EP B1 (19) (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION

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1 (19) (12) EUROPEAN PATENT SPECIFICATION (11) EP B1 (4) Date of publication and mention of the grant of the patent: Bulletin /39 (21) Application number: (22) Date of filing: (1) Int Cl.: H04W 76/02 (09.01) (86) International application number: PCT/US03/ (87) International publication number: WO 0/0649 ( Gazette 0/28) (4) A METHOD AND APPARATUS FOR PROVIDING QUALITY OF SERVICE TO VoIP OVER WIRELESS LANs VERFAHREN UND VORRICHTUNG ZUR BEREITSTELLUNG VON DIENSTQUALITÄT FÜR VOIP ÜBER DRAHTLOSE LANS PROCEDE ET APPAREIL FOURNISSANT UNE QUALITE DE SERVICE A DES RESEAUX VOIX SUR IP SUR RESEAUX LOCAUX SANS FIL EP B1 (84) Designated Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR (43) Date of publication of application: Bulletin 06/4 (73) Proprietor: Lenovo (Singapore) Pte. Ltd. Singapore 6741 (SG) (72) Inventors: ARUP, Acharya Nanuet, NY 32 (US) DILIP, Kandlur Yorktown Heights, NY 98 (US) ZON-YIN, Shae South Salem, NY 90 (US) (74) Representative: Schäfer, Horst Schweiger & Partner Patent- und Rechtsanwälte Karlstrasse München (DE) (6) References cited: WO-A-02/ WO-A-03/ US-A US-A US-A US-A POLITIS C ET AL: "Multilayer mobility management for all-ip networks: pure SIP vs. hybrid SIP/mobile IP" VTC 03-SPRING. THE 7TH. IEEE SEMIANNUAL VEHICULAR TECHNOLOGY CONFERENCE. PROCEEDINGS. JEJU, KOREA, APRIL 22-2, 03, IEEE VEHICULAR TECHNOLGY CONFERENCE, NEW YORK, NY : IEEE, US, vol. VOL. 4 OF 4. CONF. 7, 22 April 03 ( ), pages , XP ISBN: KEDMENEC D ET AL: "Issues concerning usability of networks for real-time service transport" VIDEO/IMAGE PROCESSING AND MULTIMEDIA COMMUNICATIONS, 03. 4TH EURASIP CONFERENCE FOCUSED ON 2- JULY 03, PISCATAWAY, NJ, USA,IEEE, vol. 2, 2 July 03 ( ), pages 83-88, XP ISBN: GRILO A ET AL: "IP QoS support in IEEE b WLANs" COMPUTER COMMUNICATIONS, ELSEVIER SCIENCE PUBLISHERS BV, AMSTERDAM, NL, vol. 26, no. 17, 1 November 03 ( ), pages , XP ISSN: Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). Printed by Jouve, 7001 PARIS (FR)

2 1 EP B1 2 Description BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to computer networks, and, more particularly, to voice-over-ip networks over wireless local area networks. 2. Description of the Related Art [0002] Traditional telephony carriers, which primarily utilize a public-switched telephony network ("PSTN"), are moving towards a packet-based Voice-over-IP ("VoIP") infrastructure. A key component of a typical telephony infrastructure is "call control." Call control comprises a call setup and a call teardown. Both the call setup and the call teardown involve an exchange of call control messages between two end users. Either end user may initiate the setup or teardown. The call setup allocates resources for the exchange of voice and/or data between the two end users. In contrast, the call teardown frees up those resources such that other end users may exchange voice and/or data. In VoIP, call control is achieved through Session Initiation Protocol ("SIP"). It should be noted that one of ordinary skill in the are would contemplate achieving call control through any of a variety of other known protocols. [0003] In addition to carrier networks, VoIP has been steadily ground in enterprise networks as well. In parallel with the adoption of VoIP, many enterprise networks are in the process of deploying support network access via IEEE based wireless local area networks ("LANs"). The wireless LAN standard offers a medium access method, called Point Coordination Function ("PCF"), that offers support for near-isochronous (i.e., real-time) services where an "Access Point" periodically polls individual stations for packets to transmit. However, there has been little deployment of VoIP over wireless LANs using PCF. A key reason is that most Access Points support a medium access method known as Distributed Coordination Function ("DCF"), that is contention-based, i.e., each wireless station competes for control of the wireless medium. While the DCF method works for data packets, VoIP packets, on the other hand, require timely, periodic access to the wireless medium to maintain acceptable voice quality. With increasing use of wireless LANs in the enterprise, use of IP softphones, for example, on enabled laptops and handheld devices to initiate and receive VoIP calls will explode. [0004] It is well understood that quality of service ("QoS") is required for voice traffic in terms of delay, jitter and loss. At the same time, bandwidth on wireless links is far below that of wireline links (e.g., ethernet), and, therefore, uncontrolled access to the wireless medium can introduce unacceptable delay for VoIP traffic. [000] Therefore, to make efficient use of wireless resources and provide real-time services for VoIP packets, a need exists for a method and apparatus to manage the contention resulting from VoIP call signaling on the wireless medium. Without a solution to this problem, voice quality for VoIP calls over wireless LANs will degrade to unacceptable levels as the data/voice traffic on the wireless link increases. In other words, the method and apparatus should provide sufficient QoS to support wireless voice quality comparable to that of wireline links, even in the prospect of reduced wireless bandwidth. [0006] The document WO 03/ A1 shows an apparatus and a method for providing Quality of Service for an IEEE e MAC layer. An upstream signalling goes through a quality of service basic service set. Depend end on the Quality of Service parameter a connection request is started, renegotiated or dropped. [0007] The US 03/ A1 shows a communication network wherein an proxy server response to a signalling message is done by extracting a set of data from a data store and making the set of data available for use by the application server. [0008] US 03/ A1 describes a session initiation protocol (SIP) network in which a SIP invite message from a calling party is sent to a SIP proxy server to be forwarded to the called party. [0009] D. Chen et al "Supporting VBR VoiP Traffic in IEEE WLAN in PCF Mode", July 02 pages 1 to 6 discloses an investigation of the capability of PCF mode in support of variable bit rate (VBR) VoiP traffic where the silence compression technique is employed in voice codecs so that no packets are generated in a silence period. SUMMARY OF THE INVENTION [00] In one aspect of the present invention, a method for providing quality-of-service to VoIP over a wireless local access network is provided. The method comprises sending an invite message from a calling party to a SIP proxy server and determining whether voice slots are available on an access point data packets from and to the access point being sent in frames comprising a contention-free period and a contention period. The method forwards the invite message from the SIP proxy server to a called party, and if the called party sends an acknowledgement message to a calling party in response to receiving the invite message, the method adds the calling party to the polling list of the access point, and sends packets to and receives packets from the called party during a contention-free period of the access point. [0011] In another aspect of the present invention, a machine-readable medium having instructions stored thereon for execution by a processor to perform a method for providing quality-of-service to VoIP over a wireless local access network is provided. The medium contains instructions for sending an invite message from a calling party to a SIP proxy server and determining whether voice slots are available on an access point data packets 2

