Automatic repeat request

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 data frame or packet) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) to achieve reliable data transmission over an unreliable service. If the sender does not receive an acknowledgment before the timeout, it usually re-transmits the frame/packet until the sender receives an acknowledgment or exceeds a predefined number of re-transmissions .

The types of ARQ protocols include

All three protocols usually use some form of sliding window protocol to tell the transmitter to determine which (if any) packets need to be retransmitted.

These protocols reside in the Data Link or Transport Layers of the OSI model.

A number of patents exist for the use of ARQ in live video contribution environments. In these high throughput environments negative acknowledgements are used to drive down overheads.

Tivantinib

Tivantinib (ARQ197; by Arqule, Inc.) is an experimental anti-cancer drug. It is a bisindolylmaleimide that binds to the dephosphorylated MET kinase in vitro. Tivantinib is being tested clinically as a highly selective MET inhibitor. However, the mechanism of action of tivantinib is still unclear.

Tivantinib displays cytotoxic activity via molecular mechanisms that are independent from its ability to bind MET.

Possible applications include non-small-cell lung carcinoma, hepatocellular carcinoma, and oesophageal cancer.

References

ARQ-M

ARQ-M, short for Automatic Repeat reQuest, Multiplex, is a radio telegraphy protocol used to reliably forward telex messages over partially reliable radio links. It is a low-speed system designed to match the performance of landline telex systems and allow those messages to be forwarded over long distances using shortwave radios. The first ARQ-M link was built in the Netherlands, and began exchanging messages with a counterpart in New York in 1947.

ARQ-M is similar in concept to ARQ-E, but ARQ-E has no multiplex capability and uses a different 7 bit alphabet.

History

The telex system, which developed out of the telegraph system, is based on defined electric current levels that are interpreted as a mark or space signal. These are normally sent over well-defined networks with considerable infrastructure that keeps error rates very low. In contrast, radio communications are subject to a wide variety of noises and other signal problems that leads to losses. To forward telex messages successfully over radio links, some form of error correction should be applied.