CA2142020A1 - Method and apparatus for transferring a radiotelephone call from one coverage area to another - Google Patents
Method and apparatus for transferring a radiotelephone call from one coverage area to anotherInfo
- Publication number
- CA2142020A1 CA2142020A1 CA002142020A CA2142020A CA2142020A1 CA 2142020 A1 CA2142020 A1 CA 2142020A1 CA 002142020 A CA002142020 A CA 002142020A CA 2142020 A CA2142020 A CA 2142020A CA 2142020 A1 CA2142020 A1 CA 2142020A1
- Authority
- CA
- Canada
- Prior art keywords
- control unit
- fixed control
- call
- subscriber unit
- radio
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims description 24
- 230000000977 initiatory effect Effects 0.000 claims abstract description 6
- 238000012546 transfer Methods 0.000 claims description 14
- 230000004044 response Effects 0.000 claims description 4
- 230000008878 coupling Effects 0.000 claims 3
- 238000010168 coupling process Methods 0.000 claims 3
- 238000005859 coupling reaction Methods 0.000 claims 3
- 230000006870 function Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 230000008901 benefit Effects 0.000 description 3
- 230000001413 cellular effect Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000006386 memory function Effects 0.000 description 2
- 244000228957 Ferula foetida Species 0.000 description 1
- 241001108995 Messa Species 0.000 description 1
- LGDSHSYDSCRFAB-UHFFFAOYSA-N Methyl isothiocyanate Chemical compound CN=C=S LGDSHSYDSCRFAB-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 238000012550 audit Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/08—Reselecting an access point
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/0005—Control or signalling for completing the hand-off
- H04W36/0055—Transmission or use of information for re-establishing the radio link
Abstract
Handoff between coverage areas is achieved in a radiotelephone system coupled to standard wireline switches. Upon initiation of a radiotelephone call in one radio coverage area, a directory number and radio call identifier (203) are downloaded to the subscriber unit (101) from a fixed control unit (111) associated with the coverage area. When the subscriber unit determines a handoff to a target radio coverage area is desirable, it transmits the directory number and radio call identifier to another fixed control unit (113) associated with the target radio coverage area. This fixed control unit calls the directory number and is coupled to the first fixed control unit via the standard wireline switch (115, 117). The radio call identifier is then sent to the first fixed control unit to enable the proper connection for handoff.
Description
Q~
.1VO 95/01694 PCT/US94/06471 "TRANSFERRING A RADIO TELEPHONE CALL".
=
B~(~k~round of the Invention:
This invention relates to radiotelephone commlmic~tion systems in general and more particularly to the method and 1 0 a~l,alatus of tran~re~,hlg a radiotelephone call by a subscriber unitfrom one radio coverage area to another radio coverage area.
In radiotelephone systems having more than one radio coverage area, it is well known to coordinate the service provided in the radio coverage areas by çn~hling a radiotelephone call 1 5 est~hli.ehe-l in a first of the radio coverage areas to be m~int~ined as the subscriber unit moves to a second radio coverage area. This transferring of the call service is conventionally known as h~nrloff, handover, or link transfer.
Cellular radiotelephone systems are known for their ability to 2 0 m~int~in a telephone call over a wide geographic area by h~n~ing off a telephone call between radio coverage areas (or "cells").
~n~loff techniques used in such cellular systems have been docllm~nted in the literature (see "C~ontrol Architecture" by Fluhr, et al., the Bell System Terhnic~l Journal Vol. 58, No. 1, Jan. 1979, 2 5 pp. 43-69). Generally in h~nrling off a call from one cell to another, it is necess~ry for the system to determine which cell has the best commlmic~t;on path to the subscriber unit and then instruct the subscriber unit as to which frequency it should tune in order to mzlint~in the conversation into the new, target cell. More recently, 3 0 the subscriber unit has been taking a more active role in the handoff decision-m~king process by providing information to the fixed nelwork regarding which communication ch~nnel~ are suitable for continuing the call in a target cell (see, for e~mple, United States Patent No. 5,127,100).
Q%
.1VO 95/01694 PCT/US94/06471 "TRANSFERRING A RADIO TELEPHONE CALL".
=
B~(~k~round of the Invention:
This invention relates to radiotelephone commlmic~tion systems in general and more particularly to the method and 1 0 a~l,alatus of tran~re~,hlg a radiotelephone call by a subscriber unitfrom one radio coverage area to another radio coverage area.
In radiotelephone systems having more than one radio coverage area, it is well known to coordinate the service provided in the radio coverage areas by çn~hling a radiotelephone call 1 5 est~hli.ehe-l in a first of the radio coverage areas to be m~int~ined as the subscriber unit moves to a second radio coverage area. This transferring of the call service is conventionally known as h~nrloff, handover, or link transfer.
Cellular radiotelephone systems are known for their ability to 2 0 m~int~in a telephone call over a wide geographic area by h~n~ing off a telephone call between radio coverage areas (or "cells").
~n~loff techniques used in such cellular systems have been docllm~nted in the literature (see "C~ontrol Architecture" by Fluhr, et al., the Bell System Terhnic~l Journal Vol. 58, No. 1, Jan. 1979, 2 5 pp. 43-69). Generally in h~nrling off a call from one cell to another, it is necess~ry for the system to determine which cell has the best commlmic~t;on path to the subscriber unit and then instruct the subscriber unit as to which frequency it should tune in order to mzlint~in the conversation into the new, target cell. More recently, 3 0 the subscriber unit has been taking a more active role in the handoff decision-m~king process by providing information to the fixed nelwork regarding which communication ch~nnel~ are suitable for continuing the call in a target cell (see, for e~mple, United States Patent No. 5,127,100).
Q%
In the more recently developed systems in which the subscriber unit participates in the handoffdete...~ tion, the fixed system equipment must smoothly and efficiently connect the telepho~e call from a target cell site to the call in progress. It has S been suggested in Electronic Industries ~ssof~iAtion specificationIS41 that the wireline telephone switch which initially rece*es and processes the radiotelephone call act as an anchor point for all future h~n-loff activities. The anchor wireline telephone switch then cor nects the call to the radio subscriber unit, regardless of the l O subscriber unit's cell loc~tion This plan, however, requires the wireline telephone switches to be specifically designed to handle wireless telephone services. Such use of wireline telephone switches is inefficient due to the subst~nt~ mount of overhead which must be dedicated to radiotelephone proce~ssing rather than 1~ to switch interconnection.
