Showing papers on "Media access control published in 2003"

Dynamic bandwidth allocation for quality-of-service over Ethernet PONs

Abstract: Ethernet-based passive optical network (EPON) technology is being considered as a promising solution for next-generation broadband access networks due to the convergence of low-cost Ethernet equipment and low-cost fiber infrastructures. A major feature for this new architecture is the use of a shared transmission media between all users; hence, medium access control arbitration mechanisms are essential for the successful implementation of EPON: i.e., to ensure a contention-free transmission and provide end users with equal access to the shared media. We propose to use the multipoint control protocol defined by the IEEE 802.3ah task force to arbitrate the transmission of different users, and we present different dynamic bandwidth allocation (DBA) algorithms to allocate bandwidths effectively and fairly between end users. These DBA algorithms are also augmented to support differentiated services, a crucial requirement for a converged broadband access network with heterogeneous traffic. We show that queueing delays under strict bandwidth allocation algorithms result in an unexpected behavior for certain traffic classes, and we suggest the use of DBA with appropriate local queue management to alleviate this inappropriate behavior. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed protocols.

IEEE 802.11 e contention-based channel access (EDCF) performance evaluation

Abstract: IEEE 802.11 e medium access control (MAC) is an emerging supplement to the IEEE 802.11 wireless local area network (WLAN) standard to support quality-of-service (QoS). The 802.11e MAC is based on both centrally-controlled and contention-based channel accesses. In this paper, we evaluate the contention-based channel access mechanism, called enhanced distributed coordination function (EDCF), in comparison with the 802.11 legacy MAC. The ECDF provides differentiated channel access to frames with different priorities. We also consider an optional feature of the EDCF, called contention-free burst (CFB), which allows multiple MAC frame transmissions during a single transmission opportunity (TXOP). Through our simulation study, we conclude that the EDCF can provide differentiated channel access for different traffic types. Furthermore, the CFB is found to enhance the EDCF performance by increasing the overall system throughput and achieving more acceptable streaming quality in terms of frame losses and delays.

Adaptive cross-layer protection strategies for robust scalable video transmission over 802.11 WLANs

Abstract: Robust streaming of video over 802.11 wireless local area networks poses many challenges, including coping with bandwidth variations, data losses, and heterogeneity of the receivers. Currently, each network layer (including physical layer, media access control (MAC), transport, and application layers) provides a separate solution to these challenges by providing its own optimized adaptation and protection mechanisms. However, this layered strategy does not always result in an optimal overall performance for the transmission of video. Moreover, certain protection strategies can be implemented simultaneously in several layers and, hence, the optimal choices from the application and complexity perspective need to be identified. In this paper, we evaluate different error control and adaptation mechanisms available in the different layers for robust transmission of video, namely MAC retransmission strategy, application-layer forward error correction, bandwidth-adaptive compression using scalable coding, and adaptive packetization strategies. Subsequently, we propose a novel adaptive cross-layer protection strategy for enhancing the robustness and efficiency of scalable video transmission by performing tradeoffs between throughput, reliability, and delay depending on the channel conditions and application requirements. The results obtained using the proposed adaptive cross-layer protection strategies show a significantly improved visual performance for the transmitted video over a variety of channel conditions.

Wireless Sensor Networks

Abstract: Sensor network, which is made by the convergence of sensor, micro-electro-mechanism system and networks technologies, is a novel technology about acquiring and processing information In this paper, the architecture of wireless sensor network is briefly introduced Next, some valuable applications are explained and forecasted Combining with the existing work, the hot spots including power-aware routing and media access control schemes are discussed and presented in detail Finally, taking account of application requirements, several future research directions are put forward

Shallow-Water Acoustic Networks†

Abstract: Underwater acoustic networks are generally formed by acoustically connected ocean bottom sensor nodes, autonomous underwater vehicles (AUVs), and surface stations that serve as gateways and provide radio communication links to on-shore stations. The QoS of such networks is limited by the low bandwidth of acoustic transmission channels, high latency resulting from the slow propagation of sound, and elevated noise levels in some environments. The long-term goal in the design of underwater acoustic networks is to provide for a self-configuring network of distributed nodes with network links that automatically adapt to the environment through selection of the optimum system parameters. This paper considers several aspects in the design of shallow water acoustic networks that maximize throughput and reliability while minimizing power consumption. Keywords: underwater; acoustic; communications; network; media access control (MAC); routing; ad hoc; Seaweb

