TRANSMISSION SYSTEM, TRANSMISSION APPARATUS, AND CLOCK SYNCHRONIZATION METHOD

• US 20150280897A1
• Filed: 02/04/2015
• Published: 10/01/2015
• Est. Priority Date: 03/27/2014
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: KAYAMA, RYUJI, SUZUKI, HIROYUKI, NAKANO, TAKASHI, Kobayashi, Nobuyuki, NOZAWA, AKIRA, Suda, Koji
• Granted Patent: US 9,344,266 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04L 7/0016 correction of synchronization errors

Abstract

A transmission system includes: a first transmission apparatus to distribute a synchronization clock; and one or more second transmission apparatuses each to connect to the first transmission apparatus so as to synchronize with the synchronization clock from the first transmission apparatus, the second transmission apparatus including: a selection portion to select the first or second transmission apparatus of a connection destination so as to switch the synchronization clock; an output portion to generate an inquiry signal addressed to the first transmission apparatus via the second transmission apparatus of the connection destination selected; a determination portion to determine whether or not the inquiry signal generated by the second transmission apparatus is received; and a second control portion to determine that there is a synchronization clock loop having a loop path through the second transmission apparatus of the connection destination when the determination portion receives the inquiry signal.

Claims

1. A transmission system comprising:

a first transmission apparatus configured to distribute a synchronization clock, the first transmission apparatus including;

a first control portion configured to select a clock source or second transmission apparatus of a connection destination so as to switch the synchronization clock, and generate a response signal to an inquiry signal; and

one or more second transmission apparatuses each configured to connect to the first transmission apparatus so as to synchronize with the synchronization clock from the first transmission apparatus, the second transmission apparatus including;

a selection portion configured to select the first or second transmission apparatus of a connection destination so as to switch the synchronization clock;

an output portion configured to generate the inquiry signal addressed to the first transmission apparatus via the second transmission apparatus of the connection destination selected by the selection portion;

a determination portion configured to determine whether or not the inquiry signal generated by the second transmission apparatus is received; and

a second control portion configured to determine that there is a synchronization clock loop having a loop path through the second transmission apparatus of the connection destination when the determination portion receives the inquiry signal.

2. The transmission system according to claim 1,

wherein, when the response signal to the inquiry signal is received from the first transmission apparatus, the second control portion determines a path to the first or second transmission apparatus of the connection destination selected by the selection portion as a reception path of the synchronization clock.

3. The transmission system according to claim 1,

wherein the second transmission apparatus further includes

a storage portion configured to store an identifier of the first or second transmission apparatus of the connection destination for priority order,

wherein the selection portion selects the first or second transmission apparatus of the connection destination based on the priority order in the storage portion, and

wherein, when it is determined that there is the synchronization clock loop including a path having the second transmission apparatus of the connection destination selected by the selection portion, the second control portion deletes the identifier of the second transmission apparatus of the connection destination from the storage portion.

4. The transmission system according to claim 3,

wherein the storage portion stores the identifier of the first or second transmission apparatus of the connection destination and a synchronization status message (SSM) set to the first or second transmission apparatus of the connection destination for priority order, and

wherein the selection portion selects the first or second transmission apparatus of the connection destination based on the priority order and the SSM.

5. The transmission system according to claim 1,

wherein the second transmission apparatus further includes

a transmission portion configured to record an identifier of another second transmission apparatus of a connection destination having received the inquiry signal when the inquiry signal is received from the another second transmission apparatus, transmit the inquiry signal to the first or second transmission apparatus of a connection destination selected, and transmit the response signal to the second transmission apparatus of the recorded connection destination when the response signal corresponding to the inquiry signal is received.

6. The transmission system according to claim 3,

wherein, when a predetermined signal is detected, the selection portion selects the first or second transmission apparatus of the connection destination based on the priority order in the storage portion.

7. A transmission apparatus subordinately synchronized with a synchronization clock from a master station to distribute the synchronization clock, the transmission apparatus comprising:

a selection portion configured to select a transmission apparatus of a connection destination so as to switch the synchronization clock;

an output portion configured to generate an inquiry signal addressed to the master station via the transmission apparatus of the connection destination selected by the selection portion;

a determination portion configured to determine whether or not the inquiry signal generated by the output portion is received; and

a control portion configured to determine that there is a synchronization clock loop having a loop path through the transmission apparatus of the connection destination when the determination portion receives the inquiry signal.

8. The transmission apparatus according to claim 7,

wherein, when a response signal to the inquiry signal is received from the master station, the control portion determines a path to the transmission apparatus of the connection destination selected by the selection portion as a reception path of the synchronization clock.

9. The transmission apparatus according to claim 7, further comprising:

a storage portion configured to store identification information for identifying the transmission apparatus of the connection destination and a synchronization status message set to the transmission apparatus of the connection destination for priority order,

wherein the selection portion selects the transmission apparatus of the connection destination based on the priority order in the storage portion, and

wherein, when it is determined that there is the synchronization clock loop including a path having the transmission apparatus of the connection destination selected by the selection portion, the control portion deletes the identification information for identifying the transmission apparatus of the connection destination from the storage portion.

10. The transmission apparatus according to claim 7, further comprising:

a transmission portion configured to, when the inquiry signal is received from the another transmission apparatus of the connection destination, record identification information for identifying the another transmission apparatus of the connection destination having received the inquiry signal, transmit the inquiry signal to the another transmission apparatus of the connection destination selected, and transmit the response signal to the another transmission apparatus of the recorded connection destination when the response signal corresponding to the inquiry signal is received.

11. A clock synchronization method for a transmission system including a first transmission apparatus configured to distribute a synchronization clock, and one or more second transmission apparatuses each configured to connect to the first transmission apparatus so as to synchronize with the synchronization clock from the first transmission apparatus, the clock synchronization method comprising:

selecting the first or second transmission apparatus of a connection destination so as to switch the synchronization clock;

generating an inquiry signal addressed to the first transmission apparatus via the second transmission apparatus of the selected connection destination;

determining whether or not the inquiry signal output by the second transmission apparatus is received; and

determining that there is a synchronization clock loop having a loop path through the second transmission apparatus of the connection destination when the inquiry signal is received, by the second transmission apparatus.