Showing papers in "Mobile Networks and Applications in 1998"

Vertical handoffs in wireless overlay networks

Abstract: No single wireless network technology simultaneously provides a low latency, high bandwidth, wide area data service to a large number of mobile users. Wireless Overlay Networks – a hierarchical structure of room-size, building-size, and wide area data networks – solve the problem of providing network connectivity to a large number of mobile users in an efficient and scalable way. The specific topology of cells and the wide variety of network technologies that comprise wireless overlay networks present new problems that have not been encountered in previous cellular handoff systems. We have implemented a vertical handoff system that allows users to roam between cells in wireless overlay networks. Our goal is to provide a user with the best possible connectivity for as long as possible with a minimum of disruption during handoff. Results of our initial implementation show that the handoff latency is bounded by the discovery time, the amount of time before the mobile host discovers that it has moved into or out of a new wireless overlay. This discovery time is measured in seconds: large enough to disrupt reliable transport protocols such as TCP and introduce significant disruptions in continuous multimedia transmission. To efficiently support applications that cannot tolerate these disruptions, we present enhancements to the basic scheme that significantly reduce the discovery time without assuming any knowledge about specific channel characteristics. For handoffs between room-size and building-size overlays, these enhancements lead to a best-case handoff latency of approximately 170 ms with a 1.5% overhead in terms of network resources. For handoffs between building-size and wide-area data networks, the best-case handoff latency is approximately 800 ms with a similarly low overhead.

Hierarchically-organized, multihop mobile wireless networks for quality-of-service support

Abstract: MMWN is a modular system of adaptive link- and network-layer algorithms that provides a foundation on which to build mechanisms for quality-of-service provision in large, multihop mobile wireless networks. Such networks are a practical means for creating a communications infrastructure where none yet exists or where the previously existing infrastructure has been severely damaged. These networks provide communications for such diverse purposes as tactical maneuvering and strategic planning on the battlefield, emergency relief in an area afflicted by a natural disaster, and field studies conducted by a team of scientists in a remote location. In this paper, we describe three key components of the MMWN system: the clustering procedures for defining a virtual, hierarchical control structure superimposed on a large network of mobile switches and endpoints; the location management procedures for determining the current locations of mobile endpoints relative to the hierarchical control structure; and the virtual circuit management procedures for setting up and repairing virtual circuits as switches and endpoints move. We also provide simulation results that illustrate the robustness of each of these components with respect to a broad spectrum of transmission ranges and relative mobility of switches and endpoints.

MPEG-4: an object-based multimedia coding standard supporting mobile applications

Abstract: The ISO MPEG committee, after successful completion of the MPEG-1 and the MPEG-2 standards is currently working on MPEG-4, the third MPEG standard. Originally, MPEG-4 was conceived to be a standard for coding of limited complexity audio-visual scenes at very low bit-rates; however, in July 1994, its scope was expanded to include coding of scenes as a collection of individual audio-visual objects and enabling a range of advanced functionalities not supported by other standards. One of the key functionalities supported by MPEG-4 is robustness in error prone environments. In general, the MPEG-4 standard provides solutions for coding of natural or synthetic video and audio, as well as a system for multiplex/demultiplex and description of scenes in a truly flexible manner. With focus on the mobile multimedia functionality, we present an overview of the current status as well as the details of the MPEG-4 coding standard. We also discuss profiles, a mechanism used for partitioning MPEG-4 into realizable subsets. Finally, plans for testing and verification of current MPEG-4 (Version 1) standard, ongoing work for MPEG-4 Version 2, as well as directions for MPEG-7, the next MPEG standard, are briefly discussed.

