Smooth disassociation of stations from access points in a 802.11 wlan

[0001] The present invention relates to the 802.11 IEEE standard (organized by the Institute of Electrical and Electronics Engineers) and its respective access points (APs) and stations (STAs). In particular, the present invention relates to a method by which access points can disconnect from stations (STA) in a "friendly" manner.

[0002] A wireless communication method has been proposed for the 802.11 standard. The Basic Service Set (BSS) infrastructure (i.e. a radio cell used in WLANs to increase the transmission range) of an IEEE 802.11 wireless local area network consists of an access point (AP) and a number of stations (STA) connected to the AP. APs connect stations with infrastructure.

[0003] The distribution of load on access points by stations (STAs) is an important issue that aims to enable efficient operation of a WLAN. Overloading certain access points (APs) with stations (STAs) can result in extended network response time, disconnection, etc., especially if there are APs that are too rarely used, so to optimize response time and improve overall WLAN performance and reliability during load distribution, stations (STA) are switched to less frequently used APs, to distribute the possible working load evenly between APs.

[0004] To address this problem, in the document: "Information technology - telecommunications and exchange of information between systems - local and metropolitan backbone networks - specific requirements - Part 11: Specification of transmission medium access control (MAC) and physical layer (PHY) ) wireless local network "ANSI / IEEE STD 802.11" discloses how to terminate the active connection between access points and the station.

[0005] For example, Figure 1 shows the load distribution known in the art and used by the present invention. Circle 100 symbolizes the coverage area of ​​the first AP 110 access point, characterized in that all STAs in this coverage area are served by the first AP 110 access point. Similarly, circle 200 symbolizes the second coverage area associated with access point 210. The AP 210 can support all STA stations within coverage of 200.

[0006] According to this particular example of Fig. 1., there are a total of eight STA 105 stations connected to AP 110, while only one STA 205 is connected to AP 210. Here, there is clearly an unbalanced load. To distribute the load, you can disconnect any number of STA 105a stations in the common area 215 of the two districts from the AP 110, interrupt their connections and force them to search for a connection with access point 210.

[0007] If the access point 210 is able to support STA 105a, the packets are forwarded to the AP 210 just connected. In this particular example, three STAs described as 105a will be disconnected from AP 110 and connected to AP 210 so that the ratio of STA stations connected to AP 110 to stations connected to AP 210 is five to four.

[0008] According to the 802.11 standard, the only mechanism that the AP uses to distribute the load is to issue a disconnect command to stations that it no longer wants to handle, using the confirmation of the disconnect action frame. The STA station is suddenly disconnected and needs to find another AP that can handle it as soon as possible. Again, according to the commonly accepted protocol, disconnection is an emergency because the STA stations that are about to be disconnected do not receive any warning before that they are about to be disconnected from a particular AP. Therefore, when an AP disconnects from a specific station or STAs, it is typical that as a result, the STA suffers from interruption of service and packet loss during handover when STAs are forced to immediately disconnect and look for a new access point AP they connect to.

[0009] Furthermore, the latest working version DO.5 of Task Group k of the 802.11 protocol includes two types of messages that are sent by APs to the STA. These messages are the measurement request frame and the page status report response message. The measurement request initiates the AP, requiring the STA receiving it to provide some measurements about the radio environment. Conversely, a page status report reply message is usually sent by the AP in response to a page status report request from the STA. The AP may also send an independent page status report, even if STAs have not sent such a request, as long as it sees the need to update the page status report information. The website status report provides a comprehensive picture of information about the neighboring environment and contains a list of neighboring APs. Adjacent APs on the list are those with which the STA will attempt to connect if handover occurs.

[0010] The present invention provides the AP with a mechanism for sending information indicating a candidate to disconnect to an STA prior to performing the disconnection action. The invention uses as a carrier two messages of an existing protocol, namely a measurement request frame or a page status report response frame, and creates a reason code field. A warning that the STA is a candidate to disconnect is inserted into the newly created reason code field. The invention enables STAs to increase reliability over an uninterrupted period of process activity without requiring a radical change in hardware and / or software used in the 802.11 WLAN. Both the page status report response frame and the measurement request frame can serve as a carrier of a disconnection warning message.

[0011] The invention relates to a method, device and computer program according to the independent claims 1, 13 and 16, respectively.

Fig. 1 is a Venn diagram showing load distribution between two access points both according to the prior art and the present invention.

Fig. 2 is a diagram of a measurement request frame containing a cause field according to the present invention.

Fig. 3 is a graph calculating reason codes for a measurement request according to the present invention. Fig. 4 is a diagram of the response frame of the page condition report, including the reason field according to the present invention.

Fig. 5 is a graph calculating reason codes for the response frame of a page condition report according to the present invention.

