the single TCP stream case with 1 ACK skip and no MAC retries, TCP throughput improves 30 % for short-lived and 98% for long-lived TCP transmissions. The paper concludes with potential cross-layer solutions that potentially provide further improvements, including the use of the point coordination function (PCF) to reduce contention between multiple TCP streams and returning ACK packets.

This paper is an experimental follow up to our earlier paper [1] that investigated the TCP simultaneous-send problem which arises in infrastructure mode 802.11 wireless local area networks. In particular it was observed that for file transfer traffic, 802.11 wireless nodes have a sustained supply of packets to send and hence experience a relatively high rate of MAC contention. We showed that for TCP, this resulted in competition among data and ACK packets for channel access which caused considerable deterioration in flow throughput. Simulations of TCP ACK skipping as an alleviation to the problem, showed improvements as high as 100 % when MAC retries were disabled. There were gains in other scenarios too albeit more moderate. We evaluate the same TCP simultaneous-send problem with real world experiments on a wireless-cum-wired network testbed