Fast and scalable wireless handoffs in supports of mobile Internet audio

Abstract: Future internetworks will include large numbers of portable devices moving among small wireless cells. We propose a hierarchical mobility management scheme for such networks. Our scheme exploits locality in user mobility to restrict handoff processing to the vicinity of a mobile node. It thus reduces handoff latency and the load on the internetwork. Our design is based on the Internet Protocol (IP) and is compatible with the Mobile IP standard. We also present experimental results for the lowest level of the hierarchy. We implemented our local handoff mechanism on Unix-based portable computers and base stations, and evaluated its performance on a WaveLAN network. These experiments show that our handoffs are fast enough to avoid noticeable disruptions in interactive audio traffic. For example, our handoff protocol completes less than 10 milliseconds after a mobile node initiates it. Our mechanism also recovers from packet losses suffered during the transition from one cell to another. This work helps extend Internet telephony and teleconferencing to mobile devices that communicate over wireless networks.

L 2 imbo: a distributed systems platform for mobile computing

Abstract: Mobile computing environments increasingly consist of a range of supporting technologies offering a diverse set of capabilities to applications and end-systems. Such environments are characterised by sudden and dramatic changes in the quality-of-service (QoS) available to applications and users. Recent work has shown that distributed systems platforms can assist applications to take advantage of these changes in QoS and, more specifically, facilitate applications to adapt to their environment. However, the current state-of-the-art in these platforms reflects their fixed network origins through their choice of synchronous connection-oriented communications paradigms. In this paper we argue that these paradigms are not well suited to operation in the emerging mobile environments. Furthermore, we offer an alternative programming paradigm based on tuple spaces which, we believe, offers a number of benefits within a mobile context. The paper presents the design, implementation and evaluation of a new platform based on this paradigm.

Location-aware mobile applications based on directory services

Abstract: Location-aware applications are becoming increasingly attractive due to the widespread dissemination of wireless networks and the emergence of small and cheap locating technologies. We developed a location information server that simplifies and speeds up the development of these applications by offering a set of generic location retrieval and notification services to the application. The data model and the access protocols of these services are based on the X.500 directory service and the lightweight directory access protocol LDAP since these are becoming the standard attribute-value-pair retrieval mechanisms for Internet and Intranet environments. This approach establishes a smooth migration path from conventional to location-aware applications. The paper presents the location information server concepts, defines its directory data model and access services, and discusses the implementation options of the loca- tion information server.

WebExpress: a client/intercept based system for optimizing Web browsing in a wireless environment

Abstract: This paper describes an application model and software technology that makes it possible to run World Wide Web applications in wide area wireless networks. Web technology in conjunction with today's mobile devices (e.g., laptops, notebooks, personal digital assistants) and the emerging wireless technologies (e.g., digital cellular, packet radio, CDPD) offer the potential for unprecedented access to data and applications by mobile workers. Yet, the limited bandwidth, high latency, high cost, and poor reliability of today's wireless wide-area networks greatly inhibits (to the point of infeasibility) supporting such applications over wireless networks. This paper presents the Client/Intercept computational model that makes it possible to run such distributed applications efficiently in wide area wireless networks. Furthermore, it presents WebExpress, a client/intercept based system for optimizing Web browsing, that reduces data volume and latency of wireless communications by intercepting the HTTP data stream and performing various optimizations including: file caching, forms differencing, protocol reduction, and the elimination of redundant HTTP header transmission. This paper describes these optimizations and presents some experimental results.

Multicast support for mobile hosts using mobile IP: design issues and proposed architecture

Abstract: In this paper, we consider the problem of providing multicast to mobile hosts using Mobile IP for network routing support. Providing multicast in an internetwork with mobile hosts is made difficult because many multicast protocols are inefficient when faced with frequent membership or location changes. This basic difficulty can be handled in a number of ways, but three main problems emerge with most solutions. The tunnel convergence problem, the duplication problem, and the scoping problem are identified in this paper and a set of solutions are proposed. The paper describes an architecture to support IP multicast for mobile hosts using Mobile IP. The basic unicast routing capability of Mobile IP is used to serve as the foundation for the design of a multicast service facility for mobile hosts. We believe that our scheme is transparent to higher layers, simple, flexible, robust, scalable, and, to the extent possible, independent of the underlying multicast routing facility. For example, our scheme could interoperate with DVMRP, MOSPF, CBT, or PIM in the current Internet. Where differences exist between the current version of IP (IPv4) and the next generation protocol (IPv6), these differences and any further optimizations are discussed.

