Method and system for remote procedure call via an unreliable communication channel using multiple retransmission timers

• US 5,774,479 A
• Filed: 03/30/1995
• Issued: 06/30/1998
• Est. Priority Date: 03/30/1995
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Pasco-Anderson, James A., Chen, Yue Long, Lee, Whay Chiou
• Primary Examiner(s): Baker, Stephen M.
• Application Number:
  US08/413,561
• Time in Patent Office: 1,188 Days
• Field of Search: 371/33, 395/182.13, 395/182.16, 395/200.12, 395/200.14
• US Class Current: 714/749
• CPC Class Codes: H04L 1/1685 the supervisory signal being transmitted in response to a specific request, e.g. to a polling signal
• CPC Class Codes: H04L 1/1803 Stop-and-wait protocols
• CPC Class Codes: H04L 1/1883 using multiple timers
• CPC Class Codes: H04L 2001/125 Arrangements for preventing errors in the return channel
• CPC Class Codes: H04L 67/01 Protocols
• CPC Class Codes: H04L 67/133 Protocols for remote procedure calls [RPC]
• CPC Class Codes: H04L 69/324 in the data link layer [OSI layer 2], e.g. HDLC
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A method (300) and communication system (400, 500, 600, 1300, 1400) provide a remote procedure call from a client to a server via an unreliable communication channel using a plurality of retransmission timers. The method includes transmitting, by the client to the server, a request and waiting for a confirm message and retransmitting, by the client to the server, the request after each of a predetermined sequence of time-out periods implemented by the plurality of retransmission timers until a confirm message is received.

Claims

1. A method for providing a remote procedure call from a client to a server via an unreliable communication channel using a plurality of retransmission timers, comprising the steps of:

(A) transmitting, by the client to the server, a request and waiting for a confirm message,

(B) retransmitting, by the client to the server, the request after each of a predetermined sequence of time-out periods implemented by the plurality of retransmission timers until a confirm message is received,

wherein the predetermined sequence of time-out periods begins with a primary time-out period, followed by a predetermined number of repetitions of a secondary time-out period that is preselected to be greater than the primary time-out period.

2. The method of claim 1 wherein, where a plurality of client-server pairs share a retransmission timer that determines the primary time-out period, and the primary time-out period is:

(A) greater than a predetermined duration of burst errors; and

(B) less than any round-trip delays of the client-server pairs sharing the retransmission timer.

3. The method of claim 1 wherein, where a plurality of client-server pairs share a retransmission timer that determines the secondary time-out period, and the secondary time-out period is:

(A) greater than any round-trip delays of the client-server pairs sharing the retransmission timer; and

(B) less than a predetermined time-out for disconnect of predetermined higher layer protocols.

4. The method of claim 1 wherein the predetermined sequence of time-out periods consists of at least one of:

(A) a primary time-out period T₁ that is repeated a first predetermined number of times; and

(B) a secondary time-out period T₂ that is repeated a second predetermined number of times.

5. The method of claim 4 wherein a third time-out period T₃ follows after the secondary time-out, and, where selected, is repeated a predetermined number of times.

6. The method of claim 1 wherein the predetermined sequence of time-out periods consists of a primary time-out period and a secondary time-out period that are alternately implemented for a predetermined number of cycles.

7. A communication system for providing a remote procedure call from a client to a server via an unreliable communication channel, wherein the client:

transmits a request to the server;

waits for a confirm message from the server; and

retransmits the request to the server after each of a predetermined sequence of time-out periods implemented by a plurality of retransmission timers until the confirm message is received;

and wherein the predetermined sequence of time-out periods begins with a primary time-out period and is followed by a predetermined number of repetitions of a secondary time-out period that is preselected to be greater than the primary time-out period.

