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Description  |
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FIELD OF THE INVENTION
This invention relates to radiotelephone communication systems in general and more particularly to the method and apparatus enabling local mobility for wireless local loop customers with minimum special network elements. Reference is made to
copending U.S. patent application Ser. No. 08/085,374 filed in behalf of Lodwig, et al. on Jul. 2, 1993, assigned to the same assignee as the present invention, and which may contain related material.
BACKGROUND OF THE INVENTION
Personal communications service (PCS) generically describes a form of wireless telephone communication having the characteristics of low power, short range, and low cost. It is envisioned that PCS will economically compete with both cellular
radiotelephone services and wireline telephone services. For a general overview of PCS type services and equipment see "Personal Wireless" by Bennett Z. Kobb, IEEE Spectrum June 1993, pages 21-25.
Several concepts of multiply-tiered services for PCS customers have been advanced. One key discriminator among the various service tiers is the degree of mobility accommodated by each of the tiers. A basic two service tier would include "local"
service and "enhanced" service. Both provide complete wireless telephony for voice and low speed data, voice mail, and short message services. Local service is conventionally restricted to radio coverage provided in selected geographic
subregions--public/private, indoor/outdoor--of a total PCS service area. This service is configured to provide "pedestrian" stowice to portables. Enhanced service conventionally includes the local service plus an additional "cellular-like" service to
accommodate vehicle-borne portable units moving at moderate or high speeds. Enhanced service subscribers conventionally require dual mode portables. Full mobility for either service is desirable and would include inter-system handoff and local,
regional, national, and international roaming among various interconnected systems using a standard intersystem protocol. Realizing such a wide area of mobility, however, necessitates the addition of expensive network elements to a conventional wireline
telephone system. Such network elements are location registers, specially programmed telephone exchanges, and telephony signaling networks. It is desirable that automatic delivery of incoming calls be achieved regardless of the subscribers current
location.
The fixed Public Switched Telephone Network (PSTN) in the U.S. basically consists of a large number of telephone switching offices interconnected with one another by means of interoffice trunks. Connected to the telephone network is a very
large number of customers, each of whom has a telephone set that is connected to one specific telephone switching office (end office) by a particular physical set of wires or their equivalent that go from the customer's telephone set to the end office.
For this fixed network a numbering plan is employed in the U.S. by which each telephone line (each "local loop") is identified by a particular number. This number has a geographical significance in the sense that it is structured to have an area code
which localizes it to a particular area of the country, an office code which localizes the number further to a particular end office switching system, and a line code which localizes it finally to a specific line appearance on that end office. The
entire network is arranged so that whenever a particular line indicates a customer's request for service (an ON-HOOK to OFF-HOOK transition), the end office to which the line is connected recognizes who the customer is (for billing purposes), where the
customer is, and what kind of services are authorized for the customer's particular line. This procedure is called "call origination". Dialled digits that are received from the line for a call are recognized by the end office as indicating a particular
outgoing route based on the area code and office code combination. The call is routed step by step in this fashion through the network until it reaches the far end where the destination end office recognizes the dialled area code, office code, and line
code combination as representing a local loop connected to it. This procedure is called "call routing". The called line is then alerted (rung) and when the called party answers (OFF-HOOK) the final connection for the call can then be made. This
procedure is called "call termination".
Thus, every telephone has a line or a local loop that has a number which uniquely identifies it. It is conventional logic in the telephone network that every telephone stays fixed and attached to its particular line appearance and does not move
around. A local loop, conventionally, does not provide for customer mobility.
Cellular or mobile telephone service enables customers to have telephone sets (radiotelephones) that are not attached by wires to an end office. There is no office anywhere that has a line appearance that is recognized as being associated with
the number of that radiotelephone. This means that most of the end user offices in the North American fixed telephone network are not able to deal with mobile telephones. The fixed end offices are not equipped for customers and telephone sets that are
not attached to one specific fixed line appearance all of the time. Since conventional end offices cannot identify calling parties, route calls, do billing, or provide services and features except on the basis of fixed local loops, special switching
systems, called mobile telephone switching offices (MTSO), are designed with special software and special hardware to interwork with each other via a suitable signalling network to accommodate customer mobility. The MTSOs also interface with the rest of
the fixed telephone network, usually on a trunked basis, and thus constitute a mobile telephone network separate from but ancillary to the PSTN. With this equipment, customers and their radiotelephones can move around from one place to another, from one
part of the country to another, from one city to another, and from one system to another.