3 3 EP B1 4 from and to the access point being sent in frames comprising a contention-free period and a contention period. The medium contains instructions for forwarding the invite message from the SIP proxy server to a called party, and if the called party sends an acknowledgement message to a calling party in response to receiving the invite message, the medium contains instructions for adding the calling party to the polling list of the access point, and sending packets to and receiving packets from the called party during a contention-free period of the access point. [0012] In yet another aspect of the present invention, a system for providing quality-of-service to VoIP over a wireless local access network is provided. The system contains means for sending an invite message from a calling party to a SIP proxy server and means for determining whether voice slots are available on an access point data packets from and to the access point being sent in frames comprising a contention-free period and a contention period. The system contains means for forwarding the invite message from the SIP proxy server to a called party, and if the called party sends an acknowledgement message to a calling party in response to receiving the invite message, the system contains means for adding the calling party to the polling list of the access point, and means for sending packets to and receiving packets from the called party during a contention-free period of the access point. BRIEF DESCRIPTION OF THE DRAWINGS [0013] The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: Figure 1 is an exemplary SIP configuration, in accordance with one embodiment of the present invention; Figure 2 is an exemplary operation of a superframe based on the IEEE standard, in accordance with one embodiment of the present invention; and Figure 3 is an exemplary SIP configuration, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBOD- IMENTS [0014] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a outine undertaking for those of ordinary skill in the art having the benefit of this disclosure. [001] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. [0016] It is to be understood that the systems and methods described herein may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. In particular, the present invention is preferably implemented as an application comprising program instructions that are tangibly embodied on one or more program storage devices (e.g., hard disk, magnetic floppy disk, RAM, ROM, CD ROM, etc.) and executable by any device or machine comprising suitable architecture, such as a general purpose digital computer having a processor, memory, and input/output interfaces. It is to be further understood that, because some of the constituent system components and process steps depicted in the accompanying Figures are preferably implemented in software, the connections between system modules (or the logic flow of method steps) may differ depending upon the manner in which the present invention is programmed. Given the teachers herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations of the present invention. [0017] As explained in greater detail in the disclosure herein, the present invention generally provides quality of service ("QoS") to Voice-over-IP ("VoIP") over an wireless local area network ("LAN") by providing periodic, contention-free access to a wireless link for voice packets. This is achieved by coupling Session Initiation Protocol ("SIP") signaling for call setup with the Point Coordination Function ("PCF") mode of operation of the medium access control ("MAC"). The result is that VoIP call signaling via SIP is tied with availability of periodic time-slots on the wireless medium. The periodic time-slots are used to guarantee contention-free access to the wireless link for voice packets. [0018] Accordingly, the present invention, in effect, merges two networking technologies: SIP-based VoIP and based wireless LANs. A brief overview of both technologies will now be presented. [0019] Referring now to Figure 1, an exemplary SIP configuration 0 is illustrated, in accordance with one embodiment of the present invention. SIP is a signaling protocol for VoIP. SIP comprises call messages for call setup, such as "INVITE," and for call teardown, such as "BYE." The call messages are usually sent as UDP/IP packets. [00] An exemplary call setup is described as follows. A first call endpoint ("user agent") such as an IP Phone or a laptop running an IP softphone, registers with a first SIP Proxy 1 using a SIP REGISTER message (e.g., an INVITE message). The first SIP Proxy is respon- 3

4 EP B sible for routing the INVITE message via a second SIP Proxy 11 to a second call endpoint 1. It is understood that although only two SIP Proxies 1, 11 are shown in Figure 1, any number of SIP Proxies may be used, as is known to those skilled in the art, for routing the INVITE message to the second call endpoint 1. When the second call endpoint 1 receives the INVITE message, the second call endpoint 1 initiates a SIP "0 (OK)" message, which is routed via the SIP Proxies 1, 11 to the first call endpoint. When the first call endpoint 1 receives the "0 (OK)" message, the first call endpoint initiates a SIP "ACK" message, which is routed via the SIP Proxies 1, 11 to the second call endpoint 1. When the "ACK" message reaches the first call endpoint, the call setup has succeeded. The three SIP messages (i.e., INVITE, 0 (OK), ACK) may carry a Session Description Protocol ("SDP") payload describing an IP address and associated port numbers of the first call endpoint and the second call endpoint 1. The SDP can also carry one or more media characteristics, such as codec type. [0021] Once the call setup succeeds, voice packets may be sent as RTP/UDP/IP packets directly between the first call endpoint and the second call endpoint 1 via the RTP/UDP/IP media path. When it is desired to terminate the call setup (i.e., initiate a call teardown), either the first call endpoint or the second call endpoint 1 sends a "BYE" message to the other endpoint via the SIP Proxies 1, 11. As shown in Figure 1, the second call endpoint 1 initiates the call teardown by sending a "BYE" message to the first call endpoint via the second SIP Proxy 11 and the first SIP Proxy 1. The call teardown succeeds when the second call endpoint 1 receives the 0 (OK) message wireless LANs ("walls"), when used in infrastructure mode, as is generally the case for enterprise networks, comprise one or more client machines ("stations") and a central Access Point ("AP") (not shown). A medium access protocol ("MAC") specifies which station is to gain access to a wireless link (not shown) to transmit a packet. Two modes of medium access specified for include a Distributed Coordination Function ("DCF") and a Point Coordination Function ("PCF"). In DCF mode, the stations contend with each other to gain channel access. Alternatively, in PCF mode, a central Point Coordinator ("PC") polls one of the stations (known as a "polled station") contained in a polling list of the PC. The polled station gains exclusive access to the wireless link for packet transmission/reception. The PC functionality is typically implemented in the AP. That is, the AP runs as the PC during the PCF mode. When polling the station, the PC may send a data packet to the station. Additionally, the PC may provide access to the polled station to transmit another data packet to the PC without contention from unpolled stations. This period of time where the polled station may transmit the data packet is known as a contention-free period ("CFP"). The CFP for a polled station is generally followed and/or preceded by a contention period ("CP"), in which the polled station becomes an unpolled station. That is, in the CP, the station does not have access to transmit the data packet. A "contention repetition interval" comprises a contention-free period and a contention period. [0022] The stations express their intent to the PC to be on the polling list by sending MAC management frames (i.e., control messages) to the PC. The MAC management frames comprise, among other requests, an Association Request and a Re-association Request, as is known to those skilled in the art. There are two subfields in the Association Request and the Re-association Request management frames (hereinafter "(re)assocation management frames") that allow a station to express its interest to the PC to be included in the polling list. The two subfields are CF-Pollable and CF-Poll Request, which are located in the Capatibility Information field of the (re)association management frames. The (re)association management frames are used to associate or reassociate a station with the AP. If the CF-Pollable subfield is set to 1 and the CF-Poll Request subfield is set to 0, this indicates that the station delivering the message is interested in sending and receiving packets to and from the AP during the CFP. [0023] Referring now to Figure 2, an exemplary operation of a superframe 0 based on the IEEE standard is illustrated. The superframe 0 is a logical representation of data/voice packet transmissions between a client and an AP. The superframe 0 comprises one or more time intervals known as a contention repetition interval. The contention repetition interval comprises a CFP 2 and a CP 21. During the CFP 2, PCF mode is ideally used. This is because the CFP 2 is generally intended for use by time-critical traffic such as voice packets. While in the CP 21, DCF mode is ideally used. This is because the CP 21 is generally intended for use by data traffic. [0024] Current enterprise networks deploy wlans using only the DCF mode, i.e., stations contend with each other to send packets to the AP. With DCF, there is no arbitration of wireless access by the AP, and the entire operation proceeds solely in CP. If SIP-based VOIP is deployed on DCF network, voice packets from one station may contend for channel access with other packets (voice and data) from other stations. Consequently, due to the nature of contention-based medium access, such as exponential back-off with retry attempts, voice packets may be delayed and not receive adequate QoS. Additionally, because there is no coupling of SIP call control and utlization/load on the wireless link, admitting a new voice call during high utilization of the wireless link leads to lost packets, which leads to poor voice quality. [002] Given the above overview of SIP-based VoIP, wireless LANs, and the problems associated with supporting VoIP over wlans, the present invention will now be described. In one aspect of the present invention, SIP signaling is coupled with availability of resources on the wireless link using specific MAC mechanisms before a 4

