In network application, when the transport media is changed from wire to radio waves, the communication protocol 802.11 (i.e. Wireless Local Network WLAN) is used, which was defined by IEEE. Protocol 802.11 technologies provide high speed wireless connection to the network. The 802.11 standard defines two network modes: infrastructure mode and Ad-hoc mode. In infrastructure mode, a mobile user accesses network and communicates with other mobile users through access point (AP); while in Ad-hoc mode, the mobile users communicate with each other in a peer to peer mode. To be more specific, the computer users normally using WLAN can work in two modes: infrastructure mode and Ad-hoc mode. Infrastructure mode is used for mobile nodes i.e. the wireless devices of the mobile users can access the public network through access points, while Ad-hoc mode is used for a plurality of neighboring mobile nodes to communicate with each other directly.
Referring to FIG. 1, it shows a wireless local network communicating in an infrastructure mode. In this infrastructure mode, each mobile node (or called as wireless node) communicates with other mobile nodes or fixed nodes of the network through the access point (AP). The access point is used as a bridge, transponder, gateway or firewall between the mobile nodes and the wired network. That is to say, in this infrastructure mode, the AP which is a part of the wired network infrastructure is provided as the bridge between the wireless and the wired LAN and through which the mobile nodes can communicate with Internet. FIG. 1 schematically describes an example of the mobile node, i.e. a laptop computer communicates in the infrastructure mode. Though there only shows one mobile node in FIG. 1, it should be understood that there can be many mobile nodes that communicate simultaneously in the infrastructure mode; in addition, the mobile node in FIG. 1 is a laptop computer, however, it should be understood that the mobile nodes can be other wireless devices, including and not limited to, mobile phones, Personal Digital Assistant (PDA), Palm computer, etc. The mobile node, such as the laptop in FIG. 1, normally has a wireless card with which the mobile node can exchange information with other wireless devices through AP, thus the wireless communication among mobile nodes can be realized. AP itself needs a static IP address, and it can support the access of limited number of mobile nodes within its working range (different AP has different working range, the relevant user manual may provide such data, i.e. 30 meters). The working range of AP is called Basic Service Set (BSS) and all the users of the AP share the same BSS ID.
In most wireless local networks, normally, at least one authentication server is used as shown in FIG. 1. The authentication server is used to authenticate the ID of the user on the mobile node. The authentication server can also obtain a lot of information about the user, such as the IP address of the user, the AP through which the user access the network, the time when the user access the network and the time when the user leaves, etc.
If more wireless devices need to be supported in the infrastructure network mode, the following work pattern can be used. Here, multiple APs connect together and share the same authentication server as shown in FIG. 2. FIG. 2 schematically shows an exemplary of an Extended Service Set (ESS) made up of a plurality of APs in the infrastructure mode. Here, each AP has its relevant BSS and all APs' working ranges compose an Extended Service Set (ESS), and the mobile nodes sharing the same ESS ID can roam freely among these APs without losing network connections.
When the mobile node is set to work in the infrastructure mode, it uses a static or dynamic IP address. The authentication server can locate the mobile node according to its relevant AP and IP address.
In Ad-hoc mode, the mobile nodes can communicate with each other directly. That is to say that the mobile node communicates with other mobile nodes in a peer to peer mode within its RF range instead of communicating through the inter-medium node which is the access point of infrastructure mode. When users are very close to each other, Ad-hoc mode connection is very useful for communication. FIG. 3 is the diagram of the communication in Ad-hoc mode. FIG. 3 schematically shows four neighboring mobile nodes, i.e. four laptop computers communicating in Ad-hoc mode. Here, each mobile node is equipped with a wireless card with which two or more mobile nodes can communicate with each other at the peer to peer level and said mobile nodes share a given cell coverage area. When the mobile nodes are set in Ad-hoc mode, they need to be set with static IP addresses and all the mobile nodes which communicate with each other belong to the same working group. Similarly, they also share the same ESS ID.
In the prior art, infrastructure mode is commonly used in office, hot-spot, while Ad-hoc mode is often used in the places without network infrastructure, smaller areas, or close distance communication, i.e. the communication among the exploration workers during the resource exploration in high mountains; as well as communication among rescue worker in the after earthquake or communication among colleagues at a meeting in a meeting room, etc. More specifically when the network resource is limited, as compared with infrastructure mode, Ad-hoc mode can save a great amount of resources when the communication is limited to certain local area.
