Multiplex communications – Fault recovery – Bypass an inoperative station
Reexamination Certificate
1998-04-09
2001-08-21
Olms, Douglas (Department: 2661)
Multiplex communications
Fault recovery
Bypass an inoperative station
C370S909000, C370S395430
Reexamination Certificate
active
06278690
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a local area network operating in the asynchronous transfer mode (ATM) for transmitting cells, comprising a plurality of network nodes which are provided for forming a loop in the event of a defect of an assigned transmitting line or an adjacent network node.
Such a local area network (LAN) which operates in the asynchronous transfer mode is known from DE 195 32 442 C1. This network contains a plurality of ring systems with various network nodes which are mutually coupled in a ring system via a single or a double ring. The network nodes have station connections via which they are coupled either to a station or to another network. A network node detects a node failure or a line rupture when it no longer receives cells from a neighboring node via a line of a ring. In the event of a node failure or line rupture, the network node detecting this defect informs a network management system of the location of the line rupture. The network management system controls the reconfiguration of the network in that the system informs the network node whose transmitting line has a defect. This network node then forms a loop so that cells are no longer routed to the defective line, but to the other ring.
When an asynchronous transfer mode is used in a system, payload, for example, television, picture or sound signals, is transmitted in blocks of fixed length through arrangements for digital signal processing. A cell having a predetermined number of bytes (for example 53 bytes) is denoted a fixed-length block. Each cell comprises a header field having a length of 5 bytes and an information field in which the payload is accommodated having a length of 48 bytes. Such a header field are contains address information, data for fault detection and data for control indication bytes. Address information comprises trunk identifiers and link identifiers. For transmitting a cell, a virtual channel is rendered available based on the link identifier which is also referred to as a VCI (Virtual Channel Identifier). As a rule, a VCI is changed once it has reached a switching center. A group of virtual channels is denoted a virtual path (VPI=Virtual Path Identifier) featured by the trunk identifier.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a local area network operating in the asynchronous transfer mode in which a reconfiguration of the network is carried out in a different manner if at least one line rupture or node failure occurs.
The object is achieved by a local area network of the type defined in the opening paragraph operating in the asynchronous transfer mode, in that a network node detecting a defect transmits a cell containing a message of a first type about the location of the defect to all the other network nodes involved, in that the network node detecting the defect and each network node receiving the message of the first type enters the location of the defect in its own assigned status table and in that, after the evaluation of the respective status table in a network node, the network nodes form a loop which does not use the defective transmitting line or attempt exchanging cells with an isolated or defective node.
The invention is based on the idea that a network node detecting the failure of a network node or a line rupture informs all the other network nodes involved about this defect by means of a message of a first type, so that these network nodes are aware that a connection can no longer be established with certain users. A network node cannot determine exactly whether the defect relates to a line rupture or a node failure. Only as a result of a loss of synchronization or by transmitting certain cells can there be established that the detecting network node no longer receives cells from a neighboring node over its receiving line. The network node detecting a defect then sends a message of a first type which contains information about a fault on a transmitting line of the neighboring node to all the other network nodes that can be reached and are involved. This involvement relates, for example, to all the nodes of a ring system in the local area network.
A network node receiving the message of a first type enters the message contents in an assigned status table and establishes, after evaluation, where the location of the defect is and whether an action is to be carried out. If the network node establishes that, for example, it can no longer exchange cells with another network node, that is to say, that it can no longer receive cells from the other network node or send cells to it, a loop is formed, In particular, a loop is formed in the network node whose transmitting line shows a defect. In addition, there are cases where a network node is to establish a loop even when a transmitting line is still in working order.
For enabling a network node to identify the location of the defect, the network node detecting a defect sends a message of a first type which contains details about the network node that has a transmitting line that no longer supplies cells and details about the ring to which the transmitting line belongs that no longer conveys any cells. The network node detecting a defect then establishes from which receiving line it no longer receives cells.
Such a loop is created to run either from the inner ring to the outer ring or the other way around. Where a transmitting line is defective cells intended for the defective line are looped back and transmitted over the other ring. In the case where a node can no longer exchange cells with a neighboring node or with a neighboring group, cells intended for the neighboring node are looped between rings and retransmitted over the ring which contains the receiving line that is not supplying cells. Thus, after the creation of a loop, cells are not transmitted to an isolated node and not to an isolated group either.
A network node further generates a message of a second type which indicates no defect or fault, but a planned creation, or creation to be planned of a loop. This message of the second type is necessary for the network nodes to know whether they can still reach certain network nodes and can set up connections thereto. This message, which contains details about the network node and about the ring which is no longer useful for conveying cells because of the creation of the loop, is generated only when at least one other network node does not have these details. This is the case, for example, when there is an isolated group of network nodes. This message of the second type is only sent for informative purposes and does not entail the creation of a loop.
A network node includes a switching device which carries out the transfer of received cells and thus also the creation of a loop. A control arrangement in the network node controls the switching device and is used for changing and evaluating the status table.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 5179548 (1993-01-01), Sandesara
patent: 5469428 (1995-11-01), Tokura
patent: 5600652 (1997-02-01), Kreamer
patent: 5600795 (1997-02-01), Du
patent: 5745476 (1998-04-01), Chauduri
patent: 5982747 (1999-11-01), Ramfelt
patent: 6076116 (2000-06-01), Duque-Anton
patent: 6130876 (2000-10-01), Chaudhuri
patent: 19532422 (1997-01-01), None
patent: 0641105A2 (1995-03-01), None
Du Yonggang
Herrmann Christoph
May Klaus P.
Olms Douglas
Pizarro Ricardo M.
Treacy David R.
U.S. Philips Corporation
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