Arrangement for providing a call hand-off for a mobile station from a land-line supported private base station to a cellular base station operating in a cellular system

A private wireless system is configured for providing a call hand-off capability for a mobile station communicating with a private base station operating in the wireless system. The call in the wireless system is handed off to the public cellular system whenever the mobile station is moved near the fringe of the coverage area provided by the private base station. Once the hand-off is initiated in the private base station, a process is executed in which the private base station and a local exchange carrier cooperatively switch an active call from an existing wireless communications path established between the private base station and the mobile station to a newly created wireless communications path established between the mobile station and a public base station in the cellular system.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates generally to wireless radio telephones and, more 
particularly, to radio telephones operative with a private base station 
and public base stations in a wireless system. 
2. Description of the Prior Art 
With the growing popularity of mobile stations, which enables users to 
establish and maintain telephone communications almost anywhere, increased 
user flexibility in utilization of these mobile stations is desired. One 
approach to providing the increased user flexibility while also 
encouraging greater utilization of the mobile stations is by providing 
low-power private base stations as described in the Telecommunications 
Industry Association (TIA) Interim Standard (IS)-136, dated Nov. 17, 1995. 
This standard defines a cellular radio interface specification and sets 
forth parameters through which a user may register his or her mobile 
station with a private base station. Once the user has registered the 
mobile station with the private base station, all telephone calls for this 
mobile station, outgoing as well as incoming, are routed through this 
private base station. 
A private base station, which operates in accordance with the TIA IS-136 
cellular radio interface specification, shares the same frequency spectrum 
with large cells in the public cellular system, but operates at a greatly 
reduced power level. Also, each private base station is connected to the 
public switched telephone network and has a land-line subscriber telephone 
number which allows a subscriber in the public cellular system to use his 
or her mobile station for making or receiving telephone calls through the 
public switched telephone network or other similar network that offers the 
local exchange service. One example of a land-line supported private base 
station is disclosed in copending and commonly assigned U.S. patent 
application Ser. No. 08/509,403 which was filed on Jul. 31, 1995. 
As set forth in the TIA IS-136 cellular radio interface specification, a 
mobile station is able to originate and receive telephone calls through a 
private base station so long as the mobile station is registered with the 
private base station and also remains within the coverage region of this 
private base station. Thus, if a user of the mobile station, while on a 
telephone c(all established through the private base station, moves the 
mobile station out of the coverage region for the private base station, in 
accordance with the TIA IS-136 cellular radio interface specification, the 
call is not handed off to the public cellular system. Even though the user 
is provided with audio tones notifying him or her that the mobile is 
approaching the outer limit of the private base station's coverage area, 
if the user takes no corrective measures and goes beyond the outer fringe 
of this coverage area, the call will be dropped. 
The desired hand-off does not occur since the private base stations are not 
designed as nor meant to be connected as an integral part of the network 
of the public cellular system. One option that is available to the user of 
the mobile station is to terminate the call going through the private base 
station and reestablish contact with the remote party by using the mobile 
station to place a telephone call through the public cellular system. 
While this option may have been generally satisfactory in the past, it is 
now technically feasible and desirable to provide an arrangement for 
operation of a private base station through which a hand-off to the public 
cellular system may be achieved automatically as the mobile station is 
moved beyond the coverage region provided by the private base station. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an arrangement for configuring a 
private base station with a telephone call hand-off capability is 
provided. The private base station operates in a private wireless system 
and is configurable either to permit the user of a mobile station 
communicating with a remote party through the private base station to 
manually initiate the hand-off or have the private base station 
automatically execute the hand-off when the mobile station is moved in an 
area which is at the fringe of the coverage provided by the private base 
station. 
In the execution of the hand-off, and in accordance with an aspect of the 
invention, the arrangement uses a third party call feature and either a 
call park feature or a conference bridge feature available in, for 
example, a switch at a local exchange carrier which connects the private 
base station to the public switched telephone network. Once the hand-off 
is initiated in the private base station, by either the user of the mobile 
station or automatically in the private base station, a process is 
executed in which the private base station and the switch at the local 
exchange carrier cooperatively switch a call in progress from an existing 
wireless communication path established between the private base station 
and the mobile station to a newly created wireless communication path 
established between a public base station in the cellular system and the 
mobile station.

