U.S. patent application number 14/085609 was filed with the patent office on 2014-03-20 for communication method, optical communication system, station-side optical-line terminal apparatus, and user-side optical-line terminal apparatus.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Yukio HIRANO, Hiroaki Mukai.
Application Number | 20140079396 14/085609 |
Document ID | / |
Family ID | 44672519 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140079396 |
Kind Code |
A1 |
HIRANO; Yukio ; et
al. |
March 20, 2014 |
COMMUNICATION METHOD, OPTICAL COMMUNICATION SYSTEM, STATION-SIDE
OPTICAL-LINE TERMINAL APPARATUS, AND USER-SIDE OPTICAL-LINE
TERMINAL APPARATUS
Abstract
An ONU includes the optical transceiver capable of an operation
in a power-saving mode in which power consumption is reduced by
stopping transmission while continuing reception, and a control
device that controls to tentatively validate transmission of the
optical transceiver and outputs a response signal when a control
signal is received from an OLT during an operation in a
power-saving state. Moreover, the OLT includes the control device
that allocates a transmission bandwidth to the ONU even while the
optical transceiver of the ONU operates in a power-saving mode and
stops transmission and determines whether a communication failure
occurs or the ONU is in operation in a power-saving mode based on
the response signal received by a transceiver of the OLT.
Inventors: |
HIRANO; Yukio; (Tokyo,
JP) ; Mukai; Hiroaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
44672519 |
Appl. No.: |
14/085609 |
Filed: |
November 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13395145 |
Mar 9, 2012 |
|
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PCT/JP2010/002054 |
Mar 24, 2010 |
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14085609 |
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Current U.S.
Class: |
398/67 |
Current CPC
Class: |
H04J 14/0252 20130101;
H04Q 2011/0079 20130101; H04J 14/0247 20130101; H04J 14/0227
20130101; H04J 14/0258 20130101; H04J 14/0238 20130101; H04J
14/0282 20130101; H04Q 11/0067 20130101; H04J 14/0267 20130101;
H04B 10/272 20130101 |
Class at
Publication: |
398/67 |
International
Class: |
H04J 14/02 20060101
H04J014/02 |
Claims
1. (canceled)
2. A communication method of an optical communication system in
which a plurality of user side optical-line terminal apparatuses
(hereinafter, called ONUs) is connected to a station-side
optical-line terminal apparatus (hereinafter, called OLT) by using
a common optical fiber, comprising: allocating, by the OLT, a
transmission bandwidth for transmitting a response signal during a
tentative wake-up time to the ONU that is capable of performing an
operation in a sleep mode, in which tentative deactivation of an
optical transmitter and tentative wake-up of the optical
transmitter are repeated, and transmitting a transmission bandwidth
notification to the ONU; and causing, by the OLT, a transmission
bandwidth allocation cycle with respect to the ONU transitioned to
the sleep mode to be longer than a transmission bandwidth
allocation cycle with respect to the ONU before being transitioned
to the sleep mode and transmitting, to the ONU, a sleep period
during which tentative deactivation of the optical transmitter is
allowed.
3. The communication method according to claim 2, wherein the ONU
stops power supply for laser of the optical transmitter during a
period of the tentative deactivation.
4. The communication method according to claim 2, wherein the OLT
transmits, to the ONU, a signal that grants the ONU permission to
transition to the sleep mode.
5. The communication method according to claim 2, wherein when the
sleep mode is continued after the period of the tentative
deactivation, the ONU in the sleep mode transmits a signal of
requesting transition to the sleep mode with respect to the
transmission bandwidth notification.
6. An optical communication system in which a plurality of
user-side optical-line terminal apparatuses (hereinafter, called
ONUs) is connected to a station-side optical-line terminal
apparatus (hereinafter, called OLT) by using a common optical
fiber, wherein the OLT includes: an optical transceiver connected
to the optical fiber, and a control device that allocates a
transmission bandwidth for transmitting a response signal during a
tentative wake-up time to the ONU that is capable of performing an
operation in a sleep mode, in which tentative deactivation of an
optical transmitter and tentative wake-up of the optical
transmitter are repeated, and transmits a transmission bandwidth
notification to the ONU, and causes a transmission bandwidth
allocation cycle with respect to the ONU transitioned to the sleep
mode to be longer than a transmission bandwidth allocation cycle
with respect to the ONU before being transitioned to the sleep mode
and transmits, to the ONU, a sleep period during which tentative
deactivation of the optical transmitter is allowed.
