Scanning the literature

This paper investigates the use of peer-to-peer networking, also known as ad hoc networking, to increase cell capacity and reduce energy consumption for Internet access in cellular wireless data networks. The paper shows that a direct application of the peerto-peer network model to Internet access in cellular networks significantly degrades network throughput, and results in unfair bandwidth allocation across network flows. The reduction in network throughput results from the overheads and inefficiencies of the peer-to-peer protocols. Whereas cellular network protocols are centralized and operate over a single hop, peer-to-peer protocols, such as IEEE 802.11 DCF and DSR, are distributed and operate over multiple hops. Compared to the centralized protocols, peer-to-peer protocols produce less optimal transmission schedules and increase contention for the wireless medium. Notwithstanding these drawbacks, because peer-topeer relies on short-range transmissions, it achieves lower power consumption and higher throughput per unit power than the centralized cellular protocols. The authors then describe assisted scheduling and dual-mode operation, two techniques that leverage the energy savings of peer-to-peer networking, and match the network throughput of the cellular model. In assisted scheduling, the base station periodically draws up a schedule for multi-hop transmissions within the network that maximizes throughput subject to fair perflow service. The base station devises the schedule based on information provided by mobile hosts about their location and nodes in their neighborhood. In dual-mode operation, the base station simultaneously supports flows that operate either in the peer-topeer mode or the cellular mode. Dual-mode operation allows individual flows in the network to dynamically choose the mode of operation that can provide better service, while the base station provides the two flow modes time-division access to the channel. Initially all flows operate in the peer-to-peer mode. A flow in the peer-to-peer mode switches to the cellular mode if it does not achieve the required network throughput. Once switched to the cellular mode, a flow switches back to the peer-to-peer mode whenever the network state is such that it can achieve the desired throughput. Finally, the paper evaluates the use of multi-homed host that extend the peer-to-peer network model to relay traffic between different networks. Both peer relays that forward traffic between wireless and wired networks, as well as relays that bridge different wireless network technologies, such as 802.11 and 3G, are explored. The multi-homed peer relays relieve the channel bottleneck around the base station (i.e., the base station is no longer the only destination for Internet access), and in doing so translate the spatial reuse benefits of the peer to peer network into better throughput performance.