Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1997-11-19
2002-05-21
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S410000, C370S524000
Reexamination Certificate
active
06393022
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of Integrated Services Digital Network User Part (ISUP) signaling, and more particularly to the processing and routing of ISUP signaling messages within a switching system.
BACKGROUND OF THE ART
Signaling is the process of transferring information to control the setup, holding and releasing of connections in a communications network. The network may be a public telephone network or a switched private telephone network. In a network, signaling may be divided into two parts: customer line signaling and inter-office trunk signaling. Customer line signaling refers to the interaction between a telephony agent and the switching system serving the customer. Interoffice trunk signaling is concerned with the exchange of call-handling information between switching offices within a network.
Today, communications networks commonly use two types of signaling techniques: traditional in-band signaling and out-of-band signaling. For traditional in-band signaling, signaling information is transmitted on the same wire or trunk and follows the same transmission path as the call itself. For out-of-band signaling, signaling information pertaining to a call is transmitted on a separate dedicated facility known as a signaling link.
Signaling System 7 (SS7) is an industry standard for out-of-band signaling in a communications network. In a SS7 network, signaling information is carried in packets between switching systems in much the same manner as X.25 or other packet switching protocols. An SS7 network provides increased bandwidth for call signaling and increased capability for providing advanced network services across different network platforms.
The SS7 protocol is comprised of four layers. Layers 1, 2 and 3, collectively referred to as the Message Transfer Part (MTP), provide the basic infrastructure for transporting signaling messages across the SS7 network. MTP is compliant with layers 1, 2 and 3 of the Open System Interconnection (OSI) standard. Layers 1, 2 and 3 of OSI are defined in ITU-T X.200.
Layer 4 of the SS7 protocol consists of three parts: Signaling Connection Control Part (SCCP), Integrated Services Digital Network User Part (ISUP), and Transaction Capability Application Part (TCAP). SCCP provides additional routing and network management services to MTP. TCAP provides connectionless communications between applications on a network using a generic standard language.
ISUP provides connection-oriented signaling between nodes on a communications network. This type of signaling provides the capability to set up and take down calls and to monitor the facilities on which calls are transported. Furthermore, ISUP is a service-rich protocol which provides the capability to communicate large amounts of information associated with calls over signaling links. This service-rich aspect of the ISUP protocol is particularly attractive to telephone service providers because it supports advanced network services such as, caller ID, call screening, and automatic recall, across different switching systems and telephony agents.
ISUP signaling protocol is defined in GR-246-CORE, “Bellcore Specification of Signaling System 7”, Volume 3, American National Standards Institute (ANSI) T1.113-1988, and International Telecommunications Union—Telecommunication Standardization Sector (ITU-T) Q.761, Q.762, Q.763, Q.764, Q.766, “Specifications of Signalling System No. 7 ISDN User Part.”
A telephone switching office which supports SS7 signaling is referred to as a Service Switching Point (SSP). Each switching office is assigned a unique point code for the purpose of identifying the office in the telephone network. Typically, a switching office includes a switching system which is connected to switching systems in other switching offices via inter-office trunks.
A trunk for which ISUP signaling information is handled on a separate signaling link is referred to as an ISUP trunk. An ISUP trunk that originates from and terminates at the same SSP is referred to as an ISUP loopback trunk. The point at which a trunk originates from a switching system is referred to as a near endpoint, and the point at which a trunk terminates at a switching system is referred to as a far endpoint.
FIG. 1
shows the external interfaces of a prior art switching system. Switching system
100
is connected to user terminals
115
,
136
, and
138
via customer lines
114
,
135
, and
137
respectively. User terminal
115
is a standard plain ordinary telephone service (POTS) telephone, user terminal
136
is a fax machine, and user terminal
138
is an ISDN terminal that includes a video machine and a POTS telephone.
Switching system
100
interfaces with ISUP loopback trunks
110
and ISUP inter-office trunks
111
. ISUP loopback trunks
110
originate from and terminate at switching system
100
. ISUP inter-office trunks
111
connect switching system
100
to switching system
150
. Switching system
100
has a plurality of digital trunk controllers which interface with ISUP loopback trunks
110
and ISUP inter-office trunks
111
. Signaling links
112
connect switching system
100
to SS7 network
113
. Switching system
100
has a plurality of signaling terminals which interface with signaling links
112
.
Switching system
150
is connected to user terminals
160
,
170
and
180
via customer lines
155
,
165
and
175
respectively. User terminal
160
is a standard plain ordinary telephone service (POTS) telephone, user terminal
170
is an ISDN terminal that includes a video machine and a POTS telephone, and user terminal
180
is a desktop computer system.
Switching system
150
has a plurality of digital trunk controllers which interface with ISUP inter-office trunks
111
. Signaling links
140
connect switching system
150
to SS7 network
113
. Switching system
150
has a plurality of signaling terminals which interface with signaling links
140
.
Switching system
100
processes ISUP signaling messages
120
which are associated with ISUP inter-office trunks
111
and routes them to and from signaling links
112
. Because the far endpoints of ISUP inter-office trunks
111
terminate at switching system
150
, ISUP signaling messages
120
travel through the SS7 network
113
and arrive at switching system
150
.
Switching system
100
also processes ISUP signaling messages
130
which are associated with ISUP loopback trunks
110
and routes them to signaling links
112
. Because the far endpoints of ISUP loopback trunks
110
terminate at switching system
100
, ISUP messages associated with ISUP loopback trunks
110
travel through SS7 network
113
and arrive back at switching system
100
.
Routing ISUP signaling messages associated with ISUP loopback trunks to the SS7 network presents a unique challenge for switching systems because a switching system cannot use a single point code to identify itself as both the source and the destination when routing these messages. Specifically, most switching systems detect and disallow circular routing of signaling messages to the SS7 network (i.e., the source and destination being the same SSP). To get around this problem, telephone service providers must assign an additional point code to each SSP. However, assigning an additional point code to each SSP creates extensive network management problems because in a communications network each SSP must be identified by a unique point code.
Furthermore, in the case of ISUP loopback trunks, ISUP signaling messages must be processed by the MTP layer of the SS7 protocol in switching system signaling terminals, even though the source and the destination of the messages are the same. The main purpose of the MTP layer is to provide reliable transport for signaling messages within the SS7 network, and thus, it is unnecessary for a switching system to send these messages to the SS7 network when they are destined for that same switching system.
To take advantage of the advanced services of the MTP layer, telephone service providers must allocate the resources of switching system signal
Chapman Keven Todd
Hewett Jeffrey Allen
Hyun Soon-Dong
Nguyen Chau
Nortel Networks Limited
Withrow & Terranova, P.L.L.C.
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