Encryption and decryption in communication system with wireless trunk

• US 6,097,817 A
• Filed: 12/10/1997
• Issued: 08/01/2000
• Est. Priority Date: 12/10/1997
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Omnipoint Corp. (Deutsche Telekom AG)
• Inventors: Menon, Narayan P., Bilgic, Izzet M.
• Primary Examiner(s): Swann, Tod R.
• Assistant Examiner(s): Callahan, Paul E.
• Application Number:
  US08/988,262
• Time in Patent Office: 965 Days
• Field of Search: 380/1, 380/33, 380/247, 380/248, 380/249, 455/426, 455/454, 379/34
• US Class Current: 380/270
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• CPC Class Codes: H04L 63/08 for authentication of entities cryptographic mechanisms or cryptographic arrangements for entity authentication H04L9/32
• CPC Class Codes: H04W 12/037 of the control plane, e.g. signalling traffic
• CPC Class Codes: H04W 12/04 Key management, e.g. using generic bootstrapping architecture [GBA]
• CPC Class Codes: H04W 4/18 Information format or content conversion, e.g. adaptation by the network of the transmitted or received information for the purpose of wireless delivery to users or terminals
• CPC Class Codes: H04W 74/00 Wireless channel access
• CPC Class Codes: H04W 76/10 Connection setup
• CPC Class Codes: H04W 84/14 WLL [Wireless Local Loop]; RLL [Radio Local Loop]
• CPC Class Codes: H04W 92/22 between access point controllers

Abstract

A communication system having a wireless trunk for connecting multiple phone lines over wireless communication links to a cellular network comprises a central telephone switch, such as a private branch exchange or key system, connected through one or more trunk lines to a wireless access communication unit. The wireless access communication unit preferably comprises a separate subscriber interface for each trunk line from the central telephone switch. The wireless access communication unit collects data from each of the subscriber interfaces, formats the data into a format compatible with an over-the-air protocol, and transmits the information over one or more wireless channels to a cellular base station. The wireless access communication unit thereby connects calls received from the central telephone switch'"'"'s trunk lines over a wireless trunk to a network. A controller within the wireless access communication unit interfaces the subscriber interfaces with a radio transceiver, and assists in the conversion of data from a format suitable for wireless transmission. Authentication is carried out separately for each of the subscriber interfaces, thereby allowing the wireless access communication unit to represent itself as multiple individual subscribers to the network. Upon each initial registration, each subscriber interface derives its own ciphering key from a stored user key and uses it thereafter for encryption and decryption.

Claims

1. A method for communication, comprising the steps of:

establishing a wireless communication channel between a wireless access communication unit and a base station;

setting up a call from a user connected to the wireless access communication unit to a network over said wireless communication channel;

receiving user-to-network bearer traffic at said wireless access communication unit from said user;

encoding said user-to-network bearer traffic at said wireless access communication unit;

transmitting the encoded user-to-network bearer traffic from the wireless access communication unit to the base station over said wireless communication channel;

relaying the encoded user-to-network bearer traffic from the base station to a base station controller;

relaying the encoded user-to-network bearer traffic from the base station controller over a backhaul line to a physically separate transcoding unit;

decoding the encoded user-to-network bearer traffic at the transcoding unit; and

relaying the decoded user-to-network bearer traffic from the transcoding unit to a mobile switching station.

2. The method of claim 1, further comprising the steps of:

receiving network-to-user bearer traffic at the transcoding unit from the mobile switching center;

encoding the network-to-user bearer traffic at the transcoding unit;

relaying the encoded network-to-user bearer traffic from said transcoding unit over said backhaul line to the base station controller;

relaying the encoded network-to-user bearer traffic from said base station controller to said base station;

transmitting said encoded network-to-user bearer traffic from the base station to the wireless access communication unit over said wireless communication channel; and

decoding the network-to-user bearer traffic at the wireless access communication unit.

3. The method of claim 1, wherein said step of encoding is performed using a GSM A5/1 algorithm.

4. The method of claim 1, wherein said step of relaying the encoded user-to-network bearer traffic from said base station controller over said backhaul line to the transcoding unit comprises the step of multiplexing encoded user-to-network bearer traffic from a plurality of users, including said user connected to the wireless access communication unit, onto a single digital communication channel, wherein said step of decoding the encoded user-to-network bearer traffic at the transcoding unit comprises the step of demultiplexing and decoding said encoded user-to-network bearer traffic from the plurality of users, including said user connected to the wireless access communication unit, and generating decoded user-to-network traffic from said plurality of users, and wherein said step of relaying said decoded user-to-network bearer traffic from the transcoding unit to the mobile switching station comprises the step of relaying said decoded user-to-network traffic from the plurality of users, including, said user connected to the wireless access communication unit, to the mobile switching station.

5. The method of claim 1, wherein said wireless communication channel comprises a time division duplex communication channel.

6. The method of claim 1, wherein said wireless communication channel comprises a frequency division duplex communication channel.

7. The method of claim 1, further comprising the step of deriving a ciphering key at said wireless access communication unit based upon an authentication parameter received from said mobile switching center and a user key value stored locally at said wireless access communication unit, said ciphering key used in encoding said user-to-network bearer traffic at said wireless access communication unit.

