0163 6804/97/$10 00 © 1997 IEEE roadband and mobile communications are presently the two major drivers in the telecommunications industry. Asynchronous transfer mode (ATM) is considered the most suitable transport technique for the future broadband integrated services digital network (B-ISDN), due to its ability to flexibly support a wide range of services with qualityof-service (QoS) guarantees. On the other hand, wireless local area networks (LANs) are becoming popular for indoor data communications because of their tetherlessness and increasing transmission speed. Wireless communications have been developed to a level where offered services can now be extended beyond voice and data. The combination of wireless communications and ATM, especially in local-area environments, can provide freedom of mobility with service advantages and QoS guarantees. The main challenge of wireless ATM is to harmonize the development of broadband wireless systems with B-ISDN/ATM and ATM LANs, and offer similar advanced multimedia multiservice features for the support of time-sensitive voice communications, LAN data traffic, video, and desktop multimedia applications to the wireless user [1]. Emerging standards, such as High-Performance Radio LAN (HIPERLAN) or IEEE 802.11, have been designed to provide wireless access to corporate networks, but do not yet incorporate ATM technology over the air [2].There are several open issues in the development of wireless ATM. Most of them stem from the fact that ATM was designed with reliable fixed links in mind. More precisely, ATM assumes fixed users, plentiful and constant bandwidth allocated dynamically based on users' needs, full duplex and point-to-point transmission, very good transmission quality (which is why error detection and error correction techniques are limited), and low physical-layer overhead. On the other hand, in a wireless environment users can move inside the covered range, the available bandwidth in the radio interface is limited and can vary based on the quality of the channel, transmission is usually half duplex and point-to-multipoint due to the lack of available frequencies, transmission quality is usually poor requiring advanced error detection and error correction techniques, and physical overhead is much higher than in fixed links, basically due to the synchronization delay between transmitter and receiver [3].Currently, a number of research activities are focusing on the topic of wireless ATM to resolve its problems (e.g., [4][5][6][7]). One of these activities is project Magic WAND (Wireless ATM Network Demonstrator) [8], which is investigating wireless ATM technology for customer premises networks in the framework of the Advanced Communications Technologies and Services (ACTS) program funded by the European Union. The main components of the WAND system, as shown in Fig. 1, are:• Mobile terminals (MTs), the end-user equipment, which are basically ATM terminals with a radio adapter card • Access points (APs), the base stations of the cellular environment • An ATM ...

Abstract-At first, protocol design assumed a homogeneous underlying network and resulted in end-to-end QoS protocols that applied specific QoS configuration in all routers along the path. The need, however, for accommodating network heterogeneity and flexibility, gave birth to a two-tier resource management model that utilizes separate signaling for intra-and inter-domain reservations and requires different signaling processing in domain interior and border routers. This paper gives an overview of the QoS signaling protocols designed for the Internet and describes their characteristics. Moreover, the identified protocols are classified depending on their applicability for intraor inter-domain usage. A comparison of the various protocols based on some common signaling elements is also provided and future trends in the Internet QoS signaling area are identified.

Abstract-SIP is evolving as the dominant protocol for multimedia call control in IP networks and is expected to be widely deployed in the near future. Using SIP for supporting mobility in SIPbased networks appears as a very attractive alternative to Mobile IP, taking advantage of existing SIP infrastructure and signaling, while avoiding duplication of functionality. However, existing proposals for supporting mobility with SIP are not efficient in handling micro-mobility and do not cater for all types of traffic.In this paper, we introduce Hierarchical Mobile SIP (HMSIP), for efficient micro-mobility management in SIP environments. HMSIP is a SIP-based scheme that builds on existing IP mobility protocols, aiming at integrating their key concepts in the most beneficial way. Our proposed scheme minimizes the handoff latency and the backbone signaling overhead, while catering for all types of traffic. Moreover, HMSIP can be effectively combined with micro-mobility schemes for QoS flows, producing, thus, a complete micro-mobility solution for SIP flows with QoS guarantees.

Summary'Always Best Connected' (ABC) is considered one of the main requirements for next generation networks. The ABC concept allows a person to have access to applications using the devices and network technologies that best suits his or her needs or profile at any time. Clearly, this requires the combination of a set of existing and new technologies, at all levels of the protocol stack, into one integrated system. In this paper, a considerable set of the technologies, that are expected to play a key role towards the ABC vision, are presented. Starting from a reference architecture, the paper describes the required enhancements at certain levels of a traditional protocol stack, as well as technologies for mobility and end-to-end Quality of Service (QoS) support. The paper concludes with a case study that reveals the advantages of the ABC concept.

The mobility management issue in IP access networks can be dealt with from various perspectives. A possible approach includes the use of the Session Initiation Protocol (SIP) and its associate entities for mobility signaling. Following this approach, existing SIP functionality in a network can be reused for mobility management purposes, providing efficient utilization of resources. In this paper we propose the Hierarchical Mobile SIP (HMSIP) framework, a SIP-based intra-domain mobility management approach that builds upon the general framework of SIP mobility management. The HMSIP Agent is introduced as a border network entity providing the necessary mobility functionality. Detailed location and mobility management procedures are presented. The scheme is further enhanced with additional functionality for the support of multiple HMSIP Agents across the border of a domain, maintaining a unique contact address throughout a session within the domain.