To facilitate this mobility, standards have been devised (Air Interface Specifications) by which the radiotelephones can identify themselves to whatever mobile telephone system in which they find themselves. The system can then interwork through
a suitable signalling network with other elements of the mobile telephone network to identify the customer, validate the customer's ability to get service, and record the network location of the customer at the moment.
If the called radiotelephone's current recorded network location is determined to be the originating MTSO, then that MTSO must execute a call termination procedure that includes determining whether or not the radiotelephone is in service,
establishing contact with the radiotelephone and assigning it to a radio channel, alerting the radiotelephone user and, if an answer is received, making the final connection. However, if the radiotelephone's current recorded network location is not the
originating MTSO, then the routing procedure must be extended to establish a connection with the current serving MTSO where the radiotelephone is located and that MTSO must execute the call termination procedure.
Thus, there is a clear network difference between a customer who is served by a fixed local loop where his telephone set is always found at the end of wire-like connections in the end office and a customer who is served by a radiotelephone which
is dynamically changing locations, a consequence of which is that no local loop nor its associated advantages is present for the radiotelephone customer. Since a personal communications service (PCS) is a service which closely associates a telephone
number with a customer, it would be desirable that a PCS stowice offer the advantages of both a local loop service and mobile telephone stowice without the added expense of additional network elements to obtain customer mobility.
BRIEF
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a wireless local loop system which may employ the present invention.
FIG. 2 is a block diagram of the fixed equipment architecture of a wireless local loop network which may employ the present invention.
FIG. 3 is a timing diagram of subscriber registration in the home access network which may be employed in the present invention.
FIG. 4 is a timing diagram of subscriber registration in the visited access network which may be employed in the present invention.
FIG. 5 is a timing diagram of subscriber call origination in the home access network which may be employed in the present invention.
FIG. 6 is a timing diagram of an incoming call termination in the home access network which may be employed in the present invention.
FIG. 7 is a timing diagram of subscriber call origination in the visited access network which may be employed in the present invention.
FIG. 8 is a timing diagram of an incoming call termination in the visited access network which may be employed in the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The present invention is encompassed in a radiotelephone system which uses radio as a part of the connection in the local loop so that there is a location where the customer is "located" and a fixed line appearance is found on a particular
conventional end office. That end office is oblivious to whether there is radio in the customer's local loop or not; it is just another line appearance to the end office and is treated as though the customer's telephone set were an ordinary wired
telephone.
A system which could employ the present invention is shown in the simple depiction of FIG. 1. Relatively short range radio communication is realized from one or more radio transceivers (radio port-RP) 101, 103. In the preferred embodiment, an
RP is a digital radio transceiver having a relatively low power transmitter. RPs 101, 103 are placed at convenient locations where access to subscriber loop facilities of the public switched telephone network (PSTN) 105 are accessible. Relatively short
range radio communication (relative to for example, cellular radiotelephone communication range) is realized from the RP to a wireless fixed access units (WFAU) 107,108 or portable radiotelephones 109, 110.
A WFAU in the preferred embodiment is a customer station in which the radio portion is fixed mounted to the side of the house, for example, and the customer interface is an ordinary telephone. The term wireless fixed access for this equipment is
appropriate because, although the customer station is wireless, its location is fixed. The term local loop is also appropriate because the end office side end of the radio link terminates an ordinary local loop line appearance. This form of the stowice
is thus termed wireless fixed access local loop service. It is, as far as the end office is concerned, exactly the same as the service provided to wired telephones by that same office. The portable radiotelephone operates using the same air interface
as the wireless fixed access unit. The portable 109 communicates with a radio port 103. All calls for a particular customer's WFAU or for a particular customer's portable radiotelephone would come in to the particular customer's local loop from the
particular end office. All outgoing calls go back into the network on that same local loop using the same set of radio links and the same set of radio ports. With a portable radiotelephone, however, the customer can move about freely and the service
may be termed Metropolitan Cordless Local Loop (MCLL) service.
In a system such as that depicted in FIG. 1, where there are a number of radio ports that form, collectively, a wireless access network attached to a specific end office, a portable radiotelephone subscriber may wander amongst the aggregate radio
port coverage areas forming that same wireless access network. The conventional end office is not aware that the customer is moving; it treats the customer's service as though it were a standard local loop service. All calls use the customer's local
loop, all billing is done with respect to the local loop, and all features are controlled in the end office by means of the local loop and the feature table associated with that particular local loop. All aspects of the portable's mobility are dealt
with by the elements of the access network.