It has also been suggested that a Class 5 telephone switch which supports a wireline feature commonly termed "barge-in"
can be used to implement handoff. Barge-in allows a wireline subscriber C to send a Call Identity message ~lefining a call in 2 0 progress between wireline subscribers A and B to an ISDN
supporting Class 5 switch to cause all three parties to be connected via a conference bridge. Barge-in implementation for wireless h~ntloff, however, requires ISDN capability and ccnRi~tency between Class 5 switches. Moreover, h~ntlof~ using a barge-in 2 5 feature is limited to the Class 5 switch in which the caIl was ori~in~ted so that handoff occurring between radio coverage areas supported by different Class 5 switches cannot occur using collventional barge-in techniques.
Therefore, it would be desirable to employ st~ntl~rd wireline 3 0 telephone switches to control call switching functions without regard to whether the calls are wireline or wireless calls and to route call h~n-lof~between various other standard wireline telephone switches. The anchor point radiotelephone h~ntiof~
process should be m~int~ined as a radiotelephone system function 4202C) ~0 95/01694 PCT/US94/06471 which is comp~t;hle with these standard wireline telephone switches.
~qUTr~m~rv of the Invention:
The present invention encompasses the method and apparatus for transfel~;llg a user mess~ge conveying radiotelephone call by a subscriber unit from a first radio coverage area, served by a first fixed control unit which is coupled to a wireline telephone switch, l 0 to a second radio coverage area served by a second fixed control unit. A directory number, associated with the first fixed control unit and the wireline telephone switch, is transmitted from the first fixed control unit to the subscriber unit. When a need for transfer of the radiotelephone call to the second fixed control unit from the first fixed control unit is determined, the subscriber unit transmits the directory number to the second fixed control unit .
The secon~l fixed control unit places a call using the subscriber unit transmitted directory number and is cnnnected to the first fixed control unit via the wireline telephone switch such that the 2 0 user mess~Fes are coupled to the first fixed control unit when the radiotelephone call has been transferred to the second fixed control unit.
~rief Descril~tion of the Drawin~s FIG. 1 is a block diagram of a radiotelephone system illus~lating two coverage areas and which may employ the present invention.
FIG. 2 is a diagram illustrating the flow of link transfer 3 0 establishing mess~es between some of the el~ments of the radiotelephone system which may employ the present invention.
FIG. 3 is a diagram illustrating an alternative flow of link t transfer establi~hing mesfi~ges which may be employed in the present inv~ntio~-WO 95/01694 PCT/US94/06471 ~
~14'20Z~
FIG. 4 is a mess~ge format diagram which may be used in the present invention.
nescri~tion of a P.efe~led ~,mhodiment:
A system which may advantageously use the present invention is shown in the block diagram of FIG. 1. The need to employ conventional wireline telephone switches while m~int~ining a call ~nl~hor point for radiotelephone h~n~off is met by the system of FIG.
1 when employing the present invention. The radiotelephone system of the preferred embodiment is a digital radio system conveying voice or data mess~es in ~Rsi~n~d t;meslots of a TDMA implçmçntation from the subscriber unit to the fixed transceiver and in fixed timeslots of a TDM implçm~nt~tion from the fixed transceiver to the l 5 subscriber unit on separate radio frequency ~h~nnels. The system need not be so limited to utilize the present inventio}-, as single radio frequency systems, code division multiple access systems, analog systems, and other like systems may equally benefit from the advantages of the present invention. A subscriber unit 101 includes 2 0 the functions of a transceiver, a user interface, and control and memory functions. Such a subscriber unit is simil~r to other TDM/TDMA mobile and portable radiotelephone equipment being used in digital radiotelephone systems. The fixed portion of the ~y:jleLu is illustrated as being divided into coverage area A and 2 5 coverage area B, which are essentially determined by the radio tr~n~mi~cion path between the subscriber unit 101 and the fixed transceive~s. In coverage area A, two fixed transceive~s, transceiver 103 and transceiver 105, are shown, although as few as one transceiver may be used in a coverage area. In coverage area B, two 3 0 transceiveLs~ 107 and 109, are shown.
Control of the radio equipment, other subscriber units, and basic radiotelephone system operation is provided by a fixed control unit 111, which, in the preferred embodiment is termed a radio port control unit (RPCU). A typical radio port control unit includes the 3 ~ functions of an ISDN interface coupled to a timeslot interface coupled WO 95/01694 21~2020 PCT/US94/06471 .. ~ '' ' - 't ' to one or more radio port interface cards (RPIC), all under the control of control and memory functions. An RPCU which may be llt;li7e~1 in the present invention is simils~r to model SC9600 av~ilAhl~
from Motorola, Inc. but may not need certain built-in features like voice coding. An equivalent RPCU controls the functions of the radiotelephone system in coverage area B. (ISDN - BRI (basic rate interface) or PRI (primary rate interface) - is not required for handoff for the present invention, but is desirable. However, a digital connection, end to end - RPCU to RPCU and switch to switch - is l 0 preferred.) As shown in FIG. 1, two wireline telephone switches, 115 and 117, are coupled to RPCU 111 and RPCU 113, respectively. Switches 115 and 117 may be standard ESS Class 5 end offices, eg. AT&T #5, Northern Telecom DMS 100, or other standard digital switches l 5 which are typically used to control and connect conventional wireline instrl1m~nts. As a result of the use of the present invention, these wireline telephone switches do not need special mo~iific~tion in order to pelro.~ their functions for a radiotelephone system. In this way, a conventional wireline telephone switch may be used for both 2 0 wireline and wireless switching and connect to the conventional wireline netwo~k. Although only two wireline telephone switches 115 and 117 are shown in FIG. 1, the invention is unbounded by any limiting number of switches. Conversely, it is anticipated that the present invention will also be employed in wireline and 2 5 radiotelephone systems in which more than one RPCU will be coupled to a single wireline telephone switch.
