Multiplex communications – Pathfinding or routing – Store and forward
Reexamination Certificate
1999-09-14
2002-09-17
Chin, Wellington (Department: 2665)
Multiplex communications
Pathfinding or routing
Store and forward
C370S227000, C370S392000, C370S416000, C709S235000, C709S240000
Reexamination Certificate
active
06452934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to packet forwarding apparatus (equipment) for performing the transmission of telecommunication traffic packets and further relates to a communication network having a plurality of terminals and a transport network for interconnecting the plurality of terminals.
2. Description of the Related Art
A packet switching method for controlling the transmission data in packets is broadly employed in data communication networks or local area networks whose number of nodes is large and whose bandwidth necessary for each node varies during a short period of time. This is because the packet switching method can effectively utilize a transport bandwidth as compared with a circuit switching method. The circuit switching method is a switching method for controlling the transmission data in units having a multiplexed and determined transport rate by space division multiplexing, time division multiplexing, frequency division multiplexing and code division multiplexing. It is difficult for a network using the packet switching method (hereinafter, a packet switched network) to always maintain a transport bandwidth for a designated route and monitor a transport status as in a network using the circuit switching method (hereinafter, a circuit switched network) and a delay for every node on a traffic path is large because switching is performed by the store and forward method. Therefore, in a packet switched network, it is difficult to construct a highly reliable network as compared with a circuit switched network.
On the other hand, the circuit switching method is always employed for a backbone network having a relatively small number of nodes and requiring a high reliability. The demand of a bandwidth for the backbone network has been increasing these days and a switch having a large switching unit capacity is required for the main network. The reason for that demand is that (1) it is preferable to reduce the number of switches, each of which operates for a high speed recovery from a failure, and (2) it is preferable to minimize the size and cost of the hardware by restricting the number of the circuits being applied to backbone nodes.
Most actual large scale datagram networks have a multi-layer structure where a packet switched network employs the backbone network as a transport medium. In such a communication network, the packet switched network overlays the circuit switched network. The problem with having the data network overlaying the packet switched network on the circuit switched network is that there is a brief disconnection caused by an instantaneous cut off through switching by the circuit switched network.
In the present packet forwarding protocol, the receipt confirmation of a packet is performed by a receiver side that transmits a receipt notification message (ACK packet) to a transmitter side. When the packet is not received, the receiver side outputs a resending request to the transmitter side by a non-receipt notification message (NAK packet).
In the current operated packet switched network, the data communication service is remedied by the data recovery through the data resending rather than the data switching without data loss. When a circuit having a large capacity halts the data transmission service temporarily, an enormous amount of control packets are generated for resending non-received packets and the utilization efficiency of the network bandwidth deteriorates. Since resending by the packet forwarding protocol takes time to transmit the control packet therebetween, failures may sometimes occur for the service which requires the real time responsibility for transmitting voice data and for the service necessary to keep an order of arrival packets.
In the research level, there is an attempt to perform the switching without disconnection on the packet switched network. In particular, in an asynchronous transfer mode (ATM) network, there is proposed a method for switching without disconnection in which data are always transmitted to pluralities of routes. At the time of switching, a selector on the receiver side changes the connection destination after the selector on the receiver side synchronizes a signal from the switching source route with a signal from the switching destination route.
There is a problem with the above proposal in that it is difficult to perform the synchronization of data coming from pluralities of routes. In order to solve this problem, there is proposed a method for the insertion of a cell that is marked, as described in a Japanese laid open patent No. 7-264210, and/or for transmitting a dummy cell until when there is no useful information on the both switching source and destination routes, as described in a Japanese laid open patent No. 8-139732.
The switching without disconnection in the circuit switched network is studied in the network of SONET/SDH standard, as described in Kawase et. al., “Hitless Frame Switching Scheme for SDH Networks,” (The institute of Electronics, Information and Communication Engineers, Vol. J78-BI No.12, pp. 764-772, 1995). Because the network of SONET/SDH standard is a synchronous network, it is necessary to perform accurate control as compared with the switching without disconnection in the packet switched network since the synchronization within a byte must be implemented for matching the signal phase of data coming from the pluralities of routes at the time of switching.
Although the conventional SONET/SDH method has been broadly employed in the backbone network, an installation of an optical switching method for performing the switching by using an optical switch to the backbone network is studied. The optical switching method is by switching with a light without an optical-electrical conversion of the main signal at the time of switching an optical transport route.
The feature of the optical switching method is that a switching unit capacity can be increased as compared with an electrical switching in the SONET/SDH method. However, it is difficult for an optical signal to store the data signal into a storage. Thereby, it is still difficult for an optical switching network to perform the switching without disconnection by using a buffer memory for storing a data signal.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce an amount of packet data loss when the state transition or state change occur in association with the brief disconnection in the circuit switched network (e.g., brief disconnection for the recovery from the transport route failure) upon which the packet switched network is overlaid.
The packet switched network is configured by connecting a plurality of packet forwarding apparatus with a transport link. In the packet switched network overlaying the circuit switched network, a circuit corresponds to a transport link. The packet forwarding apparatus of the present invention is assumed to include a storing means. Although most packet forwarding apparatus include the storing means for performing a switching by a store-and-forward method, it is preferred to add a storing capacity when the storing means does not have a capacity sufficient for an embodiment of the present invention. It is still preferred to insert or add a storing means into the packet forwarding apparatus for applying the embodiment of the present invention to a packet forwarding apparatus not including the storing means. When a circuit connected with the packet forwarding apparatus undergoes a brief disconnection caused by switching, after a packet data transmitted to the circuit only during the period of the brief disconnection is stored into the storing means, if a packet transmission to the circuit is halted, the data loss on the packet switched network can be avoided. The packet transmission halt is performed by receiving a brief disconnection begin notification from the circuit switched network. When the circuit switched network is going into the state transition, the brief disconnection begin notification is produced by an adminis
Chin Wellington
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Phan M.
LandOfFree
Packet forwarding apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Packet forwarding apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Packet forwarding apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2816731