Spectrum adaptive networking

Abstract: The present invention increases the available spectrum in a wireless network by sharing existing allocated (and in-use) portions of the RF spectrum in a manner that will minimize the probability of interfering with existing legacy users. The invention provides interference temperature-adaptive waveforms, and a variety of physical and media access control protocols for generating waveforms based on measurement and characterization of the local spectrum. The invention measures the local spectrum at a receiving node, generates an optimal waveform profile specifying transmission parameters that will water-fill unused spectrum up to an interference limit without causing harmful interference to primary and legacy transmitters using the same frequency bands, and enables simultaneous transmit and receive modes at a multiplicity of transceivers in a wireless network. The invention also provides closed loop feedback control between nodes, co-site interference management, intersymbol interference mitigation, wide sense stationary baseband signaling and modulation, and power limited signaling for avoiding detection and interception.

Reliable MAC layer multicast in IEEE 802.11 wireless networks

Abstract: Multicast/broadcast is an important service primitive in networks. It is supported by all IEEE 802.x standards, including 802.11. The IEEE 802.11 multicast/broadcast protocol is based on the basic access procedure of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This protocol does not provide any media access control (MAC) layer recovery on multicast/broadcast frames. As a result, the reliability of the multicast/broadcast service is reduced owing to the increased probability of lost frames resulting from interference or collisions. Recently, a few MAC protocols have been proposed to enhance the reliability and the efficiency of the 802.11 multicast/broadcast protocol. In this paper, we observe that these protocols are still unreliable or inefficient. To redress the problems of reliability and efficiency, we propose a reliable Batch Mode Multicast MAC protocol (BMMM), which in most cases reduces the number of contention phases from n to 1, where n is the number of intended receivers in the multicast/broadcast. This considerably reduces the time required for a multicast/broadcast. We then propose a Location Aware Multicast MAC protocol (LAMM), which uses station location information to further improve upon BMMM. Extensive analysis and simulation results validate the reliability and efficiency of our multicast MAC protocols. Copyright © 2003 John Wiley & Sons, Ltd.

A bandwidth guaranteed polling MAC protocol for Ethernet passive optical networks

Abstract: While the backbone networks have experienced substantial changes in the last decade; the access networks have not changed much. Recently, passive optical networks (PONs) seem to be ready for commercial deployment in access networks due to the maturity of a number of enabling technologies, long distance and reduced maintenance. Among PON technologies, the Ethernet PON (EPON) presently being standardized by the IEEE 802.3ah Ethernet in the first miles (EFM) task force is most attractive because of its high speed, low cost, familiarity, interoperability and low overhead. In this paper, we propose a novel bandwidth guarantee polling (BGP) scheme that will allow the upstream bandwidth to be shared based on the service level agreement (SLA) between each subscriber and the operator. It is able to provide bandwidth guarantee for premium subscribers according to the SLAs while providing best-effort service to other subscribers. The analytical and simulation results prove that the proposed scheme does best in what it is designed to do compared to another well-known scheme that has not considered providing differentiated services. With business customers preferring premium services with guaranteed bandwidth and residential users preferring low-cost best effort services, our scheme could benefit both groups of subscribers as well as the operators.

A summary of the HORNET project: a next-generation metropolitan area network

Abstract: Metropolitan area networks are currently undergoing an evolution aimed at more efficiently transport of data-oriented traffic. However, the incoming generation of metro networks is based on conventional technology, which prevents them scaling cost-effectively to ultrahigh capacities. We have developed a new architecture and set of protocols for the next generation of metro networks. The architecture, named HORNET (hybrid optoelectronic ring network), is a packet-over-wavelength-division multiplexing ring network that utilizes fast-tunable packet transmitters and wavelength routing to enable it to scale cost-effectively to ultrahigh capacities. A control-channel-based media access control (MAC) protocol enables the network nodes to share the bandwidth of the network while preventing collisions. The MAC protocol is designed to transport variable-sized packets and to provide fairness control to all network end users. The efficiency and the fairness of the MAC protocol is demonstrated with custom-designed simulations. The implementation of the MAC protocol and the survivability of the network have been demonstrated in a laboratory experimental testbed. The article summarizes the accomplishments of the HORNET project, including the design, analysis, and demonstration of a metro architecture and a set of protocols. The HORNET architecture is an excellent candidate for next-generation high-capacity metro networks.