It is a feature of the present invention that the local loop customer can go beyond his own home wireless access network where his local loop resides. The customer may travel, in the preferred embodiment, into the radio coverage area of a
different wireless access network in the same metropolitan area, where "metropolitan area" consists of any set of end offices equipped with wireless access networks and defined as such by the provider of wireless local loop service. This different
wireless access network may, alternatively, be attached to the same end office or to a different end office but within the same metropolitan area.
When the customer is operating in the coverage area of an access network that is not his home access network, the local loop calling rules still apply. All incoming and outgoing traffic to and from that customer must still use the local loop of
the customer's home wireless access network. That is, when the customer is to receive an incoming call when not in the home access network, the call is routed by the PSTN to the local loop of the customer's home access network. The home access network
must have a record of where the customer is currently located and be capable of extending the call to this different access network.
When the customer initiates a call while operating in a different access network, that access network recognizes that the customer's local loop is not present there and must be capable of extending the call back to the customer's home access
network where the customer's local loop resides. This is accomplished in the preferred embodiment with a set of telephone numbers. In addition to a local loop for each home subscriber, each access network utilizes a number of trunks that connect it to
an ordinary end office. That group of trunks is associated with an access network telephone number so that whenever that telephone number is dialed in the PSTN, a call will be routed to the access network via that trunk group. As the wireless local
loop customers move around within different coverage areas, their radiotelephone units are listening to the control channels in the access network they are in. Information on those control channels identify the access network and the system so that the
customer portable radiotelephone knows whether it is in its home access network or some other access network. Whenever it finds itself in a different access network, it will according to the specifications of the Air Interface standard, access that
network and perform a registration in which it identifies itself to the stowing network. As a part of that registration, the customer's portable radiotelephone provides the telephone number of its home access network. As will be described in the
following text, the portable radiotelephone will have acquired the telephone number of its home access network the last time it registered there. The home access network, whenever any subscriber registers, knows whether that subscriber is a home
customer of that network or not because a home customer will have an entry in the subscriber file in that access network. Every time one of its home customers registers, the home access network will download its access telephone number to the customer
portable radiotelephone unit and every time the customer portable radiotelephone unit registers, at home or somewhere else, it will identify its home access network number. Thus, when the portable registers in a foreign access network coverage area, it
identifies to that network the access number of its home access network. The foreign network places a call via the PSTN to that number and, when the two access networks are in communications, they will communicate by means of digital messages. The
presence of a customer in the foreign access network area will be provided to its home access network along with the access number of the foreign access network. With this registration in a foreign access network, when an incoming call arrives at the
home access network via the customer's local loop appearance, the home access network uses the number of the foreign network to extend the call through the PSTN to the foreign access network. The foreign access network can then perform the call
termination operation and connect the call to the customer when the customer answers on a particular radio channel. Similarly, when the customer originates a call while in a foreign access network area, that access network will know that it should use
the telephone number of the customer's home access network to extend the call back through the PSTN to that network to gain access to the customer's local loop. Thus, every call the customer makes or receives still uses his local loop as is required by
local loop service.
The radio transceivers useful for a WFAU or a portable radiotelephone, in the preferred embodiment, are digital transceivers having a relatively low power transmitter. The frequencies of operation are typically in the range of 1.8 GHz to 2.0 GHz
and are reciprocal to those employed by the serving RP. Of course, such frequency selection should not be construed as a limitation to the present invention and it should be noted that, while the preferred embodiment utilizes a digital transceiver for
the over-the-air link, an analog transceiver may be employed without affecting the scope of the present invention. Likewise, various forms of digital modulation and transmission (for example, code division multiple access or time division multiple
access) may be utilized without affecting the scope of the present invention. Control of the operation of the WFAU or portable radiotelephone is conventionally exercised by a microprocessor-based controller. This controller has the capability of
interfacing with the customer via a keypad, display, and other interactive ports. The controller is also coupled to the radio transmitter/receiver portions to receive and transmit system overhead information as well as process telephone calls to and
from the customer. Conventional internal memory elements are coupled to the microprocessor to hold the transceiver operations program, subscriber unit identification, and a home area access number useful in mobility.