Adaptive source rate control for real-time wireless video transmission

Abstract: Hybrid ARQ schemes can yield much better throughput and reliability than static FEC schemes for the transmission of data over time-varying wireless channels. However these schemes result in extra delay. They adapt to the varying channel conditions by retransmitting erroneous packets, this causes variable effective data rates for current PCS networks because the channel bandwidth is constant. Hybrid ARQ schemes are currently being proposed as the error control schemes for real-time video transmission. An important issue is how to ensure low delay while taking advantage of the high throughput and reliability that these schemes provide for. In this paper we propose an adaptive source rate control (ASRC) scheme which can work together with the hybrid ARQ error control schemes to achieve efficient transmission of real-time video with low delay and high reliability. The ASRC scheme adjusts the source rate based on the channel conditions, the transport buffer occupancy and the delay constraints. It achieves good video quality by dynamically changing both the number of the forced update (intracoded) macroblocks and the quantization scale used in a frame. The number of the forced update macroblocks used in a frame is first adjusted according to the allocated source rate. This reduces the fluctuation of the quantization scale with the change in the channel conditions during encoding so that the uniformity of the video quality is improved. The simulation results show that the proposed ASRC scheme performs very well for both slow fading and fast fading channels.

Mobile networking in the Internet

Abstract: Computers capable of attaching to the Internet from many places are likely to grow in popularity until they dominate the population of the Internet. Consequently, protocol research has shifted into high gear to develop appropriate network protocols for supporting mobility. This introductory article attempts to outline some of the many promising and interesting research directions. The papers in this special issue indicate the diversity of viewpoints within the research community, and it is part of the purpose of this introduction to frame their place within the overall research area.

An efficient packet sensing MAC protocol for wireless networks

Abstract: The Group Allocation Multiple Access with Packet-Sensing (GAMA-PS) protocol for scheduling real-time and datagram traffic in a wireless LAN is specified and analyzed. By maintaining a dynamically-sized cycle that changes in length depending on the amount of network traffic, GAMA-PS is able to efficiently control channel access while ensuring that there are no collisions of data packets. Each cycle contains a contention period and a group-transmission period; a station with data to send competes for membership in the “transmission group” by using packet sensing to successfully complete an RTS/CTS message exchange during the contention period. Once a station is a member of the transmission group, it is able to transmit a collision-free data packet during each cycle; as long as a station has data to send, it maintains its position in the group.

Secure and mobile networking

Abstract: The IETF Mobile IP protocol is a significant step towards enabling nomadic Internet users. It allows a mobile node to maintain and use the same IP address even as it changes its point of attachment to the Internet. Mobility implies higher security risks than static operation. Portable devices may be stolen or their traffic may, at times, pass through links with questionable security characteristics. Most commercial organizations use some combination of source-filtering routers, sophisticated firewalls, and private address spaces to protect their network from unauthorized users. The basic Mobile IP protocol fails in the presence of these mechanisms even for authorized users. This paper describes enhancements that enable Mobile IP operation in such environments, i.e., they allow a mobile user, out on a public portion of the Internet, to maintain a secure virtual presence within his firewall-protected office network. This constitutes what we call a Mobile Virtual Private Network (MVPN).

MAC protocol and traffic scheduling for wireless ATM networks

Abstract: The Medium Access Control (MAC) protocol defined in the Wireless ATM Network Demonstrator (WAND) system being developed within the project Magic WAND is presented. Magic WAND is investigating extensions of ATM technology to cover wireless customer premises networks, in the framework of the Advanced Communications Technologies and Services (ACTS) programme, funded by the European Union. The MAC protocol, known as MASCARA, uses a dynamic TDMA scheme, which combines reservation- and contention-based access methods to provide multiple access efficiency and quality of service guarantees to wireless ATM terminal connections sharing a common radio channel. The paper focuses on the description of PRADOS, a delay-oriented traffic scheduling algorithm, which aims at satisfying the requirements of the various traffic classes defined by the ATM architecture. Simulation results are presented to assess the performance of the proposed algorithm in scheduling transmission of variable bit rate connections.

