Note: Descriptions are shown in the official language in which they were submitted.
CA 0223~870 1998-04-23
METHOD FOR ADDRESSING CALL GLARE IN WIRELESS
TELECOMMUNICATIONS SYSTEMS
Cross Reference to Related Application:
This application is related to the applications of:
Michael F. Dolan, Thomas L. McRoberts, Eshwar Pitt~mp~lli, and Thomas T.
Towle entitled "Wireless Telecommunications System For Improving Performance
And Compatibility";
Deborah L. Barclay, Michael F. Dolan, Thomas L. McRoberts, Larry E.
10 Pelletier, Albert J. Sawyer and Joseph E. Seitz entitled "Method For Source Transfer
In A Wireless Telecommunications System"; and
Deborah L. Barclay, Michael F. Dolan, Thomas L. McRoberts and Thomas T.
Towle entitled "Method For Handoff Type Selection By A Target Base Station rn A
Wireless Telecommunications System' which applications are assigned to the
15 assignee of the present application, and are being filed concullc;.llly herewith.
Technical Field:
This invention relates to wireless telecommunications networks, and more
particularly, to accommodating call glare occurring in such wireless
telecommunications networks.
20 Background of the Invention:
The world-wide proliferation of wireless telecommunications presents an
opportunity for service providers positioned to benefit from an ever-growing dem~n~l
for convenient, reliable wireless service. As these service providers are well aware,
controlling expenses while providing such service, via the procurement and
25 m~intçn~nce of state-of-the-art wireless telecommunications equipment, poses a
significant challenge. Existing wireless service providers meet this challenge by
impl~...e..t;l-g wireless telecommunications networks comprised of mobile switching
centers (MSCs) interconn~cted to base stations. The MSC completes calls between
mobile stations (that is, any mobile tçrmin~l using radio tr~n~mi~sion) and other
30 parties. These "other parties" may be mobile stations or parties served by the public-
switched telephone network. Each base station is associated with a specific
geographic region and is an interface between mobile stations within its region and the
MSC.
Existing wireless telecommunications equipment places severe limitations on
35 the ability of service providers to derive varied network configurations. This is
because telecommunications equipment vendors use rigid interconnection protocolsand dispose integral functions in a number of systems which must be ~ccessed each
CA 0223S870 1998-04-23
time a call is processed. The rigidity of current telecommunications equipment is
m~nifçsted in the inability of exi~ting wireless telecommunications systems to
accommodate call glare (that is, the situation occurring when a mobile user originates
a call on a mobile station at the same time that another call is destined for the same
5 mobile station). In existing wireless networks, only the call origin~tçd by the mobile
user will be serviced. In other words, co~ )onents of an existing wireless network
cannot decide which call to service in a call glare situation. Re~lldinls on theflexibility of wireless telecommunications e~luip",~ .,1 results in inefficiencies and
raises the cost of doing business for all wireless service providers. These costs are
10 ultimately absorbed by mobile subscribers.
Therefore, there is a need in the art for addressing call glare in wireless
teleco~ "ul~ications nclwu~
Summaly of the Invention:
This need is addressed and a technological advance is achieved by providing a
15 means for the MSC to resolve call glare situations in a wireless telecG~ ications
system. Call glare results when the MSC detects that a mobile user is allc."~ling to
place a call at the same time that another user is ~llc"l~th~g to call that mobile station.
Since it is often desirable for a nclwnl~ op.,.dlor ~: deliver the call to the mobile
station as a higher priority than completion of the call the mobile station user is
20 ~llc~ ling to make, the invention allows the MSC to signal to the base station that a
connection already initi~tçd for the mobile station is to be used to deliver a call to that
mobile station.