DETAILED DESCRIPTION 
Referring now to FIG. 1, there is shown a simplified block diagram of a 
cellular switching system, its logical entities as well as the relative 
connection with the public switched telephone network and a private base 
station. The cellular concept is well known and is described in general in 
the Bell System Technical Journal, Volume 58, Number 1, January 1979, and 
specifically in an article entitled The Cellular Concept by V. H. 
MacDonald, on pages 15 through 41 of this journal. 
Included within the cellular switching system are a mobile station (MS) 10, 
mobile switching center (MSC) 12, the public switched telephone network 
(PSTN) 14, which includes a local exchange carrier (LEC) switch 11, a 
public or cellular base station (CBS) 13, a home location register (HLR) 
15, a visiting location register (VLR) 16, and a private base station 
visiting location register (P-VLR) 30. In accordance with the 
Telecommunications Industry Association (TIA) Interim Standard (IS)-136, 
dated December 1994, a private base station (PBS) 20 is illustratively 
shown connected to the public telephone switched network 14 and 
communicates with mobile station 10 in a private wireless system defined 
by this standard. Also, a subscriber station telephone set 19 is 
illustratively shown connected to the public telephone switched network 14 
in a well known manner. 
In the operation of the private wireless system, the mobile station 10 is 
capable of originating and receiving telephone calls through the private 
base station 20 while this mobile station remains registered with this 
private base station. To maintain such registration, the mobile station 10 
must remain turned ON and stay within the coverage area of the private 
base station 20. 
While registered with the private base station 20, any incoming cellular 
telephone calls for the cellular subscriber i.e, the user of mobile 
station 10, will be automatically forwarded to the land-line number (LLN) 
for the private wireless system. This land-line number is the number 
recognized in the local exchange carrier switch 11 as being assigned to 
the private base station 20. Thus the user does not incur cellular call 
charges for these incoming calls. Similarly, the cellular subscriber's 
outgoing calls will be charged at the rate set by the local exchange 
carrier. 
In the private wireless system disclosed herein, in accordance with the 
disclosed embodiment of the invention, an arrangement for configuring 
private base station 20 with a telephone call hand-off capability is 
provided. Multiple protocols for the embodiment are described in detail 
later herein. The private base station 20 and the local exchange carrier 
switch 11 cooperatively switch a call in progress from an existing 
wireless communication path established between private base station 20 
and the mobile station 10 to a newly created wireless communication path 
established between public base station 13 in the cellular system and the 
mobile station 10. 
The private base station 20 is configurable either to permit the user of 
mobile station 10, while communicating with a remote party, through this 
base station 20, to manually initiate the hand-off or to have base station 
20 automatically execute the hand-off when mobile station 10 is moved to 
the fringe of the coverage area provided by private base station 20. Such 
hand-off is executed while the user of mobile station 10 is communicating 
with a remote party located at, for example, subscriber station telephone 
set 19. 
The mobile switching center 12 is part of the overall cellular systems 
operation. For clarity, mobile switching center 12 is illustratively shown 
connected to mobile switching center 18 and network operation controller 
(NOC) 17. Like mobile switching center 12, mobile switching center 18 is 
part of the overall cellular systems operation and may similarly have an 
home location register, a visiting location register, a private base 
station visiting location register, as well as multiple cellular base 
stations associated therewith. It is understood that other mobile 
switching centers also may be part of the cellular system. The network 
operation controller 17 provides overall control and thereby ensures that 
the operation of the whole cellular system is supported and serviced. 
The hand-off executed by private base station 20 may occur while a user at 
mobile station 10 is communicating with a remote party using a mobile 
station (not shown) located in the cellular system and served by either 
mobile switching center 12 or mobile switching center 18, for example. The 
remote party may also be using a private base station (not shown) that is 
associated either with the private base station visiting location register 
30 or another private base station visiting location register (not shown) 
that is associated with, for example, mobile switching center 18. 
The mobile switching center 12 performs all the switching functions related 
to call delivery and is interconnected to the public telephone switched 
network 14, the home location register 15, the visiting location register 
16 and the cellular base station 13. The home location register 15 
maintains a data base, profile record and call routing information or a 
pointer to the call routing information for all mobile stations in a 
particular assigned home area. The visiting location register 16 maintains 
a data base for call routing information or a pointer to the call routing 
information for those mobile stations which are visiting its assigned area 
of coverage. 
