US 7,248,587 B1Granted

Error recovery of variable-length packets without sequence numbers or special symbols used for synchronizing transmit retry-buffer pointer

AssigneeAzul Systems, Inc.

InventorAnup Sharma

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Abstract

Variable-length packets transmitted over a serial link do not have packet-start fields or unique symbols to mark the beginning of each packet. Instead, a length field indicates the packet's length, allowing the end of the packet to be located. Packets also do not have sequence numbers. When an error is detected, the receiver sends a control symbol over a reverse channel to signal the transmitter. The control symbol never occurs in a normal packet. Packet buffers in the transmitter and receiver have read and write pointers and also have de-allocation pointers that are synchronized between receiver and transmitter. As packets are error checked, the receiver advances its de-allocation pointer and updates the transmitter's de-allocation pointer, allowing the packets to be discarded from the transmitter's buffer only after the receiver finishes error checking. The transmitter re-transmits packets from its buffer starting from the de-allocation pointer when its receives the control symbol.

Claims19

Dependent claims

A variable-length packet transmitter comprising:

a transmit re-try buffer for storing packet data received from a first host system serviced by the variable-length packet transmitter;
a write pointer for the transmit re-try buffer, the write pointer indicting a writing location within the transmit re-try buffer to write new packet data received from the first host system, the writing location being advanced as additional packet data is received from the first host system;
a read pointer for the transmit re-try buffer, the read pointer indicting a reading location within the transmit re-try buffer to read packet data from for transmission to a remote receiver;
a serial link to the remote receiver for sending packet data read from the transmit re-try buffer to the remote receiver;
a de-allocation pointer for the transmit re-try buffer, the de-allocation pointer indicting an over-writing location within the transmit re-try buffer wherein the write pointer is prevented from advancing past the de-allocation pointer;
and
a reverse channel from the remote receiver for receiving pointer updates from the remote receiver, the pointer updates causing the de-allocation pointer to advance to provide additional space within the transmit re-try buffer for writing packet data from the first host system,
whereby pointer updates from the remote receiver update the de-allocation pointer and the over-writing location in the transmit re-try buffer.

5 more elements

A packet communications system comprising:

a first host generating first data for transmission;
a second host generating second data and processing the first data received from the first host;
a forward link between the first host and the second host for sending the first data from the first host to the second host;
a reverse link between the second host and the first host for sending the second data from the second host to the first host;
a first transmitter on the first host and connected to drive the forward link;
a first receiver on the first host connected to receive from the reverse link;
a second transmitter on the second host and connected to drive the reverse link;
a second receiver on the second host connected to receive from the forward link;
a transmit re-try buffer, coupled between the first host and the first transmitter, for writing and storing first data received from the first host at a buffer location indicated by a write pointer and for reading first data packets from a buffer location indicated by a read pointer for transmission over the forward link;
a receive re-try buffer, coupled between the second receiver and the second host, for writing and storing first data packets received from the forward link at a buffer location indicated by a write pointer and for reading first data packets from a buffer location indicated by a read pointer for processing by the second host;
wherein a packet in the first data packets begins with a length field that indicates a variable length of the packet, the packet further comprising a data payload of variable length determined by the length field and a checksum;
a re-try pointer for the receive re-try buffer that indicates a buffer location of a boundary between packets that may contain errors and packets that have completed error processing without errors;
an error detector for the second receiver that signals a reception error for a packet sent over the forward link;
a symbol generator that generates a control symbol that is never found in the first data packets, wherein the control symbol is sent by the second transmitter over the reverse link to the first receiver to halt the first transmitter when the error detector detects the reception error;
wherein the re-try pointer for the receive re-try buffer is transmitted over the reverse link to the first receiver and forwarded to the transmit re-try buffer to reset the write pointer of the transmit re-try buffer in response to the re-try pointer when the reception error in the forward link is signaled.

12 more elements

A method for communicating packets comprising:

receiving serial data over a forward link from a transmitter and writing the serial data into a receive re-try buffer at a location indicated by a write pointer that advances with data written;
for each packet in the receive re-try buffer:
reading a length field at a starting location of a packet and decoding the length field to determine a length of the packet, wherein the length of packets varies among a plurality of allowed packet lengths encoded by the length field;
determining from the length field the starting location of a next packet that follows the packet;
reading a data payload for the packet and generating a generated checksum from the data payload;
reading a transmitted checksum for the packet and comparing the transmitted checksum to the generated checksum and signaling an error when checksums mis-match;
sending the data payload of the packet to a receiving host system and advancing a re-try pointer by the length of the packet when no error is signaled;
sending a control symbol over a reverse link to the transmitter when the error is signaled, the control symbol being an illegal sequence of bits that is not present in the data payload or the length field or the transmitted checksum for normal packets;
sending a pointer-update message over the reverse link to the transmitter, the pointer-update message containing the re-try pointer or an adjustment for the re-try pointer;
the transmitter receiving the control symbol over the reverse link and halting packet transmission over the forward link in response to the error;
the transmitter resetting a read pointer in a transmit re-try buffer in response to the pointer-update message so that the read pointer in the transmit re-try buffer points to a same packet as the re-try pointer in the receive re-try buffer;
and
the transmitter re-transmitting packets from the transmit re-try buffer starting at the same packet pointed to by the re-try pointer and the read pointer of the transmit re-try buffer in response to the error,
whereby packets are re-transmitted from a location of the re-try pointer sent from a receiver to the transmitter when the error is signaled.

11 more elements

Dependencies are inferred from the claim text.