A cellular wireless local area network with QoS guarantees for heterogeneous traffic

Abstract: A wireless local area network (WLAN) or a cell with quality-of-service (QoS) guarantees for various types of traffic is considered A centralized (ie, star) network is adopted as the topology of a cell which consists of a base station and a number of mobile clients Dynamic Time Division Duplexed (TDD) transmission is used, and hence, the same frequency channel is time-shared for downlink and uplink transmissions under the dynamic control of the base station We divide traffic into two classes: class I (real-time) and II (non-real-time) Whenever there is no eligible class-I traffic for transmission, class-II traffic which requires no delay-bound guarantees is transmitted, while uplink transmissions are controlled with a reservation scheme Class-I traffic which requires a bounded delay and guaranteed throughput is handled with the framing strategy (Golestani, IEEE J Selected Areas Commun 9(7), 1991) which consists of a smoothness traffic model and the stop-and-go queueing scheme We also establish the admission test for adding new class-I connections We present a modified framing strategy for class-I voice uplink transmissions which utilizes the wireless link efficiently at the cost of some packet losses Finally, we present the performance (average delay and throughput) evaluation of the reservation scheme for class-II traffic using both analytical calculations and simulations

Performance evaluation of the MoM mobile multicast protocol

Abstract: This paper presents a performance study of a mobile multicast protocol called MoM, which is designed to support IP multicast for mobile hosts in an IP internetwork. The protocol uses the basic unicast routing capability of IETF Mobile IP, and leverages existing IP multicast to provide multicast services for mobile hosts as well. A key feature of the MoM protocol is the use of designated multicast service providers (DMSPs) to improve the scalability of mobile multicast. Discrete-event simulation is used in the performance evaluation of the protocol. The performance study focuses on the scalability, routing efficiency, fairness, and overhead of the MoM protocol, as well as on DMSP selection policies and the deliverability of multicast messages. The simulation results suggest distinct performance advantages for the MoM protocol over other approaches for mobile multicast, such as bi-directional tunnelling, particularly as the number of mobile group members increases. Furthermore, even simple policies for choosing a DMSP from possible candidates provide reasonable tradeoffs between handoff rates, routing efficiency, deliverability of messages, and protocol overhead.

Security protocol for IEEE 802.11 wireless local area network

Abstract: As Wireless Local Area Networks (WLANs) are rapidly deployed to expand the field of wireless products, the provision of authentication and privacy of the information transfer will be mandatory. These functions need to take into account the inherent limitations of the WLAN medium such as limited bandwidth, noisy wireless channel and limited computational power. Moreover, some of the IEEE 802.11 WLAN characteristics such as the use of a point coordinator and the polling based Point Coordination Function (PCF) have also to be considered in this design. In this paper, we introduce a security protocol for the IEEE 802.11 PCF that provides privacy and authentication, and is designed to reduce security overheads while taking into account the WLAN characteristics. We prove this protocol using the original and modified BAN logic.

Group-based multicast and dynamic membership in wireless networks with incomplete spatial coverage

Abstract: In this paper we examine the problem of group-based multicast communication in the context of mobile computing with wireless communication technology. We propose a protocol in which group members may be mobile computers and such that the group membership may change dynamically. Multicasts are delivered in the same order at all group members (totally-ordered multicast). Mobile computers are resource-poor devices that communicate with a wired network through a number of spatially limited cells defining wireless links. The spatial coverage provided by wireless links may be either complete or incomplete, which makes the overall system model both general and realistic. The proposed protocol is simple and does not require any hand-off in the wired network upon movements of group members. Moreover, there is no part of the protocol requiring that group members do not move during its execution. This feature leads to mobility assumptions that are practical because they involve only the global movement of group members, e.g., assumptions of the form “a group member does not move very fast all the time”.

