Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
2000-03-23
2003-01-07
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S450000, C370S458000, C370S470000
Reexamination Certificate
active
06504840
ABSTRACT:
TECHNICAL FIELD OF INVENTION
The present invention relates to a method, a system and apparatuses for transferring data on a bitstream in a circuit switched time division multiplexed network, wherein said bitstream is divided into frames, each frame is divided into time slots, and said time slots are divided into control slots and data slots, and wherein an isochronous channel, comprising one or more data slots within each cycle of said bitstream, has been established between a first node and a second node of said network.
TECHNICAL BACKGROUND AND PRIOR ART
Today, new types of circuit-switched communication networks are being developed for the transfer of information using isochronous channels carried on time division multiplexed bitstreams, wherein a bitstream is divided into frames, each frame in turn being divided into time slots.
One example of such a network is the so-called DTM network (DTM—Dynamic Synchronous Transfer Mode). DTM is a broadband network architecture (see e.g. Christer Bohm, Per Lindgren, Lars Ramfelt, and Peter Sjödin, The DTM Gigabit Network, Journal of High Speed Networks, 3(2), 109-126, 1994, and Lars Gauffin, Lars H{dot over (a)}kansson, and Björn Pehrson, Multi-gigabit networking based on DTM, Computer Networks and ISDN System, 24(2), 119-139, April 1992).
The basic topology of a network of this kind is preferably a bus with two unidirectional optical fibers connecting a number of nodes, each node being arranged to serve one or more end users connected thereto. Note, however, that the topology may just as well be realized by any other kind of structure, e.g. a ring structure or a hub structure.
The bandwidth of each wavelength on the bus, i.e. each bitstream on each fiber, is divided into fixed size, typically 125 &mgr;s, frames which in turn are divided into fixed size, typically 64-bit, time slots. The number of slots in a frame thus depends on the network's bit-rate. The slots are divided into two groups, control slots and data slots. Control slots are used for transferring of signaling messages between said nodes for the network's internal operation. The data slots are used for the transfer of user data, also referred to as payload data. The user data is typically transferred between end user having access to said network, either directly or via a node unit providing said end user with access to said network.
Each node is hence arranged to dynamically establish isochronous communication channels, each channel comprising a set of data slots within each frame on a bitstream, for the transfer of data through the network.
When, for example, a first user connected to a first node wants to transfer information to a second user connected to a second node, said first node will allocate a number of data slots within each frame, thus defining an isochronous channel, for the first user to write data into. The first node will also send a control message in a control slot to the second node, instructing said second node to read any data being provided in said allocated data slots within said frame and to send such data so said second user.
SUMMARY OF THE INVENTION
The object of the invention is to provide a faster and more reliable way of handling communication in networks of the above-mentioned type.
This and other objects are accomplished by the invention as defined in the accompanying claims.
Hence, according to a first aspect of the invention, there is provided a method of the kind mentioned in the introduction, said method being characterized by the step of providing said bitstream with data distinguishing each data slot, within said channel, that contains non-valid data as a result of said first node not being able to transmit valid data into said each data slot, which step in turn comprises the steps of:
providing said each data slot with data designating the respective data slot as containing non-valid data;
encoding said designating data of each respective data slot as a specific bit pattern; and
transmitting said specific bit pattern on said bitstream, said specific bit pattern, when received, being recognizable as identifying a data slot which contains non-valid data.
According to a second aspect of the invention, there is provided a system for transferring data on a bitstream in a circuit switched time division multiplexed network, wherein said bitstream is divided into frames, each frame is divided into time slots, and said time slots are divided into control slots and data slots, comprising a first node for transmitting data into time slots of said bitstream; a second node for reading data from time slots of said bitstreams; means for establishing an isochronous channel, comprising one or more data slots within each cycle on said bitstream, between said first node and said second node; and means for providing said bitstream with data distinguishing each data slot, within said channel, that contains non-valid data as a result of said first node not being able to transmit valid data into said each data slot.
According to a third and a fourth aspect of the invention, there is provided sending and receiving node apparatuses, which will be further disclosed below.
The invention serves to avoid the situation wherein non-valid data, or “garbage” data, is transferred in the data slots of an allocated isochronous channel on a bitstream between two nodes as a result of the sending node not having received valid data for transmission into said channel, thus possibly resulting in the receiving node reading data from said data slots and passing it along, for example to a receiving end user, irrespective of whether or not said data slots provide valid or non-valid data, consequently making it necessary for the receiving user to distinguish valid data from non-valid data.
According to the invention, the occurrence of this type of undesired situation is prevented by the detection of the failure at the sending node to transmit data for any one of the allocated data slots and by the sending of information to the receiving node as to which data slots within said channel that contain non-valid data (or which data slots that contain valid data). Consequently, it is possible for the receiving node to handle received data accordingly, for example by only passing on valid data to a receiving end user connected to the receiving node.
In this context, it is important to note that, in a conventional network of the kind mentioned in the introduction, the nodes are not concerned with the actual information being transferred on the data slots defining said channel. The sending node merely receives data, for example from a sending end user being served by the sending node, or from another bitstream accessed by the sending node (i.e. in case of the sending node acting as a switch node), and writes said data into data slots of the channel on the bitstream between the sending and the receiving node. Correspondingly, the receiving node merely reads data from said allocated data slots and passes said read data to, for example, a receiving end user connected to the second node, or forwards said data to another bitstream accessed by the sending node (i.e. in case of the receiving node acting as switch node). In other words, with the exemption of the initial channel establishment signaling between the nodes and the mere passing of data to and from data slots allocated to the channel, the first and second nodes are basically not concerned with any control signaling or the like taking place between the communicating end users within the realms of the data slots allocated to said channel, It may hence be said that the nodes are not concerned with the content of data transferred between end users using said allocated time slots. Furthermore, data transferred in said allocated data slots from one end user to another end user may comprise control signaling or control information as well as mere data. However, the node of the network are essentially not concerned with the communication protocol at end user level. Consequently, the communication protocol at the end user level need
Bohm Christer
Boström Anders
Disen Elling
Lindgren Per
Kizou Hassan
Net Insight AB
Qureshi Afsar M
Skjerven Morrill LLP
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