Web authentication that is both secure and usable remains a challenge. Passwords are vulnerable to phishing attacks, while physical tokens face deployment obstacles. We propose to leverage the authentication infrastructure of cellular networks to enhance Web authentication. We design WebCallerID, a Web authentication scheme that uses cell phones as physical tokens and uses cellular networks as trusted identity providers. Since WebCallerID requires no user participation during authentication, it prevents security mistakes by users. WebCallerID also prevents rogue websites from replaying authentication assertions or stealing users' identities. We have implemented a prototype of WebCallerID using the OpenID framework. The prototype shows that WebCallerID seamlessly integrates into OpenID-capable Web authentication while avoiding phishing problems in OpenID and simplifying user participation.

Existing handover schemes in wireless LANs, 3G/4G networks, and femtocells rely upon protocols involving centralized authentication servers and one or more access points. These protocols are invariably complex and use extensive signaling on the wireless backhaul since they aim to be be efficient (minimal handover latency) without sacrificing robustness. However, the mobile user has little involvement especially with the so-calledcontext transferstage; this stage involves the transfer of necessary state to the new access point as well as the enforcement of security goals such as user authentication and single point of access. We propose the incorporation of usercapabilities, network-asserted proofs of user identity and access control, as a general mechanism to simplify the context transfer stage. To this end, we have designedCapAuth, a capability-based scheme that has reduced complexity, low overhead, high level of fault tolerance and is general enough to implement a range of security policies.

Proportional Fair (PF) is a frequently used channel- aware scheduling algorithm in 3G wireless networks. However, recent work by us and others has shown that, in practice, PF suffers from significant robustness issues that can unnecessarily starve "well-behaved" users. In this paper, we analyze these issues with the goal of developing an alternative scheduling algorithm more robust than PF. We start by identifying two scenarios in which PF can cause starvation. We analyze both scenarios and develop mechanisms that prevent such starvation. Then, we combine these mechanisms to propose our Parallel Adaptive Quantile-based (PAQ) scheduling algorithm. We use simulation experiments with synthetic and measurement-based traces of wireless channel conditions to show that PAQ is not only robust but also achieves comparable or better throughput and fairness than PF.

We analyze a massive social network, gathered from the records of a large mobile phone operator, with more than a million users and tens of millions of calls. We examine the distributions of the number of phone calls per customer; the total talk minutes per customer; and the distinct number of calling partners per customer. We find that these distributions are skewed, and that they significantly deviate from what would be expected by power-law and lognormal distributions.

We present an experimental characterization of the physical and MAC layers in CDMA 1xEV-DO and their impact on transport layer performance. The 1xEV-DO network is currently the fastest mobile broadband cellular network, offering data rates of up to 3.1 Mbps for both stationary and mobile users. These rates are achieved by using novel capacity enhancement techniques at the lower layers. Specifically, 1xEV-DO incorporates rapid channel rate adaptation in response to signal conditions, and opportunistic scheduling to exploit channel fluctuations. Although shown to perform well in isolation, there is no comprehensive literature that examines the impact of these features on transport layer and application performance in real networks.

Packet delay and loss are two fundamental measures of performance. Using active probing to measure delay and loss typically involves sending Poisson probes, on the basis of the PASTA property (Poisson Arrivals See Time Averages), which ensures that Poisson probing yields unbiased estimates. Recent work, however, has questioned the utility of PASTA for probing and shown that, for delay measurements, i) a wide variety of processes other than Poisson can be used to probe with zero bias and ii) Poisson probing does not necessarily minimize the variance of delay estimates.

Poisson Arrivals See Time Averages (PASTA) is a well known property applicable to many stochastic systems. In active probing, PASTA is invoked to justify the sending of probe packets (or trains) at Poisson times in a variety of contexts. However, due to the diversity of aims and analysis techniques used in active probing, the benefits of Poisson based measurement, and the utility and role of PASTA, are unclear. Using a combination of rigorous results and carefully constructed examples and counter-examples, we map out the issues involved, and argue that PASTA is of very limited use in active probing. In particular, Poisson probes are not unique in their ability to sample without bias. Furthermore, PASTA ignores the issue of estimation variance, and the central need for an inversion phase to estimate the quantity of interest ased on what is directly observable. We give concrete examples of when Poisson probes should not be used, and explain why, and offer initial guidelines on suitable alternative sending processes.

Active probing heuristics are usually based on queuing systems. However, a rigorous probabilistic treatment of probing methods has been lacking. For instance, it is not known even in principle, what can and cannot be measured in general, nor the true limitations of existing methods. We provide a probabilistic treatment for the measurement of cross traffic in the 1-hop case. We derive inversion formulae for the cross traffic process, and explain their fundamental limits, using an intuitive geometric framework.

The proliferation of wireless networks has led to a demand for providing bandwidth guarantees to mobile users that are comparable to the ones received by users in fixed networks. Error-prone communication links and user mobility make this a challenging task. We propose a bandwidth allocation scheme for cellular networks that copes with user mobility. Our proposed scheme constructs, for each user, hierarchical clusters (HCs) which are tree-like structures having sub-clusters of cells as nodes. The HC of any user represents the cells that he is expected to visit during the lifetime of his call. Bandwidth is reserved in all cells of the HC thereby providing an estimation of future resource availability. Such estimates are used to determine the feasibility of admitting new calls. In constructing HCs, we use the velocity of the user and available data on user movement. Our scheme is adaptive since it works with any amount of available data. Results of simulations are provided to demonstrate the performance obtained using our proposed scheme.