Fig. 6 shows an example of equipment that can be used to implement the present invention.

[0012] It will be understood by one of ordinary skill in the art that the following descriptions are provided to explain and not limit the scope of the invention. The skilled person understands that there are many variants that fall within the scope of the appended claims. In the present description, unnecessary detail regarding known functions and operations may be omitted so as not to impede the understanding of the present invention.

[0013] The direct authors of the invention define the invention as "friendly disconnection" because it is not a sudden interruption that is currently used for disconnections, which often results in packet loss etc. The STA station selected for disconnection is referred to as "disconnect candidate" because at some point in the near future this candidate will be disconnected from the currently serving AP. However, unlike sudden disconnections, the present invention sends a warning earlier to that particular STA that is a candidate for disconnection, so the STA may look for another AP before it disconnects from the WLAN. The measurement request frame and / or page response report, both currently existing under the 802.11k protocol, is modified to become a message carrier in which a specific STA is informed that it has been designated as a disconnection candidate.

[0014] Fig. 2 shows the measurement request frame according to the latest IEEE 802.11 k draft. The latest draft allows the STA to reject the BSS request to measure the ambient condition. A reason field has been added to the measurement request frame that provides the STA with additional information to determine the urgency of the request. If the request is particularly urgent, the station can be programmed to accept the BSS request because it has a problem and disconnection may be unavoidable.

[0015] In addition, Fig. 2 shows that the measurement request frame includes a cause field 245, which in the present example reserves bits (from 0 to 255) for different conditions.

[0016] According to the present invention, it is proposed that one of the reason field codes indicate a candidate to disconnect so that the STA can be warned that in the near future it will be disconnected from the current AP when the STA receives the measurement request frame. In other words, the station is notified in advance of the time when it can be expected to receive a disconnect action frame.

[0017] As shown in Fig. 3, in this example, the reason code field "1" indicates that the STA receiving the measurement request frame is a candidate for disconnection. The skilled person knows that it can be reserved to mark this information any of the numbers in the field of the cause, such as the number 6 or 61, or 242, etc., but for ease of clarification, 1 is selected.

[0018] Once the STA receives a warning in advance that it has been selected as a disconnection candidate, it is allowed time to scan the network for other APs so that it can connect to them before disconnection using the disconnect action frame. It should be noted that the reason code indicates that disconnection is inevitable and that the activation delay field 246 (shown in Fig. 2.) specifies how much time the STA has before it is disconnected from the currently operating AP.

[0019] Fig. 4.p illustrates yet another method by which a reason code can be provided to an STA as a prior warning that disconnection is approaching. Instead of in the measurement request frame, reason code 445 may be inserted into the response frame of the page status report. Here too, the reason code field has a range of 0 to 255 bits. Again, the activation delay field 446 can be used to specify how much time the station has before it is disconnected, if the reason code indicates that disconnection is approaching.

[0020] Fig. 6 shows an example of equipment that can be used to practice the present invention. The server 600 is usually wired to the 602 bus, as are the AP1 (601), AP2 (603), and AP3 (604) access points. It is possible that the server 600 has the ability to transmit wirelessly (as evidenced by the 606 antenna) and overtakes communication with access points (also shown as having the 606 antenna) wired (otherwise known as electric, optical) bus.

[0021] Placed at AP1, AP2, AP3, respectively, module 630, 635, 640 stores in the reason code field the computer code used to update the measurement request frame or page status report response in order to select the candidate to be disconnected (selected from STA 605, 610, 615, 620, 625 stations via the appropriate APs).

[0022] According to one aspect of the invention, the measurement request frame or page status report response frame may be generated in module 630, 635, 640 access points 601, 603, 604 or may receive them from the server 600 module 630, 635, 640 access points 601, 603, 604, and they can be updated to take account of disconnection if a selection is required. To search for an access point that will support it, the STA station usually scans all APs from the list that is part of the page status report response. When an AP is found, there may be a transfer between the AP currently serving the respective STA and the future AP. Optionally, if speed counts, the station may be given time to scan only one page and request a connection.

[0023] Thus, the AP generates the current frame and includes in it a reason code indicating the selected disconnect candidate. It is also possible that the station has some backup of the default AP assigned, so when the STA3 receives a message that it is a candidate to disconnect, it automatically scans by default its assigned specific AP.

There are other frames transmitted between APs and STAs, which can be modified to include a reason code in order to enable friendly disconnection messages in this way. It should be understood that various modifications of the present invention may be made that will not fall outside the scope of the appended claims. For example, the number of APs, STAs, etc. can all be changed as required. Additionally, although one aspect of the present invention is the ability to distribute the load without disconnecting the STA from the service, the present invention also provides a method by which a STA connected to a periodically failing AP may receive a message indicating that it should scan other access points because there may be a disconnection.