Brief Description of the Drawin~:
FIGs. 1-4 are illustrative embo-1;...~ ..1~ of wireless telecollll"u"ications
25systems in which the prcsent invention may be practiced;
FIG. 5 is a message flow diagram of mobile station call origination as
p~.r~"l"cd in the wil~,less teleconll"lmications system of FIG. 1;
FIG. 6 is a message flow diagram of soft handoff source transfer as performed
in the wileless teleco.~ ic~tions system of FIG. 3;
30FIG. 7 is a message flow diagram of inter-base station comn~uifications for soft
handoff support as ~.ro""ed in the wireless telecommunications system of FIG. 3;FIG. 8 is a message flow diagram of handoff type selection by a target base
station as p~.ro""ed in the wireless telecommunications system of FIG. 3;
FIG. 9 is a message flow diagram addressing call glare as performed in the
35wireless telecommunications system of FIG. 3;
FIG. 10 is a message flow diagram of .si~n~ling connection clearing by a target
base station as pc~ro~ cd in the wireless telecommunications system of FIG. 3.
CA 0223~870 1998-04-23
Detailed ~ ,tion:
FIGs. 1-4 are illustrative embo~im~nt~ of wireless telecommunications
systems in which the present invention may be practiced. Although four embo~1iment~
are shown for clarity, those skilled in the art will recognize that the first and second
5 packet interconnection protocols may enable numerous other arrangements of wireless
telecommunications systems.
FIG. 1 is a simplified block diagram of wireless telecommunications system
100 including mobile switching center (MSC) 102, first base station 110 and second
base station 120. MSC 102 includes control processor 104 for executing tasks
10 associated with call control and mobile station mobility management. Control
processor 104 is i~ rcomle~;led to call control processors of the first and second base
stations via .cign~ling links 131 and 133, respectively. In alternative emboflim~nt.~,
~ign~ling links 131 and 133 resources are conserved by multiplexing into a common
channel for ar,cessing control processor 104 of MSC 102. Switch fabric 106 is
interconn~cte~ to SDU 108 via user traffic (voice/data) link 135. In this embodiment,
SDU 108 provides frame selection and voice coding for all base stations in wireless
network 100 (in this example, base stations 110 and 120).
First base station 110 comprises call control processor 112 for ~lmini~tçring
functions associated with call origination and t~....;" .l;on, and controlling SDU 108
on a call-by-call basis; interconnection processor 114 for mapping proprietary
connections 137 into the standard user traffic int~ r,e 139 to the SDU; and channel
element 116 for establishing col,l.nu,lications between the base station and subscriber
eqllipment such as mobile station 160. Call control processor 112 and
intcrco~ ection processor 114 communicate with channel element 116 over
proprietary interfaces 137, as known in the art. SDU 108 is i~ rcomlected to
interconnection processor 114 via a first packet interconnection protocol over packet
oll-based link 139. SDU 108 is also intclcont~ected to call control processor 112
via a second packet illt~,reo~ e-;lion protocol over packet L~ s~o.l-based link 143 for
allowing first base station 110 to control SDU 108, as n.-cess~ry.
Sirnilarly, second base station 120 comprises call control processor 122,
interconnection processor 124 and channel element 126. Call control processor 122
and interconnection processor 124 communicate with channel element 126 over
pr~l;etary interfaces 129. Interconnection processor 124 is i~le~;o~ pctç~l to SDU
108 via a first packet interconnection protocol over packet transport-based link 141
and call control processor 122 is interconn~ctecl to SDU 108 via a second packetinterconnection protocol over packet transport-based link 145. Call processor 112 and
call control processor 122 communicate directly via ~ign~lin~ link 105.
CA 0223~870 1998-04-23
In this illustrative embodiment, SDU 108 is positioned within MSC 102. The
separation of the SDU function from a base station and its centralization enhances the
ability of service providers to enhance the efficiency of exi.~ting call processing
functions as described below.
S FIG. 2 is a simplified block diagram of wireless telecommunications system
200 including mobile switching center 202, first base station 220 and second base
station 240. Also shown is mobile station 260 served by the first base station. Mobile
switching center 202 includes call control processor 204 and switch fabric 206. Call
control processor 204 is int~ .col-l-çcted to call control processors of the first and
10 second base stations via ~ign~ling links 201 and 203, respectively. Switch fabric 206
is h~t~ rcol~l~e~;led to SDU 224 (positioned within the first base station) via user traffic
(voice/data) link 209. In this embodiment, SDU 224 provides frame selection and
voice coding for all calls initiated or handed off by means of hard handoff to base
station 220.
