Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-12-17
2002-12-03
Nguyen, Lee (Department: 2746)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S422100, C455S466000, C455S426100, C455S445000, C370S352000, C370S353000, C370S338000, C370S401000, C370S410000, C370S465000
Reexamination Certificate
active
06490451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to an improved telecommunications system, and in particular to a method and system for incorporating transport and control facilities for voice, multimedia, and data traffic into a distributed packet-switched core network. More particularly, the present invention relates to a managed, packet-switched core network including multiple nodes which together provide packet-switched management of call setup, mobility, and data transfer for a mobile terminal, thereby providing a packet-switched alternative to a network of circuit-switched Mobile Switching Center/Visitor Location Registers (MSC/VLRs).
2. Description of the Related Art
Utilization of wireless, mobile telephony systems has expanded dramatically in recent years. Such systems typically include cellular or Personal Communication System (PCS) networks. Within such networks, geographic areas are divided into “cells” served by low-power radio transmission facilities. A centralized computer and switching center, known as a Mobile Switching Center/Visitor Location Register (MSC/VLR), controls call setup between a mobile terminal (MT) and either another MT or a terminal linked directly to the Public Switched Telephone Network (PSTN), in addition to providing connectivity to other telecommunications networks.
FIG. 1
is a block diagram illustrative of an example MSC/VLR configuration within a conventional circuit-switched cellular telecommunications system
100
. As shown in
FIG. 1
, telecommunications system
100
includes the network interconnection of a cellular subsystem
101
to a Public Switched Telephone Network (PSTN)
130
and a Public Data Network (PDN)
120
. Cellular subsystem
101
is a Code Division Multiple Access (CDMA) wireless communications system in the depicted example. Also within cellular subsystem
101
are mobile terminals (MTs)
126
and
127
which may be handheld cellular phones or other mobile terminal user devices.
Cellular subsystem
101
further includes a Home Location Register (HLR)
104
, and a pair or Mobile Switching Centers (MSCs)
102
and
103
. Associated to MSCs
102
and
103
, are a pair of Visitor Location Registers (VLRs), VLR
132
and VLR
133
, respectively. HLR
104
is essentially a customer database within cellular subsystem
101
in which subscriber profile information for MTs, such as MT
126
, is permanently stored. MSCs
102
and
103
are responsible for the switching of trunk circuits as well as the processing of call setup and mobility management signaling messages. In addition to operating as switches, MSC
102
and MSC
103
also function as telecommunications gateways to PDN
120
and PSTN
130
respectively.
MSCs
102
and
103
perform the necessary switching functions for any compatible MT located within a geographic area associated with a particular MSC, called a MSC serving area. Within cellular subsystem
101
, MSC
103
provides call switching functionality between PSTN
130
and MTs
126
and
127
. MSCs
102
and
103
also monitor the mobility of their respective served MTs and manage necessary resources needed to effect location registration procedures and carry out handoff functions. Although, in the depicted example, only two MSCs are illustrated in cellular subsystem
101
, other numbers of MSCs may be employed depending on the communications system.
Each MT utilizes various radio frequency (RF) channels to communicate with a base station (BS). The RF channels utilized for control functions such as call setup during an origination attempt will be referred to hereinafter as control channels. In CDMA technology, the control channel consists of an access channel for control signaling from the MT, and a paging channel for control signaling to the MT. In contrast, RF channels utilized by MTs to convey voice or other end-user data are sometimes referred to as voice channels, and will be referred to hereinafter interchangeably as “traffic channels” (TCHs). TCHs may also be delineated according to the source of radio transmission. A Base Station (BS)
125
includes a base station transceiver subsystem (BSTS)
124
and a base station controller (BSC)
123
. A TCH for transmitting from a BSTS is called the forward TCH, while a TCH utilized by the BSTS for receiving transmissions from the MT is called the reverse TCH.
HLR
104
is utilized within cellular subsystem
101
to manage mobile subscribers. Subscriber information that associates a serving MSC (MSC-S) with a particular MT is stored in permanent subscriber records within HLR
104
. These records contain information such as the serving VLRs
132
and
133
, and subscription parameters of MTs
126
and
127
. For example, MT identity, Electronic Serial Number (ESN), and subscriber profile data are stored within HLR
104
. VLRs
132
and
133
contain a copy of the records of the MTs currently residing within their respective service areas. In addition, VLRs
132
and
133
also keep track of the current location area of each MT in terms of the last accessed cell. This information is only temporarily stored at VLRs
132
and
133
and is removed once the subscribers move out of their respective service areas for a predetermined period of time. Most network equipment manufacturers have adopted a combined MSC/VLR approach such that each VLR is co-located with a MSC.
BS
125
includes the physical equipment for providing radio coverage to defined geographical RF-coverage areas called cells. BS
125
contains the hardware necessary to communicate with MT
126
. BSC
123
performs control functions, while BSTS
124
performs the transmitting/receiving function within a given cell utilizing radio transmission/receiving equipment.
The PSTN and other networks include hierarchies of switches that are navigated to provide connections between telephones and other data terminal equipment (DTE). The primary function of a telephony switching system is to interconnect lines or trunks between telephones, DTEs, or other switches. In addition, switching facilities must perform other administrative functions besides switching such as control signaling, route selection, and toll call accounting. Conventional switches, including those incorporated into MSC/VLRs, incorporate some intelligent agent which provides management and control of switch functionality.
There are several problems associated with conventional circuit-switched MSC/VLR implementations such as that depicted in FIG.
1
. Scalability of MSC/VLR networks is one such problem. When an MSC's port, switching, signaling, or processing capacity is exhausted, an entire MSC/VLR unit is often added as the finest increment for increasing network traffic handling capacity. Given this coarse granularity for scaling a carrier's networks, much of the per-switch dedicated peripheral equipment is underutilized (signaling links, announcement peripheral, conferencing peripheral, etc., for example).
As data traffic continues to increase relative to voice traffic, a conventional MSC/VLR network becomes a less efficient telecommunications management tool. Circuit-switched MSC/VLRs utilize dedicated two-way physical channels in which at least 50% of the allocated bandwidth generally conveys silence and is thus wasted for voice traffic. For data transmission, an even greater bandwidth is typically wasted due to the asymmetric and often bursty nature of data sessions (file transfers, for example). Consequently, carriers often overlay their voice networks with a data network, thereby incurring the costs of operating two networks. Recent developments in wideband wireless transmission have introduced the likelihood that wireless, mobile telecommunications will be increasingly utilized to support multimedia data sessions. Such data sessions will exacerbate current problems with circuit-switched telecommunications.
The nature of conventional MSC/VLR network implementations can result in bottlenecks such as HLR transaction capacity which often limits traffic handling capacity of such networks. As MS
Boudreaux Paul H.
Denman Robert E.
Hanley Donald V.
Jackson Don L.
Maxwell Stewart H.
Bracewell & Patterson L.L.P.
Ferguson Keith
Fulbright Paul W.
Nguyen Lee
Nortel Networks Limited
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