5 7 EP B1 8 VoIP call is admitted. Core VoIP requires a signaling phase (usually via SIP) prior to media exchange between endpoints. The present invention can ensure that the VoIP call setup signaling succeeds only if a periodic time slot can be allocated on the wireless link using PCF. Instead of treating VoIP call setup and wireless medium access independently, availability of wireless resources is tied with VoIP call setup to ensure that if the call setup goes through, then adequate QoS is available on a wireless link for the VoIP call. The present invention integrates VoIP call control with a specific medium access method on a wlan link that can offer periodic allocation of bandwidth for VoIP packets in a timely fashion. [0026] Referring now to Figure 3, a SIP configuration 0 is shown, in accordance with one embodiment of the present invention. SIP is a call-signaling protocol for VoIP. Two AP s (a first AP 3 and a second AP 31) support a superframe comprising of CFP and CP periods, as described in greater detail in Figure 2. As previously stated, PCF mode is generally used during CFP while DCF mode is generally used during CP. Two wlan enabled SIP clients 3 (e.g., a laptop with a wlan card and a IP softphone) are shown in Figure 3: a calling party 32 (associated with the first AP 3) and a called party 3 (associated with the second AP 31). Although only two SIP clients 3 are shown in Figure 3, it is understood that a typical SIP configuration may comprise any number of SIP clients 3. Further, although in Figure 3 each SIP client 3 is associated with its own AP, one or more SIP clients 3 may be associated with a single AP. [0027] The calling party 32 sends a SIP INVITE message to an SIP Proxy Server 3 using the CP on a wireless link 34. The SIP Proxy Server 3 has a control connection to the AP for querying the AP of ongoing VoIP calls (i.e., the current calls in progress). The control connection may use any of a variety of communication protocols (e.g., client-server, http, etc.). The control connection is used for sending and/or receiving control protocol messages. Alternatively, the SIP Proxy Server 3 may internally keep track of ongoing (i.e., current) VoIP calls. Information of the current calls in progress in the AP is used to determine the number of available voice slots in the AP. Whether voice slots are available given the number of current calls in progress" varies upon implementation of the call itself (e.g., the bit rate of a voice call) and the AP, as is known to those skilled in the art. [0028] Based on current load on the AP in terms of available voice slots on the superframe 0 of Figure 2, the SIP Proxy Server 3 can either accept the SIP INVITE message for further processing or deny the call setup request. This ensures that if the call setup request is accepted, the calling party 32 will receive adequate time slots on the superframe to ensure that VoIP packets (i.e., voice packets) sent from the calling party 32 to the first AP 3 are not delayed. The VoIP packets are sent within a wireless coverage 3 of the AP [0029] Following a successful call setup, the calling party 32 adds itself to the polling list of the PC (typically implemented in the AP ) using MAC management frames. It is understood that there may be another SIP Proxy Server (not shown) associated with the called party 3 and the second AP 31. The SIP Proxy Server 3 and the first AP 3 are shown in Figure 3 as two separate machines. However, it is further understood that the SIP Proxy Server 3 and the first AP 3 may reside on the same machine. In the case of the SIP Proxy Server 3 and the first AP 3 residing on the same machine, it is understood that the communication protocol may not be necessary. [00] When either of the SIP clients 3 (i.e., the calling party 32 and the called party 3) terminates the call by sending a BYE SIP message to the SIP Proxy Server 3 on the wireless link 34, that SIP client 3 will also send a MAC management frame to the SIP Proxy Server 3 to remove itself from the list of stations polled by the PC (typically implemented in the AP ) in the CFP. As a result, the PC does not waste time during the CFP to poll a station that is not in a voice call. [0031] In addition to the calling party 32 adding itself to the polling list of the PC following a successful call setup, a similar action can be taken by the called party 3. The second AP 31 (which is connected to the called party 3) receives a SIP INVITE message sent from the calling party 32 via a router 360. The connections between the two APs and the router 360 is typically a wireline link 362. The second AP 31 forwards the SIP INVITE message to the called party 3. The second AP 31 takes this action only if it can add the called party 3 to the polling list during the CFP. In other words, the AP allows the call setup to go through only if the superframes are able to ensure that the voice packets 3 for this call can be transmitted periodically without contention. Thus, after the called party 3 receives the SIP INVITE and accepts the call by sending an ACK message via the wireless link 34 (as described in Figure 1), the called party 3 sends a MAC management frame to a PC requesting to be added to the polling list of the PC. [0032] It should be noted that the present invention applies when either or both SIP clients 3 are connected to a wireless network. When both SIP clients 3 are on wireless LANs, they each send MAC management frames to their respective APs so that their incoming and outgoing voice traffic is sent on the wireless link in PCF mode. When only one of the SIP clients 3 of a voice call is on a wireless link, then only that SIP client 3 can make use of this invention. [0033] In addition to providing QoS on the wireless link, an extension to the scheme described herein is to couple the QoS on the wireless link with QoS on the wireline channel. In enterprise networks, QoS on wireline networks is typically achieved by using separate virtual LANs ("VLANs") 36 for data and voice. This is because enterprise networks typically use a switched network such as a switched ethernet. Alternatively, enterprise net-