First base station 220 comprises call control processor 222, SDU 224 and
channel element 226. Channel element 226 is interconnected to the rest of the
coll~ol1e.lt~ ~,vithin the base station via proprietary int~ es 227. Second base station
240 comprises call control processor 242 and inte.col~ction processor 244 which are
hll~,lcol-l-.octed to ch~nnel elem~nt 246 via proprietary interfaces 247. In this
20 embo-limPnt, SDU 224 not only serves the first base station but is shown
interconn~cted to call control processor 242 and inle.~olll1ection processor 244 of the
second base station via packet transport -based .~ign~ling and user traffic link 233, and
packet ll~ls~l-based sign~lin~ link 231, respectively. Sign~ling link 231 allowsSDU 224 to be controlled by other base stations while sign~ling and user traffic link
25 233 enables col,l",ullication of coded voice between a base station (in this case,
second base station 240) and an SDU located in a di~renl base station (in this
e~mrle, first base station 220) on a call by call basis. Although SDU 224 is shown
positioned within first base station 220, second base station 240 may include the SDU
in ~lt~rl~tive embo~ Further, in alternative embo~ , a common si~n~ling
30 ch~nn~l is created by multiplexing multiple instances of ~ign~ling link 205 into a
single int~rf~ce ~L~en base station 220 and call control processor 204 of MSC 202,
or multiple in~t~ncçs of sign~ling link 207 into a single interface between base station
240 and call control processor 204.
FIG. 3 illustrates a network configuration embodiment in which the SDU
35 function is located indepen~l~ntly of both the MSC and base stations. In thisembodiment SDU 310 provides frarne selection and voice coding for all base stations
in wireless network 300 and can be ~ccessed by multiple base stations. More
CA 0223~870 1998-04-23
particularly, wireless telecommunications system 300 comprises mobile switching
center 302, SDU 310, first base station 320, and second base station 340.
MSC 302 comprises control processor 304 and switch fabric 306. In this
embodiment, control processor 304 is interconnected to first base station 320 and
second base station 340 via sign~lin~ links 301 and 303, respectively. SDU 310 is
interconnected to switch fabric 306 of MSC 302 via user traff1c link 307. SDU 310
also mAint~in~ packet ~ sl~oll-based user traffic and sign~ling links 313 and 315 to
interconnection processors associated with first base station 320 and second base
station, respectively. Packet ~ sl,o,l-based sign~ling links 321 and 323 are subject to
10 the second interconnection protocol and allow first base station 320 and second base
station 340, respectively, to control the SDU when necessary as described in detail
below.
First base station 320 comprises call control processor 322, interconnection
processor 324 and channel element 326. Channel element 326 communicates with
15 other colnpol1f,~ within the base station over proprietary links 327. In thisembodiment, first base station 320 serves mobile station 360. Similarly, second base
station 340 comprises control processor 342 and interconnection processor 344 which
are cormected to channel element 346 via proprietary interfaces 347.
Packet transport-based user traffic and sign~ling links 313, 315 are subject to
20 the first interconnection protocol and enable the communication of coded voice and
associated ~ign~ling between the base stations and SDU 310 on a call by call basis. In
alternative embo~ u ..l~, multiple in~t~n~es of ~ign~ling links 301 and 303,
respectively, may be multiplexed into common si~ling channels to reduce the
overall number of ~i~n~ling links which may be transmitted by the system. Call
control processor 322 and call control processor 342 can communicate directly via
sign~ling link 305.
FIG. 4 is a simplified diagram illu~llalhlg yet another embodiment of the
present invention including an "h~ volking processor" for performing functions
associated with ~ srollllillg data from a format used within the public switchedtelephone network to one used across an air intf~ ce.
