Telecommunications – Radiotelephone system – Special service
Reexamination Certificate
2000-11-22
2004-03-30
Chin, Vivian (Department: 2682)
Telecommunications
Radiotelephone system
Special service
C455S428000, C455S436000, C455S439000, C455S456200, C455S445000, C455S433000, C370S237000, C370S352000, C370S354000, C370S356000
Reexamination Certificate
active
06714777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to mobile communications and, more particularly, to the use of a proxy switch in a mobile communication network to improve capacity and cost-effectiveness of the communications network and to offer a platform for new mobile services.
2. Discussion of Related Art
All modern mobile communication systems have a hierarchical arrangement, in which a geographical “coverage area” is partitioned into a number of smaller geographical areas called “cells.” Referring to
FIG. 1
, each cell is preferably served by a Base Transceiver Station (BTS)
102
a
. Several BTS
102
b-n
are aggregated via fixed links
104
a-n
into a Base Station Controller (BSC)
106
a
. The BTSs and BSC are sometimes collectively referred to as the Base Station Subsystem (BS)
107
. Several BSCs
106
b-n
may be aggregated into a Mobile Switching Center (MSC)
110
via fixed links
108
a-n.
The MSC
110
acts as a local switching exchange (with additional features to handle mobility management requirement, discussed below) and communicates with the phone network (PSTN)
120
through trunk groups. Under U.S. mobile networks, there is a concept of a home MSC and a Gateway MSC. The home MSC is the MSC corresponding to the exchange associated with a Mobile Station (MS); this association is based on the phone number, e.g., area code, of the MS. (The home MSC is responsible for the HLR discussed below). The Gateway MSC, on the other hand, is the exchange used to-connect the MS call to the PSTN. Consequently, some times the home MSC and the Gateway MSC are the same entity, but other times they are not (e.g., when the MS is roaming). Typically, a Visiting Location Register (VLR)
116
is co-located with the MSC
110
and a logically singular HLR is used in the mobile network. As will be explained below, the HLR and VLR are used for storing many types of subscriber information and profiles.
Briefly, a number of radio channels
112
are associated with the entire coverage area. The radio channels are partitioned into groups of channels allocated to individual cells. The channels are used to carry signaling information to establish call connections and the like, and to carry voice or data information once a call connection is established.
At a relatively high level of abstraction, mobile network signaling involves at least two main aspects. One aspect involves the signaling between an MS and the rest of the network. With 2G (“2G” is the industry term used for “second generation”) and later technology, this signaling concerns access methods used by the MS (e.g., time-division multiple access, or TDMA; code-division multiple access, or CDMA), assignment of radio channels, authentication, etc. A second aspect involves the signaling among the various entities in the mobile network, such as the signaling among MSCs, VLRs, HLRs, etc. This second part is sometimes referred to as the Mobile Application Part (MAP) especially when used in the context of Signaling System No. 7 (SS7).
The various forms of signaling (as well as the data and voice communication) are transmitted and received in accordance with various standards. For example, the Electronics Industries Association (EIA) and Telecommunications Industry Association (TIA) help define many U.S. standards, such as IS-41, which is a MAP standard. Analogously, the CCITT and ITU help define international standards, such as GSM-MAP, which is an international MAP standard. Information about these standards is well known and may be found from the relevant organizing bodies as well as in the literature, see, e.g., Bosse, SIGNALING IN TELECOMMUNICATIONS NETWORKS (Wiley 1998).
To deliver a call from an MS
114
, a user dials the number and presses “send” on a cell phone or other MS. The MS
114
sends the dialed number indicating the service requested to the MSC
110
via the BS
107
. The MSC
110
checks with an associated VLR
116
(more below) to determine if the MS
114
is allowed the requested service. The Gateway MSC routes the call to the local exchange of the dialed user on the PSTN
120
. The local exchange alerts the called user terminal, and an answer back signal is routed back to the MS
114
through the serving MSC
110
which then completes the speech path to the MS. Once the setup is completed the call may proceed.
To deliver a call to a MS
114
, (assuming that the call originates from the PSTN
120
) the PSTN user dials the MS's associated phone number. At least according to U.S. standards, the PSTN
120
routes the call to the MS's home MSC (which may or may not be the one serving, the MS). The MSC then interrogates the HLR
118
to determine which MSC is currently serving the MS. This also acts to inform the serving MSC that a call is forthcoming. The home MSC then routes the call to the serving MSC. The serving MSC pages the MS via the appropriate BS. The MS responds and the appropriate signaling links are setup.
During a call, the BS
107
and MS
114
may cooperate to change channels or BTSs
102
, if needed, for example, because of signal conditions. These changes are known as “handoffs,” and they involve their own types of known messages and signaling.
One aspect of MAP involves “mobility management.” Briefly, different BSs and MSCs may be needed and used to serve an MS, as the MS
114
roams to different locations. Mobility management ensures that the Gateway MSC has the subscriber profile and other information the MSC needs to service (and bill) calls correctly. To this end, MSCs use a Visiting Location Register (VLR)
116
and a Home Location Register (HLR)
118
. The HLR is used to store and retrieve the mobile identification number (MIN), the electronic serial number (ESN), MS status, and the MS service profile, among other things. The VLR stores similar information in addition to storing an MSC identification that identifies the Gateway MSC. In addition, under appropriate MAP protocols, location update procedures (or registration notifications) are performed so that the home MSC of a mobile subscriber knows the location of its users. These procedures are used when a MS roams from one location to another or when a MS is powered on and registers itself to-access the network. For example a location update procedure may proceed with the MS
114
sending a location update request to the VLR
116
via the BS
107
and MSC
110
. The VLR
116
sends a location update message to the HLR
118
serving the MS
114
, and the subscriber profile is downloaded from the HLR
118
to the VLR
116
. The MS
114
is sent an acknowledgement of a successful location update. The HLR
118
requests the VLR (if any) that previously held profile data to delete the data related to the relocated MS
114
.
FIG. 2
shows in more detail the signaling and user traffic interfaces between a BS
107
and an MSC
110
in a CDMA mobile network. The BS
107
communicates signaling information using the A
1
interface. The A
2
interface carries the user traffic (e.g., voice signals) between the switch component
204
of the MSC and the BS
107
. The A
5
interface is used to provide a path for user traffic for circuit-switched data calls (as opposed to voice calls) between the source BS and the MSC.
As the number of cell sites or the number of subscribers grows, the load on the MSC
110
increases. This increased load forces the service provider to add more capacity to the system. Typically, to add more capacity, the service provider adds more switch modules to the MSC or deploys additional MSCs in the network. Either alternative involves significant cost.
Moreover, subscribers are demanding newer services, e.g., “data calls” to the Internet. For some of these services MSCs are not cost effective because they were primarily designed for voice calls. Integration of new services into the MSC is complicated or infeasible because of the proprietary and closed designs used by many MSC software architectures. That is, the software logic necessary to provide the services is not easy to add to the MSC
110
. Of
Aravamudan Murali
Naqvi Shamim A.
Sundar Rangamani
Vishwanathan Kumar K.
Chin Vivian
Milord Marceau
Winphoria Networks, Inc.
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