Referring again to FIG. 1, the service provided in the preferred embodiment can be characterized as metropolitan cordless local loop service (MCLL). Since it is desirable to provide MCLL service at low cost, dual mode subscriber equipment and
expensive infrastructure network elements for providing regional or national roaming are avoided. Nevertheless, a considerable degree of mobility is available to MCLL customers without a corresponding increase in the cost of the infrastructure. MCLL
service is provided by wireless access networks employing radio technology at the subscriber end of the local loop to achieve infrastructure costs lower than those of normal wired access, metallic or fiber. These infrastructure cost savings--along with
rapid deployment of basic telephone service--are the principal benefit of a MCLL service.
From the telephone network viewpoint, the wireless local loop (WLL) service is virtually identical to that of any other customer with wired service from the same telephone exchange. Each WLL subscriber (WFAU 107, WFAU 108, portable 109, and
portable 110) has a permanent line appearance on the PSTN local exchange. All incoming calls to a particular subscriber are first delivered by the PSTN to the customer's primary wireless access network 111,113, and all outgoing calls are delivered from
the primary wireless access network to the PSTN 105 via the customer's dedicated line appearance. All basic and supplementary telephone services and the billing for them are provided by the local exchange of the PSTN where the customer's line appearance
resides.
A subscriber using a portable 109 can expect to obtain full service mobility beyond the local access network served from RP 101 and RP 104, and throughout all of the other access networks deployed within the local metropolitan service area of the
customer's telephone carrier. Furthermore, operator assisted credit card calling permits outgoing calls to be made by a customer using a portable in an area where full service mobility is not available, that is, other metropolitan areas. Calls to
emergency services are made without formal validation from any point where compatible radio coverage exists.
Considering the elements of the preferred embodiment in more detail, a Wireless Local Loop Service (WLL) is used for loop rehabilitation or for serving new "wireline" subscribers where economics are favorable. Wireless access for WLL may be
provided by any Air Interface with appropriate cost/performance attributes. For the preferred embodiment, the access technology of the TA-NWT-001313. "Generic Criteria for Version 0.1 Wireless Access Communications Systems (WACS), Issue 1, July 1992
and Supplement 1, November, 1992, "Layers 2 and 3 Updates" is assumed. Methodologies are included for effective encrypted authentication and radio link encipherment for security and voice/data privacy, respectively.
Turning now to FIG. 2, the architecture for wireless local loop service may be perceived. The basic WLL service itself appears nearly identical to that of any other customer with wired service from the same local exchange. A Local Exchange
(LEX) 201 interfaces to a Wireless Access Network 200 that employs radio technology at the subscriber end of the local loop to achieve infrastructure costs lower than those of normal "wired" access, metallic or fiber. These infrastructure cost
savings--along with rapid deployment of basic telephone service--are benefits realized by the WLL of the present invention. It is a feature of the present invention that no special requirements are placed on the selected LEXs. Expensive telephony
signaling networks, such as SS#7, or special "mobility-related" elements, such as Home Location Registers (HLRs), Visitor Location Registers (VLRs), Service Control Points (SCPs), etc., are not required to realize a system employing the present
invention.
It is an important feature of the present invention that each WLL subscriber have a dedicated line appearance, physical or virtual, on the LEX. All incoming calls are first delivered by the PSTN to the WLL customer's home Wireless Access Network
200, and all outgoing calls are delivered from the customer's home Wireless Access Network 200 to the PSTN, via this line appearance. All basic telephone services, most supplementary services, etc., and the billing for them are provided by the LEX 201
where the subscriber's line appearance resides.
Mobility is not the primary consideration for the system, being subordinate to minimal cost. Nevertheless, considerable mobility is made available to MCLL customers with virtually no corresponding increase in the cost of the infrastructure. In
addition, the Radio Port facilities in the Access Networks have all of the capabilities necessary to support the wide area mobility of the local and enhanced services, once the additional infrastructure elements are added, and can serve as part of the
initial radio coverage deployment for such services.
Each wireless local loop customer requires one dedicated line appearance on a local switching office (local exchange). In many instances, these will be physical appearances in the form of analog lines 202. Such analog lines require the use of a
Central Office Terminal (COT) 203. For LEXs with integrated digital subscriber loop capabilities 218, no COT is required and the dedicated subscriber line appearances are virtual. Digital carrier facilities (T1 or E1) 204, 218 are used to connect a
Radio Port Control Unit (RPCU) 205 to the LEX 201. The format of this digital signal conforms to one of the major standards for Digital Subscriber Loop transport (for example, but without limitation, TR-TSY-000303 "Integrated Digital Loop Carrier System
Generic Requirements, Objectives and Interface", Issue 1, September, 1986, plus Revision 1, December 1987; Revision 2, July, 1989; Revision 3, March, 1990; Supplement 2, October, 1989 and Supplement 3, March, 1990, Bellcore.). A group of trunks 206, 213
is referred to by a single telephone access number, which is used to establish connections between different Local Access and Mobility Manager (LAMM) serving areas for MCLL service and/or for handoffs. Preferred transmission technology is one of the
common forms of multiplexed digital carrier systems (T1 or E1).