Wireless teleco"~ ications system 400 comprises MSC 402, interworking
processor 410, SDU 420, first base station 430 and second base station 440. MSC 402
includes control processor 404 which communicates with the call control processors
432 and 442 of first base station 430 and second base station 440, respectively, via
3s ~ign~ling links 403 and 405, respectively. Also shown is switch fabric 406 which is
interconnected to h~lf;~ Jlking processor 410 via user data traffic link 407. In turn,
interworking processor 410 is connected to SDU 420 via user data traffic link 411.
CA 0223~870 1998-04-23
SDU 420 provides frame selection and termination of the radio link protocol used for
data tr~n~mi~ion for all base stations in wireless network 400. SDU 420 m~int~in~
packet l~ ,ol l-based links to the first and second base stations, as described below.
First base station 430 comprises call control processor 432 and interconnection
processor 434 which co~ icate with charmel element 436 over proprietary
interfaces 437. Also shown is mobile station 460 served by the first base station 430.
In this embodiment, call control processor 432 is interconnected to SDU 420 via
packet transport-based link 413 which is subject to the second interconnection
protocol. Interconnection processor 434 is interconn~cted to SDU 420 via packet
transport-based link 415 subject to the first interconnection protocol. Second base
station 440 comprises call control processor 442 and interconnection processor 444
which are connPcted to channel element 446 via proprietary interface 447. Call
control processor 442 is interconnected to SDU 420 via packet Llanspoll-based
n~lin~ link 417 while intercormection processor 444 is connçcted to the SDU via
packet transport-based link 419. Sign~ling links 413 and 417 allow each base station
to control SDU 420 as nPcess~ry for various processes including call handoff.
Sign~ling links 415 and 419 enable the communication of coded data and associated
sign~linp. between each base station and the SDU on a call by call basis. Call control
processor 432 and call control processor 442 can colnlllullicate directly via ~ign~ling
link 405.
The central, and independent location of il~ ~or~hlg processor 410 and SDU
420 allows wireless service providers great flexibility in network configuration since
the functionality associated with these two processes can be ~ccessed by a number of
base stations. In other words, allocation of the intel ~ulLillg process and the SDU
function on a per base station basis is not ~e~ ed. Although i~ vullcing processor
410 is shown in a central location, ~It~rn~tive embo-liment~ may deploy the
hl~ vol~iilg processor in many other locations, such as a base station, MSC or within
the SDU.
The above-described illustrative embodiments are presented to exemplify the
network configuration flexibility enabled by the first and second packet
interconnection protocols for communication between the MSC and base stations vi an
SDU. Although the most common implementations of the present invention have
been shown, those skilled in the art may devise numerous other arrangements using
these packet transport protocols.
Predictably, the first and second packet transport interconnection protocols
which enable the location flexibility also affect call proces~ing. To exemplify the
impact on existing call processes, a series of message flow diagrams is presented in
CA 0223S870 1998-04-23
FIGs. 5- 10. For purposes of clarity, each message flow diagram is associated with a
wireless telecoll..llunications system depicted in FIGs. 1~. Although the association
~vith a wireless telecolll~ ~ications system is made for clarity, those skilled in the art
will recogni~ that these messages may be deployed in any number of wireless
network configurations.
FIG. 5 is a message flow diagram depicting the exchange of messages required
for origination of a call from a mobile station to another party. For purposes of
example, assume that the messages described below are exchanged within ~,vireless
telecoll~ ications system 100 as shown in FIG. 1. In this example, a user
associated with mobile station 160 wishes to place a call to another party (not shown).