As subscriber unit 101 moves about engaged in the call, it also mo..ilols the signal quality of neighhoring RPCUa by monitoring the control timeslot tr~n~missions of the neighhoring RPCUs. As the 3 0 snhs~iber unit 101 moves, for example, from coverage area A into coverage area B, it finds that the quality of the radio signal received and transmitted between the subscriber unit 101 and fixed transceiver 103 begins to deteriorate. In this instance, the subscriber unit 101 determines the quality of a radio signal which would be 3 5 transmitted between the subscriber unit 101 and transceiver 109, for WO 95/01694 ;2~4~0 PCT/US94/06471 ~mple~ would be more a~lo~-iate than the current radio chf~nn~l between the subscriber unit 101 and the fixed transceiver 103. The control and msm~ry fi.nrtionc of the subscriber unit 101, upon fletect;on of a deteriorating radio quality Rign~l, cause the subscriber unit transceiver (which in the preferred embo~imP-nt is a frequency agile transceive,-) during one of its t;meslots which are not used for its trisncmi~csion/reception to retune to the radio frequency tr~ncmi.csion from transceiver 109. A measurement of the radio r.hs3nnel quality, for ~ mple a measurement of signal to intelrelellce ratio, is performed and a dericion is made by the subscriber unit 101 to retune to the frequency of the radio rh~nn~l being used by transceiver 109. (If the radio rh~nnel frequency of transceiver 109 is the same as and coordinated with the radio r.h~nnel frequency of transceiver 103, there is no need to retune the l 5 transceiver of the subscriber unit 101. Subscriber unit 101 need only check the a~lv~l;ate timeslot in use by transceiver 1~9 for control purposes.) Once the subscriber unit 101 makes the determins~tion that a h~n~offis necess~sry to m~int~in call quality, it suspends tr~ncmicsion to the currently serving transceiver in coverage area A
2 0 (with a suspend tr~n~micsion instruction to RPCUa) and seizes an unused timeslot (marked idle in the mess2qge header field of tr~n~miR~ion from RPCUb via a transceiver coupled to it) with a tr~n~mi~æion of a handoff request message to RPCUb on this timeslot. This h~n~loff request notifies the target coverage area to 2 5 establish alternative call routing by the fixed equipment go that h~ntloff might occur. The subscriber unit then returns to the timeslnt of the currently serving RPCUa for final instructions to use the target timeslot on the radio ch~nnel associated with RPCUb.
This type of handoff has the advantage that should a cor-nec~ion 3 0 between the subscriber unit and RPCUa be lost after the handoff request is made to RPCUb, the subscriber unit may return to the target coverage area timeslot and wait for the call to be reconnecte~
there.
The process employed to realize the handoff is shown in FIG.
3 5 2. There, it is shown that the subscriber unit (SU) has initiated a NO 95/01694 ~ Q2~ PCT/US94/06471 new call 201 to the radio port control unit of coverage area A (RPCUa) and that RPCUa, finrlinE that a radio rh~nnel and timeslot was available to handle the call, responded 203 by downlo~inE to the subscriber unit (SU) call setup information, including a directory S number and a radio call i~enfifier (RCID) which is a unique call record related to this call and this subscriber unit and m~int~inetl in RPCUa. It is a feature of the present invention that the directory number 203 be a telephone number which uses the geographical number associated with the office code(s) of the wireline telephone l 0 switch which is coupled to RPCUa and then either passes that number to RPCUa (trunk call) or selects a specific groups of lines or trunks that the RPCUa may identify vwith a request for a vertical service, e.g. handoff. In the preferred embodiment, the directory number is in the form of NNN-X~ but may also include area codes where necessary. All calls initiated between RPCUa and a subscriber unit use the same directory number to identify RPCUa. It is the RCID that allows the RPCUa to ~ tin~uish between the various RPCUa active call records. After the directory number and call set-up information is transferred 2.03, voice or data m~ss~es 2 0 may then conventionally be e~h~nFed between the subscriber unit (SU) and the RPCUa and the other party by way of the wireline telephone switch 115 coupled to RPCUa (SWa). Although the directory number is conveyed to the subscriber unit (SU) upon the initiation of the radiotelephone call in the preferred embodiment, 2 5 alternative times of conveyance, for example continuous-tr~n~mis.~ion of the directory number during a control timeslot, may be employed in re~li7.ing the present invention.
VVhen the subscriber unit (SU) determines that the radio signal quality from RPCUb (the radio port control unit 113 serving 3 0 coverage area B) provides a more a~lo~l;ate signal quality, the subscriber unit (SU) seizes the idle traffic ~h~nnel of RPCUb and sends a Link Transfer request (ALT REQ) 205 to RPCUb. The ALT
REQ includes the RPCUa directory number and the radio call identifier (RCID) that is maintained in RPCUa. In response, RPCUb 3 5 sends a set up mess~ge 207 to the wireline telephone switch 117 WO 95/01694 ~14;~Q~ PCT/US94/06471 coupled to RPCUb (SWb) via a connecting basic rate interface (BRI) subscriber loop 119. (Alternatively, this connecting link may be a primary rate interface (PRI) trunk or other digital trunk connection.) This request looks like a new call input to telephone switch SWb, in which the RPCUa directory number is the called party. Wireline telephone switch 117 (SWb) then seizes a trunk to the wireline telephone switch 115 (SWa) based on this inform~tion and sends a trunk setup 209. Such interswitch commlmicA~.ion uses Et~n~Ard DS1 trunk .~ignAline, either robbed bit .~;~nA1;ng (that is, 1 0 steAlin~ the least significant bit in each DS0 timeslot at the rate of 1 out of every 6 frames, or by common channel signAlin~, e.g.
~ignAlin~ System Number 7). Once telephone switch SWa receives the intersvwitch trunk setup 209, it then conn~cts to RPCUa via either a BRI, PRI, or robbed bit DS1 trunk connection. RPCUa recognizes that the request for service on the terminal number associated with the request indicates a request for some vertical service, e.g. h~nfloff RPCUa answers the call request. Answer supervision is passed through SWa to SWb to RPCUb. It is at this time the transfer of information related to the call, e.g. the RCID is transmitted from 2 0 RPCUb to RPCUa. This process involves using idle DS0 informA~;on bits in the DS0 of choice to send the messA~es RPCUb to RPCUa.
