Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-04-04
2001-01-23
Vu, Huy D. (Department: 2735)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S351000, C370S357000, C370S391000, C370S399000
Reexamination Certificate
active
06178169
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of transmitting an asynchronous transfer mode (ATM) cell over an ATM network between an ATM input interface and an ATM output interface.
2. Related Art
In a conventional ATM network, when a cell arrives at the ATM input interface, initial values are inserted into the virtual path identifier (VPI) and virtual channel identifier (VCI) fields in the header. The VPI field provides the coarse level routing for the ATM cell and the VCI field provides the fine level routing. At each switching node between the ATM input interface and the ATM output interface, the VPI and/or VCI fields are read and the output port is selected in accordance with the value of one or both of these fields using the routing table contained in the node. Before forwarding the cell on the selected output port, the values of one or both of these fields are updated.
In each switching node, the routing table and the updating values for the VPI and/or VCI fields are set up partly by network management and partly by signalling during call set up. Consequently, a conventional ATM network provides a connection-oriented service. In a connection-oriented service, the call is set up by signalling at the commencement of the cell and cleared down at the end of the call. Alternatively, the routing table and the updating values may be set up to provide a permanent connection.
If it is desired to transmit data over a switched ATM network, for example data from a computer provided with an ATM card, it is necessary to set up a call before the data can be transmitted. If the data is then transmitted more or less continuously for the duration of the call, the connection-oriented service provided by a conventional ATM network is satisfactory. However, it is often desired to transmit data intermittently, one burst of cells at a time followed by a long pause before the next burst of cells is transmitted. However, this incurs an overhead cost of setting up and clearing down the call for each burst of cells. Thus, a conventional switched ATM network is not optimal for intermittent transmission of data.
In order to provide a connectionless service over an ATM network, it has been proposed to add a server to provide a connectionless service as an overlay to an ATM network. However, this solution suffers from the disadvantage that there is still a call set up phase, in this case between the input interface and the server.
SUMMARY OF THE INVENTION
According to one aspect of this invention there is provided a method of transmitting an asynchronous transfer mode (ATM) call from a source node to a destination node over an ATM network between an ATM input interface and an ATM output interface in a connectionless manner, said source node and destination node each having a network address, said ATM cell comprising a header and a user section, said network comprising a network of interconnected nodes at least some of which are switching nodes, said method comprising the steps of:
at the ATM input interface, setting a field in the header of the ATM cell to a value which indicates connectionless transmission and inserting a source address and a destination address into the header, the source address being the network address of the source node and the destination address being the network address of the destination node; and
at each switching node between the ATM input interface and the ATM output interface, establishing that the cell is to be forwarded in a connectionless manner by reading said field in the header, reading the destination address in the header, selecting an output port in accordance with at least the destination address, and forwarding the cell on the selected output port.
The present invention provides the advantage that the routing tables do not need to be set up by signalling for each transmission of ATM cells between a particular access node and a particular destination node. Consequently, where cells are transmitted in bursts, there is no overhead cost of setting up a call for each burst of cells.
According to another aspect of this invention, there is provided a method of operating an ATM network so as to transmit cells between a source node and a destination node over the network selectively in either a connectionless manner or a connection-oriented manner, said source node and destination node each having a network address, each ATM cell comprising a header and a user section, said network comprising a network of interconnected nodes at least some of which are switching nodes;
in the event of transmitting an ATM cell over the network in a connectionless manner between an ATM input interface and an ATM output interface, said method comprising the steps of:
at the ATM input interface, setting a field in the header of the ATM cell to a value which indicates connectionless transmission and inserting a destination address and a source address into the header, the source address being the network address of the source node and the destination address being the network address of the destination node; and
at each switching node between the ATM input interface and the ATM output interface, establishing the cell is to be forwarded in a connectionless manner by reading said field in the header, reading the destination address in the header, selecting an output port in accordance with at least the destination address and forwarding the cell on the selected output port;
in the event of transmitting an ATM cell over the network in a connection-oriented manner between an ATM input interface and an ATM output interface, said method comprising the steps of:
at the ATM input interface setting the virtual path identifier (VPI) and the virtual channel identifier (VCI) fields in the header; and
at each switching node between the ATM input interface and the ATM output interface, reading the VPI and/or VCI fields in the header, selecting an output port in accordance with the VPI and/or VCI values, updating the VPI and/or VCI fields, and forwarding the cell on the selected output port.
According to a further aspect of this invention there is provided a method of transmitting an asynchronous transfer mode (ATM) cell from a source node to a least one destination node so as to provide a multicast service over an ATM network between an ATM input interface and an ATM output interface in a connectionless manner, said network comprising a network of interconnected nodes at least some of which are switching nodes, said method comprising the steps of:
at the ATM input interface, setting a field in the header to a value which indicates connectionless transmission and inserting a source address and a destination address into the header, the source address being the network address of the source node and the destination address being the network address of the multicast service; and
at each switching node between the ATM input interface and the ATM output interface, establishing that the cell is to be forwarded in a connectionless manner by reading said field in the header, reading the destination address in the header, selecting at least one output port in accordance with at least the destination address, and then forwarding the cell on said at least one selected output port.
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Hodgkinson Terence G.
O'Neill Alan W.
British Telecommunications public limited company
Nixon & Vandehrye P.C.
Phan M.
Vu Huy D.
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