Accordingly, mobile station 160 transmits an origination message to its serving base
station (that is, base station 110). Base station 110 receives the origination message
and extends a service request message to MSC 102 over ~ign~ling link 131. In
response to this service request lllessage, base station 110 receives a connection
confirm~tion n~ssage from MSC 102 over ~ign~lin~ link 131. Subsequently, MSC
102 sends an ~ignm~nt request message to base station 110 over si~ling link 131.After base station 110 receives the ~.signm~nt request message from the mobile
switching center over si~n~ling link 131, base st~~ on 110 assigns radio resources to
the call and initiates a packet ll~sl)oll based channel establi~hm~nt procedure for
~ign~ling between call control processor 112 and SDU 108 over .ci~n~ling link 143 to
allow base station 110 to control SDU 108. Base station 110 also establishes a packet
Ll~spoll based communication link 139 between illl~lcon,lection processor 114 and
SDU 108. Subsequently, base station 110 establishes a traffic ~ nnel with mobilestation 160 and a call com~ilion is made. Base station 110 extends an ~signment
complete message to MSC 102 over .~ign~ling link 131 to indicate that it considers the
call to be in a "conversation state." In the prefell~d embodiment, the ac.~ignment
cclllpl~,t~lllessage includes a time palalllcter which indicates a more nearly exact time
at which the mobile began to use the traffic channel. Advantageously, this time of
origination allows the service provider to more accurately bill for the call.
FIG. 6 is a message flow diagram depicting messages exchanged during soft
handoff source transfer occurring when a user of a mobile station travels outside of the
geographic area of a first base station. For purposes of this example, assume that the
mobile station is mobile station 360 served by wiieless telecommunications system
300 shown in FIG. 3. Also assume that the mobile station is traveling out of thegeographic region served by the first base station 320 (also known as the "source"
base station) to the geographic area served by second base station 340 (also known as
the "target" base station). Initiation of call control transfer from the source base
CA 0223~870 1998-04-23
station to the target base station is commenced when source base station 320 realizes
that source transfer is nçcess~ry and extends a soft handoff source transfer message to
MSC 302 over .~ign~ling link 301. MSC 302 receives the soft handoffsource transfer
message and forwards it to target base station 340 over sign~ling link 303. The soft
5 handoffsource llan~r message includes information identifying the call ~;wlelllly
served by source base station 320. In this example, assume that target base station 340
~letermin~s that it will accept the source transfer (in alternative embodiment~, the
target base station may decline to accept the source transfer call). Accordingly, target
base station 340 extends a packet col~ne~lion request message to SDU 310 to create
10 ~ign~ling link 323 in response to receiving the soft handoffsource transfer message
from MSC 302. The packet connection request message çxt~n-led to the SDU
includes information which uniquely identifies the call cw~ lly served by the source
base station. SDU 310 then sends an acknowle~lgm~nt message to target base station
340. Target base station extends a soft handoff source L~a.lsr.,l acknowle~gm~ont
message to MSC 302 via si n~ling link 303. Subse~u~nll~r, MSC 302 folvv~ds the
soft handoff source transfer acknowle~l~n~nt message to source base station 320 over
~ignAIing link 301. In alternative embo~ , the soft handoffsource transfer
message could have been sent directly from the source base station 320 to the target
base station 340 across .~ ling link 305. The soft handoffsource transfer
20 acknowledgment message could also have been sent across ~ign~ling link 305. Upon
receipt of the soft handoff ~l~lsr~l acknowle~l m~nt message, source base station 320
extends a transfer prepare message to SDU 310 over link 313. SDU 310 responds
with a transfer prepare acknowle~grn~nt message to source base station 320 indicating
its re~linçss for source transfer. Upon receipt of the transfer prepare acknowleclgmçnt
25 message, base station 320 sends a source transfer commit message across ~ign~ling
link 321 to SDU 310 to cause the ~r~l of call control. SDU 310 fol ~v~ds the
source transfer commit message to target base station 340 over ~ign~ling link 323.
Target base station 340 then responds to the SDU with a source transfer commit
acknowlç~1gJn~nt message indicating that it now has control of SDU 310. SDU 310
30 fol~v~ds the source transfer commit acknowle~lgm~nt message to base station 320
across .~i~n~ling link 321. Next, target base station 340 sends a soft handoffsource
transfer complete message to MSC 302 via ~ign~lin~ link 303. This message notifies
the MSC that base station 340 now has control of the call which was previously served
by base station 320. Base station 320 then disconnects its connection 321 with SDU
35 310.