8. The method of claim 7, further comprising the step of independently obtaining said ciphering key at said mobile switching center, transmitting said ciphering key from said mobile switching center to said base station, and relaying said ciphering key from said base station to said transcoding unit, said ciphering key used at said transcoding unit for encoding network-to-user bearer traffic.

9. A communication system, comprising:

a central telephone switch;

a wireless unit connected to said central telephone switch, said wireless unit comprising an encryptor and a radio unit, whereby data received from said central telephone switch is encrypted and sent from said radio unit over a wireless communication channel;

a base station comprising a receiver, whereby encrypted messages transmitted by said wireless unit over said wireless communication channel are received at said base station;

a base station controller connected to said base station; and

a transcoding unit connected to said base station controller and physically separate therefrom, said transcoding unit comprising a decryptor for decrypting messages received by said base station and relayed to said transcoding unit across said base station controller.

10. The communication system of claim 9, wherein said transcoding unit further comprises a transcoding unit encryptor for encrypting data received from a network, and wherein said base station further comprises a transmitter, whereby encrypted data sent from said transcoding unit to said base station is transmitted across said wireless communication channel to said wireless unit.

11. The communication system of claim 10, wherein said wireless unit further comprises a wireless unit decryptor, whereby encrypted data received from said base station over said wireless communication channel is decrypted for transmission to said central telephone switch.

12. The communication system of claim 9, wherein said central telephone switch is connected to a plurality of telephone stations.

13. The communication system of claim 9, wherein said central telephone switch comprises a private branch exchange (PBX) or key telephone system (KTS).

14. The communication system of claim 9, wherein said wireless unit further comprises a non-volatile storage area comprising a user key value used in derivation of a ciphering key, said ciphering key utilized by said encryptor for encrypting said data from said central telephone switch.

15. A method for communication, comprising the steps of:

establishing, upon demand, wireless connections between a wireless access communication unit and a cellular network, said wireless access communication unit connected over a trunk interface to a plurality of users each capable of generating a call request to said wireless access communication unit;

receiving data from each user for which a wireless connection has been established;

encrypting said data independently for each wireless connection, thereby generating a plurality of encrypted data packets;

transmitting said encrypted data packets across said wireless connections from said wireless access communication unit to a base station of said cellular network;

relaying said encrypted data packets from said base station to a base station controller;

relaying said encrypted data packets from said base station controller to a physically separate transcoding unit;

decrypting said encrypted data packets at said transcoding unit, thereby regenerating said data; and

relaying said data from said transcoding unit to a mobile switching center of said cellular network.

16. The method of claim 15, further comprising the steps of

receiving network-to-user data at said transcoding unit from said mobile switching center;

encrypting said network-to-user data at said transcoding unit, thereby generating encypted network-to-user data;

relaying said encrypted network-to-user data from said transcoding unit to said base station controller;

relaying said encrypted network-to-user data from said base station controller to said base station;

transmitting said encrypted network-to-user data across said wireless connections from said base station to said wireless access communication unit; and

decrypting, independently for each user in communication with said network, said network-to-user data at said wireless access communication unit.

17. The method of claim 15, further comprising the step of generating a plurality of ciphering keys at said wireless access communication unit, a different ciphering key for each wireless connection, said ciphering keys being used in said step of encrypting said data independently for each wireless connection.

18. The method of claim 17, further comprising the step of receiving said ciphering keys at said transcoding unit, said ciphering keys being used in said step of decrypting said data packets at said transcoding unit.

19. The method of claim 17, wherein said step of generating a plurality of ciphering keys at said wireless access communication unit comprises the step of retrieving a plurality of stored user key values at said wireless access communication unit, and using said user key values and a plurality of authentication parameters received from said cellular network to derive said ciphering keys.

20. The method of claim 15, wherein said wireless access communication unit is connected by said trunk interface to a local area telephone switch which is connected to said plurality of users.

21. A wireless access communication unit, comprising:

a plurality of subscriber ports connected to a plurality of users through a local area telephone switch, whereby a plurality of communication paths can be established between said wireless access communication unit and said users;

a subscriber interface connected to each of said subscriber ports;

a radio transceiver for transmitting and receiving information over a wireless connection to a base station; and

a controller connected to said radio transceiver and said subscriber interfaces, said controller managing the transfer of data between said radio transceiver and said subscriber interfaces, wherein said controller encrypts and decrypts said data using a plurality of ciphering keys, one ciphering key for each subscriber port.

22. The wireless access communication unit of claim 21, further comprising nonvolatile memory storing a plurality of user key values, one user key value for each subscriber port, wherein said ciphering keys are derived from said user key values.

23. The wireless access communication unit of claim 22, wherein said ciphering keys are derived from said user key values and a plurality of authentication parameters received from said base station.

24. The wireless access communication unit of claim 23, wherein said ciphering keys are each derived using a GSM A8 algorithm.

25. The wireless access communication unit of claim 22, further comprising a plurality of subscriber identity modules, wherein said non-volatile memory is located in each of said subscriber identity modules, and one of said user key values is stored in each of said subscriber identity modules.

26. The wireless access communication unit of claim 21, wherein said base station is connected to a transcoding unit via a base station controller, said transcoding unit encrypting and decrypting data received from said wireless access communication unit over said base station using said ciphering keys, said transcoding unit connected to a mobile switching center.

27. The wireless access communication unit of claim 21, wherein said local area telephone switch comprises either a private branch exchange (PBX) or key telephone system (KTS).