Conventionally, the DS0 timeslot in a DS1 format has a minimum of 7 bits avAilAhle for Pulse Code Modulation (PCM) that is equal to a 56 kb/s data/voice trAn~mi~ion rate. With common chAnnel si nAlin~, 2 5 all 8 bits of each DS0 are available for a data/voice trAn~mission rate of 64 kb/s. Since the voice/data in question does not e~cee-l 32 kb/s for non-mllltiplelred traffic ~hAnnel.c, 4 or fewer of the 8 bits of the DS0 are used for the basic data/voice call (see FIG. 4). This leaves a ~I~;llillllllll of 3 bits of the 8 bits available for other uses, e.g. the 3 0 inhAn~ data chAnnçl for communications between RPCUa and RPCUb. At a minimum, this is equivalent to an 24 kb/s data channel for every RPCUb to RPCUa handof~ request. The format of the data hAn~e can be LAPb, LAPd, SS7, Q.931, or any other basic protocol used in standard data transfer operations. However, the need for 3 5 digital connection end to end is thus lemorl~trated in that without ~0 95/01694 214;~0~2~ PCT/US94/06471 this type of connection, the inb~ntl data link could not be secured and would require out of band protocols, e.g. IS41 over X.25 or SS7 to commllnicate RPCUb to RPCUa.
RPCUb sends a mess~ge to RPCUa that co~t~in~, at a .. -;.. i.. ~um in the preferred embo~iment, call control information including the RCID associated with the initial call set-up and the directory number of RPCUb (for audit and billing purposes). RPCUa then responds to RPCUb with information related to privacy (encryption information) and then sends a comm~n~l to execute the 1 0 h~n~off to the current transceiver and to the transceiver of RPCUb (which passes mess~Ees to the transceiver under its control). (This process can also be implemented using a three party connection.) After the handoffinstruction has been sent to the SU, RPCUa drops the connection between its radio transceiver and the subscriber unit l 5 (SU) and converses via the connection through RPCUb. At this time a ~leAic~te~l connection exists between RPCUa and RPCUb via trunk 125.
RPCUb sends a connect acknowledge (ACK) 219 to RPCUa using in band .~ign~ling. SWa and SWb are oblivious to the 2 0 tr~n~mission of this mess~ge because the wireline switches do not monitor this field. The DS1 format, including the in-band sign~qling bits are shown in FIG. 4. The connect acknowledge 219 mess~ge also contains the call control RCID parameter fields.
To conclude the h~ntloff, RPCUa sends an execute-ALT
2 5 message 221 to the subscriber unit (SU). The subscriber unit (SU) receives the mess~ge and moves to the channel and timeslot and sends an ALT-complete mçss~e 223 to RPCUb via the currently used radio ~h~nnel RPCUb relays the fact it received an ALT-complete mess~ge 225 to RPCUa via in band ~i~n~ling over trunk 125. RPCUa 3 0 drops the radio channel and timeslot connect;on to the subscriber unit out of a three party connection it set up. RPCUa however, retains the connection to RPCUb via trunk 125. RPCUa rem~in~ the - ~n~hor point of the call for the duration of the call even if the subscriber unit moves to another coverage area (not shown). Thus, 3 5 the ~n~hor point of the link transfer is retained within the WO 95/01694 ~42QZ~ PCT/US94/06471 i ~
radiotelephone system while m~int~ining comp~tibility with a st~ntl~rd wireline telephone switch. A simil~r process would be followed as described above for additional link transfers but once the handoff aink transfer) to the new coverage area is comrlete~-l, the connection to RPCUb is dropped in favor of the new connection.
Referring now to FIG. 3, it can be seen that a link transfer between RPCUs which are coupled to the same wireline telephone switch employ a process simil~r to that of FIG. 2 except that there is no need to set up a trunk connection between the wireline telephone 1 0 switches. Only BRI, PRI, or other local loop connections need to be set up between RPCUa, RPCUb, and the single conventional wireline telephone switch in this alternative embo~ime~t When the ALT
request 205 is received by RPCUb from the subscriber unit ~SU), RPCUb transmits a set up message 301 to its serving wireline l 5 telephone switch (SW). The wireline telephone switch SW then initiates a call set up mess~ge 303 to RPCUa. RPCUa transmits an answer mess~Ee 305 to the wireline telephone switch SW which in turn conveys the answer mess~ge 307 via a BRI to RPCUb. The connect acknowledge message 309 is transmitted to RPCUa from 2 0 RPCUb using in band sign~ling. In response, RPCUa transmits an execute ALT mess~ge 311 to the subscriber unit SU via the radio ~hp~nnel and timeslot in use. The subscriber unit SU then tr~n~mitc an ALT complete message 313 to the RPCUb on its new radio ~hs~nne and t;me lot. RPCUb then informs RPCUa of the completion of the 2 5 h~n~loff with an ALT complete message 315 via in band ~ignf3ling.
RPCUa then drops the radio channel portion of the three way call it set up.
A diagrammatic representation of the frame structure used in commlmic~tion between the wireline telephone switches 115 and 117 3 0 is shown in FIG. 4. In the ~lefe~led embo~im~nt the DS1 frame CO~lv~y:~ twenty-four timeslots at 56 Kilobits per second. Each eight bit timeslot (a DS0 timeslot) of the twenty-four DS1 slots conveys 4 bits of ADPCM effectively at 32 Kilobits per second, three bits of sign~ling effectively at 24 Kilobits per secon~ and one robbed ~ign~ling bit.
3 5 When a single DS0 slot is used to carry one call using 32 Kilobits per 4202~0 ~0 95/01694 PCT/US94/06471 secoT-tl ADPCM coded speech, it leaves four bits unused for the speech. The least significant of the rem~inin~ bits is used for st~n-l~rd bit robbed inter-office, non SS7 trunk si~n~lin~. This leaves three bits. These three bits are, in the present invention used to S provide in band si~n~lin~ between RPCUs. These mess~es are not interpreted or intercepted by the wireline telephone switch but are instead effectively end-to-end in band ~i~n~lin~ between the RPCUs.
In other words, they form a direct RPCU to RPCU link.
