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Handoff and rerouting in cellular data networks
Abstract
This chapter presents a comprehensive introduction to the field of wireless systems and their applications. We begin with the fundamental principles of wireless communications, including modulation techniques wireless system topologies, and performance ...
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Mobile computers using wireless networks, along with multimedia applications, are two emerging trends in computer systems. This new mobile multimedia computing environ- ment presents many challenges, due to the requirements of multimedia applications and the mobile nature of hosts. We present several alternative schemes for maintaining net- work connections used to provide multimedia service, as hosts move through a nano-cel- lular radio network. These algorithms modify existing connections by partially re- establishing them to perform handoffs. Using a simple analytical model, we compare the schemes on the basis of the service disruption caused by handoffs, required buffering, and excess resources required to perform the handoffs.
We describe the theory, design and ongoing prototyping of a wireless ATM LAN/PBX capable of supporting mobile users with multi-Mb/s access rates and multi-Gb/s aggregate capacities. Our proposed LAN Consists of network nodes called Portable Base Stations (PBS) providing microcell coverage. The PBSs are designed to be low-cost, compact and high-speed and can be relocated conveniently. We employ a concept ofad-hoc networking in the layout of the PBS-to-PBS interconnection. That is, the PBSs can be distributed in an arbitrary topology to form a backbone network and can be reconfigured with relative ease. The PBS-to-PBS backbone links are high-speed (Gb/s) for supporting high system capacity. Although they can either be wired or wireless, our emphasis is on wireless implementations. The user-to-PBS links, on the other hand, are primarily for mobile access (e.g., 2–20 Mb/s) and therefore are wireless. Wired connections from stationary users to PBSs are also possible. Typical mobile users are assumed to be laptops or notebook computers. Services supported include conventional data applications (e.g., over TCP/IP or SPX/IPX) as well as multimedia (video, voice and data) applications with QoS (Quality-of-Service) guarantees. A wireless ATM concept is proposed so as to provide seamless internetworking with other wired ATM local and wide-area net-works. Algorithms and control in our network are highly distributed for simple implementations and ease of mobility management. A new wireless VP/VC concept and a Homing Algorithm are described to provide ATM cell routing and connections in the network. PBS hardware and software architectures are discussed. Call management, network management and signaling are designed for simplicity, high performance and modular implementations. A fast network restoration scheme is proposed to cope with the potential link or node failures in the ad-hoc network. Error control is addressed taking the unreliable wireless links into consideration. Finally, a prototyping project called BAHAMA (Broadband Ad Hoc ATM Anywhere) for demonstrating this network concept is briefly outlined.
Handoff is the procedure by which a user's radio link is
transferred between radio ports in the network without an interruption
of the user connection. In this paper, we discuss how a wireless
asynchronous transfer mode (ATM) network may reroute a user connection
during a handoff. We propose a novel procedure called “nearest
common node rerouting (NCNR)”. NCNR is designed to perform the
rerouting of user connections due to a handoff event in a fast and
efficient manner. We conclude by comparing NCNR to other rerouting
schemes discussed in the literature
"Mobile Computing" has been a buzzword in the area of computer communications. A technology vital to mobile computing is how to communicate with mobile hosts. This paper proposes a protocol, Virtual Internet Protocol (VIP), that allows hosts to move transparently within the Internet. VIP is defined as an instance of the virtual network protocol, the general protocol supporting mobile hosts. The virtual network protocol is based on the concept of a virtual network and the propagating cache method. VIP is scalable to the total number of mobile hosts and the scale of the Internet, is free from routing loops, and tolerant of loss of control packets. VIP is currently running on operating systems based on 4.3BSD UNIX. The VIP overhead is negligible when compared with IP. 1 Introduction Computer networks such as the Internet have spread worldwide. Computers are getting smaller and smaller. Such an environment allows users to carry portable computers and use them to access networks. "...
The world of wireless telecommunications is rapidly changing. The capabilities of wireless networks are improving at a steady pace. This paper presents a protocol implementation for implementing mobility in an Asynchronous Transfer Mode (ATM) network. The vision of the authors is of one "ATM-based wireless telecommunications network" that is capable of supporting a variety of today's applications with room to grow for advanced applications of the future. 1 Introduction Wireless communication networks, e.g cellular telephony, have rapidly grown to be a sizable part of the world telecommunications market over the past two decades[2]. One reason for the rapid growth of wireless communication networks (WCN) is the mobility of a tetherless terminal. Next generation wireless networks are called Personal Communication Services (PCS) Networks and will provide for global user mobility, a life-long user identification numbering system and ability to accommodate varying data rates. The next gen...
