András Gergely Valkó

Design, implementation, and evaluation of cellular IP

Wireless access to Internet services will become typical, rather than the exception as it is today. Such a vision presents great demands on mobile networks. Mobile IP represents a simple and scalable global mobility solution but lacks the support for fast handoff control and paging found in cellular telephony networks. In contrast, second- and third-generation cellular systems offer seamless mobility support but are built on complex and costly connection-oriented networking infrastructure that lacks the inherent flexibility, robustness, and scalability found in IP networks. In this article we present cellular IP, a micro-mobility protocol that provides seamless mobility support in limited geographical areas. Cellular IP, which incorporates a number of important cellular system design principles such as paging in support of passive connectivity, is built on a foundation of IP forwarding, minimal signaling, and soft-state location management. We discuss the design, implementation, and evaluation of a cellular IP testbed developed at Columbia University over the past several years. Built on a simple, low-cost, plug-and-play systems paradigm, cellular IP software enables the construction of arbitrary-sized access networks scaling from picocellular to metropolitan area networks.

Comparison of IP micromobility protocols

We present a performance comparison of a number of key micromobility protocols that have been discussed in the IETF Mobile IP Working Group over the past several years. IP micromobility protocols complement Mobile IP by offering fast and seamless handoff control in limited geographical areas, and IP paging in support of scalability and power conservation. We show that despite the apparent differences between IP micromobility protocols, the operational principles that govern them are largely similar. We use this observation to establish a generic micromobility model to better understand design and performance trade offs. A number of key design choices are identified within the context of the generic model related to handoff quality and route control messaging. We present simulation results for Cellular IP, Hawaii, and Hierarchical Mobile IP, and evaluate the handoff performance of these protocols. Simulation results presented in this article are based on the Columbia IP Micromobility Software (CIMS), which is freely available from the Web (comet.columbia. edu/micromobility) for experimentation.

Performance aspects of Bluetooth scatternet formation

The emergence of Bluetooth as a default radio interface allows handheld electronic devices to be rapidly interconnected into ad hoc networks. Bluetooth allows large numbers of piconets to form a scatternet using designated nodes that participate in multiple piconets. We study the performance implications of forming scatternets from piconets. The contribution of our work is twofold. First, we establish a network model and define performance metrics for Bluetooth scatternets. Our model is derived from constraints specific to the Bluetooth technology, but is sufficiently abstract to relate to the more general field of ad hoc networking. Second, using a number of simulation studies, we relate scatternet parameters to performance metrics and discover correlations between scatternet formation rules and performance. These results reveal some important performance implications of scatternet design decisions and can serve as guidelines for future scatternet formation algorithms.

A pseudo random coordinated scheduling algorithm for Bluetooth scatternets

The emergence of Bluetooth as a default radio interface allows handheld devices to be rapidly interconnected into ad hoc networks. Bluetooth allows large numbers of piconets to form a scatternet using designated nodes that participate in multiple piconets. A unit that participates in multiple piconets can serve as a bridge and forwards traffic between neighbouring piconets. Since a Bluetooth unit can transmit or receive in only one piconet at a time, a bridging unit has to share its time among the different piconets. To schedule communication with bridging nodes one must take into account their availability in the different piconets, which represents a difficult, scatternet wide coordination problem and can be an important performance bottleneck in buillding scatternets. In this paper we propose the Pseudo-Random Coordinated Scatternet Scheduling (PCSS) algorithm to perform the scheduling of both intra- and inter-piconet communication. In this algorithm Bluetooth nodes assign meeting points with their peers such that the sequence of meeting points follows a pseudo random process that is different for each pair of nodes. The uniqueness of the pseudo random sequence guarantees that the meeting points with different peers the node will collide only occasionally. This removes the need for explicit information exchange between peer devices, which is a major advantage of the algorithm. The lack of explicit signaling between Bluetooth nodes makes it easy to deploy the PCSS algorithm in Bluetooth devices, while conformance to the current Bluetooth specification is also maintained. To assess the performance of the algorithm we define two reference case schedulers and perform simulations in a number of scenarios where we compare the performance of PCSS to the performance of the reference schedulers