We Claim:
It has also been suggested that a Class 5 telephone switch which supports a wireline feature commonly termed "barge-in"
can be used to implement handoff. Barge-in allows a wireline subscriber C to send a Call Identity message ~lefining a call in 2 0 progress between wireline subscribers A and B to an ISDN
supporting Class 5 switch to cause all three parties to be connected via a conference bridge. Barge-in implementation for wireless h~ntloff, however, requires ISDN capability and ccnRi~tency between Class 5 switches. Moreover, h~ntlof~ using a barge-in 2 5 feature is limited to the Class 5 switch in which the caIl was ori~in~ted so that handoff occurring between radio coverage areas supported by different Class 5 switches cannot occur using collventional barge-in techniques.
Therefore, it would be desirable to employ st~ntl~rd wireline 3 0 telephone switches to control call switching functions without regard to whether the calls are wireline or wireless calls and to route call h~n-lof~between various other standard wireline telephone switches. The anchor point radiotelephone h~ntiof~
process should be m~int~ined as a radiotelephone system function 4202C) ~0 95/01694 PCT/US94/06471 which is comp~t;hle with these standard wireline telephone switches.
~qUTr~m~rv of the Invention:
The present invention encompasses the method and apparatus for transfel~;llg a user mess~ge conveying radiotelephone call by a subscriber unit from a first radio coverage area, served by a first fixed control unit which is coupled to a wireline telephone switch, l 0 to a second radio coverage area served by a second fixed control unit. A directory number, associated with the first fixed control unit and the wireline telephone switch, is transmitted from the first fixed control unit to the subscriber unit. When a need for transfer of the radiotelephone call to the second fixed control unit from the first fixed control unit is determined, the subscriber unit transmits the directory number to the second fixed control unit .
The secon~l fixed control unit places a call using the subscriber unit transmitted directory number and is cnnnected to the first fixed control unit via the wireline telephone switch such that the 2 0 user mess~Fes are coupled to the first fixed control unit when the radiotelephone call has been transferred to the second fixed control unit.
~rief Descril~tion of the Drawin~s FIG. 1 is a block diagram of a radiotelephone system illus~lating two coverage areas and which may employ the present invention.
FIG. 2 is a diagram illustrating the flow of link transfer 3 0 establishing mess~es between some of the el~ments of the radiotelephone system which may employ the present invention.
FIG. 3 is a diagram illustrating an alternative flow of link t transfer establi~hing mesfi~ges which may be employed in the present inv~ntio~-WO 95/01694 PCT/US94/06471 ~
~14'20Z~
FIG. 4 is a mess~ge format diagram which may be used in the present invention.
nescri~tion of a P.efe~led ~,mhodiment:
A system which may advantageously use the present invention is shown in the block diagram of FIG. 1. The need to employ conventional wireline telephone switches while m~int~ining a call ~nl~hor point for radiotelephone h~n~off is met by the system of FIG.
1 when employing the present invention. The radiotelephone system of the preferred embodiment is a digital radio system conveying voice or data mess~es in ~Rsi~n~d t;meslots of a TDMA implçmçntation from the subscriber unit to the fixed transceiver and in fixed timeslots of a TDM implçm~nt~tion from the fixed transceiver to the l 5 subscriber unit on separate radio frequency ~h~nnels. The system need not be so limited to utilize the present inventio}-, as single radio frequency systems, code division multiple access systems, analog systems, and other like systems may equally benefit from the advantages of the present invention. A subscriber unit 101 includes 2 0 the functions of a transceiver, a user interface, and control and memory functions. Such a subscriber unit is simil~r to other TDM/TDMA mobile and portable radiotelephone equipment being used in digital radiotelephone systems. The fixed portion of the ~y:jleLu is illustrated as being divided into coverage area A and 2 5 coverage area B, which are essentially determined by the radio tr~n~mi~cion path between the subscriber unit 101 and the fixed transceive~s. In coverage area A, two fixed transceive~s, transceiver 103 and transceiver 105, are shown, although as few as one transceiver may be used in a coverage area. In coverage area B, two 3 0 transceiveLs~ 107 and 109, are shown.
Control of the radio equipment, other subscriber units, and basic radiotelephone system operation is provided by a fixed control unit 111, which, in the preferred embodiment is termed a radio port control unit (RPCU). A typical radio port control unit includes the 3 ~ functions of an ISDN interface coupled to a timeslot interface coupled WO 95/01694 21~2020 PCT/US94/06471 .. ~ '' ' - 't ' to one or more radio port interface cards (RPIC), all under the control of control and memory functions. An RPCU which may be llt;li7e~1 in the present invention is simils~r to model SC9600 av~ilAhl~
from Motorola, Inc. but may not need certain built-in features like voice coding. An equivalent RPCU controls the functions of the radiotelephone system in coverage area B. (ISDN - BRI (basic rate interface) or PRI (primary rate interface) - is not required for handoff for the present invention, but is desirable. However, a digital connection, end to end - RPCU to RPCU and switch to switch - is l 0 preferred.) As shown in FIG. 1, two wireline telephone switches, 115 and 117, are coupled to RPCU 111 and RPCU 113, respectively. Switches 115 and 117 may be standard ESS Class 5 end offices, eg. AT&T #5, Northern Telecom DMS 100, or other standard digital switches l 5 which are typically used to control and connect conventional wireline instrl1m~nts. As a result of the use of the present invention, these wireline telephone switches do not need special mo~iific~tion in order to pelro.~ their functions for a radiotelephone system. In this way, a conventional wireline telephone switch may be used for both 2 0 wireline and wireless switching and connect to the conventional wireline netwo~k. Although only two wireline telephone switches 115 and 117 are shown in FIG. 1, the invention is unbounded by any limiting number of switches. Conversely, it is anticipated that the present invention will also be employed in wireline and 2 5 radiotelephone systems in which more than one RPCU will be coupled to a single wireline telephone switch.
