For example, a signaling processor connecting to an ATM (Asynchronous Transfer Mode) network has a link failure detection means. If the signaling processor detects a failure that may affect transmission and reception of signaling signals in a link to a correspondent node that has been established through the ATM network, then it switches to another link in which no failure has occurred so as to maintain communication of the signaling signals.
A relevant link switching method of a signaling processor will be described with reference to FIG. 4.
Referring to FIG. 4, in a state in which signals (Sequenced Data, or SD) are transmitted and received in a link connected between a node A and a node B, if the node A detects a link failure, an MTP3 of the node A transmits an AAL-STOP signal in order to conduct link switching. When an SSCF-NNI receives the AAL-STOP signal from the MTP3, it transmits an AA-RELEASE-request to an SSCOP and changes to the state 1/4/1 (Out Of Service/Outgoing Disconnection Pending). When the SSCOP receives the AA-RELEASE-request, it transmits an END signal to the node B and changes to the state 4 (Outgoing Disconnection Pending). AAL is an abbreviation for ATM Adaptation Layer, SSCF for Service Specific Coordination Function, NNI for Network Node Interface, and SSCOP for Service Specific Connection Oriented Protocol.
If the SSCOP receives a signal (SD) (with a sequence number (SN=101)), which has been transmitted from the node B and has crossed the END transmission, after it has transmitted the END signal before it changes from the state 10 (Data Transfer Ready) to the state 4 (Outgoing Disconnection Pending), then the SSCOP notifies the SSCF-NNI of the sequence number (SN=101) of the signal with an AA-DATA-indication.
The MTP3 transmits an AAL-RETRIEVE_BSNT-request to the SSCF-NNI at any time after it has transmitted the AAL-STOP signal. In response to the AAL-RETRIEVE_BSNT-request, the SSCF-NNI notifies the MTP3 of the sequence number (SN=101) of the last signal received before it changes to the state 4 (Outgoing Disconnection Pending) with an AAL-BSNT-confirmation.
When the SSCOP receives an ENDAK signal from the node B in response to the transmitted END signal, it transmits an AA-RELEASE-confirmation to the SSCF-NNI and changes to the state 1 (Idle). When the SSCF-NNI receives the AA-RELEASE-confirmation, it changes to the state 1/1/1 (Out Of Service/Idle) and stops the link.
Examples of relevant references include JP-A 2003-124995 (hereinafter referred to as Patent Document 1) and JP-A 2004-112419 (hereinafter referred to as Patent Document 2). For example, the aforementioned technology and terms being used are described in TTC JT-Q2110 (hereinafter referred to as Non-Patent Document 1), TTC JT-Q2140 (hereinafter referred to as Non-Patent Document 2), ITU-T Q.2110 (hereinafter referred to as Non-Patent Document 3), ITU-T Q.2140 (hereinafter referred to as Non-Patent Document 4), Annex 3.1 MTP Specification of NTT Specification: Collection of Technical Conditions (ATM interface for signals) (hereinafter referred to as Non-Patent Document 5), and Shin-ichi Kuribayashi, “Easy ATM Network Signal Scheme,” Publisher: the Telecommunications Association, Seller: Ohmsha, pp.38-57 (hereinafter referred to as Non-Patent Document 6).
Patent Document 1 describes a communication control apparatus (signaling processor) having an SSCOP function part (protocol processing part) based on Recommendation Q.2110. Patent Document 1 also describes an operation of an SSCF function part based on Recommendation Q.2130. Furthermore, a release process of a connection between devices is described at paragraph [0041] of Patent Document 1.
Patent Document 2 describes an ATM communication apparatus that forms an AAL using an SSCOP and an SSCF as with Patent Document 1. Patent Document 2 describes, at paragraphs [0012] and [0013], examples of primitives between the SSCF and the Layer 3 and signals between the SSCF and the SSCOP.