Looping detection apparatus

Details Looping detection apparatus Looping detection apparatus

1998-10-07

2002-10-08

Marcelo, Melvin (Department: 2663)

Multiplex communications

Diagnostic testing

Fault detection

C370S249000, C714S025000

Reexamination Certificate

active

06463037

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a looping detection apparatus, and more particularly, to a looping detection apparatus for a communications system in which a node transmits a status enquiry message to a remote node and, when a status enquiry message is received from the remote node, sends back a status response message, to thereby confirm whether normal communication status is established with the remote node.
The present invention is applied in particular to a frame-relay communications system and utilizes the PVC (Permanent Virtual Circuit) status confirmation procedure as specified in the recommendations X.76 by the ITU-T (International Telecommunication Union-Telecommunication Sector) to detect looping caused between nodes.
(2) Description of the Related Art
Frame relay is conventionally known as a communications technique capable of achieving high-speed, low-delay communications required for communications between LANs, and at present, there already exist a large number of public and private frame-relay networks. As a protocol (NNI: Network-Network Interface) to be used in such frame-relay networks, the ITU-T recommendations X.76 have been standardized.
According to the ITU-T recommendations X.76, two-way procedure (technique according to which one node carries out both status enquiry and status response) is defined as the PVC status confirmation procedure, and when there has occurred a fault in a trunk line (including a fault of a sending line only and a fault of a receiving line only) of the frame-relay network, error is detected through confirmation of link completeness.
The following is an outline of the link completeness confirmation according to the PVC status confirmation procedure as provided by the ITU-T recommendations X.76.
The PVC status confirmation procedure employs periodic polling to confirm link completeness and to make a notification of PVC status. In the two-way PVC status confirmation procedure, a polling start procedure and a polling response procedure described below are executed by each node.
FIG. 15
is a diagram illustrating the polling start procedure and the polling response procedure. Assuming in
FIG. 15
that each node comprises STE (Signaling Terminal Equipment), an SE (Status Enquiry) message for making an enquiry about status and an ST (Status) message, which is a status response to the enquiry message, are exchanged between STEa and STEb.
In the polling start procedure, the STE periodically generates an SE message, transmits the same to a remote STE, and on receiving from the remote STE an ST message responsive to the SE message, performs a receiving process. The SE message is generated at intervals of, for example, 10 seconds, and an SE-F message of which the report type is full status is generated in a ratio of once to six message generations.
In the polling response procedure, on receiving an SE message, the STE generates an ST message responsive to the SE message, and sends the ST message back to that STE which transmitted the SE message. In response to the SE-F message, an ST-F message whose report type is full status is transmitted. If there has been a change in the status of the STE, the STE may transmit an ST-F message in response to an SE message.
In the following, explanation is made basically of the SE message and the ST message, and operations unique to the SE-F message and the ST-F message will be explained separately where appropriate.
The link completeness confirmation is made by using these messages, and to this end, each STE is provided with two storage sections PI and PR. Each of the storage sections PI and PR is configured so as to store sequence numbers V(S) and V(R). Also, each of the SE message and the ST message is formatted such that it has a part for carrying two sequence numbers N(S) and N(R).
When an SE message is transmitted from a local STE, the sequence number N(S) carried by this SE message is copied to the storage section PI of the local STE as the sequence number V(S). Similarly, when an ST message is transmitted from a local STE, the sequence number N(S) carried by this ST message is copied to the storage section PR of the local STE as the sequence number V(S).
When a local STE has received an ST message, the sequence number N(S) carried by this ST message is copied to the storage section PI of the local STE as the sequence number V(R). Further, when this local STE transmits an SE message next time, the sequence number V(R) in the storage section PI is used as the sequence number N(R) to be carried by the SE message. Similarly, when a local STE has received an SE message, the sequence number N(S) carried by this SE message is copied to the storage section PR of the local STE as the sequence number V(R). Further, when this local STE transmits an ST message next time, the sequence number V(R) in the storage section PR is used as the sequence number N(R) to be carried by the ST message.
Explanation will be now made with reference to a specific example shown in FIG.
15
.
First, it is assumed that the sequence numbers V(S) and V(R) in the storage section PI of the STEb are set to values a and b, respectively, and that the sequence numbers V(S) and V(R) in the storage section PR of the STEb are set to values x and y, respectively. Thus, the sequence numbers V(S) and V(R) in the storage section PI of the STEa are set to the values y and x, respectively, and the sequence numbers V(S) and V(R) in the storage section PR of the STEa are set to the values b and a, respectively.
When polling timing for the STEb is reached and an SE message is to be transmitted to the STEa, the sequence number V(S) in the storage section PI of the STEb, that is, a, is read out, and a value (a+1), which is the sum of the read value and the value “1,” is set as the sequence number N(S) of the SE message. Also, the sequence number V(R) in the storage section PI, that is, b, is read out and set as the sequence number N(R) of the SE message. The SE message having the sequence numbers N(S) and N(R) thus set therein is transmitted to the STEa, and at the same time the sequence number N(S) set in this SE message, that is, (a+1), is copied to the storage section PI of the STEb as the sequence number V(S).
On receiving the SE message, the STEa compares the value of the sequence number N(R) carried by the SE message with the value of the sequence number V(S) in the storage section PR thereof. In the illustrated example, both take the value b, and when the two values coincide in this manner, the STEa judges that there is no abnormality in the channel between the STEa and the STEb. When no abnormality is detected, the value (a+1) of the sequence number N(S) carried by the SE message is set as the sequence number V(R) of the storage section PR. Then, the sequence number V(S) in the storage section PR of the STEa, that is, b, is read out, and a value (b+1), which is the sum of the read value and the value “1,” is set as the sequence number N(S) of an ST message. Also, the sequence number V(R) in the storage section PR, that is, a+1, is read out and set as the sequence number N(R) of the ST message. The ST message having the sequence numbers N(S) and N(R) thus set therein is transmitted to the STEb, and at the same time the sequence number N(S) set in this ST message is copied to the storage section PR of the STEa as the sequence number V(S).
If the value of the sequence number N(R) carried by the received SE message is different from the value of the sequence number V(S) in the storage section PR, the STEa judges that the channel between the STEa and the STEb is abnormal. In this case, the value of the sequence number V(S) in the storage section PR is retained as it is, and the value of the sequence number N(S) carried by the SE message is set as the sequence number V(R) of the storage section PR. Further, the sequence number V(S) in the storage section PR of the STEa is read out, and a value obtained by adding the value “1” to the read value is set as the sequence num

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