Digital Subscriber Loop transmission facilities 208 consist of one dedicated digital subscriber loop carrier system per RF carrier equipped at a Radio Port. Preferred transmission technology is a form of High-speed Digital Subscriber Loop (HDSL)
compatible with one of the common multiplexed digital carrier systems (T1 or E1). Normal, interexchange trunk facilities connections 210 to the PSTN 212 consist of whatever facilities may exist in the local exchange network, however, one of the common
forms of multiplexed digital carrier systems (T1 or E1) is preferred. The Central Office Terminal (COT) 203 manages the interfaces with the physical analog subscriber line appearances 202 at the Local Exchange (LEX) 201 and with the digital cartier
facilities 204 to a RPCU 205. Standard signaling notifies the Local Access and Mobility Manager (LAMM) 207 of ringing signal on any subscriber line and performs all on-hook, off-hook, out-dialing and other procedures as directed by the LAMM 207. A/D
CODECs (not shown) are located in the COT 203 and the capability is provided to interconnect an available time slot in the digital carrier facilities 204 to/from the RPCU 205, with any subscriber line appearance, as required. The Local Exchange (LEX)
201 is any existing PSTN switching system designed to provide normal exchange services to fixed subscribers. All primary and supplementary services are controlled and all billing information is assembled here.
The Radio Port Control Unit (RPCU) 205 provides interfaces to a number of Radio Ports via the Digital Subscriber Loop transmission facilities 208 and provides all logic necessary to support the Air Interface. This includes transcoding between
the PCM of the local digital network and the voice coding scheme of the relevant Air Interface physical channel structure, and multiplexing/de-multiplexing of the Air Interface signaling protocol. The RPCU 205 contains a small Time Slot Interchanger
(TSI) to interconnect any time slot in the digital carrier facilities 204 with another in the Digital Subscriber Loop transmission facilities 208 representing the radio link dynamically assigned at access time. The TSI also facilitates handoff, when
appropriate, among the group of radio coverage areas connected to the RPCU 205.
Alternatively, a Local Access and Mobility Manager (LAMM) may be integrated with an RPCU 216 as shown in FIG. 2. The LAMM 216, coupled to LEX 217, and LAMM 207 terminates the signaling channel(s) of the digital carrier facilities 218,204 and the
Digital Subscriber Loop transmission facilities 220,208 interfaces to the radio ports RP 222, 224 and performs all necessary protocol conversions. It provides the logic to control the alerting, access, authentication and encryption processes on the Air
Interface, to correlate the Subscriber Terminal Identity with the appropriate subscriber line appearance and to manage all interconnections via the TSIs in the RPCU 205,216. It also participates in inter-RPCU handoff and in re-connect on loss of signal.
The LAMM 207 maintains a Permanent Subscriber Information Store (PSIS) in a conventional storage element, indexed by the Subscriber Terminal Id and the subscriber line Id, which contains all information required for managing the operations of
those MCLL customers whose primary ("home") Wireless Access Network corresponds to the Radio Ports 224 controlled by the LAMM 207. Some of the data fields contained in the PSIS are described below. The LAMM 207 also maintains a Temporary Subscriber
Information Store (TSIS), which contains all information required for managing the operations of those WLL customers who are currently resident in the radio coverage area of the RPs controlled by the LAMM and whose home Wireless Access Network
corresponds to Radio Ports controlled by a different LAMM. Some of the data fields contained in the TSIS are described below.
A Radio Port (RP) contains one or more digital transceivers and all necessary software for operating in either a local or an enhanced access mode. It interfaces to the RPCU 205 via Digital Subscriber Loop transmission technology modified to
accommodate Air Interface requirements.
The Wireless Fixed Access Unit (WFAU) is a personal communications system (PCS) customer radiotelephone packaged for permanent mounting in or on customer premises at a fixed location. It interworks with the RP infrastructure and is equipped with
an interface supporting connection of a standard wireline telephone set. All supervisory and address signaling is provided and appropriate electrical levels are maintained at this interface.