As subscriber unit 101 moves about engaged in the call, it also mo..ilols the signal quality of neighhoring RPCUa by monitoring the control timeslot tr~n~missions of the neighhoring RPCUs. As the 3 0 snhs~iber unit 101 moves, for example, from coverage area A into coverage area B, it finds that the quality of the radio signal received and transmitted between the subscriber unit 101 and fixed transceiver 103 begins to deteriorate. In this instance, the subscriber unit 101 determines the quality of a radio signal which would be 3 5 transmitted between the subscriber unit 101 and transceiver 109, for WO 95/01694 ;2~4~0 PCT/US94/06471 ~mple~ would be more a~lo~-iate than the current radio chf~nn~l between the subscriber unit 101 and the fixed transceiver 103. The control and msm~ry fi.nrtionc of the subscriber unit 101, upon fletect;on of a deteriorating radio quality Rign~l, cause the subscriber unit transceiver (which in the preferred embo~imP-nt is a frequency agile transceive,-) during one of its t;meslots which are not used for its trisncmi~csion/reception to retune to the radio frequency tr~ncmi.csion from transceiver 109. A measurement of the radio r.hs3nnel quality, for ~ mple a measurement of signal to intelrelellce ratio, is performed and a dericion is made by the subscriber unit 101 to retune to the frequency of the radio rh~nn~l being used by transceiver 109. (If the radio rh~nnel frequency of transceiver 109 is the same as and coordinated with the radio r.h~nnel frequency of transceiver 103, there is no need to retune the l 5 transceiver of the subscriber unit 101. Subscriber unit 101 need only check the a~lv~l;ate timeslot in use by transceiver 1~9 for control purposes.) Once the subscriber unit 101 makes the determins~tion that a h~n~offis necess~sry to m~int~in call quality, it suspends tr~ncmicsion to the currently serving transceiver in coverage area A
2 0 (with a suspend tr~n~micsion instruction to RPCUa) and seizes an unused timeslot (marked idle in the mess2qge header field of tr~n~miR~ion from RPCUb via a transceiver coupled to it) with a tr~n~mi~æion of a handoff request message to RPCUb on this timeslot. This h~n~loff request notifies the target coverage area to 2 5 establish alternative call routing by the fixed equipment go that h~ntloff might occur. The subscriber unit then returns to the timeslnt of the currently serving RPCUa for final instructions to use the target timeslot on the radio ch~nnel associated with RPCUb.
This type of handoff has the advantage that should a cor-nec~ion 3 0 between the subscriber unit and RPCUa be lost after the handoff request is made to RPCUb, the subscriber unit may return to the target coverage area timeslot and wait for the call to be reconnecte~
there.
The process employed to realize the handoff is shown in FIG.
3 5 2. There, it is shown that the subscriber unit (SU) has initiated a NO 95/01694 ~ Q2~ PCT/US94/06471 new call 201 to the radio port control unit of coverage area A (RPCUa) and that RPCUa, finrlinE that a radio rh~nnel and timeslot was available to handle the call, responded 203 by downlo~inE to the subscriber unit (SU) call setup information, including a directory S number and a radio call i~enfifier (RCID) which is a unique call record related to this call and this subscriber unit and m~int~inetl in RPCUa. It is a feature of the present invention that the directory number 203 be a telephone number which uses the geographical number associated with the office code(s) of the wireline telephone l 0 switch which is coupled to RPCUa and then either passes that number to RPCUa (trunk call) or selects a specific groups of lines or trunks that the RPCUa may identify vwith a request for a vertical service, e.g. handoff. In the preferred embodiment, the directory number is in the form of NNN-X~ but may also include area codes where necessary. All calls initiated between RPCUa and a subscriber unit use the same directory number to identify RPCUa. It is the RCID that allows the RPCUa to ~ tin~uish between the various RPCUa active call records. After the directory number and call set-up information is transferred 2.03, voice or data m~ss~es 2 0 may then conventionally be e~h~nFed between the subscriber unit (SU) and the RPCUa and the other party by way of the wireline telephone switch 115 coupled to RPCUa (SWa). Although the directory number is conveyed to the subscriber unit (SU) upon the initiation of the radiotelephone call in the preferred embodiment, 2 5 alternative times of conveyance, for example continuous-tr~n~mis.~ion of the directory number during a control timeslot, may be employed in re~li7.ing the present invention.
VVhen the subscriber unit (SU) determines that the radio signal quality from RPCUb (the radio port control unit 113 serving 3 0 coverage area B) provides a more a~lo~l;ate signal quality, the subscriber unit (SU) seizes the idle traffic ~h~nnel of RPCUb and sends a Link Transfer request (ALT REQ) 205 to RPCUb. The ALT
REQ includes the RPCUa directory number and the radio call identifier (RCID) that is maintained in RPCUa. In response, RPCUb 3 5 sends a set up mess~ge 207 to the wireline telephone switch 117 WO 95/01694 ~14;~Q~ PCT/US94/06471 coupled to RPCUb (SWb) via a connecting basic rate interface (BRI) subscriber loop 119. (Alternatively, this connecting link may be a primary rate interface (PRI) trunk or other digital trunk connection.) This request looks like a new call input to telephone switch SWb, in which the RPCUa directory number is the called party. Wireline telephone switch 117 (SWb) then seizes a trunk to the wireline telephone switch 115 (SWa) based on this inform~tion and sends a trunk setup 209. Such interswitch commlmicA~.ion uses Et~n~Ard DS1 trunk .~ignAline, either robbed bit .~;~nA1;ng (that is, 1 0 steAlin~ the least significant bit in each DS0 timeslot at the rate of 1 out of every 6 frames, or by common channel signAlin~, e.g.
~ignAlin~ System Number 7). Once telephone switch SWa receives the intersvwitch trunk setup 209, it then conn~cts to RPCUa via either a BRI, PRI, or robbed bit DS1 trunk connection. RPCUa recognizes that the request for service on the terminal number associated with the request indicates a request for some vertical service, e.g. h~nfloff RPCUa answers the call request. Answer supervision is passed through SWa to SWb to RPCUb. It is at this time the transfer of information related to the call, e.g. the RCID is transmitted from 2 0 RPCUb to RPCUa. This process involves using idle DS0 informA~;on bits in the DS0 of choice to send the messA~es RPCUb to RPCUa.