7. The optical communication system according to claim 6, wherein
the ONU stops power supply for laser of the optical transmitter
during a period of the tentative deactivation.
8. The optical communication system according to claim 6, wherein
the OLT transmits, to the ONU, a signal that grants the ONU
permission to transition to the sleep mode.
9. The optical communication system according to claim 6, wherein
when the sleep mode is continued after a period of the tentative
deactivation, the ONU in the sleep mode transmits a signal of
requesting transition to the sleep mode with respect to the
transmission bandwidth notification.
10. A user-side optical-line terminal apparatus of an optical
communication system that connects a plurality of user-side
optical-line terminal apparatuses to a station-side optical-line
terminal apparatus by using a common optical fiber, comprising: an
optical transceiver that is connected to the optical fiber and is
capable of performing an operation in a sleep mode in which power
consumption is reduced by repeating tentative stop of a
transmitting unit for a predetermined sleep period and tentative
wake-up of the transmitting unit after the predetermined sleep
period; and a control device that, when a transmission bandwidth is
allocated by the station-side optical-line terminal apparatus
during the sleep mode, causes the optical transceiver to transmit a
response signal to the station-side optical-line terminal
apparatus, wherein an allocation cycle of the transmission
bandwidth when transitioned to the sleep mode is longer than an
allocation cycle of the transmission bandwidth before being
transitioned to the sleep mode, and the control device performs
wake-up control of tentatively stopping the transmitting unit of
the optical transceiver during the sleep period between the
transmission bandwidth allocated by the station-side optical-line
terminal apparatus by a time division manner and a subsequent
transmission bandwidth and tentatively activating the transmitting
unit of the optical transceiver to transmit a response signal in a
transmission bandwidth after the sleep period.
11. The user-side optical-line terminal apparatus according to
claim 10, wherein the optical transceiver stops power supply for
laser of the transmitting unit during the sleep period.
12. The user-side optical-line terminal apparatus according to
claim 10, wherein the optical transceiver operates in the sleep
mode after receiving a signal that grants permission to transition
to the sleep mode from the station-side optical-line terminal
apparatus.
13. The user-side optical-line terminal apparatus according to
claims 10, wherein during the sleep mode, when the sleep mode is
continued, the control device causes the optical transceiver to
transmit a signal of requesting transition to the sleep mode as a
response signal in the allocated transmission bandwidth.
14. A station-side optical-line terminal apparatus of an optical
communication system that connects a plurality of user-side
optical-line terminal apparatuses to a station-side optical line
terminal apparatus by using a common optical fiber, comprising: an
optical transceiver connected to the optical fiber; and a control
device that allocates a transmission bandwidth for transmitting a
response signal during a tentative wake-up time to the user-side
optical-line terminal apparatus that is capable of performing an
operation in a sleep mode, in which tentative deactivation of an
optical transmitter for a predetermined sleep period and tentative
wake-up of the optical transmitter after the sleep period are
repeated, and transmits a transmission bandwidth notification to
the user-side optical-line terminal apparatus, and causes a
transmission bandwidth allocation cycle with respect to the
user-side optical-line terminal apparatus transitioned to the sleep
mode to be longer than a transmission bandwidth allocation cycle
with respect to the user-side optical-line terminal apparatus
before being transitioned to the sleep mode and transmits, to the
user-side optical-line terminal apparatus, a sleep period during
which tentative deactivation of the optical transmitter is
allowed.
15. The station-side optical-line terminal apparatus according to
claim 14, wherein the control device causes the optical transceiver
to transmit, to the user-side optical-line terminal apparatus, a
signal that grants the user-side optical-line terminal apparatus
permission to transition to the sleep mode.
