Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-03-22
2003-09-16
Ton, Dang (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S394000, C370S410000, C714S746000
Reexamination Certificate
active
06621796
ABSTRACT:
FIELD OF INVENTION
The present invention involves the field of telecommunications. More particularly, the present invention involves the use of Automatic Repeat Request (ARQ) in wireline and wireless telecommunications systems and data networks.
BACKGROUND
Automatic Repeat Request (ARQ) is a commonly used technique in telecommunications systems and data networks. It is used to ensure the reliable delivery of protocol data units (PDUs) from a sending entity (herein referred to as a sender) to a receiving entity (herein referred to as a receiver). In general, ARQ employs an error detection code during data transmission. The error detection code allows the receiver to determine whether a given PDU was correctly received. ARQ also employs a feedback mechanism, which the receiver uses to notify the sender that a PDU was or was not correctly received. The sender may then retransmit the PDU based on the feedback provided by the-receiver.
Generally, there are three main ARQ types: Stop-and-Wait, Go-Back-N, and Selective Repeat. In accordance with the Stop-and-Wait ARQ, a sender does not send a PDU to the receiver until it receives positive acknowledgment from the receiver that the previous PDU has been received. In accordance with the Go-Back-N ARQ, the sender may transmit one or more PDUs before it receives positive acknowledgement (Ack) from the receiver regarding previous PDUs. If, however, the sender receives a negative acknowledgement (Nack) from the receiver indicating that a previous PDU was not received, the sender retransmits the missing or incorrectly received PDU, as well as all subsequent PDUs, whether or not they were received correctly. In accordance with the Selective Repeat ARQ, the receiver provides a combination of negative acknowledgments and positive acknowledgments. The sender then retransmits those PDUs which were not received, but the sender does not retransmit, as in Go-Back-N ARQ, all subsequent PDUs. Of course, there are any number of different variants associated with each of the three main ARQ types.
Normally, PDUs are delivered from the sender to the receiver without allowing for the loss of these PDUs. The reason for this is that conventional ARQ techniques retransmit a PDU until it is successfully received at the receiver and acknowledged at the sender. However, indefinite retransmission is unrealistic and undesirable. Accordingly, it is sometimes advantageous to terminate the retransmission process and discard the PDU.
The mechanism employed to discard PDUs should, of course, efficiently discard the PDUs in a timely manner. In doing so, the chance of transmitting obsolete data is minimized. For instance, there are many applications, such as real-time voice and video applications, where the data being transmitted is useful for only a very short period of time. Beyond that, the data is obsolete. Transmitting such data is not only useless, it wastes network resources as well as bandwidth.
The discard mechanism employed should also discard PDUs in an effective manner so as to avoid, or at least minimize, situations that could lead to deadlock. In addition, the discard mechanism should provide a discard signaling scheme that guards against such things as PDU identification ambiguity, de-allocation of input buffer space at the receiver before a corresponding PDU is actually discarded at the sender, or the like. Moreover, the discard mechanism should provide a way to notify the receiver when PDUs have been discarded at the sender, even if there is no provision in the protocol for explicit signaling.
Additionally, the discard mechanism should take into consideration the segmentation and reassembly of upper layer data packets, such as Internet Protocol data packets, wherein segmentation and reassembly is a common technique used in transporting upper layer data packets. For the purpose of simplicity, upper layer data packets are simply referred to herein below as “data packets”. Where segmentation and reassembly of data packets is employed, several PDUs may be required to transport the data associated with a single data packet. Accordingly, the receiver must be able to determine, among other things, the correct sequence of the PDUs, and determine the data packet to which each PDU belongs. Typically, this is accomplished by assigning each PDU a sequence number, where sequence numbers may, for example, range from 0 to 2
k−1
in accordance with a modulo
2
format, where k represents the number of bits which comprise a sequence number, and by adding a start bit and stop bit to the first and last PDU associated with each data packet respectively. The discard mechanism must be able to recognize when a PDU associated with a data packet has been discarded and, at the sender, discard the entire data packet with which the discarded PDU is associated. Also, if the receiver has already received any PDU associated with that data packet, the discard mechanism must be able to notify the receiver to discard these PDUs as well.
Of course, there are a number of known discard mechanisms for ARQ. One such discard mechanism involves a receiver-initiated discarding signaling scheme. However, this technique is not overly attractive, particularly because the sender, and not the receiver, is a better position to determine how and when to cease the retransmission of and the discarding of PDUs.
In accordance with another discard mechanism described in co-pending U.S. patent application Ser. No. 09/179,952, “ARQ Discard Capability,” a single bit called the receive packet enforcement bit (RPEB) in the header portion of each PDU is used to notify the receiver that it should not expect to receive PDUs having a lower sequence number, and that the receiver should accept that PDU out of sequence. Although that application does show that the RPEB could be applied to Selectively Repeat ARQ, the application is primarily directed at discard signaling for the Go-Back-N type ARQ.
In co-pending U.S. patent application Ser. No. 09/245,866, “Prime ARQ Control Flow Including Cell Discard,” yet another discard mechanism is described. In this application, however, the discard mechanism is designed to be used in conjunction with prime ARQ, a variable of Go-Back-N and Selective Repeat ARQ.
Accordingly, it would be desirable to provide a discard mechanism that exhibits each of the various capabilities described above. More particularly, it would be desirable to provide a sender-initiated discard mechanism that is specifically designed to operate efficiently and effectively with Selective Repeat ARQ.
SUMMARY OF THE INVENTION
The present invention involves the use of ARQ techniques to help ensure the reliable delivery of data packets, herein referred to as protocol data units (PDUs) from a sender to a receiver. More specifically, the present invention involves a Selective Repeat ARQ technique which employs a sender-initiated PDU discard mechanism that is specifically designed to be used in conjunction with Selective Repeat ARQ.
Accordingly, it is an objective of the present invention to provide a discard mechanism for selectively repeat ARQ that employs sender-initiated signaling rather than receiver-initiated signaling.
It is another objective of the present invention to provide a sender-initiated, discarding mechanism for Selective Repeat ARQ that takes into consideration the segmentation and reassembly of data packets.
It is still another objective of the present invention to provide a sender-initiated discard mechanism for selective repeat ARQ, even when there is no explicit discard signaling capability.
In accordance with a first aspect of the present invention, the above-identified and other objects are achieved by a method for discarding data units for Selective Repeat ARQ. The method involves transmitting a first data unit from a sender to a receiver and initiating a first timer in connection with the transmission of the first data unit. The method also involves transmitting a second data unit from the sender to the receiver, and initiating a second timer in connection with the second data unit be
Phan Tri H.
Telefonaktiebolaget LM Ericsson (publ)
Ton Dang
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