Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
2000-01-21
2003-09-16
Etienne, Ario (Department: 2157)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C709S237000, C709S233000, C709S235000
Reexamination Certificate
active
06622172
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of data communication. In particular, the present invention relates to data communication involving the Transmission Control Protocol (TCP) where acknowledgement transmissions by the receiving entity are dynamically delayed in response to the congestion window size of a sending entity that is connected to the receiving entity via an asymmetric connection.
BACKGROUND
Currently, practically all forms of information exchange and communication subsist on data communication. For example, data communication is a necessary operation in the transmission of facsimile documents. Another important example of the ubiquity of data communication is the Internet where data communication is vital in enabling large files to be downloaded from Web sites to an Internet surfer's computer. A further example of the indispensability of data communication can be seen in its application in network technology. In a network of computers, the computers communicate with each other through data communication.
Hence, it is clear that the operation of all these systems fundamentally depend on data communication. The speed of data communication translates into the speed of information exchange and communication. Therefore, faster data communication means faster information exchange and communication.
Typically, the process of transmitting information across a network connection between computers using data communication involves a two-way transmission of data. When a sending entity wishes to send information to a receiving entity, the sender's computer, which is connected to the receiver's computer through the network connection, initiates a sequence of communication processes that involve the processing of the information. The processing of information usually includes the breaking up of information into packets of data. These data packets are transmitted to the receiver's computer through the network's connection between the computers. Upon receiving these data packets, the receiver computer assembles these data packets into the same information that the sender intended for the receiver to receive.
Upon the arrival of these data packets at the receiver's computer, the receiver's computer acknowledges to the sender's computer that the receiver's computer has received the data packets. The receiver's computer does this by sending packets of data that are known as acknowledgement packets. These acknowledgement packets are transmitted in response to the data packets received by the receiver's computer.
A common and typical way of breaking up information on the sender's computer and, re-forming the same information on the receiver's computer is through the use of the Transmission Control Protocol (TCP). The TCP is a communication protocol that is widely used within the Internet domain for the above purposes of breaking up information and re-forming information on the sender and receiver's computers, respectively. An example of a sender's computer is a server for a web site. An example of a receiver's computer is an Internet surfer's computer. The TCP communication protocol is implemented on both the sender and receiver's computers. The TCP communication protocol is also responsible for causing acknowledgement packets to be transmitted in response to data packets received by the receiver's computer.
The TCP communication protocol is an end-to-end reliable transport protocol.
The TCP communication protocol is also known as a “gentleman”communication protocol, because this protocol provides for data communication between computers of the sender and receiver while having regard to congestion conditions in the Internet. TCP does this by allowing the sender's computer to start transmission only with small numbers of data packets. As the'sender's computer receives acknowledgement packets from the receiver's computer, indicating the successful transmission and reception of the earlier transmitted data packets, the sender's computer is allowed to increase the number of data packets that the sender's computer can transmit subsequently. For example, the sender's computer starts by transmitting one data packet to the receiver's computer. Upon receiving an acknowledgement packet from the receiver's computer acknowledging the one data packet that was transmitted, the sender's computer transmits two further data packets to the receiver's computer. As the sender's computer transmits the data packets to the receiver's computer, the sender's computer using the TCP communication protocol monitors the number of data packets transmitted and constantly updates a parameter inherent to the TCP communication protocol known as the congestion window size. Hence, when the congestion window size is set to one, the sender's computer transmits one packet of data to the receiver's computer. When the sender's computer receives an acknowledgement packet from the receiver's computer in response to that one data packet transmitted earlier, the congestion window size is increased to two. With an increased congestion window size, the sender's computer is allowed to transmit, and therefore transmits, two data packets. When the receiver's computer receives the two data packets, the receiver's computer acknowledges each of the two data packets by consecutively transmitting two acknowledgement packets. For each acknowledgement packet received by the sender's computer, the congestion window size is increased by one. Hence, upon receiving the two consecutively transmitted acknowledgement packets from the receiver's computer, the congestion window size is raised to four. By this arrangement, the TCP communication protocol imposes on the sender's computer a condition that the congestion window size increases exponentially as the sender's computer continues to transmit data packets and receive acknowledgement packets in response to those data packets. This exponentially increasing behavior of the congestion window size is known as the slow start stage of the data communication process between the sender and receiver's computers. However, as mentioned hereinbefore, the TCP communication protocol is a gentleman's communication protocol. Therefore the TCP communication protocol cannot allow the sender's computer to exponentially increase the number of data packets that the sender's computer transmits infinitely because this causes congestion in the network connection between the sender and receiver's computers. The TCP communication protocol participates in congestion control by setting a value that dictates the maximum congestion window size before the growth rate of the congestion window size slows down. This value is known as the Slow Start Threshhold (SSTHRESH) value.
When the sender's computer's congestion window size reaches the SSTHRESH value, the congestion window size grows linearly, i.e., by one each time a “window” full of acknowledgement packets are received. The ultimate size that the congestion window size can grow to is limited by the transmission buffer in the receiver's computer. When the sender's computer does not receive acknowledgement packets within a certain time from the receiver's computer for the data packets received in that window, the sender's computer times out and consequently retransmits lost data packets. The sender's computer also reduces the congestion window size to 1. This means that as the data communication between the sender and receiver's computers continues, the sender's computer resumes data communication by transmitting one data packet to the receiver's computer. In the same manner as described above, the congestion window size exponentially increases. However, through a congestion control mechanism inherent to the TCP communication protocol, the SSTHRES
Berkowitz Marvin C.
Etienne Ario
Kent Ridge Digital Labs
Nath & Associates PLLC
Novick Harold L.
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