The private base station visiting location register 30 performs the 
interface functions between a private base station, such as station 20, 
and both the home location register 15 and the visiting location register 
16 for holding both call routing information and order of registered 
position information for mobile stations that are currently registered 
with the private base station. The private base station visiting location 
register 30 is also responsible for administering spectrum utilization and 
operations of the private base station 20. A private base station visiting 
location register suitable for use as register 30 is disclosed in 
copending and commonly assigned U.S. patent application Ser. No. 
08/509,406 filed on Jul. 31, 1995. 
The private base station 20 qualifies for private (or non-public) mode 
time-division-multiple-access (TDMA) cellular operation under the TIA 
IS-136 cellular radio interface, which permits a cellular mobile station 
to register with a private base station to receive or originate calls 
through a land-line connected to the public telephone switched network 
instead of through a cellular base station, such as cellular base station 
13, connected in the regular public cellular system. Specifically, this 
radio interface provides the digital control channel in accordance with 
TIA IS-136.1 and the traffic channels and control channel in accordance 
with TIA IS-136.2 for communication with the mobile station. 
The private base station 20 is limited to a very low level of transmitted 
power for restricting its coverage range to a relatively small area. This 
allows the private base station to reuse the same radio frequency spectrum 
used by the macro cellular systems as long as the frequency of use 
selected by the private base station is different from the cell for the 
regular public or macro cellular system in whose area of coverage the 
private base station is located. The operating frequency spectrum for the 
private base station is selected in a way that insures no interference to 
the macro cellular system. This is achieved by directing the private base 
station to perform channel scanning and interference measurements before 
selecting its operating frequencies. While operating in its normal mode 
awaiting receipt of an incoming call or an off-hook request from a 
registered mobile station, the private base station 20 continually 
broadcasts digital control channel information containing its identity and 
system parameters. 
A TIA IS-136 compliant mobile station can search for a private base 
station's control channel transmission using a number of techniques. One 
of these may be based on the mobile station's prior knowledge of the 
private base station's existence. Another may be in response to a mobile 
station user manually directing the mobile station to search for the 
private base station. In yet another technique the mobile station, upon 
finding the control channel of the private base station, automatically 
goes through a series of controlled procedures to obtain registration with 
the private base station. 
Once a mobile station, for example, station 10, obtains a successful 
registration with the private base station 20, the private base station 20 
makes a modem connection to the private base station visiting location 
register 30 to update the mobile station's temporary listed directory 
number (TLDN). The temporary listed directory number in this case is the 
private base station's land-line number (LLN). Hence, when an incoming 
call is directed to a particular mobile station, information including the 
temporary listed directory number for this mobile station is accessed from 
the private base station visiting locating register 30 through the home 
location register 15 or the visiting location register 16 and the call is 
routed to the private base station's LLN. It is also understood that the 
temporary listed directory number may be stored in either the home 
location register 15 or the visiting location register 16, and the mobile 
switching center 12 then accesses this TLDN from this register. The 
private base station 20 detects the ring for an incoming call and sends an 
alerting signal or page to the registered mobile station. Following the 
mobile station's response to the alerting signal, private base station 20 
establishes a traffic channel for the mobile station and generates an 
off-hook condition to connect the incoming call through the private base 
station to the mobile station. 
The cellular user is provided with a visual notification in the mobile 
station 10 when this station is registered with the private base station 
20 in the private wireless system. The mobile station features while in 
the private wireless system are advantageously arranged to be very similar 
to those available while operating in the public cellular system for 
providing convenience and case of use for the user. Such features are 
easily incorporated in a cellular telephone interface such as is described 
in U.S. patent application entitled "Streamlined User Interface For A 
Wireless Telephone," commonly assigned herewith and filed on Nov. 15, 1995 
on behalf of J. W. Davidson et al. Similarly, these features are easily 
incorporated in a cellular telephone such as AT&T's portable cellular 
phone model 3770. 
FIG. 2 shows a first protocol of a call hand-off process for handing-off an 
active call from the private wireless system to the public cellular system 
with minimal disruption to the parties conversing in the call. In the 
execution of the process, telephone communications are switched from a 
first path, which includes a wireless communications path between the 
mobile station 10 and the private base station 20, to a second path, which 
includes a wireless communications path between the mobile station 10 and 
the public base station 13, for maintaining the communications between the 
mobile station and a remote telephone station. 
