Elias C. Efstathiou

Stimulating Participation in Wireless Community Networks

Wireless Community Networks (WCNs) are wide-area wireless networks whose nodes are owned and managed by volunteers. We focus on the provision of Internet access to mobile users through WCN-controlled wireless LAN access points (APs). We rely on reciprocity: a person participates in the WCN and provides ‘free’ Internet access to mobile users in order to enjoy the same benefit when mobile. Our reciprocity scheme is compatible with the distinctive structure of WCNs: it does not require registration with authorities, relying only on uncertified free identities (public-private key pairs). Users sign digital receipts when they consume service. The receipts form a receipt graph, which is used as input to a reciprocity algorithm that identifies contributing users using network flow techniques. Simulations show that this algorithm can sustain reciprocal cooperation. We have implemented our algorithm to run on common APs.

Controlled Wi-Fi Sharing in Cities: A Decentralized Approach Relying on Indirect Reciprocity

In densely populated cities, Wi-Fi networks-private or otherwise-are ubiquitous. We focus on the provision of citywide broadband communication capability to mobile users through private Wi-Fi networks that are in range but belong to others. We form a club that relies on indirect reciprocity: Members participate in the club and provide free Wi-Fi access to other members in order to enjoy the same benefit when they are away from their own Wi-Fi network. Our club scheme does not require registration with an authority and does not rely on centrally issued club identities: Members create their own identities (public-private key pairs) and receive signed digital receipts when they provide Wi-Fi service to other members. These receipts form a distributed receipt graph, parts of which are used as input to an indirect reciprocity algorithm that classifies club members according to their contribution. We show that our algorithm can sustain cooperation within the club and is robust to attacks by free-riders. We implement and evaluate our proposed club algorithms on commodity Wi-Fi routers and dual-mode cellular/Wi-Fi phones. Because we anticipate that Wi-Fi telephony will be a popular club application, we present and evaluate a secure and decentralized architecture for citywide voice (and multimedia) communications that is compatible with our club both from an architectural as well as an incentives perspective.

Peer-to-peer wireless LAN consortia: economic modeling and architecture

We address the incentive issues that arise in a peer-to-peer WLAN consortium (P. Antoniadis et al., 2003). We explore the use of flexible rules on reciprocity to guide domain policies and develop a suitable economic model that demonstrates the basic characteristics of our system.

A self-managed scheme for free citywide Wi-Fi

We present a self-managed scheme that could fuel the deployment of free public wireless networks in cities; we call it peer-to-peer wireless network confederation (P2PWNC). Unlike existing approaches, P2PWNC does not rely on central planning but on an ad hoc community of broadband Internet subscribers (the peers) with Wi-Fi access points (APs). These APs provide wireless access to peers that are away from home but within the range of another P2PWNC AP. In the P2PWNC scheme, wireless service is provided to those peers who consistently provide service to passerby peers, based on an algorithm that detects non-simultaneous multi-way peer-to-peer exchanges. This indirect reciprocity algorithm runs in isolation on every peer AP, resists Sybil attacks, and promotes cooperation without relying on trusted authorities, certified identities, or tamperproof modules. We discuss P2PWNCs design and show preliminary results that support its feasibility.

Public infrastructures for internet access in metropolitan areas

Wireless Community Networks (WCNs) are metropolitan-area networks with nodes owned and managed by volunteers. These networks can be used to build large scale public infrastructures for providing ubiquitous wireless broadband access through the private contributions of individual community members who use their hotspots to forward foreign traffic from and to nearby low-mobility users. We have designed and developed a prototype aggregation scheme that (1) assumes that community members are selfish and do not trust each other and uses a secure incentive technique to encourage their contribution; (2) protects the real-world identities of community providers and clients by relying only on disposable opaque identifiers (public/private key pairs); (3) is fully distributed, open to all, and does not rely on any authority to resolve disputes or to control membership; (4) applies a Quality-of-Service mechanism to protect the resources of hotspot owners and punish or reward users with different QoS levels according to their contribution; (5) is automated, using standard, widely available hardware and software that we have developed for some of the main available platforms (Linux-based WLAN access points and Windows Mobile-based cell phones). Thus, it can easily complement cellular networks in metropolitan areas where some WCNs provide wide coverage.

Designing a peer-to-peer wireless network confederation

We present the peer-to-peer wireless network confederation (P2PWNC), a P2P system designed to enable the sharing of WLAN bandwidth among residential hotspots. The benefits of joining the confederation outweigh the costs, and its token-based incentive mechanism prevents free-riding.

Experimental evaluation of community-based WLAN voice and data services

The purpose of this work is to experimentally evaluate the quality of voice and data services over community-based WLAN access networks. We use P2PWNC, the Wireless LAN roaming architecture that we have developed, as the basis for the provision of ubiquitous citywide WLAN access and set up an infrastructure for secure voice and data communications on top of it. Our scheme was designed with widely available, low-cost WLAN equipment in mind. Thus, we wish to estimate the performance penalty our proposed mechanisms incur for such devices and study their limitations as to the support for secure data and multimedia communications. In this work, we measure the maximum number of simultaneous voice calls that a P2PWNC-enabled access point can sustain, and the TCP throughput achieved by a single mobile station in the presence of simultaneous TCP flows by other P2PWNC users, when IPsec is employed to secure communications.

Service discovery and provision for autonomic mobile computing

Service discovery and related service advertisements, redirection and provision decisions are essential processes in networks supporting mobile communications in order for these systems to be self-configurable with zero or minimal administration overhead. More so in mobile networks, i.e. networks where the network infrastructure is moving and the topology is constantly changing. Finally, the servers themselves offering the services might be mobile, wirelessly connected and battery powered and thus power limited and energy constrained, with a finite horizon of operation and service availability. For this reason they will probably have rather selective policies for service advertisement and provision. In this paper we review our previous work on topics in this area and put it under this new perspective, providing our vision for a general autonomic framework for service advertisement, discovery, provision decision, redirection etc.

Self-organised peering of wireless LAN hotspots

We argue that access to wireless LAN (WLAN) hotspots can be shared in a peer-to-peer manner. In the hotspot-sharing scheme that we propose, peers are encouraged to keep their residential WLANs open, offering Internet access to peers passing by. We call our scheme peer-to-peer wireless network confederation (P2PWNC). Payments in P2PWNC are only ‘in kind’. We are motivated by the widespread availability of wireless LAN equipments and the proliferation of residential broadband connections. P2PWNC enables unified wireless LAN roaming without central authorities and without the administrative overhead that is usually associated with such efforts. In this paper, we present and evaluate the decentralised design of P2PWNC. Copyright

Trustworthy Accounting for Wireless LAN Sharing Communities

The Peer-to-Peer Wireless Network Confederation (P2PWNC) is de-signed to be an open self-organizing Wireless LAN (WLAN) roaming association where users from one WLAN can access all other WLANs belonging to the same P2PWNC. Unlike other WLAN roaming schemes, P2PWNC is open to all types of WLANs and particularly to residential networks owned by individual householders. Without an identity certifying authority, trustworthy accounting of transactions in the P2PWNC is challenging, but accounting is necessary in order to enforce the basic P2PWNC ’rule of reciprocity’. We show that even though the P2PWNC accounting mechanism and its purpose-built Public Key Infrastructure are open to Sybil attacks, there exists a user authentication algorithm that excludes all free riders and that can also make the percentage of unfair exclusions it causes very small simply by using more system memory.