Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Patent
1996-08-27
1998-09-15
Kizou, Hassan
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
370228, 370395, 340827, H04L 122, H04L 1256
Patent
active
058090118
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/Fl 95/00103 filed Feb. 27, 1995.
BACKGROUND OF THE INVENTION
The invention relates to a method for rerouting a packet-mode data connection.
In principle, the method of the invention may be applied to any connection-oriented packet-switched communications network (e.g. X.25 or Frame Relay), but the invention is primarily intended for an ATM (Asynchronous Transfer Mode) network (allowing high-speed connections) for which it is especially well suited due to its internal characteristics.
ATM is a new connection-oriented packet-switched technique, where the problems of traditional packet networks have been solved by employing short, fixed-size (53-byte) packets, called cells. Each cell consists of a 48-byte payload segment and a 5-byte header. However, the ATM technology is not described here in any greater detail, as the method of the invention does not require any special applications of the ATM technology. A detailed description of the ATM technology is available e.g. in specification).
In an ATM network (as in other connection-oriented packet networks), connections may be secured by using one or more spare routes between the nodes, in addition to the main route. Thus, when necessary, traffic may be transferred from one route to another. One additional requirement for the ATM network is that the cell order of a connection be maintained. Because the above mentioned cell headers have no sequence numbers allowing their reorganization at the receiving end, the connection must always follow the same route through the network.
However, it is highly probable that transferring traffic from one route to another will cause the cell order to disrupt, resulting in loss of data, at least when the delay of the new route is shorter than that of the old route.
SUMMARY OF THE INVENTION
It is the object of the present invention to eliminate the above disadvantage and to provide a method where a (virtual) connection transmitting packet-mode data is transferred from one route to another with minimum loss of data.
The idea of the invention is to realize the transfer within a certain time window so that, during a period of time, both nodes will receive from both routes, but the transmission in the opposite end functions, however, so that data is received from only one route at a time. The time window is initiated when the node starting the rerouting also starts to listen to a new connection, and the time window is closed when the opposite node ceases to listen to the route to be deactivated. For both nodes, rerouting is terminated in the same way, i.e. when the node independently (using time-out) ceases to listen to the route to be deactivated.
The method of the invention allows the different ends of the connection, typically located far apart, to transfer to a new route at different points of time, since both ends will receive, for a while, traffic pertaining to one particular connection from two different routes. Such non-simultaneity leads to interruptions in systems where transfer from one route to another takes place instantly. Non-simultaneity is difficult to prevent as the request for transfer in a typical network usually passes via several network elements. The response times of these elements are not deterministic (in addition, the requests for transfer are typically processed by software), wherefore it is difficult to determine the exact moment of transfer. Maintenance of an exact real time in the whole network is also difficult.
As described below, the method of the invention also facilitates the control of conflicts caused by the differing interpretations at the different ends of a connection.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention and its preferred embodiments will be described in greater detail with reference to examples in accordance with the accompanying drawings, in which:
FIG. 1 shows a section of a packet-switched network where there are two possible routes between two nodes,
FIG. 2 is a time diagram illustratin
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Hyun Soon-Dong
Kizou Hassan
Nokia Telecommunications Oy
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