16. A control device of a user-side optical-line terminal apparatus
of an optical communication system that connects a plurality of
user-side optical-line terminal apparatuses to a station-side
optical-line terminal apparatus by using a common optical fiber,
wherein: during a sleep mode in which it is repeated to tentatively
stop a transmitting unit of an optical transceiver connected to the
optical fiber for a predetermined sleep period by power control,
when a transmission bandwidth is allocated by the station-side
optical-line terminal apparatus, the control device causes the
optical transceiver to transmit a response signal to the
station-side optical-line terminal apparatus, a transmission
bandwidth allocation cycle when transitioned to the sleep mode is
longer than a transmission bandwidth allocation cycle before being
transitioned to the sleep mode, and the control device performs
wake-up control of tentatively stopping the transmitting unit
during the sleep period and tentatively activating the transmitting
unit to transmit a response signal in a transmission bandwidth
after the sleep period.
17. The control device according to claim 16, wherein the control
device causes power supply for laser of the transmitting unit to be
stopped during the sleep period.
18. The control device according to claim 16, wherein the control
device causes the optical transceiver to be operated in the sleep
mode after receiving a signal that grants permission to transition
to the sleep mode from the station-side optical-line terminal
apparatus.
19. The control device according to claim 16, wherein during the
sleep mode, when the sleep mode is continued after the sleep
period, the control device causes the optical transceiver to
transmit a signal of requesting transition to the sleep mode as a
response signal in the allocated transmission bandwidth.
20. A control device of a station-side optical-line terminal
apparatus of an optical communication system that connects a
plurality of user-side optical-line terminal apparatuses to a
station-side optical-line terminal apparatus by using a common
optical fiber, wherein: the control device allocates a transmission
bandwidth for transmitting a response signal during a tentative
wake-up time to the user-side optical-line terminal apparatus that
is capable of performing an operation in a sleep mode, in which
tentative deactivation of an optical transmitter and tentative
wake-up of the optical transmitter are repeated by power control,
and transmits a transmission bandwidth notification to the
user-side optical-line terminal apparatus, and the control device
causes a transmission bandwidth allocation cycle with respect to
the user-side optical-line terminal apparatus transitioned to the
sleep mode to be longer than a transmission bandwidth allocation
cycle with respect to the user-side optical-line terminal apparatus
before being transitioned to the sleep mode and transmits, to the
user-side optical-line terminal apparatus, a sleep period during
which tentative deactivation of the optical transmitter is
allowed.
21. The control device according to claim 20, wherein the control
device causes the optical transceiver to transmit, to the user-side
optical-line terminal apparatus, a signal that grants the user-side
optical-line terminal apparatus permission to transition to the
sleep mode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of and claims the benefit
of priority under 35 U.S.C. .sctn.120 from U.S. application Ser.
No. 13/395,145, filed Mar. 9, 2012, the entire contents of which is
incorporated herein by reference, and which is a national stage of
International Application No. PCT/JP2010/002054, filed Mar. 24,
2010.
FIELD
[0002] The present invention relates to a communication system in
which a plurality of terminals is connected by a common line and a
communication method, and, for example, relates to a PON (Passive
Optical Network) system or the like that is composed of an OLT
(Optical Line Terminal: station-side terminal apparatus) and a
plurality of ONUs (Optical Network Unit: user-side terminal
apparatus).
BACKGROUND
[0003] In the PON system, communication is performed while
synchronizing between an OLT and ONUs so that data in an upstream
direction to be transmitted from the ONUs does not collide. The OLT
plans to give transmission permission to each ONU so that data in
the upstream direction does not collide. At this time, delay due to
a distance from each ONU is considered. Therefore, the OLT measures
round trip time from each ONU, however, there is a variation of
transmission paths, such as jitter and wander, in a transmission by
optical fibers, so that measurement needs to be performed
periodically.
[0004] On the other hand, data communication is not always
performed, and, for example during nighttime, data communication is
not performed at all. However, measurement of the round-trip time
is periodically performed as above regardless of the presence or
absence of data communication. Maintaining the ONU in a state
capable of constant communication for measuring the round-trip time
even when data communication is not performed results in wasting
power. Therefore, a technology is studied in which the ONU is
intermittently transitioned to a power-saving state by requesting
transition to the power-saving state from the ONU.
[0005] Moreover, a PON system is studied in which when there is no
upstream data from an ONU, useless transmission bandwidth is not
allocated to such ONU to improve throughput (Patent Literature 1).