In the execution of the hand-off of telephone communications occurring in 
the mobile station from the private base station 20 to the cellular base 
station 13, in accordance with the first described protocol of the 
embodiment of the invention, the arrangement uses third party call and 
call park features presently available on a 5ESS.RTM. electronic switch 
manufactured by AT&T Corp. The 5ESS electronic switch is well known and is 
described in general in the AT&T Technical Journal, Volume 64, Number 6, 
Part 2, July-August 1985. The 5ESS electronic switch may easily function 
as the local exchange carrier switch 11, and thereby provide access for 
the private base station 20 to the public switched telephone network 14. 
Available on most local exchange carrier switches, the third party call 
feature, like three-way calling, permits a subscriber at a first telephone 
to send a switch-hook flash signal to the local exchange carrier switch 
for placing the other party to the call in progress on hold in the switch 
and obtaining dial tone at the telephone. In the application of the third 
party call feature, the subscriber at the first telephone is able to make 
a telephone call to a second telephone number while leaving the other 
party to the call on hold. 
The call park feature is invoked by a code transmitted to the switch 11 
from the private base station 20. This feature is described in detail in, 
for example, AT&T's 5ESS Switch Business and Residence Custom Services 
Feature Descriptions, Document Number 235-190-101, Issue 5, dated November 
1993, pages 8-92 through 8-107. By way of general operation, the call park 
feature simply provides a way for a subscriber at a first telephone 
connected to the switch 11 to place a remote party to a conversation on 
hold in the switch, disconnect from the call, and then from a different 
telephone reconnect to the party placed on hold by dialing an appropriate 
call park feature access code recognized by the switch. 
In order to achieve the hand-off operation, the call park feature is first 
set up in the switch 11 for the private base station 20. This feature may 
be provided, by way of example, either as part of the service provided by 
the provider of the private base station or alternatively, the base 
station owner may request to be provided with this feature. Once 
available, the feature is accessed by the base station 20 over the 
subscriber line connecting this base station to the switch 11. Both a call 
park feature code and a call park access or retrieval number may be 
obtained from the switch 11 by the base station 20. 
The base station is suitably programmed with the call park feature code 
necessary to place a remote party on hold in a parked state in the switch 
11. And the call park feature access number can be provided by the base 
station 20 to the mobile station 10 during communications with this mobile 
station (e.g., this number could be a dedicated number obtained from the 
switch 11), or alternatively the mobile station user may already have the 
knowledge of this number through the service provider (e.g., this number 
could be a universal call park access number for use at switch 11). Thus 
the mobile station 10 is also suitably programmed with the call park 
feature access number (either the dedicated number or the universal call 
park access number) for later use by this mobile station. Also, it is 
possible that the mobile station be allowed to use an abbreviated 
universal feature access number which when dialed by the mobile station 
will be mapped by the mobile switching center 12 to the appropriate 
feature access number for the switch 11 where the call has been parked. 
This mapping and routing of the call to the proper feature access number 
can be accomplished by using the mobile station's registration information 
along with the private base station visiting location register 30. 
For security purposes, a personal identification number (PIN) may be 
transmitted to the switch 11 by the base station 20 during the process 
when the base station 20 dials the call park feature code to park a call. 
This PIN is then stored by the switch 11 and required to be again provided 
by the mobile station 10 before access to the party on hold is granted to 
this mobile station as it calls through the cellular network. The PIN may 
advantageously be the assigned MIN for mobile station 10 which is provided 
to the switch 11 at the same time that the call park feature code is 
dialed by the base unit 20 during the execution of the hand-off process, 
described later herein. Thus, when the mobile station 10 accesses the 
switch 11, it can use its MIN to gain access to and reconnect to the party 
placed on hold. Also, it is possible that mobile switching center 12 can 
pass on to switch 11 the calling number ID of the mobile station which 
will automatically be used as the PIN. This will eliminate the need of 
sending the PIN separately by the mobile station. 
As long as the user of the mobile station 10 remains well within the 
coverage area of the private base station 20, communication remains 
satisfactory and no hand-off of communications is necessary or performed. 
Once the user of the mobile station 10 moves near the fringe of the 
private base station coverage area, however, the private base station 20 
sends a warning tone to the mobile station user. If the user still 
continues to move further out of the private base station coverage area 
and the private base station is suitably configured, an impending hand-off 
tone is sent to the user from the private base station and the mobile 
station hand-off process is executed. Otherwise, the user dials a feature 
code to start execution of the mobile station hand-off process. 