Customer site bridged emulated LAN services via provider provisioned connections

Abstract: Methods for provisioning Virtual Local Area Network (VLAN) services are presented. The methods provide for Protocol Data Unit (PDU) transport in service provider and carrier communications networks using tunneling technologies via virtual connections established between Provider Edge equipment (PEs), providing learning bridge functionality at Customer Located Equipment (CLE), while PEs multiplex VLAN traffic onto the tunnels based on VLAN IDentifiers, with each VLAN ID corresponding to a peer remote site participating in a customer VLAN. Advantages are derived from a less restrictive use of VLAN IDs which need only be unique in the access network portion of the service provider's network, Media Access Control ADDRess (MAC ADDRs) tracking is performed only by peer CLEs which store only peer MAC ADDRs, automatic MAC ADDR—VLAN ID associativity determination via the CLE performed learning bridge function, thereby reducing virtual private LAN service provisioning.

Dynamic wireless network

Abstract: A Dynamically Reconfigurable Dynamic Wireless Network for connecting a local area network (“LAN”) to wireless Mobile Stations. Backbone Access Points (“Backbone APs”) are physically connected to the LAN. Levels of Wireless Access Points (“Wireless APs”) are daisy-chained together and connected to the Backbone AP, providing an extended area of network coverage. Mobile stations are connected to either Backbone APs or Wireless APs. Dynamic Reconfiguration prevents single point failures. Each AP contains a router, Address Resolution Protocol (“ARP”) cache, and Distributed Routing Table (“DR Table”). The DR Table maintains the Media Access Control (“MAC”) address and the Internet Protocol (“IP”) address of each AP below it in the Distributed Routing Tree. Additionally, each DR Table also maintains the IP address for the device each AP is connected. The Distributed Routing Tree is dynamically reconfigured to minimize transmission hops or to maximize signal strength between Mobile Stations and the LAN.

Control structures for contention-based packet data services in wideband CDMA

Abstract: A method and system for transmitting packet data over a cellular telecommunications network is presented. A novel medium access control (MAC) logical layer is implemented between a service option layer and multiplex sublayer. The MAC layer handles the multiple accesses of packet users over selected dedicated traffic channels. The MAC layer provides a multiple access control function for packet data users only. Users requiring only circuit switched services (voice calls) are not serviced through the MAC layer multiple access control function. If a user has simultaneous circuit switched and packet data services operating, the MAC layer multiple access control function handles the packet data services, while the circuit switched services are handled simultaneously by bypassing the MAC layer multiple access control function.

A performance analysis of the 802.11 wireless lan medium access control

Abstract: We study the performance of the IEEE 802.11 protocol. We present an extension of a methodology for the collocated one-hop case which allows the incorporation of channel errors. The results closely agree with simulation results. A delay analysis is also presented. We also present an extension of this methodology to the multi-hop case with non-collocated nodes. The approach uses specific topology dependent relations. Specific results are presented for the ring and mesh topologies, and compared against simulation results. 1. Introduction. Wireless networking technologies are increasingly becoming widespread. Various wireless communication standards have evolved which try to provide protocols and standards for medium access control in the shared wireless medium. The IEEE 802.11 protocol(3), Bluetooth(7), HomeRF(9) (now disbanded) and the HiperLAN(8) are examples of such standards. The IEEE 802.11 protocol is the most widely used. The IEEE 802.11 standard defines two layers. The first layer is the Physical layer (PHY), which specifies the modulation scheme used and signaling characteristics for the transmission through radio frequencies. The second layer is the media access control (MAC) layer. This layer determines how the medium is used. This chap- ter provides an overview of the medium access control mechanism, specifically the Distributed Coordination function, DCF, in the IEEE 802.11 protocol. The description is followed by performance analysis of DCF for both single hop and multi-hop wireless networks. Bianchi in (1) has analyzed IEEE 802.11 DCF for the single hop or the collocated case. The goodput analysis for the collocated case presented in Section 3.1, extends Bianchi's work by taking into account wireless channel errors and retry counts. A new delay analysis for the collocated case is also presented. Analyzing 802.11 protocol in multi-hop scenarios poses many new challenges. Section 3.2 presents a methodology for performance analysis of 802.11 DCF in multi-hop networks. The application of the methodology to a ring topology is also presented. The numerical results show good agreement with ns-2 simulation