Experiences with network-based user agents for mobile applications

Abstract: Wireless networks are characterized by simple end devices and limited bandwidth One solution to address these and other limitations of the wireless mobile environment that has been widely pursued is the placement of proxies, or agents, inside the network to assist with application processing that would normally take place on end devices These agents can additionally manipulate data to reduce bandwidth requirements and assist in providing services The design and implementation of a user agent is heavily impacted by the application it supports In this paper we present our experiences with user agents in two different types of applications: telephony-based Personal Communication Services (PCS) and two-way messaging To provide low latency service, the PCS user agents are mobile so that they may be kept close to their end devices The design of the PCS agents limits migration overhead to the transfer of approximately 100 bytes of information in about 150 milliseconds To provide advanced messaging services, the messaging user agent supports flexible messages while limiting air interface bandwidth usage The messaging agents reduce uplink bandwidth usage by approximately 35% when applied to a cellular PCS system, and reduce message payloads by 97%

Adaptive rate controlled, robust video communication over packet wireless networks

Abstract: Video transmission over wireless packet networks is gaining importance due to the concept of universal personal communication. Further, it is considered an important step towards wireless multimedia. The challenge however is to achieve good video quality over mobile channels, where typically the channel conditions vary due to signal fading. Hence this paper investigates adaptive rate controlled video transmission for robust video communication under packet wireless environment. A combination of mobile and an ATM backbone network is assumed in this work. An error resilient design for the video coder, as proposed in Rajugopal et al. (1996) is employed here. This video coder comprises wavelet transform (WT), multi-resolution motion estimation (MRME) and a robust design for zero tree quantization. Two configurations, one employing MRME and the other using 1D-WT for temporal analysis, are considered for the video coder. Adaptive dynamic rate control is required to adapt the video communication to the channel conditions. It provides more channel protection when the channel is severe and improves the source rate and hence the performance when the conditions are favorable. An algorithm for dynamic rate control under varying channel conditions is proposed in this paper. It is evaluated under narrowband and broadband channel conditions. From the results, it is concluded that the dynamic rate control is very effective in optimizing the quality under varying mobile channel conditions. It was observed that the dynamic rate control provides at least an acceptable video quality under severe channel conditions and a good video quality when the channel conditions are favorable.

Comparative analysis of wireless ATM channel access protocols supporting multimedia traffic

Abstract: Extension of multimedia services and applications offered by ATM networks to wireless and mobile users has captured a lot of recent research attention. Research prototyping of wireless ATM networks is currently underway at many leading research and academic institutions. Various architectures have been proposed depending on the intended application domain. Successful implementation of wireless connectivity to ATM services is significantly dependent on the medium access control (MAC) protocol, which has to provide support for multimedia traffic and for quality-of-service (QoS) guarantees. The objective of this paper is to investigate the comparative performance of a set of access protocols, proposed earlier in the literature, with more realistic source traffic models. Data traffic is modeled with self-similar (fractal) behavior. Voice traffic is modeled by a slow speech activity detector (SAD). Video traffic is modeled as a H.261 video teleconference, where the number of ATM cells per video frame is described by a gamma distribution and a first-order discrete autoregressive process model. A comparison of the protocols based on simulation data is presented. The goal of the paper is to identify appropriate techniques for effectively and efficiently supporting multimedia traffic and QoS. Simulation results show that boundaries between different types of services are necessary for multimedia traffic. Reservation for certain traffic type especially video can significantly improve its quality. Reducing the number of collisions is an important issue for wireless networks since contentions lead not only to potentially high delay but also result in high power consumption.