6 9 EP B1 works may use packet level QoS such as Differentiated Services. The Differentiated Services field of an IP header of the packet (previously known as Type-of-Service or "TOS" field) can be instantiated with different code points (Differentiated Service Code Point or "DSCP") to tag packets with different levels of QoS. With the present invention, packets on the wireless link that are received at the AP from a wireless client during CFP can automatically be placed on the voice VLAN 36 on the wireline side (if the enterprise network is a switched ethernet) or tagged with an appropriate DCSP codepoint for voice level QoS (if the enterprise network uses Differentiated Services). Thus, the present scheme of prioritizing packets on the wireless link 34 can be coupled with the QoS mechanism being used in the wireline side to provide seamless QoS between the wireless and wireline portions of an enterprise network. [0034] An additional aspect of our invention relates to mobility of a wireless station between the different APs (e.g., the first AP 3 and the second AP 31), while a VoIP call is in progress. For example, the calling party 32 could move from the range of the first AP 3 to the range of the second AP 31. There are two scenarios: 1) the APs belong to the same IP subnet and 2) the APs belong to different IP subnets. [003] In the first scenario, MAC management frames are used to forward packets to a wireless station (e.g., the calling partying 32, the called party 3). The IP address of the client remains unchanged. As mentioned earlier, if the wireless station changes its AP while a VoIP call is in progress, it re-associates with the "new" AP using a Re-association Request such that the client is directly added to the polling list at the new AP (implementing the PC). In other words, the wireless station does not do a SIP level call setup before adding itself to the polling list at the new PC. This is because as far as the SIP session is concerned, the IP address of the wireless station is unchanged. That is, the wireless station re-associates with the new PC directly in PCF mode. [0036] In the second scenario, the IP address of the wireless station changes. Therefore, the wireless station needs to send a SIP RE-INVITE message to the other wireless station. This message can be sent only after the client has associated itself with the new AP. SIP RE- INVITE is a SIP call setup message after an INVITE message has already been sent. It should be noted that the MAC level management frame that is sent is an Association Request rather than a Re-Association request since the new and the previous APs do not have any association, a new association needs to be created between the wireless station and the new AP. That is, the Association Request is sent to the new AP with the CF-Pollable and CF Poll-Request subfields of the Capability Information field set such that the wireless station is directly added to the polling list of the PC at the new AP. This allows voice packets of the ongoing call to be transmitted on the wireless link without contention. [0037] Yet another aspect of present invention relates to how the AP determines which packets of a wireless station should be sent using the PCF mode. When a wireless station is added to the polling list of the PC, it is polled by the PC to check if it has any packet to transmit. It can potentially send either a data packet or a voice packet. Similarly when a particular wireless station s turn is reached in the polling list, the corresponding AP is free to transmit any packet to the wireless client. However, it may be wasteful if the CFP is used to transmit packets (either to or from a wireless station) that do not need QoS (e.g., data packets). Thus, the additional mechanism proposed herein is that when a wireless station is polled by the PC, only voice packets should be transmitted. This is easily achieved for packets on the "uplink" (i.e., from a wireless station to the AP) because the station, as part of the SIP call setup, is aware of the tuple <Source IP Address, Source Port#, Destination IP Address, Destination Port#>, and any packet with a matching 4-tuple belongs to the voice call and is sent during the PCF. Thus, it is easy to identify voice packets from data packets on the wireless station side. As used herein, the term "wireless station side" refers to the period that the wireless station transmits packets to the AP, and the term "AP side" refers to the period that the AP transmits packets to the wireless station. [0038] On the AP side, identifying voice packets from data packets is generally not straightforward. However, with the present scheme of integrating the SIP proxy with the wireless AP, either on the same machine or on different machines with a control connection, as described herein, the AP is able to distinguish voice packets from data packets. This is possible because SIP INVITE and ACK messages contain the IP address and port numbers of both endpoints. Thus, when SIP INVITE and ACK messages flow through the SIP Proxy on the AP, it keeps track of the IP address and port# that will be used by each point. This enables the PC to distinguish voice packets from data packets on the "downlink" (i.e., from the AP to a wireless station). Any packet that matches the IP address and port pairs will be sent using the PCF mode. All other packets will be sent using the DCF mode. It should be further noted that the type of client device to which this invention can be applied may include any device with both a wireless LAN connection and a SIPbased IP Phone. Claims 1. A method for providing quality-of-service to VoIP over a wireless local access network,, comprising: sending a SIP INVITE message from a calling party (32) to a SIP proxy server (3); determining whether voice slots are available on an access point (), data packets from and to the access point being sent in frames comprising a contention-free period and a contention peri- 6

7 11 EP B1 12 od; if voice slots are available on the access point (), forwarding the SIP INVITE message from the SIP proxy server (3) to a called party (3), and if the called party (3) sends an acknowledgement message to the calling party (32) in response to receiving the SIP INVITE message, adding the calling party (32) to the polling list of the access point (), and sending packets to and receiving packets from the called party (3) during a contention-free period of the access point (). 2. The method of claim 1, further comprising if the voice slots are not available on the access point (), sending a termination message from the SIP proxy server (3) to the called party (3). 3. The method of claim 1, wherein if the called party (3) sends an acknowledgement message to a calling party (32) in response to receiving the SIP IN- VITE message comprises if the called party (3) sends a SIP ACK message to a calling party (32) in response to receiving the SIP INVITE message. 4. The method of claim 1, wherein sending a termination message from the SIP proxy server (3) to the called party (3) comprises sending a SIP BYE message from the SIP proxy server (3) to the called party (3).. The method of claim 1, wherein adding the calling party (32) to the polling list of the access point () comprises sending a MAC management frame from the calling party (32) to the access point () requesting the calling party (32) be added to the polling list. 6. The method of claim, wherein sending a MAC management frame from the calling party (32) to the access point () requesting the calling party (32) to be added to the polling list comprises sending a MAC management frame from the calling party (32) to a point coordinator of the access point (). 7. The method of claim 1, further comprising adding the called party (3) to the polling list of the access point (). 8. The method of claim 7, wherein adding the called party (3) to the polling list of the access point () comprises sending a MAC management frame from the called party (3) to the access point () requesting the called party (3) be added to the polling list The method of claim 8, wherein sending a MAC management frame from the called party (3) to the access point () requesting the called party (3) be added to the polling list comprises sending a MAC management frame from the called party (3) to a point coordinator of the access point ().. The method of claim 1, further comprising adding the called party (3) to the polling list of a new access point (31). 11. The method of claim, wherein adding the called party (3) to the polling list of the new access point (31) comprises sending a MAC management frame from the called party (3) to the new access point (31) requesting the called party (3) be added to the polling list. 12. The method of claim 11, wherein sending a MAC management frame from the called party (3) to the new access point (31) requesting the called party (3) be added to the polling list comprises sending a MAC management frame from the called party (3) to a point coordinator of the new access point (31). 13. The method of claim 1, further comprising if the voice slots are available on the access point (31), at least one of sending a termination message from the called party (3) to the calling party (32) and sending a termination message from the calling party (32 to the called party (3). 14. The method of claim 13, wherein at least one of sending a termination message from the called party (3) to the calling party (32) and sending a termination message from the calling party (32) to the called party (3) comprises at least one of sending a SIP BYE message from the called party (3) to the calling party (32) and sending a termination message from the calling party (32) to the called party (3). 1. The method of claim 14, further comprising if at least one of the calling party (32) and the called party (3) sends a confirmation message, removing at least one of the calling party (32) and the called party (3) from the polling list of the access point (). 16. The method of claim 1, wherein if at least one of the calling party (32) and the called party (3) sends a confirmation message comprises if at least one of the calling party (32) and the called party (3) sends a SIP OK message. 17. The method of claim 1, wherein removing at least one of the calling party (32) and the called party (3) from the polling list of the access point () 7

