While high throughput is the key for a number of important applications of sensor networks, performance of the state-of-the-art approach is often poor in practice. This is because if even one of the channels used in its pipeline is bad, the pipeline stalls and throughput degrades significantly.In this paper, we propose a new protocol called P 3 (Practical Packet Pipeline) that keeps its packet pipeline flowing despite the quality differences among channels. P 3 exploits sender and receiver diversities through synchronous transmissions (constructive interference), involving concurrent transmissions from multiple senders to multiple receivers at every stage of its packet pipeline. To optimize throughput further, P 3 uses node grouping to enable the source to transmit in every pipeline cycle, thus fully utilizing the transmission capacity of an underlying radio.Our evaluation results on a 139-node testbed show that P 3 achieves an average goodput of 178.5 Kbps while goodput of the state-of-the-art high throughput protocol PIP (Packets In Pipeline) is only 31 Kbps. More interestingly, P 3 achieves a minimum goodput of about 149 Kbps, while PIP's goodput reduces to zero in 65% of the cases.

In recent years, many different kinds of wireless access networks have been deployed for the Internet and have become inseparable parts of the Internet. But TCP, the most widely used transport protocol of the Internet, was designed for stationery hosts. In particular, TCP faces severe challenges when user moves around in these networks and handoff occurs frequently.In this paper, TCP HandOff (TCP-HO), a practical end-to-end mechanism, is proposed for improving TCP performance in heterogeneous mobile environments. TCP-HO assumes that a mobile host is able to detect the completion of handoff immediately and has a coarse estimation of new wireless link's bandwidth. When a mobile host detects handoff completion, it will immediately notify the server through two duplicate ACKs, whose TCP option also carries the bandwidth of new wireless link. After receiving this notification, the server begins to transmit immediately and keeps updating ssthresh according to the bandwidth from mobile host and its new RTT samples. This updating will be stopped after four RTT samples or after congestion is detected.TCP-HO has been implemented in FreeBSD 5.4. Experimental results show that TCP-HO does improve TCP performance without adversely affecting cross traffic in a heterogeneous mobile environment.