Route optimization in mobile ATM networks

Abstract: This paper presents an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, and applies this algorithm to the handoff management problem in mobile ATM (Asynchronous Transfer Mode) networks based on the PNNI (Private Network-to-Network Interface) standard. The route optimization algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a “crossover node” such that adjusting the connection from that crossover node results in an optimally routed connection. Handoff management schemes that perform local rerouting of connections have been proposed in order to support fast handoffs. These methods result in suboptimally routed connections. In this paper, we demonstrate how this route optimization algorithm can be used to optimize the route of a connection after such a handoff is executed, as the second phase of a two-phase handoff scheme. This route optimization procedure can also be executed as part of the handoff procedure resulting in a one-phase handoff scheme. Applying this route optimization algorithm, we propose two one-phase schemes, the one-phase optimal scheme and the one-phase minimal scheme. A comparative performance analysis of one- and two-phase handoff schemes is presented. Measures of comparison are handoff latency and the amount of network resources used by a connection. Handoff latency in the one-phase optimal scheme is greater than that in the two-phase schemes, and handoff latency in the one-phase minimal scheme is smaller than that in the two-phase schemes. The one-phase methods show a significant increase in efficiency of the connection compared to the two-phase methods.

A routing architecture for mobile integrated services networks

Abstract: A drawback of the conventional Internet routing architecture is that its route computation and packet forwarding mechanisms are poorly integrated with congestion control mechanisms. Any datagram offered to the network is accepted; routers forward packets on a best-effort basis and react to congestion only after the network resources have already been wasted. A number of proposals improve on this to support multimedia applications; a promising example is the Integrated Services Packet Network (ISPN) architecture. However, these proposals are oriented to networks with fairly static topologies and rely on the same conventional Internet routing protocols to operate. This paper presents a routing architecture for mobile integrated services networks in which network nodes (routers) can move constantly while providing end-to-end performance guarantees. In the proposed connectionless routing architecture, packets are individually routed towards their destinations on a hop by hop basis. A packet intended for a given destination is allowed to enter the network if and only if there is at least one path of routers with enough resources to ensure its delivery within a finite time. Once a packet is accepted into the network, it is delivered to its destination, unless resource failures prevent it. Each router reserves resources for each active destination, rather than for each source–destination session, and forwards a received packet along one of multiple loop-free paths towards the destination. The resources and available paths for each destination are updated to adapt to congestion and topology changes. This mechanism could be extended to aggregate dissimilar flows as well.

Dynamic capacity allocation and hybrid multiplexing techniques for ATM wireless LANs

Abstract: We consider digital wireless multimedia LANs and time-varying traffic rates. To deal effectively with the dynamics of the time-varying traffic rates, a Traffic Monitoring Algorithm (TMA) is deployed to dynamically allocate channel capacities to the heterogeneous traffics. The TMA is implemented as a higher level protocol that dictates the capacity boundaries within two distinct framed transmission techniques: a Framed Time Domain-Based (FTDB) technique and a Framed CDMA (FCDMA) technique. The performance of the TMA in the presence of the FTDB technique is compared to its performance in the presence of the FCDMA technique for some traffic scenarios. The performance metrics used for the TMA-FTDB and TMA-FCDMA combinations are channel capacity utilization factors, traffic rejection rates, and traffic delays. It is found that the TMA-FTDB is superior to the TMA-FCDMA when the speed of the transmission links is relatively low and the lengths of the transmitted messages are relatively short. As the speed of the transmission links and the length of the transmitted messages increase, the TMA-FCDMA eventually outperforms the TMA-FTDB.

Multicast support for mobile hosts using mobile IP

Abstract: In this paper, we consider the problem of providing multicast to mobile hosts using Mobile IP for network routing support. Providing multicast in an internetwork with mobile hosts is made difficult...

Wireless ATM MAC performance evaluation, a case study: HIPERLAN type 1 vs. modified MDR

Abstract: This paper deals with wireless ATM and in particular with MAC (Medium Access Control) mechanisms. The requirements for wireless ATM MAC are discussed, and contention-based and TDMA/reservation based MAC protocols are compared. The objective is to find out the suitability of current wireless MAC schemes for ATM interworking, in comparison to new wireless ATM MAC proposals. Two candidate mechanisms, EY-NPMA used in HIPERLAN type 1, and a modified MDR protocol, are discussed in more detail and their performance in different traffic scenarios is evaluated through simulations.

