Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1999-07-26
2003-07-15
Ton, Dang (Department: 2666)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S244000
Reexamination Certificate
active
06594228
ABSTRACT:
TECHNICAL FIELD
A backup procedure employing standby signalling links for improving signalling performance reliability of interfaces controlled by such links, particularly in a DSS2 asynchronous transfer mode network.
BACKGROUND
Conventional signalling protocols enable autonomous network elements, for example switching or router systems in a network and end-user systems attached to the network, to communicate via physical links therebetween in order to inter-operate. Implementation of a signalling protocol within the individual network elements is typically modelled as a stack of functional layers that pass messages between themselves. Each layer has a specific interface to the layers immediately above and below it, and each layer effects a particular purpose or function, the details of which are abstracted from the other layers. The lowest three layers of the protocol stack are: physical, data link and network; otherwise known as layers one (L1), two (L2) and three (L3), respectively.
The physical layer (L1) interfaces directly with a physical transmission medium. It provides for the transparent transmission of a digital data stream across the physical link between network elements. The intelligence managing the data stream and protocols residing above the physical layer are transparently conveyed by the physical layer.
The data link layer (L2) is primarily responsible for providing a reliable communications path across the physical layer on behalf of the network layer. Typically this entails that the link layer perform error detection and in some cases, error correction. The data link control functions at this layer establish a peer-to-peer relationship across each physical link between network elements.
The function of the network layer (L3) generally is to provide reliable, in sequence delivery of protocol data between higher layer (e.g., transport layer) entities. In order to do this, the network layer must have an end-to-end addressing capability. A unique network-layer (end-to-end) address is assigned to each network-layer capable network element, which may communicate with its peers over a route of intermediate elements through the network. In connection-oriented type networks, the network layer also provides call processing functionality. Digital subscriber signalling system no. 2 is a well known example of such a network layer protocol.
The digital subscriber signalling system no. 2 (DSS2) is an asynchronous transfer mode (ATM) protocol which specifies the procedures for establishing, maintaining and clearing of network connections at the user-network interface (UNI) of a broadband integrated service digital network (B-ISDN). The DSS2 signalling specification stipulated by the International Telecommunications Union, Telecommunications Standardization Sector (ITU-T) in
Broadband Integrated Services Digital Network
(
B
-
ISDN
)—
Digital Subscriber Signalling System No
. 2 (
DSS
2)—
User—Network Interface
(
UNI
)
Layer
3
Specification For Basic Call/Connection Control
, ITU-T, Q.2931 (February 1995) does not provide any support for signalling link redundancy.
In non-associated signalling, a signalling link controls multiple interfaces. Failure of the interface carrying the signalling link will result in the tearing down of all calls controlled by the signalling link, even though the interfaces carrying the actual calls are still operational. When non-associated signalling is employed, the reliability of the signalling performance for the interfaces controlled by the signalling link may be unacceptable. The present invention improves such reliability by providing a backup procedure employing standby signalling links.
Proxy Signalling is an optional capability, as specified by the ATM Forum, in
ATM UNI Signalling Specification, Version
4.0, af-sig-0061.000, which allows a user known as a proxy signalling agent (PSA), to perform signalling for one or more users that do not support signalling. A single PSA can control a large number of interfaces on different switches in the ATM network. The reliability of proxy signalling is improved by using a backup PSA. The present invention supports redundant PSAs when they operate in an active and standby fashion; that is, with only one of the PSAs active at any time to provide messages at ATM Layer 3 (i.e. the network layer).
SUMMARY OF INVENTION
The present invention applies to the interface between terminal or endpoint equipment and a communications network, such as an ATM network or other connection-based communications system. In an ATM-based embodiment, when non-associated signalling is used, the invention allows the peer DSS2 (Layer 3) signalling entities at the terminal equipment and ATM Switch to use two ATM Adaptation Layer Service Specific Sublayer (SAAL Layer 2, or datalink layer) connections, i.e. an active and a standby. When proxy signalling is used, the invention allows a redundant pair of PSAs operating in an active/standby fashion to control the same interfaces on an ATM switch using different DSS2 signalling links from each PSA, but terminating on one DSS2 link in the ATM switch. The invention thus enables the Layer 3 entity at the ATM Switch to use up to four Layer 2 connections, i.e. two connections to the active PSA and two connections to the standby PSA. In both cases, only one of the Layer 2 connections is active at any time to carry signalling messages.
The invention provides a method of improving the signalling performance reliability of an interface between two signalling agents and a network element (such as an ATM switch in a DSS2 asynchronous transfer mode network). In the case of a non-redundant signalling agent, a Layer 2 connection (the “primary link”) is established between a first Layer 2 port of the signalling agent and a first Layer 2 port of the network element; and, a Layer 2 connection (the “primary backup link”) is established between a second Layer 2 port of the signalling agent and a second Layer 2 port of the network element. The Layer 2 ports are coupled to Layer 3 segments of the signalling agent and the network element respectively, in accordance with established network communication protocols.
During normal operation of the signalling link, the primary link is maintained in an active state in which all signalling messages directed to the interface are transferred between the Layer 3 segments over the primary link. The primary backup link is maintained in a standby state, such that it is active between the second set of Layer 2 ports, but inactive between the Layer 3 segments.
Upon abnormal operation of the primary link, the primary link is temporarily switched into an inactive state to prevent further transfer over the primary link of signalling messages directed to the interface; and, the primary backup link is switched into an active state in which all signalling messages directed to the interface are transferred between the Layer 3 segments over the primary backup link.
In the case of redundant primary and secondary proxy signalling agents, a Layer 2 connection (the “primary link”) is established between a first Layer 2 port of the primary signalling agent and a first Layer 2 port of the network element; a Layer 2 connection (the “primary backup link”) is established between a second Layer 2 port of the primary signalling agent and a second Layer 2 port of the network element; a Layer 2 connection (the “secondary link”) is established between a first Layer 2 port of the secondary signalling agent and a third Layer 2 port of the network element; and, a Layer 2 connection (the “secondary backup link”) is established between a second Layer 2 port of the secondary signalling agent and a fourth Layer 2 port of the network element. The Layer 2 ports are coupled to Layer 3 segments of the signalling agents and the network element respectively, in accordance with established network communication protocols.
During normal operation the primary signalling agent is active, and the primary link is maintained in an active state in which all signalling messages directed to the interface
Naidoo Nilanthren V.
Rakocevic Vladimir
Alcatel Canada Inc.
Oyen Wiggs Green & Mutala
Ton Dang
Tran Phuc
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