8 13 EP B1 14 comprises sending a MAC management frame from the at least one of the calling party (32) and the called party (3) to the access point () requesting the at least one of the calling party (32) and the called party (3) be removed from the polling list. 18. The method of claim 17, wherein sending a MAC management frame from the at least one of the calling party (32) and the called party (3) to the access point () requesting the at least one of the calling party (32) and the called party (3) be removed from the point coordinator of the polling list. 19. The method of claim 1, further comprising if the called party sends an acknowledgement message to a calling party (32) in response to receiving the SIP IN- VITE message, moving at least one of the calling party (32) and the called party (3) to a new access point in a same IP subnet, and adding the at least one of the calling party (32) and the called party (3) to the polling list of the new access point (31).. The method of claim 1, further comprising if the called party (3) sends an acknowledgement message to a calling party (32) in response to receiving the SIP INVITE message, moving at least one of the calling party (32) and the called party (3) to a new access point in a different IP subnet, adding the at least of one of the calling party (32) and the called party (3) to the polling list of the new access point, and sending a re-invite message to at least one of the calling party (32) and the called party (3). 21. The method of claim 1, wherein sending packets to and receiving packets from the calling party (32) during a contention-free period of the access point () comprises sending packets to the access point (), wherein the access point () forwards the packets to at least one of the called party (3) and the calling party (32). 22. The method of claim 21, wherein sending packets to the access point () further comprises sending packets from the access point () to a voice VLAN via a wireline network, wherein the wireline network is a switched network. 23. The method of claim 22, wherein sending packets to the access point () further comprises sending packets from the access point.() to a voice VLAN via a wireline network, wherein the wireline network is a switched ethernet The method of claim 23, wherein sending packets from the access point () to a voice VLAN via a wireline network further comprises sending packets from the access point () to a voice VLAN (36) via a wireline network using packet level quality-ofservice techniques. 2. The method of claim 24, wherein sending packets from the access point () to a voice VLAN (36) via a wireline network using packet level quality-ofservice techniques comprises sending packets from the access point () to a voice VLAN (36) via a wireline network using Differentiated Services. 26. A machine-readable medium having instructions stored thereon for execution by a processor to perform a method for providing quality-of-service to VoIP over a wireless local access network, comprising: sending a SIP INVITE message from a calling party (32) to a SIP proxy server (3); determining whether voice slots are available on an access point (), data packets from and to the access point being sent in frames comprising a contention-free period and a contention period; and if voice slots are available on the access point (), forwarding the SIP INVITE message from the SIP proxy server (3) to a called party (3), and if the called party (3) sends an acknowledgement message to a calling party (32) in response to receiving the SIP INVITE message, adding the calling party (32) to the polling list of the access point (), and sending packets to and receiving packets from the called party (3) during a contention-free period of the access point (). 27. The machine-readable medium of claim 26, wherein the method further comprises if the voice slots are not available on the access point (), sending a termination message from the SIP proxy server (3) to the called party (3). 28. An system for providing quality-of-service to VoIP over a wireless local access network, comprising: means for sending a SIP INVITE message from a calling party (32) to a SIP proxy server (3); means for determining whether voice slots are available on an access point () ), data packets from and to the access point being sent in frames comprising a contention-free period and a contention period; means for forwarding the SIP INVITE message from the SIP proxy server (3) to a called party (3) if voice slots are available on the access point, and if the called party (3) sends an acknowledgement message to a calling party (32) in response to receiving the SIP INVITE message, means for adding the calling party (32) to the 8

9 1 EP B1 16 polling list of the access point (), and means for sending packets to and receiving packets from the called party (3) during a contentionfree period of the access point (). 29. The system of claim 28, further comprising means for sending a termination message from the SIP proxy server (3) to the called party (3).. The system of claim 28, wherein one machine comprises the SIP proxy server (3) and the access point (3). 31. The system of claim 28, wherein a first machine comprises the SIP proxy server (3) and a second machine comprises the access point (3). 32. The system of claim 31, further comprising a communication protocol between the first machine and the second machine for allowing the SIP proxy server (3) and the access point (3) to communicate. Patentansprüche 1. Verfahren zur Bereitstellung von Dienstqualität für VoIP über ein drahtloses lokales Netzwerk, aufweisend: Senden einer SIP INVITE Nachricht von einem anrufenden Teilnehmer (32) an einen SIP Proxy-Server (3); Ermitteln, ob Sprach-Slots auf einem Zugangspunkt () verfügbar sind, wobei Datenpakete von und zu dem Zugangspunkt in Datenübertragungsblöcken, aufweisend einen kollisionsfreien Zeitraum und einen Zeitraum mit Kollision, gesendet werden; falls Sprach-Slots auf dem Zugangspunkt () verfügbar sind, Weiterleiten der SIP INVITE Nachricht von dem SIP Proxy-Server (3) an einen angerufenen Teilnehmer (3), und falls der angerufene Teilnehmer (3) eine Rückmeldungs-Nachricht an den anrufenden Teilnehmer (32) als Antwort auf den Empfang der SIP INVITE Nachricht sendet, Hinzufügen des anrufenden Teilnehmers (32) zu der Sendeaufrufs-Liste des Zugangspunkts () und Senden von Paketen an und Empfangen von Paketen von dem angerufenen Teilnehmer (3) während eines kollisionsfreien Zeitraums des Zugangspunkts (). 2. Verfahren nach Anspruch 1, weiterhin aufweisend, falls die Sprach-Slots auf dem Zugangspunkt () nicht verfügbar sind, ein Senden einer Beendigungs- Nachricht von dem SIP Proxy-Server (3) an den angerufenen Teilnehmer (3) Verfahren nach Anspruch 1, wobei falls der angerufene Teilnehmer (3) eine Rückmeldungs-Nachricht an einen anrufenden Teilnehmer (32) als Antwort auf die SIP INVITE Nachricht sendet beinhaltet falls der angerufene Teilnehmer (3) eine SIP ACK Nachricht an einen anrufenden Teilnehmer (32) als Antwort auf die SIP INVITE Nachricht sendet. 4. Verfahren nach Anspruch 1, wobei das Senden einer Beendigungs-Nachricht von dem SIP Proxy-Server (3) an den angerufenen Teilnehmer (3) ein Senden einer SIP BYE Nachricht von dem SIP Proxy- Server (3) an den angerufenen Teilnehmer (3) beinhaltet.. Verfahren nach Anspruch 1, wobei das Hinzufügen des anrufenden Teilnehmers (32) zu der Sendeaufrufs-Liste des Zugangspunkts () ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem anrufenden Teilnehmer (32) an den Zugangspunkt () mit der Anforderung, den anrufenden Teilnehmer (32) zu der Sendeaufrufs-Liste hinzuzufügen, beinhaltet. 6. Verfahren nach Anspruch, wobei das Senden eines MAC Leitungs-Datenübertragungsblocks von dem anrufenden Teilnehmer (32) an den Zugangspunkt () mit der Anforderung, den anrufenden Teilnehmer (32) zu der Sendeaufrufs-Liste hinzuzufügen, ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem anrufenden Teilnehmer (32) an einen Punkt-Koordinator des Zugangspunkts () beinhaltet. 7. Verfahren nach Anspruch 1, weiterhin aufweisend ein Hinzufügen des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste des Zugangspunkts (). 8. Verfahren nach Anspruch 7, wobei das Hinzufügen des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste des Zugangspunkts () ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an den Zugangspunkt () mit der Anforderung, den angerufenen Teilnehmer (3) zu der Sendeaufrufs-Liste hinzuzufügen, beinhaltet. 9. Verfahren nach Anspruch 8, wobei das Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an den Zugangspunkt () mit der Anforderung, den angerufenen Teilnehmer (3) zu der Sendeaufrufs-Liste hinzuzufügen, ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an einen Punkt-Koordinator des Zugangspunkts () beinhaltet. 9