The aim of Wireless ATM is to provide multi-media services to mobile users. While existing research on Wireless ATM are focussed on handovers of unicast connections, handovers of multicast connections have not been investigated. While conventional multicast join and leave operations occur over the same path, this is not the case during mobile host migrations in a Wireless ATM network. In this paper, we reveal how handovers of multicast connections can be achieved in a manner irrespective of whether these multicast trees are source-, server- or core-based. More importantly, we demonstrate how the enhanced hybrid handover protocol incorporating crossover switch discovery can be used to support handovers of heterogeneous (i.e., unicast and multicast) connections in a uniform and unified manner, for Wireless ATM LANs employing either the centralised or distributed connection management scheme.
To date, various connection rerouting methods for connection-oriented mobile networks have been proposed. The previous methods, however, are limited to specific topologies or environments. In this paper, we propose the connection-information-based rerouting widely applicable to various connection-oriented mobile networks. This method requires neither a specific topology nor a complex connection, enables fast rerouting, provides appropriate route optimality, and can be extended easily.
In a connection-oriented wireless LAN, the mobility of mobile
hosts results in the establishment and disconnection of new and old
virtual circuits. The resulting increase in signalling traffic along
with the need to support multimedia stream handovers demand a fast,
continuous and bandwidth-efficient handover protocol. We adopt a
handover scheme based on partial re-establishments, where a new partial
path converges to an existing path. Connection rerouting (CR) operations
are then performed at the convergence/crossover switch (CX). To achieve
localised handovers, a wireless cell clustering scheme is proposed. The
clustering of base stations to cluster switches (CLSs) provides fast
intra-cluster handovers since the CR operations are performed at the
CLS. To support fast inter-cluster handovers, four CX discovery schemes
(loose select, prior path, distributed hunt and backward tracking) are
introduced. Simulation results obtained from a trace-driven mobile
network simulator on four different network topologies (random, star,
tree and hierarchical redundancy) reveal that both prior path and
distributed hunt discoveries outperform the others by providing the
fastest convergence with shorter resulting paths and higher circuit
reuse efficiency
The next generation personal communications network (PCN) will
likely consist of an ATM-based B-ISDN backbone interconnecting wireless
mobile networks. Support of user terminal mobility, particularly the
capability for fast and seamless handoffs, over the B-ISDN is an
expected requirement that is not currently met. We propose extensions to
the B-ISDN user transport and signaling network architectures and
signaling protocols to meet these requirements. The proposed extensions
optimizes the handoff delay over the B-ISDN while minimizing the
resources allocation, chances of handoff failure, and the call
processing load in the intelligent network (IN). The network
architecture extensions are backward compatible to current B-ISDN
standards and implementations
In ATM networks, two levels of connections are defined: virtual
path connections and virtual channel connections. Virtual paths are the
building blocks of the virtual channels. This hierarchy, known as
“the virtual path concept”, provides considerable advantages
in the design of high-speed networks. In the paper the authors show that
this concept has the advantage of providing a means of improving the
survivability of virtual channels. To this end, they present a simple
rerouting protocol, which can be invoked upon the failure of an
intermediate link or node of a virtual path. This protocol reroutes all
the affected virtual channels to an alternative virtual path. Due to the
simplicity of the protocol, it can be completed rapidly, thus fulfilling
an essential requirement of any rerouting scheme
Supporting mobility in asynchronous transfer mode (ATM)-based broad-band networks with wireless access links poses many technical challenges. One of the most important of these challenges is the need to reroute ongoing connections to/from mobile users as these users move among base stations. Connection rerouting schemes must exhibit low handoff latency, maintain efficient routes, and limit disruption to continuous media traffic while minimizing reroute updates to the network switches. In this paper we propose, describe an implementation for, and experimentally evaluate the performance of five different connection rerouting schemes. We show that one of these schemes, which operates in two phases, executes very fast reroutes (with a measured latency of 6.5 ms) in a real-time phase and, if necessary, reroutes again in a nonreal-time phase to maintain efficient routing. The scheme also results in negligible disruption to both audio (e.g., a 1-in-100 chance of a single packet loss at CD-quality audio rates of 128 kb/s) and low-bit-rate video (e.g., a 2-in-100 chance of a single packet loss for 1-Mb/s video) traffic during connection rerouting. Based on these results, we conclude that simple handoff schemes coupled with a connection management architecture are sufficient for supporting low-bit-rate continuous media applications over ATM-based wireless networks
The micro- and picocellular architectures proposed for wireless
ATM LANs lead to wireless terminals frequently changing their point of