8. The communication system of claim 7 wherein:

upon starting processing, an initial request is sent by the client and the predetermined primary time-out period T₁ is begun by a first timer;

the client then waits for T₁ to expire;

where a confirm message is received during T₁, the client cancels T₁ and recycles to starting processing;

where T₁ expires without the client'"'"'s receiving a confirm message, the client sends a redundant request and a predetermined secondary time-out period T₂ is begun by starting a second timer;

the client then waits for T₂ to expire;

where a confirm message is received during T₂, the client cancels T₂ and recycles to starting processing;

where T₂ expires without the client'"'"'s receiving a confirm message, the client sends a subsequent request, starts another time-out period of length T₂, then recycles to waiting for T₂ to expire, repeating sending the subsequent request until one of;

(1) the client receives a confirm message; and

(2) a predetermined number of subsequent requests have been sent.

9. The communication system of claim 7 for executing an idempotent procedure, wherein the server, upon receiving a request from the client:

executes a predetermined procedure; and

sends a confirm message to the client.

10. The communication system of claim 7 for executing a non-idempotent procedure, wherein the server:

waits for one of an initial request, a redundant request, and a subsequent request;

where an initial request has been received, the server executes a predetermined procedure and sends a confirm message to the client;

where one of a redundant request and a subsequent request is received, the server executes a predetermined procedure and sends a confirm message to the client;

where a previously received request is an initial request, and one of a redundant request and a subsequent request is next received, the server refrains from responding to the request; and

where a previously received request is an initial request, and another initial request is next received, the server executes the predetermined procedure and sends a confirm message to the client.

11. A communication system for synchronizing transmission of encoded data between an encoder and a decoder over an unreliable communication channel, the communication system providing a remote procedure call characterized by the decoder transmitting a request for synchronization to the encoder and retransmitting the request after each of a predetermined sequence of time-out periods implemented by a plurality of retransmission timers until a confirmation message is received by the decoder from the encoder, wherein:

the encoder includes an encoder state machine having one state to which the encoder always returns after it resets itself and sends a confirm message to the decoder upon receipt of each reset request from the decoder; and

the decoder includes a decoder state machine comprising;

a first processing state (D0) in which an initial request is sent;

a first waiting state (D1) for causing the decoder to wait for a primary time-out period before sending a redundant request; and

a second waiting state (D2) for causing the decoder to wait for a secondary time-out period before sending a subsequent request;

wherein primary time-out period is preselected to be greater than or equal to a predetermined error event time and wherein the secondary time-out period is preselected to be greater than the primary time-out period.

12. The communication system of claim 11 wherein, for each encoder-decoder pair,

in state D0, upon the decoder state machine receiving a reset confirmation, performing, by the decoder state machine, a reset operation, and returning to the D0 state;

while in state D0, one of;

(A) waiting, by the decoder state machine, for an encoder to initiate synchronization; and

(B) decoding, by the decoder state machine, being already in synchronization with the encoder, data in accordance with a predetermined decoding scheme;

upon the decoder state machine detecting a loss of synchronization, sending, by the decoder state machine, a reset request, starting a timer T₁, and going into state D1;

waiting, while in state D1, by the decoder state machine, for one of;

a reset confirmation and expiration of T₁ ;

discarding, in state D1, by the decoder state machine, data without the data being decoded, and ignoring further loss of synchronization indications;

resetting, by the decoder state machine, where a reset confirmation is received, to state D0;

sending, by the decoder state machine, where T₁ expires, an additional reset request, starting timer T₂, and going to state D2;

waiting, by the decoder state machine, while in state D2, until expiration of timer T₂ for reset confirmation;

discarding, by the decoder state machine, in state D2, data and ignoring further loss of synchronization indications;

returning, by the decoder state machine, where a reset confirmation is received, to state D0; and

sending, by the decoder state machine, where T₂ expires, another reset request and restarting the T₂ timer, and repeating sending reset requests until one of;

a reset confirmation is received and a predetermined number of reset requests have been sent.

13. The communication system of claim 12 wherein retransmission timers for the primary time-out period and the secondary time-out period are implemented by virtual timers.

14. The communication system of claim 13 wherein the virtual timers are slotted time clocks.