Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1996-06-25
2004-07-20
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000, C370S409000
Reexamination Certificate
active
06765908
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of digital networking systems, and more particular to systems and methods for controlling the transfer of message packets over a digital network. The invention particularly provides an system and method by which message packets which are provided for transfer using a “connectionless” packet transfer methodology can be transferred over a network using a virtual circuit packet transfer methodology.
BACKGROUND OF THE INVENTION
Digital networks have been developed to facilitate the transfer of information, including data and programs, among digital computer systems and numerous other types of devices. A variety of types of networks have been developed and implemented using diverse information transfer methodologies. In modem networks, information is transferred through a mesh of switching nodes which are interconnected by communication links in a variety of patterns. The mesh interconnection pattern can allow for a number of paths to be available through the network from each computer system or other device which may transmit information as a source device, to another computer system or other device, which is to receive the information as a destination device, so that if one switching node or communication link is congested or inoperative, the information can be routed around the congested or inoperative portion of the network.
Information transferred from a source device to a destination device is generally transferred in the form of fixed- or variable-length packets, which are transferred through the network in accordance with one of several general packet transfer methodologies. In one packet transfer methodology, termed a “connectionless” data transfer methodology, each information packet that is transmitted by a source device to a destination device includes, in addition to the information to be transferred, destination address information which identifies the particular device that is to receive the packet, along with an identifier identifying the particular switching node to which the destination device is connected. Each switching node in the network is provided with a database that stores network topology information, which describes the entire topology of the network, and a routing table that provides, among other information, routing information identifying the path to be taken from the switching node to any other switching node in the network. When a switching node receives a packet that is to be transferred to a particular destination device, it (that is, the switching node) will use the routing table to identify a communication link over which the packet is to be transmitted.
Each switching node that receives the packet will perform a similar operation, until the packet is transferred to a switching node which is connected to the destination device. At that point, the switching node will identify the particular communication link connected between it and the destination device, and will transfer the packet to the destination device. Similar operations occur for each packet transferred through the network, so that each switching node will make a routing decision, to identify a particular communication link over which it is to transfer each packet that it receives, for each packet. The routing decision is overhead that may delay delivery of packets to their respective destinations, but if the packet traffic between particular source and destination devices is relatively low, which may be the case if the network allows relatively large packets to be transferred, and if the delay in delivery is not critical, the connectionless methodology can provide good service. On the other hand, since each switching node makes a routing decision effectively “on-the-fly” for each packet, if a portion of the network becomes congested or otherwise unavailable, each switching node can easily take that into account in its routing decision.
Another packet transfer methodology alleviates the necessity of requiring the switching nodes to make an “on the fly” routing decision for each of the packets which they receive. In this packet transfer methodology, packets are transferred through the network's switching nodes over constructs which are generally termed “virtual circuits,” “virtual connections” and the like (generally, “virtual circuits”). When a source device wishes to transfer information to a destination device, initially a preliminary operation will be performed to establish a virtual circuit over communication links defining a path from the source device, through a series of switching nodes to the destination device. As with the connectionless methodology, each switching node that operates using the virtual circuit methodology may include a network topology database that stores network topology information, which describes the entire topology of the network as well the identifiers for the various destination devices and the switching nodes to which they are connected, which network topology database can be used to assist in identifying a path through the various switching nodes of the network for the virtual circuit.
In addition to the network topology database, each switching node in the virtual circuit methodology will also be provided with a virtual circuit database that associates each of the virtual circuits maintained by the respective switching node with a particular one of the communication links. After a virtual circuit is established, the source device can transfer packets using the virtual circuit database Each packet will include, as well as the data to be transferred, an identifier that identifies the particular virtual circuit to be used in transferring the packet. The source device will initially transfer the packet to the switching node connected thereto, and that switching node will use virtual circuit identifier and the virtual circuit database to identify a communication link over which it (that is, the switching node) is to transfer the packet. These operations will be performed for each switching node along the virtual circuit which receives the packet. When the last switching node along the virtual circuit receives the packet, that switching node will transfer the packet to the particular destination device associated with the virtual circuit. These operations will be repeated for each of the packets transferred from the source device to the destination device. In addition, similar operations may also be performed in connection with packets which the destination device may transfer to the source device, since a single virtual circuit, once established, may be used to transfer packets in both directions between the original source device and the original destination device.
At the end of a communications session between the source device and the destination device, in which one or a number of packets may be transferred, the devices may close the virtual circuit. In that operation, packets are transferred between the source and destination devices which, among other things, can enable the switching nodes along the virtual circuit to expunge the virtual circuit information relating to the particular virtual circuit being closed from their respective virtual circuit databases. Thereafter, the virtual circuit identifier and other resources, including the entries in the respective virtual circuit databases associated with the closed virtual circuit, can be used for other virtual circuits.
There are several benefits of using the virtual circuit methodology in some environments. One benefit is that, in the virtual circuit methodology, routing decisions at each switching node need only be made while a virtual circuit is being established, instead of each time a packet is received which is to be transferred to a particular destination device as in the connectionless methodology. However, as indicated above, there is some overhead in the message traffic and routing decisions which are required to establishing a virtual circuit and in closing the virtual circuit at the end of the communications sessi
Hyun Soon-Dong
Lucent Technologies - Inc.
Nguyen Chau
LandOfFree
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