Once the hand-off is initiated in the private base station 20, by either 
the user of the mobile station 10 or automatically in the private base 
station, the process is executed in which the private base station and the 
local exchange carrier switch 11 collectively switch the call in progress 
from an existing wireless communications path established between the 
private base station and the mobile station to a newly created wireless 
communications path established between a cellular base station, such as 
cellular base station 13, in the cellular system and the mobile station 
10. 
The execution of the hand-off process is conveniently described in the 
following steps, which may be more easily understood when read in 
conjunction with the flowchart shown in FIG. 2. 
1) From an active call the user presses a feature code (e.g. #T). This 
sends to the PBS a hand-off trigger. 
1a) The PBS detects low signal strength from the MS and sends to the MS 
hand-off warning tones, after which the PBS proceeds with the following 
process. 
2) The PBS sends a switch-hook flash to the LEC. 
3) The LEC places the other party on hold and returns a dial tone to the 
PBS. 
4) The PBS sends a deregistration message to the MS. 
5) The MS ceases communications with the PBS and releases its channel. 
6) The MS selects and registers With the public cellular system. The 
registration with the public system will automatically update the MS's 
Temporary Listed Directory Number (TLDN) with the corresponding HLR/VLR. 
7) The public cellular system accepts the MS registration. 
8) After step 4, the PBS sends a call park feature code in order to invoke 
the call park feature and optionally a PIN at the LEC. 
9) The LEC places the other party on hold into the parked state. 
10) The MS dials the call park feature access number over the cellular 
network. 
11) The cellular network routes the call park feature access number to the 
LEC. 
12) The LEC connects the parked party and the call from the MS. 
13) The call with parked party is established with MS through cellular 
network. 
The entire hand-off process for the mobile station may be achieved within 5 
seconds. This time is subject to the number of digits that are transmitted 
to the switch 11 by both the private base station 20 as well as the mobile 
station 10 during the hand-off process. The hand-off may be achieved in 
less time, for example, if the PIN and/or MIN are not provided to the 
switch 11. 
Although numerous switches presently available in the art serve as the LEC 
switch 11, many do not have a call park capability. Nevertheless, it is 
possible to achieve a call hand-off for a private wire ess system which 
has a private base station connected to a switch without such feature. 
In the execution of the hand-off of the mobile station from the private 
base station 20 to the cellular base station 13, in accordance with a 
second described protocol of the embodiment, the arrangement uses third 
party call and conference bridge features available at the local exchange 
carrier switch 11. This switch 11 also provides access for the private 
base station 20 to the public switched telephone network 14. 
Available on most local exchange carrier switches, the conference bridge 
feature permits a subscriber at a telephone to conference an additional 
party into an existing conversation in the local exchange carrier switch 
by using, for example, the third party call feature for dialing an 
additional telephone number and then bridging a party associated with a 
first call and the additional party associated with this second call 
together. In the application of the conference bridge feature, in 
accordance with the disclosed embodiment, the subscriber at the telephone 
is able to disconnect from the conference bridge and have the other 
parties remain connected in the switch. 
Although the hand-off process will not be instantaneous as it appears to a 
user in a public cellular system using this second described protocol, 
nevertheless, it will be reasonably fast. Moreover, the private base 
station user can notify the other party of the impending short 
interruption after receiving the hand-off tone in the mobile station. 
The execution of the hand-off process is conveniently described in the 
following steps, which may be more easily understood when read in 
conjunction with the flowchart shown in FIG. 3. 
1) From an active call the user presses a feature code (e.g. #T). This 
sends to the PBS a hand-off trigger. 
1a) The PBS detects low signal strength from the MS and sends to the MS 
station the hand-off warning tones, after which the PBS proceeds with the 
following process. 
2) The PBS sends a switch hook flash to the LEC. 
3) The LEC places the other party or land-line call on hold and returns a 
dial tone to the PBS. 
4) The PBS sends a deregistration message to the MS. 
5) The MS ceases communications with the PBS and releases its channel. 
6) The MS selects and registers with the public cellular system and remains 
in the idle mode. The registration with the public system will 
automatically update the MS's Temporary Listed Directory Number (TLDN) 
with the corresponding HLR/VLR. 
7) The public cellular system accepts the MS registration. 
8) After step 4, the PBS dials the Mobile Identification Number (MIN) of 
the MS to place a call to the MS through the cellular network. 
9) The cellular network routes the call to the MS. 
10) The MS is then paged. 
11) The user at the MS receives the page alert signal. 
12) The user of the MS answers. 
13) The cellular network is updated that the MS call is established. 