attachment to the network. Because ATM connections have quality of
service (QoS) guarantees which must be maintained, handover must be as
seamless as possible. We present a novel architecture and protocol which
primarily aims to keep the interruption period due to handover low,
rather than seeking to keep the process entirely lossless. We compare
the tradeoffs made, with those in other schemes from the literature, and
give quantitative results from an implementation of our scheme on a 10
Mbits/s-1 prototype wireless ATM LAN
An architecture is presented for a high-speed cellular radio
access network based on ATM transport technology. Central to this
approach is a new concept known as the virtual connection tree which
avoids the need to involve the network call processor for every cell
handoff attempt. Such an approach can readily support a very high rate
of handoffs, thereby enabling use of physically small radio cells to
provide very high system capacity, but may occasionally cause the volume
of traffic to be handled by one cell site to exceed that cell site's
capacity. A simple analytical methodology is developed which can be used
for admission control, the purpose of which is to limit the number of
in-progress calls such that two new quality of service metrics (overload
probability and average time in overload) can be kept suitably low.
Finally, a general framework is presented for overall system
organization and signaling
The increasing deployment of wireless access technology, along
with the emergence of high speed integrated service networks, such as
ATM, promises to provide mobile users with ubiquitous access to
multimedia information in the near future. One of the key problems in
building connection-oriented ATM networks that support host mobility is
designing mechanisms for rerouting virtual circuits to maintain data
flow to and from mobile hosts. Ideally, VC rerouting must be done fast
enough so as to cause minimal disruption to applications while
minimizing the signaling overhead. In this paper, we evaluate the impact
of several virtual circuit rerouting strategies on application
performance. We initially identify the primitive operations required by
any rerouting policy and use this to analytically quantify the cost of
each rerouting policy in terms of wireless link disruption as a function
of various network parameters. We then evaluate the effect of the VC
rerouting policy on application-level performance using simulations. Our
results show that the effect of rerouting policies are strongly
dependent on the transport protocol policies and application QoS
requirements, in addition to the network topology
In this paper we present an architecture for a picocellular network and a novel communication protocol for mobile users in such networks. The cell size in these networks is very small -- typically of the order of a room in a building, resulting in an environment where the movement between cells is very rapid. This makes the problems of tracking and maintaining communication between mobile users non-trivial. To better track these mobile users we propose an architecture consisting of a two level hierarchy of fixed nodes. This architecture combined with the idea of groups ensures that seamless communication is maintained between mobile users. Groups are special collections of picocells and represent regions where a mobile user is likely to be located in the near future. Thus, messages addressed to this mobile user are multicast to all the picocells in the group guaranteeing delivery and obviating the need for messages to be forwarded between picocells. The mobile user will therefore see...
. Mobile wireless networks pose interesting challenges for routing system design. To produce feasible routes in a mobile wireless network, a routing system must be able to accommodate roving users, changing network topology, and fluctuating link quality. We discuss the impact of node mobility and wireless communication on routing system design, and we survey the set of techniques employed in or proposed for routing in mobile wireless networks. 1. Introduction Mobile wireless networking has enjoyed a dramatic increase in popularity over the last few years, although the technology has existed for more than twenty years and has been commercially available for more than ten years. This recent popularity can be attributed to two factors: (1) advances in hardware design resulting in affordable, portable, low-power, wireless communication and computation devices; and (2) rapid growth in the communications infrastructure resulting in ubiquitous and affordable access to telephone and data net...
The rapidly advancing technology of cellular communication and wireless LAN makes ubiquitous computing feasible where the mobile users can have access to the location independent information and the computing resources. Multimedia networking is another emerging technological trend of the 1990s and there is an increasing demand for supporting continuous media traffic in wireless personal communication environment. In order to guarantee the strict performance requirements of realtime traffic, the connection-oriented approaches are proving to be more efficient compared to the conventional datagram based networking. This dissertation deals with a network architecture and its design issues for implementing the connection-oriented services in a mobile radio environment. The wired backbone of the proposed wireless LAN comprises of high speed ATM switching elements, connected in a modular fashion, where the new switches and the user devices can be dynamically added and reconnected for maintai...