Conventionally, the DS0 timeslot in a DS1 format has a minimum of 7 bits avAilAhle for Pulse Code Modulation (PCM) that is equal to a 56 kb/s data/voice trAn~mi~ion rate. With common chAnnel si nAlin~, 2 5 all 8 bits of each DS0 are available for a data/voice trAn~mission rate of 64 kb/s. Since the voice/data in question does not e~cee-l 32 kb/s for non-mllltiplelred traffic ~hAnnel.c, 4 or fewer of the 8 bits of the DS0 are used for the basic data/voice call (see FIG. 4). This leaves a ~I~;llillllllll of 3 bits of the 8 bits available for other uses, e.g. the 3 0 inhAn~ data chAnnçl for communications between RPCUa and RPCUb. At a minimum, this is equivalent to an 24 kb/s data channel for every RPCUb to RPCUa handof~ request. The format of the data hAn~e can be LAPb, LAPd, SS7, Q.931, or any other basic protocol used in standard data transfer operations. However, the need for 3 5 digital connection end to end is thus lemorl~trated in that without ~0 95/01694 214;~0~2~ PCT/US94/06471 this type of connection, the inb~ntl data link could not be secured and would require out of band protocols, e.g. IS41 over X.25 or SS7 to commllnicate RPCUb to RPCUa.
RPCUb sends a mess~ge to RPCUa that co~t~in~, at a .. -;.. i.. ~um in the preferred embo~iment, call control information including the RCID associated with the initial call set-up and the directory number of RPCUb (for audit and billing purposes). RPCUa then responds to RPCUb with information related to privacy (encryption information) and then sends a comm~n~l to execute the 1 0 h~n~off to the current transceiver and to the transceiver of RPCUb (which passes mess~Ees to the transceiver under its control). (This process can also be implemented using a three party connection.) After the handoffinstruction has been sent to the SU, RPCUa drops the connection between its radio transceiver and the subscriber unit l 5 (SU) and converses via the connection through RPCUb. At this time a ~leAic~te~l connection exists between RPCUa and RPCUb via trunk 125.
RPCUb sends a connect acknowledge (ACK) 219 to RPCUa using in band .~ign~ling. SWa and SWb are oblivious to the 2 0 tr~n~mission of this mess~ge because the wireline switches do not monitor this field. The DS1 format, including the in-band sign~qling bits are shown in FIG. 4. The connect acknowledge 219 mess~ge also contains the call control RCID parameter fields.
To conclude the h~ntloff, RPCUa sends an execute-ALT
2 5 message 221 to the subscriber unit (SU). The subscriber unit (SU) receives the mess~ge and moves to the channel and timeslot and sends an ALT-complete mçss~e 223 to RPCUb via the currently used radio ~h~nnel RPCUb relays the fact it received an ALT-complete mess~ge 225 to RPCUa via in band ~i~n~ling over trunk 125. RPCUa 3 0 drops the radio channel and timeslot connect;on to the subscriber unit out of a three party connection it set up. RPCUa however, retains the connection to RPCUb via trunk 125. RPCUa rem~in~ the - ~n~hor point of the call for the duration of the call even if the subscriber unit moves to another coverage area (not shown). Thus, 3 5 the ~n~hor point of the link transfer is retained within the WO 95/01694 ~42QZ~ PCT/US94/06471 i ~
radiotelephone system while m~int~ining comp~tibility with a st~ntl~rd wireline telephone switch. A simil~r process would be followed as described above for additional link transfers but once the handoff aink transfer) to the new coverage area is comrlete~-l, the connection to RPCUb is dropped in favor of the new connection.
Referring now to FIG. 3, it can be seen that a link transfer between RPCUs which are coupled to the same wireline telephone switch employ a process simil~r to that of FIG. 2 except that there is no need to set up a trunk connection between the wireline telephone 1 0 switches. Only BRI, PRI, or other local loop connections need to be set up between RPCUa, RPCUb, and the single conventional wireline telephone switch in this alternative embo~ime~t When the ALT
request 205 is received by RPCUb from the subscriber unit ~SU), RPCUb transmits a set up message 301 to its serving wireline l 5 telephone switch (SW). The wireline telephone switch SW then initiates a call set up mess~ge 303 to RPCUa. RPCUa transmits an answer mess~Ee 305 to the wireline telephone switch SW which in turn conveys the answer mess~ge 307 via a BRI to RPCUb. The connect acknowledge message 309 is transmitted to RPCUa from 2 0 RPCUb using in band sign~ling. In response, RPCUa transmits an execute ALT mess~ge 311 to the subscriber unit SU via the radio ~hp~nnel and timeslot in use. The subscriber unit SU then tr~n~mitc an ALT complete message 313 to the RPCUb on its new radio ~hs~nne and t;me lot. RPCUb then informs RPCUa of the completion of the 2 5 h~n~loff with an ALT complete message 315 via in band ~ignf3ling.
RPCUa then drops the radio channel portion of the three way call it set up.
A diagrammatic representation of the frame structure used in commlmic~tion between the wireline telephone switches 115 and 117 3 0 is shown in FIG. 4. In the ~lefe~led embo~im~nt the DS1 frame CO~lv~y:~ twenty-four timeslots at 56 Kilobits per second. Each eight bit timeslot (a DS0 timeslot) of the twenty-four DS1 slots conveys 4 bits of ADPCM effectively at 32 Kilobits per second, three bits of sign~ling effectively at 24 Kilobits per secon~ and one robbed ~ign~ling bit.
3 5 When a single DS0 slot is used to carry one call using 32 Kilobits per 4202~0 ~0 95/01694 PCT/US94/06471 secoT-tl ADPCM coded speech, it leaves four bits unused for the speech. The least significant of the rem~inin~ bits is used for st~n-l~rd bit robbed inter-office, non SS7 trunk si~n~lin~. This leaves three bits. These three bits are, in the present invention used to S provide in band si~n~lin~ between RPCUs. These mess~es are not interpreted or intercepted by the wireline telephone switch but are instead effectively end-to-end in band ~i~n~lin~ between the RPCUs.
In other words, they form a direct RPCU to RPCU link.
