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Shortened timeout period during frame retry in a communication link
| Details |
Inventors: Gregg, Thomas A.; Hoke, Joseph M.; Ing, Albert; Lee, Chin;
Assignee: International Business Machines Corporation (Armonk, NY)
Primary Examiner: Nguyen; Hoa T.
Assistant Examiner: Hua; Ly V.
Attorney, Agent or Firm: Cutter; Lawrence D.
A system and method for asynchronously transmitting data across fibers in a serial manner. Frames are provided as a mechanism to transmit associated data serially and tie the data being transmitted to a particular buffer set. Each outstanding request for each buffer set is individually timed to detect lost frames, and each buffer set maintains a state that keeps track of the progress and sequence of received frames. When transmission errors occur in the frames, the errors may affect only the information field and there is enough information in the header to identify the frame. A request can then be sent back to the other end of the fibers to retransmit the frame. In some instances, the frame cannot be retransmitted because the content of the data may have been changed by other operations in the systems. To speed recovery in these situations, the requester of the retransmitted frame sets a much shorter timer while waiting for the response since the retransmitted frame will be sent quickly, if at all. |
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DETAILED DESCRIPTION The present invention is embodied in a system and method for asynchronously transmitting data blocks between two information handling systems.
Two carriers are used to interconnect two systems and to provide serial data transmission in both directions.
Together, these carriers and the supporting hardware is called a link.
Information frames are provided as a mechanism to transmit data serially on the fiber.
A frame contains all or part of the contents of: a request; a response; or a data area.
The protocol for data transmission includes a request sent from one information handling system to another, followed by optional data areas transmitted in either direction, followed by a response sent back to the requesting system.
Each sequence of "request, data, and response" is called an operation, and multiple operations may be interleaved over the link.
For each operation, strict ordering of the request, data, and response is maintained.
The system maintains state information as to the progress of each operation that has originated or to which it is responding.
To maintain the state information, the frame headers of the requests and responses include an indicator (the A bit) informing the receiver that data areas are associated with either the request or response.
A collection of timers is used to time each individual operation.
The timers are initialized to a predetermined value and count down.
A timer is initialized and started when a request is sent, and it is stopped when the response is received.
If the timer reaches zero before the response is received, a higher level recovery procedure is invoked.
According to an embodiment of the present invention, when a frame that has been damaged by a transmission error is received, a request for retransmission is sent to the other end of the link.
If the operation is a read and if the damaged frame contains a data area, the timer for this operation is reinitialized to a smaller predetermined value before the request for retransmission is sent
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Fault Detection 
