Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-06-23
2001-07-24
Patel, Ajit (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S477000
Reexamination Certificate
active
06266337
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to packet transmission systems and, more specifically, to a system and method for reducing overhead associated with packet retransmissions in a packet-based network.
BACKGROUND OF THE INVENTION
Packet-based communication networks (such as the Internet) transfer information between computers and other equipment using a data transmission format known as packetized data. The stream of data from a data source (e.g., a host computer) is divided into variable or fixed length “chunks” of data (i.e., packets). Switches (e.g. routers) in the network route the packets from the data source to the appropriate data destination. In many cases, the packets may be relayed through several routers before they reach their destination. Once the packets reach their destination, they are reassembled to regenerate the stream of data.
Conventional packet-based networks use a variety of protocols to control data transfer throughout a network. For example, the Internet Protocol (“IP”) defines procedures for routing data through a network. To this end, IP specifies that the data is organized into frames, each of which includes an IP header and associated data. The routers in the network use the information in the IP header to forward the packet through the network. In the IP vernacular, each router-to-router link is referred to as a hop.
The Transmission Control Protocol (“TCP”) defines additional functions such as data flow control and reliable data transfer. TCP specifies that the data is organized into segments, each of which includes a TCP header and associated data. TCP specifies that a destination must acknowledge segments that it successfully receives. Thus, after the destination receives a segments that has not been corrupted in transit and all previous packets were received, the destination sends an acknowledgment message to the source. In simplified terms, if the source does not receive an acknowledgment within a predefined period of time, the source retransmits the segment. (There are additional situations in which TCP will initiate a retransmission. Inasmuch as these situation are well known in the art, they will not be discussed in detail here.)
Retransmission schemes used by protocols such as TCP, while generally effective, reduce the usable bandwidth of the network. That is, the resources of the network are essentially wasted when they are used to transmit data that has previously been transmitted. Due to ever increasing demand for network bandwidth and the relatively high cost of providing additional bandwidth in conventional data networks, a need exists for a method of compensating for losses in the effective bandwidth of data networks.
SUMMARY OF THE INVENTION
The invention provides a method of reducing data traffic associated with the retransmission of packets over a predefined path in an IP-based network. The predefined path does not include the final destination of the packet Thus, packets that were successfully transmitted over the predefined path, might not successfully reach the final destination. In this case, the source of the packet (e.g., a host computer) may attempt to retransmit the packet through the network via the predefined path.
In accordance with one embodiment of the invention, packets to be transmitted over the predefined path are analyzed to determine whether they have been previously sent over the path. If so, a retransmission message is sent over the path instead of the packet. When a retransmission message is received at the other end of the path, the actual packet (which was stored in a data memory during the prior transmission) is retrieved from the data memory and routed to the final destination in the usual manner.
In one embodiment, the invention is implemented using devices installed on each end of an IP hop. For example, the devices may be installed between the routers on each end of the IP hop. The device on the sending end of the hop intercepts each packet that the router sends over the hop. A packet that was not previously sent over the hop is copied into a cache and sent over the hop intact. On the other hand, when the incoming packet was previously sent over the hop, the device sends a retransmission packet instead of the packet. The retransmission packet includes information that identifies the packet being retransmitted.
The device on the other end of the hop intercepts each packet coming from the hop. When the incoming packet is not a retransmission packet, the device copies the packet to a cache and passes the packet to the router on that end of the hop. When the packet is a retransmission packet, the device retrieves the corresponding packet from the cache and sends that packet to the router.
In another embodiment, the method of the invention is implemented by installing appropriate software modules in the equipment (e.g., routers) on the ends of the path. The equipment is configured so that packets are processed as above and stored in the internal memory of the equipment, as necessary.
A system utilizing the teachings of the invention may provide additional data throughput because it typically will be more efficient to send a retransmission packet (which might not contain any data) instead of the entire packet (which may contain hundreds of bytes of data).
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Expand Network Ltd.
Friedman Mark M.
Patel Ajit
Phunkult Bob A.
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