On the Analysis of Cellular IP Access Networks

Mobile IP represents a simple and scalable global mobility solution but lacks support for fast handoff control and real-time location tracking found in cellular networks today. In contrast, third generation cellular systems offer seamless mobility support but are built on complex and costly connection-oriented networking infrastructure that lacks the inherent flexibility, robustness and scalability found in IP networks. Future wireless networks should be capable of combining the strengths of both approaches without inheriting their weaknesses. In this paper we present analysis of Cellular IP, a new host mobility protocol which represents one such approach. Cellular IP incorporates a number of important cellular system features but remains firmly based on IP design principles. The protocol presented in this paper is implemented as extensions to the ns simulator.

4+4: an architecture for evolving the Internet address space back toward transparency

We propose 4+4, a simple address extension architecture for Internet that provides an evolutionary approach to extending the existing IPv4 address space in comparison to more complex and disruptive approaches best exemplified by IPv6 deployment. The 4+4 architecture leverages the existence of Network Address Translators (NATs) and private address realms, and importantly, enables the return to end-to-end address transparency as the incremental deployment of 4+4 progresses. During the transition to 4+4, only NATs and end-hosts need to be updated and not the network routers. The 4+4 architecture retains the existing semantics of Internet names and addresses, and only proposes simple changes to the network layer that focus entirely on address extension. Encapsulation is used as the main tool to maintain backward compatibility. We present the design, implementation, and evaluation of the 4+4 architecture and discuss our implementation experiences and results from local and wide-area Internet experimentation. The 4+4 source code is freely available from the Web (comet.columbia.edu/ipv44) for experimentation.

Voice QoS in third-generation mobile systems

We analyze voice quality and system performance in third-generation mobile communication systems. We argue that in these networks that are expected to integrate voice, data, and multimedia services, the transport network can no longer be considered as a lossless transparent traffic channel. Rather, proper dimensioning is needed even for plain voice services. Furthermore, the efficient utilization of the network resources shared by voice and data traffic requires sophisticated traffic management in the statistical multiplexing environment. The contribution of the paper is twofold: first, voice quality in the cellular transport network is analyzed and network dimensioning criteria are derived. Second, building on advances reported in the literature and taking into consideration current standardization activities, a joint performance model is established for the air interface (AI) and the transmission network (TN) allowing for the analysis of end-to-end service performance within a uniform framework. To demonstrate the applicability of this model, we point to some performance problems in the multiservice environment and suggest and evaluate traffic management actions to overcome these.

Throughput of ideally routed wireless ad hoc networks

We investigate the throughput of ad hoc networks using ideal shortest path routing between randomly selected source-destination pairs. Our results not only confirm the n-1/2 decay of the throughput that was published earlier in the literature, but also provides an approach to acquire the relation of various network parameters. This way the effects of changes in the routing, traffic generation algorithms or other network characteristics can be predicted using a first order approximation.

A cellular IP testbed demonstrator

Cellular IP is a wireless Internet access technology that operates on mobile hosts, base stations and Internet gateways. Cellular IP combines the capability of cellular networks to provide high performance handoff and efficient location management of active and idle mobile users with the inherent flexibility, robustness and scalability found in IP networks. We provide an overview of the cellular IP routing, handoff and paging algorithms and their implementation in a pico-cellular testbed. The protocol has been under development at Columbia University for the past several years initially as a joint project between the Center for Telecommunications Research and Ericsson Research.

Global internet roaming with ROAMIP

Reachability and session continuity represent two distinct services that global mobility protocols should provide. Reachability is the possibility for Internet hosts to initiate sessions to mobile users. Session continuity refers to mechanisms that ensure that active transport or application layer sessions are not broken due to mobility. We present ROAMIP, a global mobility architecture that uses application layer solutions for global reachability and reuses transparent Mobile IP tunnelling mechanisms to ensure session continuity. ROAMIP eliminates long triangular routes, yet it is compatible with mobility unaware correspondent hosts. It is applicable to IPv6 as well as IPv4 networks. The ROAMIP architecture naturally lends itself to easy, gradual deployment and can reuse existing Mobile IP or SIP message formats. We conclude the paper by showing example traces from an experimental implementation.