Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Protection at a particular protocol layer
Reexamination Certificate
1998-08-18
2001-01-23
Peeso, Thomas R. (Department: 2767)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Protection at a particular protocol layer
C713S150000, C713S160000, C380S247000, C380S270000
Reexamination Certificate
active
06178512
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to private wireless networks for communication between a number of wireless terminals, both public and private, which are free to join and leave the network at any time. The network may be configured so that all the wireless terminals communicate through a base station, or so that the devices communicate directly with one another.
Wireless networks are intended to offer flexible and cost-effective alternatives to wired networks, for example as Local Area Networks (LANs). An advantage of wireless over fixed networks is the ease with which new networks can be created and with which new devices, known as wireless terminals, can be added to the network. Some wireless network standards exist, for example IEEE 802.11 in the USA and HIPERLAN in Europe, whilst others are under development, for example Wireless Asynchronous Transfer Mode (WATM). Such standards define the format of a transmission frame, within which control and data transfer functions can take place. The format and length of transmission frames may be fixed or dynamically variable.
Known wireless networks, for instance as disclosed in U.S. Pat. No. 5,274,841, typically operate in one of two different configurations:
1. A base station orientated configuration in which wireless terminals can only communicate with each other with the support of a base station, which is responsible for all wireless terminals within a certain radio coverage area. The base station itself may be connected to further wired networks for communications beyond the radio coverage area. The base station may be a separate unit, or it may be a wireless terminal with additional functionality.
2. A peer to peer configuration in which wireless terminals communicate directly with one another. One of the wireless terminals is typically chosen dynamically to perform the control function.
The first configuration is generally considered to be most suitable for networks with a relatively fixed structure, while the second is considered most suitable for the generation of dynamic networks, such as for document exchange at a meeting.
In order for a wireless network to realise the advantage of flexibility, the procedure for wireless terminals joining and leaving the network should be as simple as possible. The act of a wireless terminal joining a network is known as association and needs to be scheduled within the data transmission format defined for the wireless network. Examples of known techniques for association include dynamic framelength slotted ALOHA, described in GB-B-2 069 799, carrier sense multiple access and address based tree resolution algorithms.
A problem with known wireless networks is that security can be compromised if the network is open to any wireless terminal, but flexibility is sacrificed if access is limited to a known set of wireless terminals.
SUMMARY OF THE INVENTION
An object of the present invention is to enable the use of a wireless network comprising both public and private users, maintaining a high degree of security in communications between private users.
According to a first aspect of the present invention there is provided a method of operating a wireless network, wherein transmission of data takes place in transmission frames subdivided into time slots, the wireless network comprising a controller and a variable number of public and private wireless terminals, the method comprising the controller maintaining a list of wireless terminals currently registered with the network, determining the lengths of successive transmission frames and allocating time slots within said frames for various purposes, each frame including a control section which details the allocation of time slots in the remainder of the transmission frame, characterised by a part of the control section being unencrypted, to allocate time slots in an unencrypted part of the transmission frame for unencrypted data exchange, and another part of the control section being encrypted, to allocate time slots in an encrypted part of the transmission frame for encrypted data exchange.
According to a second aspect of the present invention there is provided a controller for a wireless network having a plurality of public and private wireless terminals, the controller comprising means for maintaining a list of wireless terminals currently registered with the network, means for encryption, means for determining the lengths of successive transmission frames and means for allocating time slots within each of said frames for various purposes, each frame including a control section which details the allocation of time slots in the remainder of the transmission frame, characterised by means for generating a part of the control section in an unencrypted form, for allocating time slots in an unencrypted part of the transmission frame for unencrypted data exchange, and another part of the control section in encrypted form, for allocating time slots in an encrypted part of the transmission frame for encrypted data exchange.
According to a third aspect of the present invention there is provided a wireless terminal for use in a wireless network constituted by at least one wireless terminal and a controller which in operation generates transmission frames, each transmission frame including a control section, the wireless terminal comprising transceiver means and means for storing encryption data, characterised by means for obtaining encryption control data from the control section of a received transmission frame, means for determining which fields within a transmission frame are encrypted, means for decrypting received data transmitted in an encrypted part of a transmission frame and means for encrypting data to be transmitted in an encrypted part of a transmission frame.
The present invention is based upon the recognition, not present in the prior art, that having separate encrypted and unencrypted fields within a transmission frame format enables a private network to allow access by public wireless terminals without compromising security.
By means of the present invention a wireless network can comprise both public and private wireless terminals, with communication between private wireless terminals remaining secure.
REFERENCES:
patent: 5243653 (1993-09-01), Malek et al.
patent: 5274841 (1993-12-01), Natarajan et al.
patent: 0748073A1 (1996-12-01), None
patent: 2069799 (1981-08-01), None
PHB 34,177, U.S. application No. 09/102,838, filed: Jun. 23, 1998.
Peeso Thomas R.
Piotrowski Daniel J.
U.S. Philips Corporation
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