Operations, Administrative and Maintenance (OAM) functions provide the means for managing the deployment and configuration of the wireless access portions of the infrastructure, the customer information required to provision the stowice and all
relevant alarms and routine maintenance. (The OAM element does not appear in FIG. 2).
The subscriber unit (portable radiotelephone or WFAU) uses identification and security data and other relevant information to connect and maintain telephone calls. The following items of information are maintained in the internal memory of each
subscriber terminal: SU ID--subscriber unit (terminal) identity (Programmed into the terminal off-line); AUTH ID--authentication identity used in verifying the subscriber unit's identity (Programmed into the terminal off-line); CIPHER KEY--private
session key to be provided by the subscriber unit with each service request access and used to encipher all RF transmissions beyond the initial access message (Programmed into the subscriber unit off-line); HOME AREA ACCESS NUMBER--a phone number to be
provided by the subscriber unit to the serving LAMM at initial registration and used to establish a connection to the subscriber unit's home Wireless Access Network for reporting the subscriber unit's initial registration or for accessing the customer's
line appearance for an outgoing call (Supplied to the subscriber unit by the LAMM at each registration with the home Wireless Access Network); ANCHOR NETWORK ACCESS NUMBER--A phone number to be provided by the subscriber unit to the target LAMM when
requesting a handoff (Alternate Link Transfer-ALT). (Supplied by the serving LAMM at call set-up time and may be either the access number of the serving LAMM or that of the subscriber unit's home Wireless Access Network); SERVICE PROVIDER ID--identity
of the Service Provider in whose service area the subscriber unit is currently registered (Supplied by the LAMM as System Information); ALERT AREA--identity of a group of Radio Ports that represent the alerting (or registration) area in which the
subscriber unit last registered (Supplied by the LAMM as System Information); ALERT PHASE--portion of the alerting super-frame during which the subscriber unit's alerts will be transmitted (Assigned by the LAMM at registration. This field is always null
when the subscriber unit is not in-service); ALERT ID--temporary identity, assigned by the LAMM at registration, and used by the system to initiate contact with the subscriber unit (This field is always null when the terminal is not in-service); and CALL
ID--Radio Call Identifier assigned by the serving LAMM for each call-related access by a subscriber unit (Null except during a call-related access).
Each WLL customer must have an entry in the Permanent Subscriber Information Store (PSIS) of the particular LAMM in the PCS service provider's service area associated with the customer's dedicated line appearance. PSIS entries are created by
administrative action and, at a minimum, include the following items of information: LINE ID--the internal identity of the customer's dedicated line appearance on the local exchange; SU ID--the subscriber unit (terminal) identity; AUTH ID--the
authentication identity used in verifying the subscriber unit's identity; ALERT AREA --the identity of a group of Radio Ports that are defined as constituting an alerting (or registration) area. If this field identifies an area controlled by the LAMM,
the subscriber unit is currently resident in its primary Wireless Access Network, otherwise, the subscriber unit is operating in another area controlled by a different LAMM; ALERT PHASE--the portion of the alerting super-frame during which a subscriber
unit's alerts are transmitted (Assigned by the LAMM at registration, de-assigned at power down or notification of registration in a different radio coverage area. This field is always null when the subscriber unit is not in-service in its home Wireless
Access Network area); ALERT ID--a temporary identity, assigned by the LAMM at registration, used by the system to initiate contact with a subscriber unit, and de-assigned at power down or notification of registration in a different radio coverage area
(This field is always null when the terminal is not in-service in its home Wireless Access Network area); CALL ID--the Radio Call Identifier assigned by the serving LAMM for each call-related access by a subscriber unit (Null except during a call-related
access); CIPHER KEY--the private session key, provided by the subscriber unit with each service request access, and used to encipher all RF transmissions beyond the initial access message (Null except during an access); REMOTE AREA ACCESS NUMBER--a phone
number used to establish a connection for delivery of an incoming call to a subscriber unit currently operating in a different radio coverage area (Provided by the LAMM controlling the other area when sending notification of the subscriber unit's initial
registration there. Null if the terminal is currently registered in the "home" area); EXTENDED TERM--a count of the number of incoming calls terminated in a Wireless Access area other than the "home" area; and EXTENDED ORIG--a count of the number of
outgoing calls originated from a Wireless Access area other than the "home" area.
For each WLL subscriber unit (portable radiotelephone or WFAU) currently registered in its service area but not listed in the PSIS, the LAMM must maintain an entry in its TSIS. These entries are created automatically by the LAMM at the time of
the subscriber unit's initial registration in the alert area and | | |