10 17 EP B1 18. Verfahren nach Anspruch 1, weiterhin aufweisend ein Hinzufügen des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste eines neuen Zugangspunkts (31). 11. Verfahren nach Anspruch, wobei das Hinzufügen des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste des neuen Zugangspunkts (31) ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an den neuen Zugangspunkt (31) mit der Anforderung, den angerufenen Teilnehmer (3) zu der Sendeaufrufs-Liste hinzuzufügen, beinhaltet. 12. Verfahren nach Anspruch 11, wobei das Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an den neuen Zugangspunkt (31) mit der Anforderung, den angerufenen Teilnehmer (3) zu der Sendeaufrufs- Liste hinzuzufügen, ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem angerufenen Teilnehmer (3) an einen Punkt-Koordinator des neuen Zugangspunkts (31) beinhaltet. 13. Verfahren nach Anspruch 1, weiterhin aufweisend, falls die Sprach-Slots auf dem Zugangspunkt (31) verfügbar sind, zumindest eines aus einem Senden einer Beendigungs-Nachricht von dem angerufenen Teilnehmer (3) an den anrufenden Teilnehmer (32) und einem Senden einer Beendigungs-Nachricht von dem anrufenden Teilnehmer (32) an den angerufenen Teilnehmer (3). 14. Verfahren nach Anspruch 13, wobei zumindest eines aus einem Senden einer Beendigungs-Nachricht von dem angerufenen Teilnehmer (3) an den anrufenden Teilnehmer (32) und einem Senden einer Beendigungs-Nachricht von dem anrufenden Teilnehmer (32) an den angerufenen Teilnehmer (3) zumindest eines aus einem Senden einer SIP BYE Nachricht von dem angerufenen Teilnehmer (3) an den anrufenden Teilnehmer (32) und einem Senden einer Beendigungs-Nachricht von dem anrufenden Teilnehmer (32) an den angerufenen Teilnehmer (3) beinhaltet. 1. Verfahren nach Anspruch 14, weiterhin aufweisend, falls zumindest einer des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) eine Bestätigungs-Nachricht sendet, ein Entfernen zumindest eines des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) aus der Sendeaufrufs-Liste des Zugangspunkts (). 16. Verfahren nach Anspruch 1, wobei falls zumindest einer des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) eine Bestätigungs- Nachricht sendet beinhaltet, falls zumindest einer des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) eine SIP OK Nachricht sendet. 17. Verfahren nach Anspruch 1, wobei das Entfernen zumindest eines des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) aus der Sendeaufrufs-Liste des Zugangspunkts () ein Senden eines MAC Leitungs-Datenübertragungsblocks von dem zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) an den Zugangspunkt () mit der Anforderung, den zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) aus der Sendeaufrufs-Liste zu entfernen, beinhaltet. 18. Verfahren nach Anspruch 17, wobei das Senden eines MAC Leitungs-Datenübertragungsblocks von dem zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) an den Zugangspunkt () mit der Anforderung, den zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) aus dem Punkt-Koordinator der Sendeaufrufs-Liste zu entfernen, beinhaltet. 19. Verfahren nach Anspruch 1, weiterhin aufweisend, falls der angerufene Teilnehmer eine Rückmeldungs-Nachricht an den anrufenden Teilnehmer (32) als Antwort auf den Empfang der SIP INVITE Nachricht sendet, ein Verschieben zumindest eines des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) zu einem neuen Zugangspunkt in einem gleichen IP-Subnetz und ein Hinzufügen des zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste des neuen Zugangspunkts (31) beinhaltet.. Verfahren nach Anspruch 1, weiterhin aufweisend, falls der angerufene Teilnehmer (3) eine Rückmeldungs-Nachricht an den anrufenden Teilnehmer (32) als Antwort auf den Empfang der SIP INVITE Nachricht sendet, ein Verschieben zumindest eines des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) zu einem neuen Zugangspunkt in einem unterschiedlichen IP-Subnetz, ein Hinzufügen des zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) zu der Sendeaufrufs-Liste des neuen Zugangspunkts und ein Senden einer neuen Einladungs-Nachricht an zumindest einen des anrufenden Teilnehmers (32) und des angerufenen Teilnehmers (3) beinhaltet. 21. Verfahren nach Anspruch 1, wobei das Senden von Paketen an und das Empfangen von Paketen von

