Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2001-02-06
2003-02-04
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S338000, C370S522000, C455S560000
Reexamination Certificate
active
06515985
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems, and specifically to methods and apparatus for transmission of cellular signaling, voice and other data over packet-switched networks.
BACKGROUND OF THE INVENTION
Existing cellular communication networks are dependent on an infrastructure of circuit-switched wireline trunks. Typically, cellular operators maintain separate trunk networks for signaling, voice and other data. As cellular networks grow, the economic burden on the operators of maintaining or leasing these trunks becomes ever heavier. Communications among switches in a cellular network and between one cellular network and another must generally pass through switching equipment and lines belonging to public switched telephone networks (PSTNs), adding the expense of transfer fees to inter-network calls.
FIG. 1
is a block diagram that schematically illustrates a cellular communications system
20
, as is known in the art. The system in this example includes two cellular networks
22
and
24
, belonging to respective cellular operators “Cellco
1
” and “Cellco
2
.” The networks are connected to one another through a PSTN
26
. A subscriber of network
22
communicates with a base transceiver station (BTS)
36
in the network using a mobile station (MS)
64
. Typically, the BTS communicates with and is controlled by a base station controller (BSC)
34
. When the user of MS
64
originates a call, appropriate signaling is sent from BTS
36
to BSC
34
, and from the BSC to a mobile switching enter (MSC),
32
. Typically, the signaling is in accordance with SS7 signaling specifications established by the International Telecommunications Union (ITU-T), as described in the Q.700 series of standards. The signaling to and from the MSCs is indicated in this figure and in other figures in this application by solid lines. Voice and other data communications are indicated by dashed lines.
Assuming that MS
64
initiates a call with another MS in another part of the network, say in communication with a MSC
28
, MSC
32
sets up the call by sending a signaling message to a signaling transfer point (STP)
38
or
40
. The STP sends the message on to MSC
28
. The MSCs exchange messages through the STP in order to set up the call, and maintain this signaling link during the call for purposes of subscriber roaming, inter alia. Once the call is set up, a voice connection between MSC
32
and MSC
28
is established. In the present example, in which there is no direct voice line connecting MSC
28
and MSC
32
, a third MSC
30
acts as a “tandem,” i.e., a circuit switch for conveying voice signals between the other two MSCs.
When the user of MS
64
wishes to make a call to a subscriber of network
24
, MSC
32
must send a signaling message to STP
38
or
40
indicating that such a call is to be set up. The STP then signals an STP
44
or
46
belonging to PSTN
26
, which signals an STP
48
or
50
in network
24
, which finally signals the appropriate one of MSCs
54
,
56
or
58
in network
24
. Once the call is set up, MSC
32
transmits a voice stream from MS
64
through a tandem switch
62
in PSTN
26
. The tandem switch passes the voice on to the appropriate MSC in network
24
. In other words, the signaling and voice carried between networks
22
and
2
must pass through separate circuit switches (STPs and tandems) of PSTN
26
, with charges levied by the PSTN for both.
A further feature of many cellular networks is a short message service (SMS), provided by a SMS center
42
or
52
. The SMS enables network subscribers to send data messages to other subscribers. These data messages are normally carried over the signaling (solid) lines in the cellular network. The popularity of SMS is creating a growing burden on the cellular signaling infrastructure.
Generally speaking, because cellular networks have been developed primarily for circuit-switched transmission, they are not well suited for packet-switched data. For this reason, the European Telecommunications Standards Institute (ETSI) has proposed a general packet data service (GPRS) to operate in conjunction with Global System for Mobile (GSM) cellular networks. When a MS in a GSM network with GPRS wishes to send and/or receive packet-switched data, the MS makes contact with a “serving GPRS support node” (SGSN not shown in the figures) through the BSC with which the MS is in communication. The packet data are transmitted and received by the BSC through the SGSN, separately from the voice channels that go through the MSC. The SGSN is connected to a packet data network, such as the internet, rather than to the existing cellular and PSTN infrastructure. The SGSN likewise maintains its own separate mobility management and security facilities. Implementation of GPRS requires a substantial investment in new network infrastructure, and users must have suitable, GPRS-compatible MSs. The GPRS can also be used to carry SMS messages by “tunneling” over the packet data network.
Solutions are becoming available for enabling MSCs to exchange voice, as well as data, over packet-switched links, in place of the circuit-switched links in traditional cellular networks. For this purpose, a packet gateway, such as the AS5300 Voice-over-internet-Protocol (VoiP) gateway, produced by Cisco Systems (San Jose, Calif.), can be coupled to the MSC voice output. Signaling, however, is still conveyed over existing circuit-switched lines. In order to set up a new call, the MSC signals one or the STPs, just as described above with reference to system
20
. The signals are then sent to the packet gateway, in order to control transmission of packet data to a corresponding gateway at another MSC that receives the call. While enabling communications between MSCs to be routed over packet-switched links, this solution greatly complicates the cellular signaling network.
As an enhancement to this concept, a central signaling gateway is added at the STP to receive the signals sent by the MSC. An example of a signaling gateway of this sort is the Signaling Gateway USP, produced by Nortel Networks (Saint John, New Brunswick). The signaling gateway invokes a media gateway controller to take over the function of call set-up from the MSC, which is normally responsible for this function in conventional cellular systems. During call setup, the media gateway controller directs a media gateway at the MSC site, such as the above-mentioned AS5300 device, to set up connections over a packet-switched link to the media gateway at the receiving MSC site.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved apparatus and methods for conveying communications signaling, and particularly cellular and other SS7 -based signaling over packet-switched networks.
It is a further object of some aspects of the present invention to provide apparatus and methods for convergence of cellular signaling, voice and data over a common network, in particular a packet-switched network.
It is yet a further object of some aspects of the present invention to enable existing cellular equipment, particularly existing MSCs, to convey signaling over packet-switched links while minimizing the changes required in the cellular equipment for this purpose.
In preferred embodiments of the present invention, an integrated packet-switching gateway is coupled to a cellular network switch, typically to a MSC. The switch is normally adapted and programmed, in the absence of the gateway, to communicate with other switches in the cellular network over circuit-switched links, as is known in the art. The integrated gateway, however, converts the signaling, voice and other data output by the switch to packets, and routes the packets over a common packet-switched network to other switches in the cellular network. Similarly, the gateway receives packets sent from other switches over the packet-switched network and passes them to the appropriate inputs of the cellular network switch, which sends and receives signaling, voice and other data through t
Arbetov Vladimir
Durakovsky Leonid
Geron Roie
Gottfried Ofer
Shmulevich Oren T.
Abelman ,Frayne & Schwab
Airslide Systems Ltd.
Harper Kevin C.
Yao Kwang Bin
LandOfFree
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