Relocating context information in header compression

Abstract

A method of relocating the header compression context in a packet network which transmits packets having compressed headers. A connection is established between a mobile terminal and a first network entity and context information used with compression and decompression of the headers of the packets is stored at the mobile terminal and the first network entity. The context information updating is stopped in the mobile terminal and in the first network entity and after that, a snapshot of the compression and decompression context information is taken and stored in the first network entity. The connection between the first network entity and the mobile terminal is changed to a connection between the mobile terminal and a second network entity. The context information snapshot stored by the first network entity is transferred to the second network entity to be stored therein as the context information of the second network entity. The stored context information at the mobile terminal and the second network entity is then used for compression and decompression of the headers of the packets.

The invention claimed is: 
     
       1. A method of relocating the header compression context in a packet network which transmits packets having compressed headers, said method comprising:
 establishing a connection between a mobile terminal and a first network entity including storing context information used with compression and decompression of the headers of the packets at the mobile terminal and the, first network entity; 
 stopping the context information updating in the mobile terminal and in the first network entity; 
 taking a snapshot of the compression and decompression context information in the first network entity including storing said context information snapshot in the first network entity; and 
 changing the connection between the first network entity and the mobile terminal to a connection between the mobile terminal and a second network entity including transferring the context information snapshot stored by the first network entity to the second network entity which is stored by the second network entity as the context information of the second network entity and using the stored context information at the mobile terminal and the second network entity for compression and decompression of the headers of the packets. 
 
     
     
       2. A method in accordance with  claim 1  wherein:
 said context information updating is stopped by disabling the mobile terminal and the first network entity decompressors from sending acknowledgements to the compressor of the opposite side. 
 
     
     
       3. A method in accordance with  claim 1  wherein:
 said context information updating is stopped by stopping the mobile terminal to compress and transmit uplink data and stopping the first network entity to compress and transmit downlink data. 
 
     
     
       4. A method in accordance with  claim 3  wherein:
 said taking a snapshot of the compression and decompression context information in the first network entity is delayed until said transmitted uplink data and downlink data has been received and decompressed. 
 
     
     
       5. A method in accordance with  claim 1  wherein:
 said context information updating is stopped by discarding in the first network entity compression/decompression acknowledgements from the mobile terminal. 
 
     
     
       6. A method in accordance with  claim 1  wherein:
 said context information updating is stopped by disabling in the first network entity to send compression/decompression acknowledgements to the mobile terminal. 
 
     
     
       7. A method in accordance with  claim 5  wherein:
 sending a context update request from the first network entity to the second network entity, in response to a detection of a context update request sent by the mobile terminal in the first network entity; and 
 sending the first packet from the second network entity to the mobile terminal as a packet containing said context update request. 
 
     
     
       8. A method in accordance with  claim 5  wherein:
 sending a context update request from the first network entity to the second network entity, in response to a detection of out-of synchronism of the context information in the first network entity; and 
 sending the first packet from the second network entity to the mobile terminal as a packet containing said context update request. 
 
     
     
       9. A method in accordance with  claim 1  wherein:
 transferring the context information snapshot stored by the first network entity to the second network entity before changing the connection between the first network entity and the mobile terminal to a connection between the mobile terminal and a second network entity. 
 
     
     
       10. A method in accordance with  claim 1  wherein:
 said method is used in accordance with Robust Header Compression (ROHC) implemented in a UMTS system. 
 
     
     
       11. A method in accordance with  claim 10  wherein:
 performing said relocation overlapping with serving radio network subsystem (SRNS) relocation. 
 
     
     
       12. A packet network in which packets having compressed headers are transmitted between a mobile terminal and network entities, said network comprising:
 a connection is arranged to established between a mobile terminal and a first network entity;   context information used with compression and decompression of the headers of the packets is arranged to be stored at the mobile terminal and the first network entity;   the context information updating in the mobile terminal and in the first network entity is arranged to be stopped;   a snapshot of the compression and decompression context information is arranged to be taken at and stored in the first network entity;   the connection between the first network entity and the mobile terminal is arranged to be changed to a connection between the mobile terminal and a second network entity, whereby the context information snap-shot stored by the first network entity is arranged to be transmitted to and stored in the second network entity as the context information of the second network entity; and   the stored context information at the mobile terminal and the second network entity is arranged to be used for compression and decompression of the headers of the packets.   
     