11 19 EP B1 dem anrufenden Teilnehmer (32) während eines kollisionsfreien Zeitraums des Zugangspunkts () ein Senden von Paketen an den Zugangspunkt () beinhaltet, wobei der Zugangspunkt () die Pakete an zumindest einen des angerufenen Teilnehmers (3) und des anrufenden Teilnehmers (32) weiterleitet. 22. Verfahren nach Anspruch 21, wobei das Senden von Paketen an den Zugangspunkt () weiterhin ein Senden von Paketen von dem Zugangspunkt () zu einem Sprach-VLAN über ein drahtgebundenes Netzwerk beinhaltet, wobei das drahtgebundene Netzwerk ein Koppelnetz ist. 23. Verfahren nach Anspruch 22, wobei das Senden von Paketen an den Zugangspunkt () weiterhin ein Senden von Paketen von dem Zugangspunkt () zu einem Sprach-VLAN über ein drahtgebundenes Netzwerk beinhaltet, wobei das drahtgebundene Netzwerk ein Switched Ethernet ist. 1 der angerufene Teilnehmer (3) eine Rückmeldungs-Nachricht an den anrufenden Teilnehmer (32) als Antwort auf den Empfang der SIP INVITE Nachricht sendet, Hinzufügen des anrufenden Teilnehmers (32) zu der Sendeaufrufs-Liste des Zugangspunkts () und Senden von Paketen an und Empfangen von Paketen von dem angerufenen Teilnehmer (3) während eines kollisionsfreien Zeitraums des Zugangspunkts (). 27. Maschinenlesbares Medium nach Anspruch 26, wobei das Verfahren weiterhin, falls die Sprach-Slots auf dem Zugangspunkt () nicht verfügbar sind, ein Senden einer Beendigungs-Nachricht von dem SIP Proxy-Server (3) an den angerufenen Teilnehmer (3) aufweist. 28. System zur Bereitstellung von Dienstqualität für VoIP über ein drahtloses lokales Netzwerk, aufweisend: 24. Verfahren nach Anspruch 23, wobei das Senden von Paketen von dem Zugangspunkt () zu einem Sprach-VLAN über ein drahtgebundenes Netzwerk weiterhin ein Senden von Paketen von dem Zugangspunkt () zu einem Sprach-VLAN (36) über ein drahtgebundenes Netzwerk mittels Dienstqualität-Techniken auf Paketebene beinhaltet. 2. Verfahren nach Anspruch 24, wobei das Senden von Paketen von dem Zugangspunkt () zu einem Sprach-VLAN (36) über ein drahtgebundenes Netzwerk mittels Dienstqualität-Techniken auf Paketebene ein Senden von Paketen von dem Zugangspunkt () an ein Sprach-VLAN (36) über ein drahtgebundenes Netzwerk mittels differenzierten Diensten (Differentiated Services) beinhaltet. 26. Maschinenlesbares Medium aufweisend darauf gespeicherte Instruktionen zum Ausführen durch einen Prozessor zum Durchführen eines Verfahrens zur Bereitstellung von Dienstqualität für VoIP über ein drahtloses lokales Netzwerk, aufweisend: Senden einer SIP INVITE Nachricht von einem anrufenden Teilnehmer (32) an einen SIP Proxy-Server (3); Ermitteln, ob Sprach-Slots auf einem Zugangspunkt () verfügbar sind, wobei Datenpakete von und zu dem Zugangspunkt in Datenübertragungsblöcken, aufweisend einen kollisionsfreien Zeitraum und einen Zeitraum mit Kollision, gesendet werden; und falls Sprach-Slots auf dem Zugangspunkt () verfügbar sind, Weiterleiten der SIP INVITE Nachricht von dem SIP Proxy-Server (3) an einen angerufenen Teilnehmer (3), und falls Mittel zum Senden einer SIP INVITE Nachricht von einem anrufenden Teilnehmer (32) an einen SIP Proxy-Server (3); Mittel zum Ermitteln, ob Sprach-Slots auf einem Zugangspunkt () verfügbar sind, wobei Datenpakete von und zu dem Zugangspunkt in Datenübertragungsblöcken, aufweisend einen kollisionsfreien Zeitraum und einen Zeitraum mit Kollision, gesendet werden; Mittel zum Weiterleiten der SIP INVITE Nachricht von dem SIP Proxy-Server (3) an einen angerufenen Teilnehmer (3), falls Sprach- Slots auf dem Zugangspunkt verfügbar sind, und falls der angerufene Teilnehmer (3) eine Rückmeldungs-Nachricht an einen anrufenden Teilnehmer (32) als Antwort auf den Empfang der SIP INVITE Nachricht sendet, Mittel zum Hinzufügen des anrufenden Teilnehmers (32) zu der Sendeaufrufs-Liste des Zugangspunkts () und Mittel zum Senden von Paketen an und Empfangen von Paketen von dem angerufenen Teilnehmer (3) während eines kollisionsfreien Zeitraums des Zugangspunkts (). 29. System nach Anspruch 28, weiterhin aufweisend Mittel zum Senden einer Beendigungs-Nachricht von dem SIP Proxy-Server (3) an den angerufenen Teilnehmer (3).. System nach Anspruch 28, wobei eine Maschine den SIP Proxy-Server (3) und den Zugangspunkt (3) aufweist. 31. System nach Anspruch 28, wobei eine erste Maschine den SIP Proxy-Server (3) aufweist und eine 11

12 21 EP B1 22 zweite Maschine den Zugangspunkt (3) aufweist. 32. System nach Anspruch 31, weiterhin aufweisend ein Kommunikationsprotokoll zwischen der ersten Maschine und der zweiten Maschine um zu ermöglichen, dass der SIP Proxy-Server (3) und der Zugangspunkt (3) kommunizieren. Revendications gestion MAC par l appelant (32) au point d accès () demandant l ajout de l appelant (32) à la liste d invitation à émettre. 6. Procédé selon la revendication, dans lequel l envoi d une trame de gestion MAC par l appelant (32) au point d accès () demandant l ajout de l appelant (32) à la liste d invitation à émettre comprend l envoi d une trame de gestion MAC par l appelant (32) à un coordinateur de point du point d accès (). 1. Procédé fournissant une qualité de service à Voix sur IP (VoIP) sur un réseau local sans fil, comprenant : l envoi d un message SIP INVITE par un appelant (32) à un serveur mandataire SIP (3) ; la détermination s il y a des tranches vocales disponibles à un point d accès (), des paquets de données étant envoyés du et au point d accès dans des trames comprenant une période sans collision et une période avec collision ; si des tranches vocales sont disponibles au point d accès (), le réacheminement du message SIP INVITE depuis le serveur mandataire SIP (3) vers un appelé (3), et si l appelé (3) envoie un message d acquittement à l appelant (32) en réponse à la réception du message SIP INVITE, l ajout de l appelant (32) à la liste d invitation à émettre du point d accès (), et l envoi de paquets à l appelé (3), et la réception de paquets de celui-ci, dans une période sans collision du point d accès (). 2. Procédé selon la revendication 1, comprenant en outre, si les tranches vocales ne sont pas disponibles au point d accès (), l envoi d un message de terminaison par le serveur mandataire SIP (3) à l appelé (3). 3. Procédé selon la revendication 1, dans lequel si l appelé (3) envoie un message d acquittement à un appelant (32) en réponse à la réception du message SIP INVITE comprend si l appelé (3) envoie un message SIP ACK à un appelant (32) en réponse à la réception du message SIP INVITE. 4. Procédé selon la revendication 1, dans lequel l envoi d un message de terminaison par le serveur mandataire SIP (3) à l appelé (3) comprend l envoi d un message SIP BYE par le serveur mandataire SIP (3) à l appelé (3).. Procédé selon la revendication 1, dans lequel l ajout de l appelant (32) à la liste d invitation à émettre du point d accès () comprend l envoi d une trame de Procédé selon la revendication 1, comprenant en outre l ajout de l appelé (3) à la liste d invitation à émettre du point d accès (). 8. Procédé selon la revendication 7, dans lequel l ajout de l appelé (3) à la liste d invitation à émettre du point d accès () comprend l envoi d une trame de gestion MAC par l appelé (3) au point d accès () demandant l ajout de l appelé (3) à la liste d invitation à émettre. 9. Procédé selon la revendication 8, dans lequel l envoi d une trame de gestion MAC par l appelé (3) au point d accès () demandant l ajout de l appelé (3) à la liste d invitation à émettre comprend l envoi d une trame de gestion MAC par l appelé (3) à un coordinateur de point du point d accès ().. Procédé selon la revendication 1, comprenant en outre l ajout de l appelé (3) à la liste d invitation à émettre d un nouveau point d accès (31). 11. Procédé selon la revendication, dans lequel l ajout de l appelé (3) à la liste d invitation à émettre du nouveau point d accès (31) comprend l envoi d une trame de gestion MAC par l appelé (3) au nouveau point d accès (31) demandant l ajout de l appelé (3) à la liste d invitation à émettre. 12. Procédé selon la revendication 11, dans lequel l envoi d une trame de gestion MAC par l appelé (3) au nouveau point d accès (31) demandant l ajout de l appelé (3) à la liste d invitation à émettre comprend l envoi d une trame de gestion MAC par l appelé (3) à un coordinateur de point du nouveau point d accès (31). 13. Procédé selon la revendication 1, comprenant en outre, si les tranches vocales sont disponibles au point d accès (31), au moins l un de l envoi d un message de terminaison par l appelé (3) à l appelant (32) et de l envoi d un message de terminaison de l appelant (32) à l appelé (3). 14. Procédé selon la revendication 13, dans lequel au moins l un de l envoi d un message de terminaison par l appelé (3) à l appelant (32) et de l envoi d un 12

