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Selective Repeat is part of the automatic repeat request (ARQ). With selective repeat, the sender sends a number of frames specified by a window size even without the need to wait for individual ACK from the receiver as in Go-Back-N ARQ. The receiver may selectively reject a single frame, which may be retransmitted alone; this contrasts with ...
Automatic repeat request (ARQ), also known as automatic repeat query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a message) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) to achieve ...
This re-transmission process is known as ARQ (automatic repeat request). The problem with Stop-and-wait is that only one frame can be transmitted at a time, and that often leads to inefficient transmission, because until the sender receives the ACK it cannot transmit any new packet.
NORM operates on top of the User Datagram Protocol (UDP), and ensures reliable communication based upon a negative acknowledgement (NACK), selective Automatic Repeat Request (ARQ) mechanism, as opposed to the positive acknowledgement (ACK) approach that the standard Transmission Control Protocol (TCP) uses. In other words, receivers using NORM ...
However, ARQ requires the availability of a back channel, results in possibly increased latency due to retransmissions, and requires the maintenance of buffers and timers for retransmissions, which in the case of network congestion can put a strain on the server and overall network capacity. [10] For example, ARQ is used on shortwave radio data ...
Retransmission, essentially identical with automatic repeat request (ARQ), is the resending of packets which have been either damaged or lost. Retransmission is one of the basic mechanisms used by protocols operating over a packet switched computer network to provide reliable communication (such as that provided by a reliable byte stream, for example TCP).
One common simplification of selective-repeat is so called SREJ-REJ ARQ. This operates with w r =2 and buffers packets following a gap, but only allows a single lost packet; while waiting for that packet, w r =1 and if a second packet is lost, no more packets are buffered. This gives most of the performance benefit of the full selective-repeat ...
As a result, hybrid ARQ performs better than ordinary ARQ in poor signal conditions, but in its simplest form this comes at the expense of significantly lower throughput in good signal conditions. There is typically a signal quality cross-over point below which simple hybrid ARQ is better, and above which basic ARQ is better.