     
       13. A packet network in accordance with  claim 12  wherein:
 said context information updating is arranged to be stopped by disabling the mobile terminal and the first network entity decompressors from sending acknowledgements to the compressor of the opposite side. 
 
     
     
       14. A packet network in accordance with  claim 12  wherein:
 said context information updating is arranged to be stopped by stopping the mobile terminal to compress and transmit uplink data and stopping the first network entity to compress and transmit downlink data. 
 
     
     
       15. A packet network in accordance with  claim 14  wherein:
 said taking a snapshot of the compression and decompression context information in the first network entity is arranged to be delayed until said transmitted uplink data and downlink data has been received and decompressed. 
 
     
     
       16. A packet network in accordance with  claim 12  wherein:
 said context information updating is arranged to be stopped by discarding in the first network entity compression/decompression acknowledgements from the mobile. 
 
     
     
       17. A packet network in accordance with  claim 12  wherein:
 said context information updating is arranged to be stopped by disabling in the first network entity to send compression/decompression acknowledgements to the mobile terminal. 
 
     
     
       18. A packet network in accordance with  claim 16  wherein:
 a context update request is arranged to be sent from the first network entity to the second network entity, in response to a detection of a context update request sent by the mobile terminal in the first network entity; 
 the first packet is arranged to be sent from the second network entity to the mobile terminal as a packet containing said context update request. 
 
     
     
       19. A packet network in accordance with  claim 16  wherein:
 a context update is arranged to be sent request from the first network entity to the second network entity, in response to a detection of out-of-synchronism of the context information in the first network entity; and 
 the first packet is arranged to be sent from the second network entity to the mobile terminal as a packet containing said context update request. 
 
     
     
       20. A packet network in accordance with  claim 12  wherein:
 the context information snapshot stored by the first network entity is arranged to be transferred to the second network entity before changing the connection between the first network entity and the mobile terminal to a connection between the mobile terminal and a second network entity. 
 
     
     
       21. A packet network in accordance with  claim 12  wherein:
 said packet network is a UMTS system, wherein Robust Header Compression (ROHC) is implemented. 
 
     
     
       22. A method comprising:
 establishing a connection between a mobile terminal and a first network entity, wherein the first network entity includes a transmitter having a compressor that compresses packet headers and a receiver having a decompressor that decompresses packet headers;   storing context information used with the compressing and decompressing of the packet headers in the first network entity;   stopping acknowledgments to the mobile terminal to stop context information updating at a compressor of the mobile terminal;   stopping the context information updating in the compressor of the first network entity;   taking a snapshot of the stored context information; and   transmitting the context information snapshot to a second network entity to be used as the context information for compression and decompression of the headers of the packets in the second network entity for communication between the mobile terminal and the second network entity.   
     
     
       23. The method of claim 22, further comprising:
 sending an indication to the mobile terminal of a handover of the communication connection from the first network entity to the second network entity.   
     
     
       24. The method of claim 23, comprising transmitting the snapshot of the context information to the second network entity before sending the indication of handover to the mobile terminal. 
     
     
       25. The method of claim 22 wherein the stopping acknowledgments to the mobile terminal occurs after taking the snapshot of the stored context information. 
     
     
       26. The method of claim 22, comprising transmitting the snapshot of the context information to the second network entity before handover of the communication connection from the first network entity to the second network entity. 
     
     
       27. A method of communication in a first network entity, the method comprising:
 communicating with a mobile terminal, wherein the first network entity includes a transmitter having a compressor that compresses packet headers and a receiver having a decompressor that decompresses packet headers;   storing context information used with the compressing and decompressing of packet headers in the first network entity for communication between the first network entity and the mobile terminal;   disabling acknowledgments sent to a compressor of the mobile terminal to stop context information updating at the compressor of the mobile terminal;   stopping the context information updating in the compressor of the first network entity;   taking a snapshot of the stored context information; and   transmitting the context information snapshot to a second network entity to be used as the context information for compression and decompression of the headers of the packets in the second network entity for communication between the mobile terminal and the second network entity.   
     
     
       28. The method of claim 27, further comprising:
 sending an indication to the mobile terminal of handover of the communication connection from the first network entity to the second network entity.   
     
     
       29. The method of, claim 27, wherein the snapshot of the context information is transmitted to the second network entity before handover of the communication connection from the first network entity to the second network entity.