Polling-based MAC protocols for improving real-time performance in a wireless PROFIBUS

Abstract: The idea of having a wireless PROFIBUS is appealing, since this can bring benefits like reduced cabling need and mobile stations to the factory floor. However, unfortunately, wireless transmission is error prone, which affects the timeliness and reliability behavior users expect from a fieldbus system (hard real time). In this paper, we compare two different approaches for the medium access control (MAC) and link layer of a wireless PROFIBUS system with respect to their so-called real-time performance in the presence of transmission errors. Specifically, we compare the existing PROFIBUS MAC and link layer protocol with a simple round-robin protocol. It is shown that round-robin delivers significantly better real-time performance than the PROFIBUS protocol under bursty error conditions. In a second step, we propose three add-ons to round-robin and we show that they further increase the real-time performance of round-robin. The add-ons take certain characteristics of the wireless medium into account.

Coordination of competing protocols

Abstract: A wireless telecommunications terminal employing both an IEEE 802.11 radio and a Bluetooth radio is disclosed. The illustrative embodiment employs a novel preemption scheme that ensures that Bluetooth preemptions of the 802.11 radio are not fatal to the 802.11 media access control (MAC) error-correction mechanism. The illustrative embodiment thus enables what appears to be concurrent 802.11 and Bluetooth activity by a single wireless telecommunications terminal. The preemption scheme does not require any changes to the 802.11 and Bluetooth protocols, or to the radios. It will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for protocols other than IEEE 802.11 and Bluetooth that might interfere with each other.

Data processing system and method for permitting a server to remotely access asset information of a mobile client

Abstract: A data processing network configuration includes a server and an access point wired to a network and a mobile system wirelessly connected to the access point. The access point receives and stores a request to retrieve information from the mobile system. The mobile system, when in a powered down state, powers its wireless network adapter periodically to poll the access point to discover the stored request for information. The mobile system responds to discovery of the stored request by retrieving the requested information from nonvolatile storage of the mobile system and transmitting the requested information via the wireless network adapter while otherwise remaining powered down. The information request may be a system management request and the request packet may include a Media Access Control (MAC) address repeated multiple times. The access point stores pending requests in a table having an entry for each associated mobile system.

Multi-channel MAC protocol for mobile ad hoc networks

Abstract: This paper introduces a new MAC scheme operating on multiple channels that maximizes network performance and provides differentiated services in mobile ad hoc networks (MANETs). Specifically, the IEEE 802.11 in ad hoc mode, the most popular MAC protocol in mobile ad hoc networks, is extended from single channel to multiple channels operation. The current standard allows the practical use of three channels in 802.11b and eight in 802.11a, but multiple channel operation is not supported in ad hoc mode. The proposed protocol ensures maximum performance, low delay, reliability, efficiency and fairness, while allowing transmission priorities to be set on a per-channel basis. In addition, a solution is provided for the hidden multi-channel problem, which arises when only one network interface card is used. Basic considerations for mobility management in a multi-channel environment is also given. We show through simulation that the multi-channel MAC protocol greatly outperforms the original IEEE 802.11 MAC protocol.

Communications protocol between a gateway and an access point

Abstract: A communications protocol in a computer readable medium of a general purpose computer system that operates as a special purpose controller when executing at least one program for broadcasting information. The communications protocol includes an access point location, an access point Internet protocol (IP) address, a media access control (MAC) address, a number of access point radios, and a radio type protocol of each access point radio.

System and Method for Multi-Access

Abstract: A system and a method allowing a user terminal (18) in a network to simultaneously access a plurality of radio based access networks (19, 20) of diverse access technologies. Characteristic features of the invention are access selection adapters (22, 23), each one associated with a respective radio based access network, and an access technology independent access selector (26). An access adapter has means (32) for receiving access technology dependant information from its respective access network and means (31) for translating the information into access technology independent status information. The access selector comprises an access selection algorithm (33) interacting with applications (27) resident in the user terminal and with each access adapter for selection of a radio access network based on an individual QoS profile associated with each respective application and on said access technology independent status information. The invention also relates to a method for service scheduling.