14) After step 8, the PBS delays a sufficient time, typically 5 seconds, to 
allow the MS call to be established throughout the cellular network and 
then generates a switch-hook flash. Before generating the switch-hook 
flash, the PBS may detect audible ring tone and then ring tone ceasing to 
confirm that the call has been established with the MS. The PBS then 
disconnects. 
15) The LEC bridges the land-line call to the dialed MS call. 
16) The MS user is able to converse with the land-line party through the 
cellular network. 
In the execution of the hand-off of the mobile station from the private 
base station 20 to the cellular base station 13, in accordance with a 
third described protocol of the embodiment, the arrangement employs third 
party call and conference bridge features available at the local exchange 
carrier switch 11. In addition, a service control point (SCP) in an 
advanced intelligent network (AIN) is also employed in the execution of 
the hand-off process. The SCP is an intelligent network service platform 
offered as an integral part of the AT&T Corp. Intelligent Network family 
of products and services. The SCP is generally described in a marketing 
document entitled AT&T A-I-Net Service Control Point (SCP), Powerful and 
Reliable Service Platform for Intelligent Networks, dated 1995. 
The execution of the hand-off process is conveniently described in the 
following steps, which may be more easily understood when read in 
conjunction with the flowchart shown in FIG. 4. 
1) From an active call the user presses a feature code (e.g. #T). This 
sends to the PBS a hand-off trigger. 
1a) The PBS detects low signal strength from the MS and sends to the MS the 
hand-off warning tones, after which it proceeds with the following 
process. 
2) The PBS sends a switch hook flash to the LEC. 
3) The LEC places the other party or land-line call on hold and returns a 
dial tone to the PBS. 
4) The PBS sends a deregistration message to the MS. 
5) The MS ceases communications with the PBS and releases its channel. 
6) The MS selects and registers with the public cellular system and remains 
in the idle mode. The registration with the public system automatically 
updates the MS's Temporary Listed Directory Number (TLDN) with the 
corresponding HLR/VLR. 
7) The public cellular system accepts the MS registration. 
8) After step 4, the PBS dials a number that is assigned an AIN Dialed 
Number Trigger. 
9) The LEC recognizes the AIN trigger number and queries the SCP. 
10) The SCP recognizes the AIN trigger number and sends a request to the 
LEC to collect dialed digits. 
11) The LEC sends either a prompt tone or a second dial tone to the PBS. 
This is a prompt to the PBS to dial the digits of the MIN for the MS. 
12) The PBS then dials the MIN of the MS to place a call to this MS through 
the cellular network. 
13) The LEC collects the dialed digits (MIN) from the PBS. 
14) The LEC sends the dialed MIN. 
15) The SCP receives the dialed MIN. 
16) The LEC associates the party on hold with the outgoing call for routing 
this party on hold to the MS via the cellular network. 
17) The SCP sends the dialed MIN and routing request to the serving HLR or 
the VLR of the MS. 
18) The HLR/VLR receives routing request and retrieves the TLDN. 
19) The HLR/VLR sends a response back to the SCP. 
20) The SCP compares the received TLDN with the MIN. If the received TLDN 
does not match the MIN, an allowance is made for the possibility that the 
MS has not been able to register with the cellular network anc repeats 
steps 17 to 20. These steps are cycled through only `N` times to prevent 
unnecessary delays. N is typically 3, i.e. 3 attempts with interval of 2 
secs. 
21) If a favorable TLDN is received within N attempts, the SCP sends a 
redirection response to the LEC and proceeds to step 23. 
22) If a favorable TLDN is not received within N attempts, a message (e.g. 
call transfer failed) is played to the party on hold. 
23) The LEC receives the response from the SCP. 
24) The LEC routes the call to the TLDN. 
25) The MS is paged. 
26) The user receives the page alert. 
27) The PBS generates a switch-hook flash and disconnects from the 
land-line call. 
28) The user answers and is able to converse with the party on hold. 
While the foregoing invention has been described in terms of the above 
embodiment, and protocols for this embodiment, it will be readily apparent 
to those skilled in the art that various modifications can be made. For 
example, a private wireless system which supports two land lines may be 
employed for providing a hand-off capability. In such a system, while the 
remote party is on hold, the system may initiate a second call through the 
land-line to the mobile station's cellular number and then bridge the call 
internally. Accordingly, such modifications are contemplated as being 
within the knowledge of one skilled in the art and may be utilized without 
departing from the spirit and scope of the claimed invention.