In the prior art, i.e. the US patent application US2003/0054818A1 entitled as “SYSTEM AND METHOD FOR CONCURRENT OPERATION OF A WIRELESS DEVICE IN TWO DISJOINT WIRELESS NETWORKS” discloses a dual mode wireless device. It can operate in two wireless network modes, i.e. infrastructure mode and Ad-hoc mode. The dual mode device has a wireless controller inserted in the wireless card which has two virtual wireless network adaptors thereon. One is for infrastructure mode and the other for Ad-hoc mode. The wireless control driver controls the switching between the two network modes. This patent application is also related to the switching between infrastructure mode and Ad-hoc mode. It is the switching performed on the network facilities in which the controller controls the two network modes within said one device while the two modes are independent to each other. Each mode accesses its own application program and does not know other's sessions of accessing applications and communicates separately. It can be seen from this application that the technology disclosed by this patent application can not realize accessing the same application and sharing the session for accessing the application when the two communication modes are automatically switched. Therefore, a method and device are needed through which users can access the application with the same session when the two communication modes are switched automatically. This will save the users' network resources and cost when accessing the network applications.
In addition, the US patent application US2004/0063458A1 entitled “WIRELESS LAN COMMUNICATION SYSTEM” discloses a wireless communication system that supports a dual-mode switching and also realizes the automatic switching between infrastructure mode and Ad-hoc mode. The wireless communication system of that patent application judges whether it is necessary to switch from infrastructure to Ad-hoc modes by monitoring data pack. If data pack marked with target address is detected, the channel search will be conducted. When suitable channel is found, the communication mode will be switched to Ad-hoc mode and establish connection between the source and the target. In this system, the source or target workstation is made up of date transfer receiver, wireless interface, data pack header analyzer, channel search engine, switch controller and data cache. When it is necessary to switch from Ad-hoc mode back to infrastructure mode, one party of the source and target workstation of the connection which is already established will send a data pack requesting to switch back to infrastructure mode. Then the two parties will switch back to infrastructure mode. From the above mentioned description of the patent application, the patent application mainly focus on that the network layer parses the data pack and judges whether the target can use Ad-hoc mode or not to switch communication channels. It judges whether to switch or not by adding the header of data pack as identity and it is mainly used for data transfer between two points. Meanwhile, it requires that the two sides of the communication should have the capacity of workstations. Comparatively speaking, this will make the switching between the two modes more complicated. Therefore, a more flexible technical solution is needed to automatically switch between the two modes.
In addition, according to the usage of the wireless local network nowadays, some popular network applications such as network gaming, network chatting, e-meeting, etc., usually operate in infrastructure mode. In certain cases, as a result of the access by too many mobile nodes in infrastructure mode, the network resources get scarce and the operation efficiency is very poor; under that circumstance, if part of the users can be switched to Ad-hoc mode, the resources of the whole network will be balanced. As a matter of fact, in the application of the wireless local network nowadays, when the resources in infrastructure mode are restricted, it is seldom considered to balance the network resource by switching the network applications from infrastructure mode to Ad-hoc mode.
Consider the following scenario, the airport ABC provides network gaming and chatting platform only based on infrastructure mode for the passengers waiting for their airplanes. The Airport ABC charges the passengers' fee according to their network usage or connection time. Most of passengers would like to play network games using a mobile node, such as laptop, PDA, which can access WLAN. But there comes the issue of resource restriction. For example, all the APs in the airport can only support about 200 concurrent users, but there may be more than 400 users wanting to play the network game at the same time. With the current WLAN infrastructure, the principle of “First come, first serve” has to be applied. Consequently, half of the users fail to connect to the network. This causes the low quality of service (QoS) and depresses customer satisfaction. To solve this issue, one way is to add more APs to enlarge the capacity but it will raise the investment (meanwhile per unit cost of connection is increased and potential users may be lost). Also it's not a long-term solution since the number of users/connections is changing. In infrastructure mode, resource allocation can't be dynamically changed according to variation of connections.