Project EXODUS: experimental mobile multimedia deployment in ATM networks

Abstract: This paper reports on European Commission sponsored research within the EXODUS project. The project carries out research in the context of the evolution towards UMTS and performs personal and terminal multimedia mobility experiments using fixed and wide-band radio access in an international ATM network. After introducing the EXODUS platform and services, the paper presents an IN-based functional model which is suitable for support of mobile multimedia services in ATM networks. Interworking and mobility management issues are discussed, and information flows for call handling are presented. The paper includes a presentation of the mobility management and enhanced INAP protocols which have been developed by the EXODUS project.

Interaction of TCP and data access control in an integrated voice/data CDMA system

Abstract: This paper considers the interaction between a proposed data access control scheme and the standardized error recovery schemes on the radio link of a voice/data CDMA system. A data access control scheme for combined voice-data CDMA systems has been proposed and studied in previous literature. The scheme aims to maintain a certain target voice signal to interference ratio (SIR); this is achieved by controlling the data load according to the measured voice SIR. The data users are allowed to transmit in a radio-link time slot with a certain permission probability, which is determined by the base station based on the measured voice SIR in the previous slot. As per the IS-99 standards, however, data transmission operates under the framework of TCP, which is a higher level end-to-end protocol. The TCP data unit, called a segment, is typically equivalent to several tens of physical layer frames; hence, a segment transmission takes up several tens of slots. Due to changes in the number of voice users in talkspurt (which occur on a time scale shorter than a segment transmission time), the slot level data access control scheme can introduce significant variability in the segment transmission time. The effect of such variability on the TCP timers, which operate at the segment level, is of interest. In this paper, an approximate upper bound on the data throughput, taking the presence of TCP into account, is computed. The results provide one with an insight into the interaction of the access control scheme with TCP; they also give practical pointers as to choosing suitable parameters and operating points for the scheme.

An Efficient Location Management Protocol for Wireless ATM Customer Premises Networks

Abstract: In this paper we present a new location management protocol for wireless ATM networks, called LMCP (Location Management and Control Protocol) This protocol is based on the PNNI (Private Network-to-Network Interface) routing functionality to advertise the movement of mobile terminals within pre-defined areas Moreover, LMCP uses specialized entities to store and retrieve the current location area of mobile terminals These entities are located in mobility enhanced switches that control the execution of other mobility procedures (eg handovers) The main benefit from the application of LMCP is the establishment of connections that do not contain any misrouted segments Furthermore, it requires minor modifications to the PNNI and enables its inter-working with other location management mechanisms The protocol is compared with other similar mechanisms, and its efficiency is demonstrated by the results of an analytical model

A layered protocol architecture for multimedia wireless-PCS networks

Abstract: Coupled with the growing interest in the Universal Mobile Telecommunication System (UMTS) as a standard for future mobile communications, the need for a set of functions to effectively support multimedia teleservices in such an environment is also increasing Starting from the idea that multimedia means the integrated manipulation of different information and hence the independent handling of separate information is not satisfactory, an enhanced protocol architecture for the support of multimedia teleservices in Wireless Personal Communication Systems based on UMTS is proposed It involves Physical, MAC, Data Link, and Network layers A Synchronisation Sub-Layer is introduced on the MAC level with the main aim of assuring a rough multimedia inter-stream synchronisation over the air interface, which is a first step prior to a fine end-to-end synchronisation performed by higher layers Proposed functions, their basic algorithms, their location in the protocol stack, as well as the signalling exchange among modules implementing them, on network and user sides, are described in detail in the paper The resulting architecture well fits the demanding nature of multimedia services and can be easily interfaced with the wired backbone of the system