1. Field of the Invention
The present invention relates to a network access method of Local Area Network (LAN) terminals and a network system thereof, more particularly, present invention relates to a network access method of LAN terminals and a network system thereof designed to support network association between a terminal and an Access Point (AP) in an IEEE 802.11 Wireless Local Area Network (WLAN) environment.
2. Description of the Related Art
Various authentications such as Medium Access Control (MAC) based authentication and IEEE 802.11 standard based authentication are being used as major Wireless Local Area Network (WLAN) authentication methods.
That is, according to the IEEE 802.11 standard, there are two major authentication methods, namely, the Open System authentication method and the Shared Key authentication method.
The Open System authentication method accepts all wireless terminals according to an extended meaning of authentication. This authentication method directly allows access to any wireless terminal attempting access with an Service Set Identifier (SSID) of an Access Point (AP). Access is carried out by an authentication exchange, which constitutes two frames. A first frame of a mobile terminal is an authentication subtype and a management frame. Although IEEE 802.11 does not officially call this frame an authentication request, this frame is actually used for this purpose. Upon receiving an authentication request frame, an AP processes the authentication request and replies with a response frame.
The Shared Key authentication method uses a Wired Equivalent Privacy (WEP) Key, and thus is used only by APs or terminals having WEP Key capability. IEEE 802.11 requires Shared Key authentication to all terminals having WEP Key capability. Shared Key realization requires equal distribution of WEP Keys to terminals and APs before authentication. Shared Key authentication procedures need four authentication subtype management frames, in which the first frame has an information element for identifying an authentication algorithm and sequence number like a frame in an Open System authentication. The second frame of the Shared Key authentication procedures acts to challenge. The third frame acts to respond to a challenge from a mobile terminal. The mobile terminal constitutes a frame with three information elements such as an authentication algorithm identifier, a sequence number and a challenge syntax. The challenge syntax is encoded according to the WEP set in the terminal. Upon receiving the third frame, an AP decodes the third frame to execute a WEP integration test, and if integration is confirmed, replies with a successful state code. Successful challenge syntax decoding proves that WEP Key set in the mobile terminal is identical with that set in the AP, and means that access is allowed.
An IEEE 802.11 standard mobile terminal as described above is set with both Open System and Shared Key authentications, which are optional with a user. That is, if an AP uses Open System authentication, the user sets the terminal with Open System authentication, and if the AP uses Shared Key authentication, the user sets the terminal with Shared Key authentication. In this way, access procedures may be executed so that the user can normally use a network.
Since some of recently commercialized APs can respond to an authentication mode requested by terminals through automatic detection, it is possible to utilize these APs. A terminal can attempt authentication according to Shared Key authentication to detect the current authentication-setting state of a corresponding AP. However, an AP capable of automatically detecting and accepting user's authentication mode will be an optimum solution for the purpose of maximizing user's convenience. If a terminal retrieves APs in an early stage, it is possible to detect any APs using the WEP mode. When attempting to access the APs where such a WEP has been set, the authentication mode of the terminal is forcibly changed into the Shared Key authentication mode so that an access request is sent to a corresponding AP. Then, the AP can accept the Shared Key authentication mode access request.
In general, even though a WEP is set to an AP, if the AP is adapted to use the Open System authentication, a terminal is unconditionally authenticated by the IEEE 802.11 standard and thus allowed to access the AP even though the WEP Key value of the terminal is not identical with that set in the AP. However, although access is allowed, the user cannot actually use the network since user packets encoded according to a different WEP Key are not properly decoded in the AP. For these reasons, network access via the WEP Key of the AP is not allowed in fact, and audio data for voice communication is not transmitted or received. Thus, a user cannot trust any authentication state displayed on the terminal. The user may continuously attempt access based upon the authentication state even though network access is not allowed in fact. There are problems in that this increases the confusion of the user and thus maximizes inconvenience.