A new measurement-based admission control method for IEEE802.11 wireless local area networks

Abstract: The upcoming IEEE 802.11e standard supports the applications with QoS requirements by using differentiated medium access mechanism for different traffic categories. In order to protect the high priority data flows and improve network performance in a heavy-loaded IEEE 802.11e network, a new measurement-based distributed call admission control method is introduced in this paper. The proposed method is based on the measurement of the existing traffic load over IEEE 802.11e network. Depending on the amount of the existing traffic load, the admission controller decides whether or not to allow a data unit to have the right to access the wireless medium. The simulation results show that the proposed mechanism works well.

Multi-rate aware routing protocol for mobile ad hoc networks

Abstract: This paper introduces multi-rate aware routing scheme that helps to improve the resource utilization and to minimize the power consumption in mobile ad hoc networks (MANET). The existing MANET routing protocols (e.g., AODV, DSR, and TORA) attempt to minimize the number of hops between source-destination pairs. These routing protocols are all designed under the assumption of using only single data rate in the wireless channel (e.g., IEEE 802.11). Currently, 802.11b supports the various data rate, 11 Mbps, 5.5 Mbps, 2 Mbps and 1 Mbps according to channel conditions between mobile terminals, through several modulation schemes that are optimized for channel conditions. So if we utilize this multi-rate support from MAC and physical layers when packets are routed in mobile ad hoc networks, we can achieve better performance in throughput and resource utilization. In this paper, we propose a multi-rate aware sub layer (MAS), which is independent of IP protocol and enables the full utilization of the multi-rate channel characteristics. The key function of MAS is to change the next hop node to another node through which higher data rates are available, in the basis of two-hop neighbor information and link states. We show through simulation that multi-rate aware protocol outperforms traditional MANET routing protocols due to its utilization of multi-rate support.

TRACE: time reservation using adaptive control for energy efficiency

Abstract: Time reservation using adaptive control for energy efficiency (TRACE) is a time frame based media access control (MAC) protocol designed primarily for energy-efficient reliable real-time voice packet broadcasting in a peer-to-peer, single-hop infrastructureless radio network. Such networks have many application areas for various scenarios that obey a strongly connected group mobility model, such as interactive group trips, small military or security units, and mobile groups of hearing impaired people. TRACE is a centralized MAC protocol that separates contention and data transmission, providing high throughput, bounded delay, and stability under a wide range of data traffic. Furthermore, TRACE uses dynamic scheduling of data transmissions and data summarization prior to data transmission to achieve energy efficiency, which is crucial for battery operated lightweight radios. In addition, energy dissipation is evenly distributed among the nodes by switching network controllers when the energy from the current controller is lower than other nodes in the network, and reliability is achieved through automatic controller backup features. TRACE can support multiple levels of quality-of-service, and minimum bandwidth and maximum delay for voice packets are guaranteed to be within certain bounds. In this paper, we describe TRACE in detail and evaluate its performance through computer simulations and theoretical analysis.

Method for supporting traffics with different quality of service by high speed down link packet access system

Abstract: PROBLEM TO BE SOLVED: To provide a service of traffics with a different quality in an REL system of the third generation of a mobile communication system. SOLUTION: On the basis of the request condition of the service, the setting request of a radio link is transferred from a core network successively to a service radio network controller, a control radio network controller and a base station and on the basis of the service condition, data scheduling is performed on the media access control layer of the base station in a high speed down link packet access system (HSDPA). COPYRIGHT: (C)2003,JPO

Method of minimizing reverse channel interference caused by an abnormally high number of access attempts in a wireless communications system

Abstract: When an overload condition is determined to exist at a base station in a wireless communications system based on the number of unsuccessful access attempts to access the system relative to the successful access attempts to access the system, the base station broadcasts a message to each mobile terminal within its coverage area that changes at least one access probe-related parameter associated with at least one of: the number, the frequency, and the power intensity of the access probes made by these mobile terminals as they attempt to establish access to the wireless network. By so limiting these access probes in some manner when an overload condition is present, the interference caused on the reverse link by many mobile terminals attempting access is reduced.

