Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-03-31
2003-06-10
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S439000, C455S445000
Reexamination Certificate
active
06577867
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) movement, 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 ANSI-41D 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 conducting 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 directly 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 may 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 (used as an alternative to the handoff back message) is received by a tandem 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 may not be released, and network resources will be wasted.
These scenarios are illustrated in
FIGS. 1
,
2
,
3
, and
4
.
FIG. 1
is a network signaling and nodal operation diagram illustrating basic prior art handoff back operations, wherein the telecommunications network
10
includes a telephone
40
, an anchor MSC
60
, a tandem
1
MSC
70
, a tandem
2
MSC
80
, a 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 that a handoff operation to an adjacent candidate MSC, such as the tandem
2
MSC
80
, is appropriate, the serving MSC
90
sends 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
. In this illustration, the serving MSC
90
has also 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
, which allows the handoff operation to proceed.
The serving MSC
90
, upon receipt of the HandoffBack response
167
, sends a Handoff Order message
190
to the served MS
50
. This action directs the MS
50
to move to the available voice channel on the target MSC
80
. Upon arrival
200
of the MS
50
on the voice channel of the target MSC
80
, a FacilitiesRelease message
202
is sent from the target MSC
80
to the serving MSC
90
. This indicates that the handoff operation has been successful and that the facilities used by the serving MSC
90
are no longer needed. The serving MSC
90
, in turn, sends a FacilitiesRelease response
204
to the target MSC
80
, releasing the trunk connection
135
and marking the inter-MSC trunk
135
as idle. The target MSC
80
, in turn, marks the inter-MSC trunk
135
as idle and the handoff back process is complete. The resulting call connection between the telephone
40
and the MS
50
comprises the series of switches
100
connected by trunks
120
and
130
. The telephone
40
is connected to the Anchor MSC
60
by way of line connection or wireless interface
110
, and the MS
50
is connected to the new serving MSC
80
using the wireless network interface
137
.
The scenario
20
just described, is a classic prior art handoff back operation from a serving switch
90
to a tandem switch
80
, where the tandem switch
80
is trunk-connected to the serving switch
90
along the call path. In this scenario, the handoff back operation is directed toward the tandem
2
MSC
80
. However, the command operates in exactly the same manner if the Anchor MSC
60
is physically located in the place of the tandem
2
MSC
80
, such that the target switch
100
is the Anchor MSC
60
, instead of the tandem
2
MSC
80
. As long as the handoff back is made to the immediately previous switch in the call path, no network resources are wasted, and the ANSI-41 protocol operation functions in an efficient manner.
A successful sequence of handoff operations in the prior art can also be seen in the network signaling and nodal operation diagram of FIG.
2
. 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 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 anchor 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
6
Jenkens & Gilchrist P.C.
Maung Nay
Telefonaktiebolaget LM Ericsson (publ)
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