13 23 EP B1 24 message de terminaison de l appelant (32) à l appelé (3) comprend au moins l un de l envoi d un message SIP BYE de l appelé (3) à l appelant (32) et de l envoi d un message de terminaison de l appelant (32) à l appelé (3). 1. Procédé selon la revendication 14, comprenant en outre, si au moins l un de l appelant (32) et de l appelé (3) envoie un message de confirmation, le retrait d au moins l un de l appelant (32) et de l appelé (3) de la liste d invitation à émettre du point d accès (). de paquets à l appelant (32) et la réception de paquets de celui-ci dans un période sans collision du point d accès () comprend l envoi de paquets au point d accès (), le point d accès () réacheminant les paquets vers au moins l un de l appelé (3) et de l appelant (32). 22. Procédé selon la revendication 21, dans lequel l envoi de paquets au point d accès () comprend en outre l envoi de paquets du point d accès () à un VLAN vocal via un réseau filaire, le réseau filaire étant un réseau commuté. 16. Procédé selon la revendication 1, dans lequel si au moins l un de l appelant (32) et de l appelé (3) envoie un message de confirmation comprend si au moins l un de l appelant (32) et de l appelé (3) envoie un message SIP OK Procédé selon la revendication 22, dans lequel l envoi de paquets au point d accès () comprend en outre l envoi de paquets du point d accès () à un VLAN vocal via un réseau filaire, le réseau filaire étant un réseau Ethernet commuté. 17. Procédé selon la revendication 1, dans lequel le retrait d au moins l un de l appelant (32) et de l appelé (3) de la liste d invitation à émettre du point d accès () comprend l envoi d une trame de gestion MAC par l au moins un de l appelant (32) et de l appelé (3) au point d accès () demandant que l au moins un de l appelant (32) et de l appelé (3) soit retiré de la liste d invitation à émettre. 18. Procédé selon la revendication 17, dans lequel l envoi d une trame de gestion MAC par l au moins un de l appelant (32) et de l appelé (3) au point d accès () demande que l au moins un de l appelant (32) et de l appelé (3) soit retiré du coordinateur de point de la liste d invitation à émettre. 19. Procédé selon la revendication 1, comprenant en outre, si l appelé envoie un message d acquittement à un appelant (32) en réponse à la réception du message SIP INVITE, le transfert d au moins l un de l appelant (32) et de l appelé (3) sur un nouveau point d accès dans un même sous-réseau IP, et l ajout de l au moins un de l appelant (32) et de l appelé (3) à la liste d invitation à émettre du nouveau point d accès (31).. Procédé selon la revendication 1, comprenant en outre, si l appelé (3) envoie un message d acquittement à un appelant (32) en réponse à la réception du message SIP INVITE, le transfert d au moins l un de l appelant (32) et de l appelé (3) sur un nouveau point d accès dans un sous-réseau IP différent, l ajout de l au moins un de l appelant (32) et de l appelé (3) à la liste d invitation à émettre du nouveau point d accès, et l envoi d un message de réinvitation à au moins l un de l appelant (32) et de l appelé (3). 21. Procédé selon la revendication 1, dans lequel l envoi Procédé selon la revendication 23, dans lequel l envoi de paquets du point d accès () à un VLAN vocal via un réseau filaire comprend en outre l envoi de paquets du point d accès () à un VLAN vocal (36) via un réseau filaire utilisant des techniques de qualité de service au niveau des paquets. 2. Procédé selon la revendication 24, dans lequel l envoi de paquets du point d accès () à un VLAN vocal (36) via un réseau filaire utilisant des techniques de qualité de service au niveau des paquets comprend l envoi de paquets du point d accès () à un VLAN vocal (36) via un réseau filaire utilisant des Services Différenciés. 26. Support lisible par ordinateur sur lequel sont mémorisées des instructions destinées à être exécutées par un processeur en vue d exécuter un procédé fournissant une qualité de service à VoIP sur un réseau local sans fil, comprenant : l envoi d un message SIP INVITE par un appelant (32) à un serveur mandataire SIP (3) ; la détermination s il y a des tranches vocales disponibles à un point d accès (), des paquets de données étant envoyés du et au point d accès dans des trames comprenant une période sans collision et une période avec collision ; et si des tranches vocales sont disponibles au point d accès (), le réacheminement du message SIP INVITE depuis le serveur mandataire SIP (3) vers un appelé (3), et si l appelé (3) envoie un message d acquittement à l appelant (32) en réponse à la réception du message SIP INVITE, l ajout de l appelant (32) à la liste d invitation à émettre du point d accès (), et l envoi de paquets à l appelé (3), et la réception de paquets de celui-ci, dans une 13

14 2 EP B1 26 période sans collision du point d accès (). 27. Support lisible par ordinateur selon la revendication 26, dans lequel le procédé comprend en outre, si les tranches vocales ne sont pas disponibles au point d accès (), l envoi d un message de terminaison par le serveur mandataire SIP (3) à l appelé (3). 28. Système fournissant une qualité de service à VoIP sur un réseau local sans fil, comprenant : un moyen d envoi d un message SIP INVITE par un appelant (32) à un serveur mandataire SIP (3) ; un moyen de détermination s il y a des tranches vocales disponibles à un point d accès (), des paquets de données étant envoyés du et au point d accès dans des trames comprenant une période sans collision et une période avec collision ; un moyen de réacheminement du message SIP INVITE depuis le serveur mandataire SIP (3) vers un appelé (3) si des tranches vocales sont disponibles au point d accès, et si l appelé (3) envoie un message d acquittement à l appelant (32) en réponse à la réception du message SIP INVITE, un moyen d ajout de l appelant (32) à la liste d invitation à émettre du point d accès (), et un moyen d envoi de paquets à l appelé (3), et de réception de paquets de celui-ci, dans une période sans collision du point d accès () Système selon la revendication 28, comprenant en outre un moyen d envoi d un message de terminaison par le serveur mandataire SIP (3) à l appelé (3). 3. Système selon la revendication 28, dans lequel une machine comprend le serveur mandataire SIP (3) et le point d accès (3). 31. Système selon la revendication 28, dans lequel une première machine comprend le serveur mandataire SIP (3) et une seconde machine comprend le point d accès (3) Système selon la revendication 31, comprenant en outre un protocole de communication entre la première machine et la seconde machine permettant au serveur mandataire SIP (3) et au point d accès (3) de communiquer. 0 14

15 EP B1 1

16 EP B1 16

17 EP B1 17

18 EP B1 REFERENCES CITED IN THE DESCRIPTION This list of references cited by the applicant is for the reader s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard. Patent documents cited in the description WO A1 [0006] US A1 [0007] US A1 [0008] Non-patent literature cited in the description D. Chen et al. Supporting VBR VoiP Traffic. IEEE WLAN in PCF Mode, July 02, 1-6 [0009] 18