Multiplex communications – Diagnostic testing – Fault detection
Patent
1996-08-26
1999-05-18
Pham, Chi H.
Multiplex communications
Diagnostic testing
Fault detection
370218, 370237, G01R31/08
Patent
active
059057149
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for rerouting a packet-mode data connection.
In principle, the method of the invention can be applied in any packet switched network but the invention is primarily intended for a FR network (Frame Relay network) for which its features (the use of buffering) are very well suited. However, the invention can also be used in a (generally faster) ATM (Asynchronous Transfer Mode) network, for example.
Replacing previous packet network connections, Frame Relay is a packet network technique for transmitting frames of varying lengths, a heavily stripped-down version of a nowadays generally used protocol (X.25) that requires a lot of processing. By stripping operations that have become in a way unnecessary with time because of improvements in the quality of the transmission network, frame relay in the Frame Relay technique has become faster and more efficient.
ATM is a new packet-switching technique in which the problems of conventional packet networks have been solved by introducing short packets of a standard length (53 bytes) known as cells. Each cell contains a payload part of 48 bytes and a header of 5 bytes in length.
However, in this connection the FR or ATM technology will not be described any further as the method of the invention is not connected to any FR or ATM specific arrangements, but the node devices of the network are only required to have an ability to buffer. Frame Relay service is generally described in the CCIT recommendation I.233, "Frame Mode Bearer Services", a the related protocol recommendation Q.922. For a more detailed description of the Frame Relay technique, a reference is made to the article "An Overview of Frame Relay Technology", Data-pro Management of Data Communications, McGraw-Hill Incorporated, April 1991. A closer description of the ATM technology can be found, for example, in the CCITT recommendation I.610, "B-ISDN operation and maintenance principles and functions", CCITT Study Group XVIII Geneva, Jun. 9-19, 1992, or in the recommendation I.361, "B-ISDN ATM Layer Specification", CCITT; ANSI T1.617 Annex D.
In packet networks, connections can be "protected" by having one or two alternative routes between nodes in addition to the main route. In this case, traffic can be transferred from one route to another if necessary. One of the requirements of the ATM network is, for example, that the order of the cells in the connection will remain invariable in the network. Because the ATM headers of the data cells do not have a sequence number to make the rearrangement of the cells possible, the connection has to travel via the same route through the network.
Transferring traffic from one route to another leads very probably to changes in the order of the cells and thus, loss of data, in case the delay of the new route is smaller than that of the old route.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the above-mentioned disadvantage and to achieve a method in which a virtual connection transmitting packet-mode data is transferred from one route to another as fast as possible with a minimum loss of traffic, even in conflict situations in which the nodes at the termination points of the route have contradictory information about the routes in use.
The idea of the invention is to accomplish a dialogue which is based on mutual message exchange between the nodes, and on the basis of which the nodes will buffer data in their transmitters only when needed and also, until they can ascertain that they are transferring data to the same route so that the order of the packets at the opposite end will not be changed. The opposite end is notified of the need for buffering in each rerouting situation by a message exchange.
The method of the invention provides maximum probability that the packet data will reach its destination and do so in the correct order. Traffic is lost only when an active route becomes physically faulty, and eventhen, only the traffic already transmitted in between the appearance and
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Nguyen Steven
Nokia Telecommunications Oy
Pham Chi H.
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