Video Streaming over Wireless LANs: A Cross-layer Approach

Abstract: Robust streaming of video over 802.11 Wireless Local Area Networks (WLAN) poses many challenges, including coping with bandwidth variations, data losses and heterogeneity of the receivers. Currently, each network layer (including physical layer, media access control, transport, and application layers) provides a separate solution to these challenges by providing its own optimized adaptation and protection mechanisms. However, this layered strategy does not always result in an optimal overall performance for the transmission of video. Moreover, certain protection strategies can be implemented simultaneously in several layers, and hence the optimal choices from the application and complexity perspective need to be identified. In this paper, we evaluate different error control and adaptation mechanisms available in the different layers for robust transmission of video, namely Media Access Control (MAC) retransmission strategy, application-layer Forward Error Correction (FEC), bandwidth-adaptive compression using scalable coding, and adaptive packetization strategies. Subsequently, we propose a novel adaptive cross-layer protection strategy for enhancing the robustness and efficiency of scalable video transmission by performing tradeoffs between throughput, reliability and delay depending on the channel conditions and application requirements. The results obtained using the proposed adaptive cross-layer protection strategies show a significantly improved visual performance for the transmitted video over a variety of channel conditions.

Distributed Energy Aware MAC Layer Protocol for Wireless Sensor Networks.

Abstract: Due to the fact that sensor nodes are untethered and unattended, energy management is a critical issue in communication mechanism of a wireless sensor network. In this paper, we address this problem and propose a novel solution based on media access control technique. Our protocol DE-MAC exploits the inherent features of TDMA to avoid the main sources of energy wastage: collision and control packet overhead. It uses the concept of periodic listen and sleep in order to avoid idle listening and overhearing. However, unlike existing MAC-layer protocols, DE-MAC treats the critical nodes differently in a distributed manner. Motivated by the fact that a weaker node should be used less frequently in a routing in order to accomplish load balancing, DE-MAC performs a local election procedure and chooses the worstoff node/nodes as the winner/winners and makes them sleep more than the other neighboring nodes. Since the election procedure is fully integrated with the TDMA slot assignment, our protocol suffers no extra throughput loss. We evaluate DE-MAC and present the simulation results which explicitly show the gain in performance.

An analytical model for IEEE 802.11e EDCF differential services

Abstract: Having been originally developed as an extension of the wired LANs, IEEE 802.11 lacks support for QoS and differential services. Since its introduction various extensions and modifications have been studied to address this current need and the IEEE 802.11 Task Group E is responsible for developing a QoS-aware MAC protocol that considers several service differentiation mechanisms. In this paper, we first consider the enhanced DCF access method of IEEE 802.11e. We then introduce an analytical model, which can be used to calculate the traffic priority and throughput corresponding to the configuration of multiple DCF contention parameters under saturation condition. A detailed simulation is provided to validate the proposed model.

Access network delay in networked games

Abstract: The end-to-end delay (also referred to as latency) experienced by gaming users has a significant impact on the quality of online games. In this paper we concentrate on the delay introduced in access networks. This access network delay depends on the access technology used, the network load, the link rate configured on the access links (also referred to as the last mile link) and the size of the packets generated by the games. We characterize this access network delay by means of measurements. First, we focus on this delay in actually deployed access networks: dial-up, cable and Asymmetric Digital Subscriber Line (ADSL) access. In these access networks the access network delay shoots up as soon as the gaming user (or somebody else on the user's home network) saturates the user's last mile link with traffic generated by applications (e.g. web browser) other than the games. Therefore, we also characterize the access network delay in a laboratory set-up of a QoS-enabled ADSL network. In this set-up we show that it is possible to (logically) segregate the game traffic from the other traffic to such an extent that the game packets are not excessively delayed while at the same time a large part of the link capacity can be consumed by the other traffic.

Multi-access call setup

Abstract: In a multi-access communication system (1), a terminal (30) is kept reachable through a first access network (10), which is most resource efficient one of the available access networks for keeping the terminal reachable. The terminal scans passively for the existence of usable base stations (24) for other access networks (20) of the system 81) and reports data associated with such existences to the first access network (10). When a request for a call to the temrinal (30) is received, a paging is performed in the first access network (10). The paging message comprises information about preferred access network, based on the reported data of the existence of usable base stations or access points (24) of other access networks (20). The terminal (30) connects to the preferred access network and performs a call set-up directly in the preferred access network.