Telecommunications – Radiotelephone system – Including public cordless extension system
Reexamination Certificate
2000-07-21
2002-03-12
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Including public cordless extension system
C455S072000, C455S422100, C455S426100, C455S552100
Reexamination Certificate
active
06356766
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to providing a compressed data service in DECT/GSM Interworking.
BACKGROUND OF THE INVENTION
FIG. 1
shows a functional reference configuration for conventional interworking between a DECT (digital European cordless telephone) system and a GSM (global system for mobiles) system.
FIG. 1
shows that the DECT portable part (PP)
1
communicates with the DECT fixed part (FP)
2
over an air interface
3
. The fixed part
3
communicates with a GSM mobile switch centre (MSC)
4
over the standard GSM A-Interface
5
. The fixed part comprises at least one radio fixed part (RFP)
6
, which communicates wirelessly with the portable part, and a cluster control fixed part (CCFP)
7
which handles communications between the fixed part and the mobile switch centre.
In the signalling plane of the A-interface mapping takes place only on the CC/NWK and MM/NWK levels, so the DECT system does not use the lower layers of the A-interface. Documents [12] to [18] listed below provide detailed definitions of how GSM services are provided over the DECT air interface.
Document [14] cited below defines the implementation of bearer services. This takes as its basis that in the DECT/GSM interface the GSM error correcting protocol RLP is terminated to the interworking unit (IWU) of the DECT fixed part, and the DECT air interface (based on the C data profile) provides its own error correction over the DECT air interface by re-transmitting the MAC (medium access control) layer protocol and by the DLC (data link control) layer re-transmitting the LAPU protocol.
This protocol model is illustrated in
FIG. 2
, where block
8
represents the DECT portable part, block
9
represents the DECT fixed part and block
10
represents the GSM mobile switch centre interworking unit. Thus, in this standard implementation the RLP and LAPU protocols function independently; the RLP protocol operating over the A-interface (
11
in
FIG. 2
) between GSM and DECT and the LAPU protocol operating over the DECT air interface (
12
in FIG.
2
). The LAPU protocol runs all the way from the CCFP to the PP, so during provision of a data service—in which the system carries signals representing data that has been provided to the system in a digital form by a user of the DECT portable part, or that is to be provided by the system to that user in a digital form—situations where data might be lost in DECT internal handover can be taken care of either by the DECT MAC layer error correction or by the LAPU. However, error correction in the event of external handover is unclear.
Currently only the DECT C-data profile defines the use of V.42bis compression over the U-plane link by using C-plane Call Control (CC) negotiation for the compression parameter negotiation. No such functionality is defined for the DECT A/B profiles. (See documents [20] and [22]).
A significant weakness of the system described above is the relatively low data transmission level it provides over the radio interface: the highest available data rate is 9600 bps (bits per second). However, DECT provides a higher capacity over its air interface and could support higher transmission speeds.
The present invention aims to address this problem.
According to the present invention from a first aspect there is provided a DECT fixed part for providing a communications link between a DECT portable part and a GSM mobile switch centre, the fixed part comprising a compression negotiation means for: receiving from one of the portable part and the mobile switch centre a first message specifying a form of compression for a data service; and using that first message, determining a second message to be sent to the other of the portable part and the mobile switch centre to request it to adopt a corresponding form of compression for the data service; so as to allow the provision of a compressed data service between the portable part and the mobile switch centre.
The compression negotiation means preferably acts so as to, in effect, translate messages specifying forms of data service compression between the protocols of the links between the fixed part and the portable part and the first part and the mobile switch centre. The first message may suitably be a CC-SETUP message received from the portable part, in which case the second message may suitably be a SETUP message that is sent to the mobile switch centre. The first message may be a SETUP message received from the mobile switch centre, in which case the second message may suitably be a CC-SETUP message that is sent to the portable part.
One or more XID messages between the fixed part and the mobile switch centre may be used to establish an acceptable form of compression.
SUMMARY OF THE INVENTION
According to the present invention from a second aspect there is provided a method for providing a compressed data service across a communications link between a DECT portable part and a GSM mobile switch centre via a DECT fixed part, comprising: one of the portable part and the mobile switch centre sending to the fixed part a first message specifying a form of compression for a data service; the fixed part using that first message to determine a second message to be sent to the other of the portable part and the mobile switch centre to request it to adopt a corresponding form of compression for the data service; and the fixed part sending that message to the said other of the portable part and the mobile switch centre.
Preferably, if the said other of the portable part and the mobile switch centre determines that the said form of compression is not acceptable to it then it sends to the fixed part another first message specifying another form of compression for the data service. This step can be repeated. In this way, the fixed part suitably facilitates the establishment of a compressed data service that extends from end to end, between the portable part and the mobile switch centre. Once a form of data service compression has been established then one of the portable part and the mobile switch centre preferably begins to compress user data according to that compression scheme and transmits it towards the other of the portable part and the mobile switch centre. The user data is preferably not compressed or decompressed by the fixed part. On receipt the data is preferably decompressed by the said other of the portable part and the mobile switch centre.
Preferably, if the fixed part determines that a form of compression for the compressed data service that is acceptable to both the portable part and the mobile switch centre cannot be established then it sends a message to the mobile switch centre to request a form of data service compression between the fixed part and the mobile switch centre. In this case, the fixed part suitably includes compression/decompression means for compressing/decompressing data sent/received over the data service to/from the mobile switch centre.
Preferably, if the fixed part determines that a form of compression between the fixed part and the mobile switch centre cannot be established then it sends a message to the mobile switch centre to request no data service compression between the fixed part and the mobile switch centre.
The mobile switch centre suitably has an interworking unit that includes compression/decompression means. The fixed part preferably includes an interworking unit that preferably provides the compression negotiation means described above and/or preferably performs the steps described above for the fixed part. The portable part preferably includes compression/decompression means.
The negotiation procedures described above are preferably performed by means of the DECT A/B-profile.
The compression may be V.42bis compression, preferable with one or more of the said messages specifying parameters that may include one or more of: type of data compression, number of possible codewords in the algorithm and maximum encodable data string length.
REFERENCES:
patent: 5131016 (1992-07-01), Broughton et al.
patent:
Hunter Daniel
Nokia Mobile Phones Ltd.
Perman & Green LLP
Woldetatios Yemane
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