FIG. 7 is a message flow diagram olltlining the messages exchanged among
base stations during soft handoff add target procedures. "Soft handoff add target"
CA 0223~870 1998-04-23
refers to the process in which additional base stations become involved in the
connection to the mobile station without disruption to the voice link. A traditional
soft handoff scenario requires base stations participating in the handoffto exchange
required control data. These control messages are passed between the base stations
5 via the MSC. The latency introduced due to this procedure often does not meet the
stringent timing le~luire~ for successful soft handoff in a wireless
telecommunications system. FIG. 7 illu~ les direct base station to base station
colnnlu~lications ~lçcignP~l to improve the timing for the exchange of data and thus,
allow for con~ictçntly succçccful soft handoffs. For purposes of example, assume that
10 the messages described below are e~ch~nged within wireless telecomml-nic~tionsystem 300 as shown in FIG. 3. For clarity, first base station 320 will be referred to as
the "source" base station intlic~ting that it is the base station which currently has
control of a call to which second base station 340 (also referred to as the "target" base
station) is to be added. In accordance with the plef~lled embo-liment, source base
15 station 320 ~etermines that a handoff is required and issues a handoff request message
to target base station 340 via cign~ling link 305. Target base station 340 ~l~t~ ...;nes
that it will accept the handoff. Accordingly, i~ col~nection processor 344 in the
target base station extends a packet-based connection request to SDU 310 to create
cign~ling and user traffic link 315. SDU 310 colllplctes connection 315 and returns a
20 connection acknowleclgment message to target base station 340 indicating that the
connection has been established.
Target base station 340 then extends a handoffrequest acknowleclgmPnt
message to source base station 320 over ci~n~ling link 305. SDU 310 begins to send
packetized user traffic messages to target base station 340 across link 315 immPrli~tely
25 after the connection acknowle~gmPnt message is sent. In turn, the target base station
chAnnPl element 346 extends forward traffic ch~nnçl data frames to the mobile station
parl~ r~ting in the call which is being handed off. Upon receiving the first forward
traffic channel data frame, target base station channel element 346 begins to send
reverse idle f~ames to SDU 310 via interconnection processor 344 over link 315.
Upon ~l~t.. i~.~l ;on by SDU 310 that link 315 to base station 340 is a~lopl;ately
established, the SDU extends a packet-based connected message to source base station
320 via sign~ling link 321. Subsequently, source base station 320 extends a handoff
direction message to the mobile station participating in the call. More particularly,
source base station 320 sends a si~n~ling message to SDU 310 cont~ining a handoff
35 direction message. SDU 310 sends the handoff direction message to the mobile
station via link 313 which is intern~lly connected to base station channel element 326.
The mobile station extends a mobile station acknowledgment order to acknowledge
CA 0223~870 1998-04-23
the handoff direction message received. The mobile station acknowledgment order is
delivered to SDU 310 via ~ign~ling link 313. SDU 310 then informs source base
station 320 of succes~fill delivery of the handoffdirection message via a data forward
sign~ling delivered message which is sent on ~ign~ling link 321.
The mobile station extends a handoffcompletion message to SDU 310 via
links 327/313 and 347 /315 after completion of the soft handoffto the target base
station. Subsequently, the SDU forwards the handoffcompletion message to source
base station 320 via sign~ling link 321 and source base station 320 extends a handoff
performed message to MSC 302 via sign~ling link 301 to inform it that the mobile10 station's active location has been changed.
The introduction of the first and second interconnection protocols enables
several types of call handoffs in a wireless teleco.~ ,ications system as the mobile
station moves from one base station to another. More particularly, the various types of
handoff which occur include hard handoff, semi-soft handoff, soft handoff and soft
15 handoffwith consolidation. In the p,c;f~ d embo-limPnt when a target base station
receives a request from a source base station indicating that a handoffof a call is
requested, the target base station dete. . ~ e~ which resources are available for the call.
