Method for conducting handoff back communication scenarios

Details Method for conducting handoff back communication scenarios Method for conducting handoff back communication scenarios

1999-12-16

2002-08-27

Maung, Nay (Department: 2681)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C455S439000, C455S445000, C455S560000

Reexamination Certificate

active

06442388

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to mobile cellular telecommunications, and more particularly, to a method of utilizing existing signaling protocols, such as the American National Standards Institute (ANSI)-41 protocol, to implement more efficient handoff back operations.
2. History of Related Art
Within a telecommunications network that supports Mobile Station (MS) roaming, several methods have been devised to transfer communications for active call connections maintained by any one MS as it moves away from one serving switch toward another. The American National Standards Institute (ANSI)-41 D Standard includes several procedures and messages to implement such inter-system (inter-exchange) handoff forward operations (i.e., transferring the active call connection of a MS from the serving switch to a target switch which is not currently trunk-connected in the call), and handoff back operations (i.e., transferring the active call connection from the serving switch to a target switch which is already trunk-connected within the call path). While several scenarios are offered for handling handoff forward operations with a tandem switch, only two scenarios are available when a handoff back operation must be accomplished. Further, the handoff back call connection operation is only valid for use when the target switch is connected directly to the serving switch (i.e., there is a direct trunk connection therebetween). Thus, for example, the handoff back message cannot be used to transfer a call connection from a serving Mobile Switching Center (MSC) to an anchor MSC using the anchor MSC as the target switch If there is a tandem MSC located along the call path between the anchor MSC and the serving MSC.
While it is possible to invoke the handoff back operation under such circumstances (i.e., where multiple switches are trunk-connected along a call path, and the target switch is not immediately trunk-connectable to the serving switch), the result will be that trunks between the various switches (connected before handoff) will not be released after the handoff operation occurs. Thus, network resources are wasted.
Another problem occurs when a HandoffToThird message is received by a tandem or anchor switch which does not support a handoff operation with path minimization. The result is a RETURN ERROR or REJECT response sent back to the requesting switch. Alternatively, no response at all may be received by the requesting switch. When this occurs, the serving switch must send a FacilitiesDirective message back along the call path, past the tandem switch, so that the handoff can occur. However, once again, previously connected trunks along the call path will not be released, and network resources will be wasted.
These scenarios are illustrated in
FIGS. 1
,
2
,
3
, and
4
. A successful sequence of handoff operations in the prior art can be seen in the network signaling and nodal operation diagram of FIG.
1
. In this case, a successful handoff back with tandem using the HandoffToThird message and path minimization are shown within a telecommunications network
15
including a telephone
40
, an anchor MSC
60
, a tandem
1
MSC
70
, a serving MSC
90
, and a MS
50
are shown. There is an active call connection between the telephone
40
and MS
50
, using switches
60
,
70
, and
90
, which are connected by trunks
120
and
130
. The telephone
40
(which may be a wireline telephone or another MS) is connected to the switches
60
,
70
, and
90
by way of a residential line connection or wireless network interface
110
, and the MS
50
is connected to the serving MSC using a wireless network interface
140
.
If the serving MSC
90
operates to determine that a handoff operation to a nearby candidate MSC, such as the anchor MSC
60
, is appropriate, the serving MSC
90
may send a HandoffMeasurementRequest message
150
to the anchor MSC
60
. In response, the candidate MSC
60
performs location measurements according to its internal programming algorithms, and returns the results to the serving MSC
90
in the form of a HandoffMeasurementRequest response
160
. Based on the response
160
content, the serving MSC
90
determines that the call should be handed off to the anchor MSC
60
, which is now also considered the target MSC
60
. The anchor MSC
60
will be directed to receive the MS
50
using the handoff back call connection with path minimization operation, and the MS
50
will be moved to the designated channel
107
of the anchor MSC
60
. Directing the anchor MSC
60
to receive the MS
50
involves sending a HandoffToThird message
290
from the serving MSC
90
to the tandem
1
MSC
70
, which in turn directs the tandem
1
MSG
70
to perform an intersystem handoff task with path minimization; sending a HandoffToThird message
320
from the tandem
1
MSC
70
to the anchor MSC
60
, which results in directing the anchor MSC
60
to perform task minimization and verifies that the designated channel
107
of the anchor MSC
60
is available to support the MS
50
; and sending a HandoffToThird response along the call path from the anchor MSC
60
to the serving MSC
90
(steps
330
and
340
).
Moving the MS
50
to the designated channel
107
of the anchor MSC
60
requires sending a Mobile Handoff Order
190
from the serving MSC
90
to the MS
50
and receiving the MS
50
on the designated channel
107
at arrival step
200
.
Directing the tandem
1
MSC
70
and serving MSC
90
to release the first and second inter-MSC trunks
120
and
130
, and marking the first and second inter-MSC trunks
120
and
130
as idle requires sending a FacilitiesRelease message along the call path from the anchor MSC
60
to the serving MSC
90
(i.e., steps
220
and
230
), sending a FacilitiesRelease response
260
along the call path from the serving MSC
90
to the tandem
1
MSC
70
, and sending a FacilitiesRelease response
270
along the call path from the tandem
1
MSC
70
to the anchor MSC
60
. At this point, the call path includes only the telephone line or wireless network interface
110
, the anchor. MSC
60
, and the wireless network interface
280
between the telephone
40
and the MS
50
. No unused inter-MSC trunks
120
,
130
are left connected, and network resources are conserved.
FIG. 2
is a network signaling and nodal operation diagram illustrating prior art handoff back operations, wherein the telecommunications network
10
includes a telephone
40
, an anchor MSC
60
, a tandem
1
MSC
70
, tandem
2
MSC
80
, serving MSC
90
, and a MS
50
. There is an active call connection between the telephone
40
and MS
50
, using a series of switches
100
, which are connected by trunks
120
,
130
, and
135
. The telephone
40
(which may be a wireline telephone or another MS) is connected to the switches by way of a residential line connection or wireless network interface
110
and the MS
50
is connected to the serving MSC using a wireless network interface
140
.
If the serving MSC
90
operates to determine whether a handoff operation to an adjacent candidate MSC, such as the tandem
2
MSC
80
, is appropriate, the serving MSC
90
may send a HandoffMeasurementRequest message
150
to the tandem
2
MSC
80
. In response, the candidate MSC
80
performs location measurements according to its internal programming algorithms, and returns the results to the serving MSC
90
in the form of a HandoffMeasurementRequest response
160
. Based on the response
160
content, the serving MSC
90
determines that the call should be handed off to the tandem
2
MSC
80
, which is now also considered the target MSC
80
. Further, the serving MSC
90
has determined that the tandem
2
MSC
80
is already trunk-connected along the call path.
At this point, a HandoffBack message
163
is sent from the serving MSC
90
to the target MSC
80
, which directs the target MSC
80
to initiate a handoff back task. If a voice channel on the target MSC
80
is available, a HandoffBack response
167
is returned to the serving MSC
90

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