In this PON system, when an OLT detects a state in which there is
no user data for a preset given period, the OLT deregisters the ONU
and notifies the ONU of temporary stop of an optical link.
Thereafter, a transmission bandwidth is not allocated to the ONU
and transmission of a frame for maintaining the link is also
suppressed, so that the ONU can reduce the number of times of
transmission of a frame.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent Application Laid-open
No. 2007-274534
SUMMARY
Technical Problem
[0007] In the PON system described in Patent Literature 1, because
a link is disconnected with respect to the ONU that does not
transmit certain data, the load of the ONU can be reduced. However,
when the ONU resumes transmission of upstream data, a discovery
process of discovering an unconnected ONU is performed again and a
link is newly established to re-register the ONU. Therefore, for
example, when communication at a low bit rate continues, this
communication method cannot be used. Moreover, because the OLT
disconnects a link to an ONU, when communication abnormality occurs
in the ONU or an upstream communication line itself, the
abnormality cannot be detected. Furthermore, because the OLT
deletes registration of the ONU, the ONU in a communication
abnormal state is not discovered even by the discovery process and
thus discovery of communication abnormality becomes difficult.
Solution to Problem
[0008] According to the present invention, there is provided a
communication method of an optical communication system in which a
plurality of ONUs is connected to an OLT by using a common optical
fiber, including the following steps (a) to (e): (a) the ONU
notifying the OLT of transition to a power-saving state in which an
optical transmitter is deactivated; (b) the OLT detecting a
power-saving state of the ONU based on this notification; (c) the
OLT allocating a transmission bandwidth to the ONU in which the
optical transmitter is inactive and transmitting a transmission
bandwidth notification to the ONU; (d) the ONU, which has received
the transmission bandwidth notification, tentatively waking up the
optical transmitter and transmitting a response signal to the OLT
to transition to a power-saving state again; and (e) the OLT
monitoring a transmission bandwidth allocated to the ONU in which
the optical transmitter is inactive and detecting whether the ONU
is in a power-saving state or a failure occurs in a communication
with the ONU based on the response signal.
[0009] According to the present invention, there is provided
another communication method of an optical communication system in
which a plurality of ONUs is connected to an OLT by using a common
optical fiber, including the following steps (a) to (e): (a) the
ONU notifying the OLT of transition to a sleep mode in which an
optical transmitter is deactivated for a predetermined sleep
period; (b) the OLT detecting a sleep mode transition of the ONU
based on this notification; (c) the OLT allocating a transmission
bandwidth to the ONU in the power-saving state in the sleep period
and transmitting a transmission bandwidth notification to the ONU;
(d) the ONU, to which the transmission bandwidth notification is
allocated, waking up the optical transmitter and transmitting a
response signal in the transmission bandwidth when returning to a
non-sleep mode from the sleep mode, whereas being capable of
omitting transmission of the response signal when continuing the
sleep mode; and (e) the OLT monitoring a transmission bandwidth
allocated to the ONU in which the optical transmitter is inactive,
detecting whether the ONU is in the sleep mode or a failure occurs
in a communication with the ONU based on the response signal, and
suppressing a failure detection that is based on the response
signal in the sleep period.
[0010] According to the present invention, there is provided an ONU
including: an optical transceiver that is connected to the optical
fiber and is capable of an operation in a power-saving state in
which power consumption is reduced by stopping transmission while
continuing reception; and a control device that controls transition
of the optical transceiver to a power-saving state and, when a
control signal is received from the OLT during an operation in a
power-saving state, controls to tentatively validate transmission
of the optical transceiver and outputs a response signal.
[0011] According to the present invention, there is provided an OLT
including: an optical transceiver connected to the optical fiber;
and a control device that allocates a transmission bandwidth to the
user-side optical-line terminal apparatus even while an optical
transceiver of the user-side optical-line terminal apparatus
operates in a power-saving state and stops transmission, and
determines whether a failure occurs in a communication with the
user-side optical-line terminal apparatus or the ONU is in
operation in a power-saving state based on the response signal
received by the transceiver of the station-side optical-line
terminal apparatus.