For example, the source base station may request a soft handoff but the target base
station may only have resources for a hard handoff. This resource data is conveyed to
20 the source base station so that agle. ~"~l~t of the handoff type is reached before the
handoff procedure is commenced.
FIG. 8 is a message flow diagram depicting the messages exc~nged in
wireless telecol"l"ullications system 300 for dete~mining handofftype selection by a
target base station. In the ~lef. llcd embodiment, the source base station may allow
25 one or more handofftype options which are conveyed to the target base station. This
particular embodiment ~ul)~l l~ both a m~n~ted handoff type (i.e., the source base
station allows only one handoff) or multiple handofftypes. Advantageously, there is a
red~lction in the number of messages exchanged during a handoff scenario due to an
increased efficiency in the handoffexecution as a result of the handofftype selection
30 proces~. Further, all the handoff messages including the list of allowed handoff types
can be circulated through the MSC across ~ign~ling links 301 and 303, thereby also
allowing the MSC to exercise control of the handoff types allowed.
For purposes of example, assume that control of mobile station 360, currently
served by source base station 320, requires a handoff. The handoff type selection
35 process begins when call controller 322 of source base station 320 extends a handoff
required message to MSC 302 via sign~ling link 301. MSC 302 receives the handoffrequired message and extends a handoffrequest message to call controller 342 of
CA 0223~870 1998-04-23
target base station 340 over .cign~ling link 303. The handoffrequest message includes
a list of allowed handofftypes as formnl~ted by call controller 322 of the source base
station.
Target base station 340 detçrmines which, if any, of the handofftype options it
5 will select to process this call. If the target base station de~ es that it may
accommodate the requested handoff, inte.comlection processor 344 extends a connect
message to the SDU to establish user traffic and ~ign~ling link 315. SDU 310
responds to the connect message by establishing sign~ling link 315 to interconnection
processor 344 of the target base station. Next, the target base station remains idle
10 while waiting to receive fol~v~d traffic channel frames from the source base station.
As soon as the first forward traffic channel data frame is received in target base station
channel element 346, channel element 346 begins to send reverse idle frames to SDU
310 via links 315 and 347. Upon receipt of the idle frames, SDU 310 ~letermin~s if
the connection bclv~.,n the mobile station and channel element 346 of the target base
15 station has been apl).ol,.;ately established and SDU 310 extends a packet connection
established message to source base station 320 via sign~ling link 313. In addition,
target base station call controller 342 extends a handoffrequest acknowle~lgm~ntmessage to MSC 302 via ~ lin~ link 303. MSC 302 then extends a handoff
command message to source base station call controller 322 so that the handoff can be
20 completed.
Another common oc~;u...nce in wireless telecommunications systems is
referred to as "glare". A glare situation occurs when a user ~U.,~ Jts to make a call at
the same time that another party is alle~ ing to call the same user. Traditionally,
wireless telecommllniç~tions systems have been unable to accommodate call glare. In
25 other words, the mobile origin~tP~I call is serviced by default. With the establi~hmtont
of the first and second interconnection protocols, a call glare situation is ~letect~ble by
both the MSC and the mobile station. However, it is the re~l,ol1sibility of the MSC to
resolve the situation by allowing only one call to be connected. More particularly,
when the mobile station has initi~tecl a call and the MSC has elected to reject the
30 inili~t~ d call and instead deliver the inco~ing call to the mobile station, the MSC must
transmit this information to the serving base station so that activities in the network
may be synchronized. The base station must signal its acceptance of the delivery of
the incoming call. In some embo-liment.~, the base station may reject delivery of the
incoming call in which case the MSC must proceed to service the call origin~tefl by
35 the mobile user.
FIG. 9 describes how sign~ling between the MSC and a base station can be
used to synchronize the network to a new call direction in glare situations (that is, how
CA 0223~870 1998-04-23
to allow a mobile initiated call to be interrupted for delivery of a call to the mobile).