We Claim:
Claims (10)
1. A method of transferring a user message conveying radiotelephone call by a subscriber unit from a first radio coverage area, served by a first fixed control unit which is coupled to a wireline telephone switch, to a second radio coverage area served by a second fixed control unit, comprising the steps of:
transmitting a directory number, associated with the first fixed control unit and the wireline telephone switch, from the first fixed control unit to the subscriber unit;
storing said transmitted directory number at the subscriber unit;
transmitting said stored directory number from the subscriber unit to the second fixed control unit when a need for transfer of the radiotelephone call to the second fixed control unit from the first fixed control unit is determined;
calling said subscriber unit transmitted directory number from the second fixed control unit; and connecting the second fixed control unit call to the first fixed control unit via the wireline telephone switch whereby the user messages from the second fixed control unit are coupled to the first fixed control unit when the radiotelephone call has been transferred to the second fixed control unit.
transmitting a directory number, associated with the first fixed control unit and the wireline telephone switch, from the first fixed control unit to the subscriber unit;
storing said transmitted directory number at the subscriber unit;
transmitting said stored directory number from the subscriber unit to the second fixed control unit when a need for transfer of the radiotelephone call to the second fixed control unit from the first fixed control unit is determined;
calling said subscriber unit transmitted directory number from the second fixed control unit; and connecting the second fixed control unit call to the first fixed control unit via the wireline telephone switch whereby the user messages from the second fixed control unit are coupled to the first fixed control unit when the radiotelephone call has been transferred to the second fixed control unit.
2. A method in accordance with the method of claim 1 wherein said step of transmitting a directory number from the first fixed control unit to the subscriber unit further comprises the step of transmitting said directory number in response to an initiation of the radiotelephone call in the first coverage area.
3. A method in accordance with the method of claim 1 wherein said step of transmitting said stored directory number from the subscriber unit further comprises the step of measuring by the subscriber unit a radio signal quality in the second radio coverage area whereby said need for transfer of the radiotelephone call is determined.
4. A method in accordance with the method of claim 1 further comprising the step of transmitting radio call control information from the first fixed control unit to the subscriber unit.
5. A method in accordance with the method of claim 4 further comprising the steps of storing said transmitted radio call control information at the subscriber unit and transmitting said stored radio call control information from the subscriber unit to the second fixed control unit when a need for transfer of the radiotelephone call to the second fixed control unit from the first fixed control unit is determined.
6. A method in accordance with the method of claim 5 wherein said step of connecting the second fixed control unit to the first fixed control unit further comprises the step of coupling said subscriber unit transmitted radio call control information to the first fixed control unit.
7. A radiotelephone system having at least two radio coverage areas and employing a wireline telephone switch to couple radiotelephone calls to the wireline telephone network, the radiotelephone system having the capability of handoff of a subscriber unit radiotelephone call from a first radio coverage area to a second radio coverage area, and comprising:
a first fixed control unit coupled to the wireline telephone switch and associated with the first radio coverage area, said first fixed control unit having means for providing a directory number associated with the first fixed control unit and the wireline telephone switch to the subscriber unit;
a second fixed control unit, associated with the second radio coverage area, said second fixed control unit having:
means for accepting a first message, including said directory number, from the subscriber unit for initiation of a handoff, means for placing a call to said directory number, and means for coupling a second message to said first fixed control unit via the wireline telephone switch.
a first fixed control unit coupled to the wireline telephone switch and associated with the first radio coverage area, said first fixed control unit having means for providing a directory number associated with the first fixed control unit and the wireline telephone switch to the subscriber unit;
a second fixed control unit, associated with the second radio coverage area, said second fixed control unit having:
means for accepting a first message, including said directory number, from the subscriber unit for initiation of a handoff, means for placing a call to said directory number, and means for coupling a second message to said first fixed control unit via the wireline telephone switch.
8. A radiotelephone system in accordance with claim 7 further comprising means for initiating a radiotelephone call between the subscriber unit and the first fixed control unit and wherein said means for providing a directory number to the subscriber unit further comprises means for transmitting said directory number to the subscriber unit in response to said radiotelephone call initiation.
9. A radiotelephone system in accordance with claim 7 wherein said first fixed control unit further comprises means for transmitting radio call control information to the subscriber unit.
10. A radiotelephone system in accordance with claim 9 wherein said means for accepting a first message further comprises means for accepting said radio call control information and wherein said second fixed control unit further comprises means for coupling said radio call control information to the first fixed control unit.
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-
1994
- 1994-06-08 WO PCT/US1994/006471 patent/WO1995001694A1/en not_active Application Discontinuation
- 1994-06-08 PL PL94307565A patent/PL174337B1/en unknown
- 1994-06-08 EP EP94921266A patent/EP0659321A4/en not_active Withdrawn
- 1994-06-08 RU RU95108253A patent/RU2110154C1/en active
- 1994-06-08 JP JP7503502A patent/JPH08500953A/en not_active Ceased
- 1994-06-08 AU AU72055/94A patent/AU7205594A/en not_active Abandoned
- 1994-06-08 BR BR9405437-1A patent/BR9405437A/en unknown
- 1994-06-08 CN CN94190451A patent/CN1111472A/en active Pending
- 1994-06-08 HU HU9500643A patent/HUT71357A/en unknown
- 1994-06-08 CA CA002142020A patent/CA2142020A1/en not_active Abandoned
- 1994-07-01 MX MX9405035A patent/MX9405035A/en not_active IP Right Cessation
-
1995
- 1995-02-28 KR KR95700861A patent/KR0145984B1/en not_active IP Right Cessation
- 1995-03-02 FI FI950967A patent/FI950967A/en unknown
-
1996
- 1996-04-29 US US08/639,538 patent/US5590172A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| AU7205594A (en) | 1995-01-24 |
| US5590172A (en) | 1996-12-31 |
| HUT71357A (en) | 1995-11-28 |
| HU9500643D0 (en) | 1995-04-28 |
| CN1111472A (en) | 1995-11-08 |
| EP0659321A4 (en) | 1999-03-10 |
| FI950967A0 (en) | 1995-03-02 |
| RU2110154C1 (en) | 1998-04-27 |
| FI950967A (en) | 1995-03-02 |
| EP0659321A1 (en) | 1995-06-28 |
| WO1995001694A1 (en) | 1995-01-12 |
| PL174337B1 (en) | 1998-07-31 |
| MX9405035A (en) | 1995-01-31 |
| BR9405437A (en) | 1999-09-08 |
| JPH08500953A (en) | 1996-01-30 |
| PL307565A1 (en) | 1995-05-29 |
| KR0145984B1 (en) | 1998-08-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20000608 |