Telephonic communications – Plural exchange network or interconnection – With interexchange network routing
Reexamination Certificate
1999-03-03
2002-08-20
Matar, Ahmad (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
With interexchange network routing
C379S211020, C379S219000, C370S360000
Reexamination Certificate
active
06438223
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to Directory Number portability in telecommunication systems, and more particularly to allowing a subscriber to keep a single Directory Number when relocating to a different access point among one or more interconnected telecommunication systems.
ACRONYMS
It is customary for the telecommunication industry to use acronyms when referring to established components and services. The ones that are used in this disclosure are listed as follow:
AIN
Advanced Intelligent Network
AT
Access Tandem
CdPN
Called Party Number
CLEC
Competitive Local Exchange Carrier
DN
Directory Number
FCI
Forward CaII Indicator
GAP
Generic Address Parameter
GTT
Global Title Translations
HLR
Home Location Register
IAM
Initial Address Message
ILEC
Incumbent Local Exchange Carrier
IN
Intelligent Network
IP
Intelligent Peripheral
ISDN
Integrated Services Digital Network
ISUP
ISDN User Protocol
LATA
Local Access Transport Area
LEC
Local Exchange Carrier
LIDB
Line Identification Database
LNP
Local Number Portability (Service Provider's)
LRN
Location Routing Number
LSMS
Local Service Management System
LTT
Line Translation Table
MSC
Mobile Switching Center
MTP
Message Transfer Part
NPA
Numbering Plan Area
NRA
Network Routing Address (see LRN)
NXX
Office Code
ONS
One Number Service - the number portable service provided
by the present invention
OS
Operations Systems
PODP
3/6/10 Digit Public Office Dialing Plan Trigger
POTS
Plain Old Telephone Service
PX
Programmable switch (also known as Intelligent Peripheral)
RT
Routing Table
SCCP
Signaling Connection Control Part
SCP
Service Control Point
SDS
Specific Digit String Trigger (PODP is the term used for
this document)
SMS
Service Management System
557
Signaling System 7
SSP
Service Switching Point
STP
Signal Transfer Point
TCAP
Transaction Capabilities Applications Protocol
VLR
Visitor Location Register
BACKGROUND OF THE INVENTION
A Directory Number (DN) in traditional telephone systems is used to ring a telephone on a given line of a given local telephone exchange. A local exchange may be one of many interconnecting exchanges that constitute what is known as the Public Switched Telephone Network (PSTN). Each exchange, also referred to as a switch in PSTN, is provisioned with a plurality of access points or telephone lines, each addressable by a 4-digit extension [YYYY]. Subscribers may call each other on the PSTN by dialing each others Directory Number. In North America the DN is a 10 digit number and until recently it also represents the address of the exchange provisioning the DN. Each exchange is identified by a 6-digit exchange code [NPA-NXX] and the DN has been formed by concatenating the exchange code with the exchange extension in the format [NPA-NXX]-[YYYY].
The Directory Number (DN) then has been serving a dual function, namely as an address for an exchange and its extension, and also as a subscriber ID (identity) number by which the subscriber could be reached. It works well if the subscriber is fixed at the originally assigned access point or line. The problem arises when the subscriber moves to another access point. If the new access point is still served by the same exchange, the subscriber is usually allowed to keep the same number since the exchange could be reconfigured to provision the same extension number at the new access point. However, when the new access point is served by a different exchange, the subscriber can no longer retain the existing DN since the new exchange will have an exchange code different from that encoded in the original DN. The subscriber will have to be given a new DN appropriate for the new exchange. In either case, every time a subscriber makes a move, it may be days or weeks before the new service is in place.
Even if the subscriber has not moved outside the service area of an existing exchange, the subscriber may wish to switch to a more competitive service provider or to subscribe to other types of telecommunication services such as wireless, or internet or cable telephony.
From the foregoing description, it can be seen that there are three general types of number portability arising from moving from one access point to another. The first is Service Provider Portability which allows a subscriber to change access/service provider without changing the DN. The second is Location Portability which allows a subscriber to change physical locations without changing the Directory Number. The third is Service Portability which allows a subscriber to change service (e.g., POTS to ISDN) without changing the DN. In all cases, whenever the subscriber moves to a different exchange, the existing DN is no longer compatible with the address of the new exchange.
The lack of number portability is inconvenient for today's subscribers who tend to be more mobile and use a variety of telecommunication services. Furthermore, this impedes deregulation in the telecommunication industry, as it gives the incumbent service provider unfair advantage over a competing service provider. This is because a subscriber may be reluctant to change service provider if it also means a change of Directory Number.
Call forwarding is one prior art solution to location number portability. Call forwarding basically engages two directory numbers on two lines and redirects a first Directory Number to a second Directory Number. Depending on the capability of the switched network, there are two ways of implementing call forwarding. One is to encode the second Directory Number directly into the exchange switch. The other, when the switch is part of an IN/AIN switched network, is to trigger the switch on the DN to lookup second Directory Number from a network database.
FIG. 1A
illustrates a conventional call forwarding scheme by encoding the call forwarding information into the exchange switch. A subscriber has a Directory Number DN
1
on a telephone line L
1
provisioned on an exchange X
1
. The subscriber is able to forward calls for DN
1
to DN
2
, where DN
2
is on a telephone line L
2
provisioned on an exchange
2
. The exchange X
1
is programmed to respond to call-forwarding requests by the subscriber. In step (
0
), the subscriber can dial a special call-forwarding setup code on L
1
and input into X
1
the forwarding number DN
2
. The exchange X
1
encodes this information in its Routing Table (RT) so that if a call to DN
1
is received, it is rerouted to DN
2
on X
2
accordingly.
FIG. 1A
shows a network of exchanges X
0
, X
1
and X
2
interconnected by voice trunks. Typically, when a call connection is to be made, a call stream is established serially from one exchange to another forming a series of circuits until the destination exchange is reached. Given the DN, each exchange has a RT that indicates which is the next exchange in the stream to establish the link. In order to setup the linkage (call setup) efficiently, the status and control signals associated with a call are carried in a digital network using a Signaling System
7
(SS
7
) protocol on it own network. The signaling is in the form of a digital packet know as Initial Address Message (IAM). The IAM packet is routed between exchanges or other points of the digital network by a Signal Transfer Point (STP) which is essentially a digital packet router. In the example shown, a call to DN
1
originates from a line L
0
of the exchange X
0
. The exchange X
0
determines from its RT that DN
1
resides in an exchange X
1
and proceeds to set up the call. The call setup involves, in step (
1
), forming an IAM
0
(DN
1
) packet to be routed from X
0
to X
1
by the STP, and with which the a circuit between X
0
and X
1
is made available. At X
1
, its RT indicates that DN
1
is forwarded to DN
2
at X
2
. Then in step (
2
) an IAM
1
(DN
2
) packet reflecting the redirection is routed form X
1
to the exchange X
2
that is provisioning DN
2
to set up the next leg of the circuit. In this way, a call made to DN
1
is forwarded to connect at DN
2
.
The switch-based call-forwarding scheme has several d
Eskafi Farokh H.
Kazerouni Mohammad D.
Knowlin Thjuan P.
Matar Ahmad
Open Telephone Network, Inc.
Skjerven Morrill & MacPherson LLP
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