For purposes of example, assume that the messages described in message flow
diagram FIG. 9 are exch~nged within wireless telecommunications system 300 as
shown in FIG. 3. The process begins when mobile station 360 l~ il'i an
origination message over an air interface to its serving base station (in this example,
first base station 320). Base station 320 acknowledges receipt of the origination
message with a base station acknowle~lgm~nt order which is delivered to the mobile
station. Subsequently, base station 320 extends a service request message to MSC 302
to create .~ign~ling link 301 and to forward the origination request. MSC 302 responds
10 to base station 320 with a connection confirm~tion message indicating establi~hment
of link 301. In this embodiment, the service request message includes mobile identity
information such as its electronic serial number. MSC 302 then extends an
~eSignml~nt request message to base station 320 requesting that the base stationallocate radio resources for the call. The ~signment request message includes a call
15 direction element indicating the MSC's desire to change the direction of the call from
mobile origin~tç~l to mobile tc l.li~ e~l In this embo-liment functions ~.~o.l.,cd by
SDU 310 are sepal~led from the base station so MSC 302 identifies SDU 310 in itsacsignment request message. Upon receipt of the ~s~ignment request message, basestation 320 initiates the packet-based channel establi~hment procedure as described in
20 FIG. 5. Next, base station 320 sends a channel ~signment message over the control
channel of the radio int~rf~e to initiate an establi~hm~nt of a radio traffic channel to
the mobile station. The mobile station and network then exchange n~cess~ry
messages to acquire the mobile station and pro~.ly connect it.
After the radio traffic channel and packet mode channel have been established,
25 base station 320 extends an aesignmPnt complete m~ss~ge to MSC 302 and indicates
its acceptance of the call direction change by including a call direction
acknowle~gm~nt element. Base station 320 then extends an alerting message to themobile station to cause ringing at the station via established links. When the call is
~ .~1, a com~ecl order is transmitted to base station 320. Base station 320 then30 extends a connccl message to MSC 302 indicating that the call has been answered at
the mobile station and is in a conversation state.
FIG. 10 is a message flow diagrarn depicting messages exchanged within
wireless telecommunications system 300 to remove lmn~cess~ry connections. More
particularly, during operation of a call that makes use of a soft handoff, a target base
35 station may be supplying a set of resources to support the call. A sign~linp. connection
specific to the call is also created between the MSC and the target base station.
Traditionally, when resources at the target base station are no longer required, they
CA 0223~870 1998-04-23
must be removed from the call under direction of the MSC In the pler~ d
embodiment of the present invention, the target base station directly interacts with the
MSC to remove such a sign~ling connection.
For purposes of example, assume that soft handoff has occurred and resources
5 at the target base station are no longer required. Accordingly, source base station 320
extends a soft handoff drop target message to MSC 302 to be fol ~valded to target base
station 340. Target base station 340 removes its packet connection 315 to SDU 310
and sends a soft handoffdrop target acknowle.lgment message to MSC 302 via link
303 to be fol~ded to source base station 320. Target base station 340, re~ ing that
10 it has no more radio resources allocated to the call, sends a clear request message to
MSC 302 to request clearing of sign~ling link 303.
MSC 302 extends a clear command message to the target base station to
instruct it to release the associated dedicated resource (that is, ~ign~ling link 303). ~n
response to the clear command message, the target base station sends a clear complete
15 message and releases ~ign~ling link 303. Note that in alternative embodiments, the soft
handoff drop target and soft handoff drop target acknowle.l~ment messages is
exchanged via ~ign~lin~ link 305.
Advantageously, the first and second interconnection protocols allow
flexibility in MSC/base station commllnie~tions which enables the above-described
20 network configuration and call proce~ g and control. Although the present invention
has been illustrated using plefelled embo lim~nt~, those skilled in the art may devise
other arrangements without departing from the scope of the invention.
