Rutgers University
Department of Electrical and Computer Engineering
Ph.D. Thesis Abstract

Protocol Design and Performance Analysis for handoff Control in Mobile ATM Networks


Jun Li

 Future access networks are expected to provide universal access for a variety of network services, especially for mobile services. The concept of {\it Mobile ATM} has been proposed to meet this requirement. A mobile ATM network consists of a core network with regular ATM switches plus wireless access points of different kinds. The core ATM network is enhanced with mobility support functions for location management and handoff control, while supporting heterogeneous mobile services such as GSM, GPRS, UMTS and wireless ATM. This thesis studies the handoff control process in mobile ATM networks from four aspects - system architecture, protocol design, performance analysis and system implementation

In system architecture design, we propose a W-UNI (wireless user-to-network) interface at radio link, in addition to the mobility enhanced M-UNI (mobile user-to-network) and M-NNI (mobile network-to-network) interfaces within the wired ATM network. All signaling messages of nonATM mobile terminals are converted to the W-UNI interface through an interworking function. Chapter 2 introduces the mobile ATM architecture by describing how each mobility support functions work over W-UNI, M-UNI and M-NNI interfaces.

In a mobile ATM network, a particular alternate path rerouting algorithm will be preferable for some mobiles services but not others. Thus, to support a variety of mobile services it is essential that the protocol design for handoff control allow multiple alternative path rerouting algorithms. Hence we propose a  unified handoff control protocol which has a common ATM signaling syntax for alternative path rerouting algorithms. In Chapter 3, the detailed handoff control procedure is described along with signaling sequence and state diagram illustrations. This work has been done in support of the mobile ATM baseline in the wireless ATM group of ATM Forum. Additional design work in Chapter 4 focuses on handoff path rerouting in PNNI hierarchical networks, lossless control in the handoff transition period, and handoff control for multicast connections.

User mobility and handoff path rerouting may cause changes in the network traffic distribution that affect the overall network utilization. In Chapter 5, we propose a  Flow Model to analyze the network traffic distribution in a mobile environment. The model defines network traffic as stochastic processes (flows) for a given set of OD (origin-destination) pairs over the network. For every OD pair, the flow has a routing function which describes the fraction of the flow carried by each network link. User mobility is characterized by a transition probability between flows. Handoff path rerouting algorithms are defined by transformations of routing functions among different flows. Using this model, we observe a smoothing effect when the mobility pattern is balanced and a clustering effect when the mobility pattern is unbalanced. Based on the flow model with routing functions, we present an analytical methodology to evaluate handoff path rerouting algorithms. Three typical path rerouting algorithms are compared through both analysis and simulations.

Based on the above proposed protocols, proof-of-concept research prototypes have been implemented. In these systems, the mobility of both IP terminals and ATM terminals can be supported through a common mobile ATM core network. The prototype system has been used to validate the proposed protocols, gain experimental insight into system performance, and support example mobile applications. In Chapter 6, we present the software architecture for the prototype systems and give some experimental results on the handoff control delay within the mobile ATM network.


Ph.D. Dissertation Director: Professor Roy D. Yates

August, 1999

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