Communication system, method of controlling the same, and storage medium

• US 8,831,007 B2
• Filed: 09/27/2012
• Issued: 09/09/2014
• Est. Priority Date: 10/07/2011
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Asai, Hitoshi, Takada, Tomoyuki, Takahashi, Naoto, Umehara, Makoto, Tachiwa, Wataru
• Primary Examiner(s): Thompson, Jr., Otis L
• Application Number:
  US13/629,407
• Publication Number:
  US 20130090762A1
• Time in Patent Office: 712 Days
• Field of Search: None
• US Class Current: 370/395.62
• CPC Class Codes: H04J 3/062 Synchronisation of signals having the same nominal but fluctuating bit rates, e.g. using buffers pulse-stuffing H04J3/07; asynchronous-synchronous conversion H04L5/24; speed conversion H04L25/05; speed conversion in computers G06F5/06
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04L 12/40013 Details regarding a bus controller

Abstract

A communication system including a parent station and a plurality of child stations, the parent station and the plurality of child stations being line-connected or loop-connected in a plurality of stages, and the parent station comprises a decision unit configured to decide, based on information representing states of the plurality of child stations, which one a first data relay method of transmitting data to a subsequent station in accordance with a clock reproduced from data received from a preceding station and a second data relay method of transmitting data to the subsequent station in accordance with a local clock generated in a local station should be employed by each of the plurality of child stations.

Claims

1. A communication system including a parent station and a plurality of child stations,

said parent station and said plurality of child stations being line-connected or loop-connected in a plurality of stages, and

said parent station comprising a decision unit configured to decide, based on information representing states of said plurality of child stations, which one a first data relay method of transmitting data to a subsequent station in accordance with a clock reproduced from data received from a preceding station and a second data relay method of transmitting data to the subsequent station in accordance with a local clock generated in a local station should be employed by each of said plurality of child stations.

2. The system according to claim 1, wherein

the information representing the states of said plurality of child stations is the number of relay stations representing the number of child stations that relay data transmitted from said parent station, and

said decision unit decides the relay method to be employed by each of said plurality of child stations based on the number of relay stations and a predetermined allowable number of relay stations.

3. The system according to claim 2, wherein when the number of relay stations exceeds the allowable number of relay stations, said decision unit decides to cause a child station located at a position corresponding to an integer multiple of the allowable number of relay stations to employ the second data relay method and a child station corresponding to another position to employ the first data relay method.

4. The system according to claim 1, wherein

the information representing the states of said plurality of child stations is a data error rate in each of said plurality of child stations, and

said decision unit decides the relay method to be employed by each of said plurality of child stations based on each data error rate and a predetermined allowable value.

5. The system according to claim 4, wherein said decision unit decides to cause a preceding station of a child station whose data error rate exceeds the allowable value to employ the second data relay method.

6. The system according to claim 4, wherein each of said plurality of child stations comprises a measurement unit configured to measure the data error rate in the local station based on a test signal output from said parent station.

7. The system according to claim 6, wherein said measurement unit measures the data error rate in the local station based on a difference between the test signal and a test signal that should originally be received.

8. The system according to claim 1, wherein

the information representing the states of said plurality of child stations is a jitter amount of the reproduced clock in each of said plurality of child stations, and

said decision unit decides the relay method to be employed by each of said plurality of child stations based on each jitter amount and a predetermined allowable value.

9. The system according to claim 8, wherein said decision unit decides to cause a preceding station of a child station whose jitter amount exceeds the allowable value to employ the second data relay method.

10. The system according to claim 1, wherein each child station comprises:

a reception unit configured to receive data received from the preceding station in synchronism with the reproduced clock and output the data as first data;

a first selector unit configured to select one of the local clock and the reproduced clock and output the clock as a transmission clock;

a buffer unit configured to receive the first data in synchronism with the reproduced clock, extract the first data in synchronism with the transmission clock, and output the first data as second data;

a generation unit configured to generate arbitrary data having a predetermined length;

a second selector unit configured to select one of the first data, the second data, and the arbitrary data and output the data as third data;

a selector control unit configured to control said first selector unit and said second selector unit; and

a transmission unit configured to transmit the data to the subsequent station in accordance with the transmission clock,

wherein when the local station employs the second data relay method, and said decision unit decides to change to the first data relay method,

said selector control unit controls said first selector unit and said second selector unit to select the reproduced clock as the transmission clock during a period where a phase difference between the reproduced clock and the local clock is not more than an allowable value and then select the first data as the third data during an idle period where no valid data is transmitted, and

when the local station employs the first data relay method, and said decision unit decides to change to the second data relay method,

said selector control unit controls said first selector unit and said second selector unit to select the local clock as the transmission clock and the arbitrary data as the third data during the period where the phase difference between the reproduced clock and the local clock is not more than the allowable value, and after transmission of the arbitrary data, select the second data as the third data.

12. A non-transitory computer-readable storage medium storing a computer program that causes a computer to function as a parent station of a communication system of claim 1.

11. A method of controlling a communication system including a parent station and a plurality of child stations,

the parent station and the plurality of child stations being line-connected or loop-connected in a plurality of stages, the method comprising:

in the parent station,

deciding, based on information representing states of the plurality of child stations, which one a first data relay method of transmitting data to a subsequent station in accordance with a reproduced clock reproduced from data received from a preceding station and a second data relay method of transmitting data to the subsequent station in accordance with a local clock generated in a local station should be employed by each of the plurality of child stations.

13. A communication system in which a plurality of communication stations are line-connected or loop-connected,

wherein each of the communication stations comprises a switching unit configured to switch between a first data relay method of transmitting data to a subsequent station in accordance with a reproduced clock reproduced from data received from a preceding station and a second data relay method of transmitting data to the subsequent station in accordance with a local clock generated in a local station, and

a communication station that operates as a parent station comprises:

a determination unit configured to determine a topology of the communication system;

a decision unit configured to decide, based on the topology determined by said determination unit, a communication station that uses one of the first data relay method and the second data relay method; and

a notification unit configured to notify the communication station of a decision result by said decision unit.

14. The system according to claim 13, wherein said decision decides, based on a predetermined number of communication stations continuously connected by the first data relay method, the communication station that uses one of the first data relay method and the second data relay method.

15. The system according to claim 14, wherein when the number of communication stations in the communication system exceeds the predetermined number of communication stations continuously connected by the first data relay method, said decision unit decides to cause a communication station located at a position corresponding to an integer multiple of the number to employ the second data relay method and a communication station corresponding to another position to employ the first data relay method.

16. The system according to claim 13, wherein

said determination unit determines a position on the communication system where a data error rate exceeds a predetermined value, and

said decision unit decides, based on the position determined by said determination unit, the communication station that uses one of the first data relay method and the second data relay method.

17. The system according to claim 16, wherein said decision unit decides to cause a preceding station of a communication station whose data error rate exceeds the predetermined value to employ the second data relay method.

18. The system according to claim 16, wherein each of the communication stations comprises a measurement unit configured to measure the data error rate in the local station based on a received test signal.

19. The system according to claim 18, wherein said measurement unit measures the data error rate in the local station based on a difference between the received test signal and a test signal that should originally be received.

20. The system according to claim 16, wherein said decision unit decides, based on a jitter amount of the reproduced clock in the communication station, the communication station that uses one of the first data relay method and the second data relay method.

21. The system according to claim 20, wherein said decision unit decides to cause a preceding station of a communication station whose jitter amount exceeds a predetermined value to employ the second data relay method.