[0012] According to the present invention, there is provided
another ONU including: an optical transceiver that is connected to
the optical fiber and is capable of an operation in a sleep mode in
which power consumption is reduced by intermittently stopping a
transmitting unit while continuing reception by a receiving unit;
and a control device that performs control to intermittently stop
the transmitting unit in the sleep mode, and, is configured to be
capable of omitting transmission of a response signal to the OLT
when a transmission bandwidth is allocated by the OLT in a stop
period of the transmitting unit in the sleep mode and the sleep
mode is continued, and transmits the response signal when a
transmission bandwidth is allocated between periodic stop periods
of the transmitting unit.
[0013] According to the present invention, there is provided
another OLT including: an optical transceiver connected to the
optical fiber; and a control device that allocates the transmission
bandwidth to the user-side optical-line terminal apparatus even
while an optical transceiver of the user-side optical-line terminal
apparatus operates in the sleep mode and stops transmission, and
determines whether a failure occurs in a communication with the
user-side optical-line terminal apparatus or the user-side
optical-line terminal apparatus is in operation in a sleep mode by
monitoring a transmission bandwidth allocated to the user-side
optical-line terminal apparatus in the sleep mode between the
intermittent transmission stop periods of the optical
transceiver.
Advantageous Effects of Invention
[0014] The communication method, the optical communication system,
the station-side optical-line terminal apparatus, and the user-side
optical-line terminal apparatus according to the present invention
can perform failure detection in a power-saving operation by an
intermittent communication.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a configuration diagram illustrating a
configuration of a communication system according to an embodiment
of the present invention.
[0016] FIG. 2 is a sequence diagram illustrating a communication
method according to a first embodiment of the present
invention.
[0017] FIG. 3 is a flowchart illustrating a communication control
of an OLT according to the first embodiment of the present
invention.
[0018] FIG. 4 is a flowchart illustrating a communication control
of an ONU according to the first embodiment of the present
invention.
[0019] FIG. 5 is a sequence diagram illustrating a communication
method (at the time of occurrence of a failure) according to the
first embodiment of the present invention.
[0020] FIG. 6 is a sequence diagram illustrating a communication
method (at the time of power-off) according to the first embodiment
of the present invention.
[0021] FIG. 7 is a sequence diagram illustrating a communication
method (modified example) according to the first embodiment of the
present invention.
[0022] FIG. 8 is a sequence diagram illustrating a communication
method according to a second embodiment of the present
invention.
[0023] FIG. 9 is a flowchart illustrating a communication control
of an OLT according to the second embodiment of the present
invention.
[0024] FIG. 10 is a flowchart illustrating a communication control
of an ONU according to the second embodiment of the present
invention.
[0025] FIG. 11 is a sequence diagram illustrating a communication
method (at the time of occurrence of a failure) according to the
second embodiment of the present invention.
[0026] FIG. 12 is a sequence diagram illustrating a communication
method (at the time of power-off) according to the second
embodiment of the present invention.
[0027] FIG. 13 is a sequence diagram illustrating a communication
method (modified example) according to the second embodiment of the
present invention.
[0028] FIG. 14 is a flowchart illustrating a communication control
(modified example) of an OLT according to the second embodiment of
the present invention.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0029] Hardware Configuration
[0030] FIG. 1 is a diagram illustrating a configuration example of
the first embodiment of a PON system according to the present
invention. As shown in FIG. 1, the PON system in the present
embodiment includes an OLT 1 and ONUs 10-1 to 10-3. The OLT 1 and
the ONUs 10-1 to 10-3 are connected by a subscriber line 30 via a
splitter 40. The splitter 40 splits the subscriber line 30
connected to the OLT 1 into the number of the ONUs 10-1 to 10-3.
Moreover, the ONU 10-1 is connected to terminals 20-1 and 20-2. In
the present embodiment, the number of the ONUs is three as an
example, alternatively, the number of the ONUs is not limited
thereto and can be any number.
[0031] The OLT 1 includes a PON control unit 2 that performs a
process on the OLT side based on a PON protocol, a reception buffer
3 as a buffer that stores therein upstream data to be received from
the ONUs 10-1 to 10-3, a transmission buffer 4 as a buffer that
stores therein downstream data to be transmitted to the ONUs 10-1
to 10-3, an optical transceiver 5 that performs a transmission and
reception process of an optical signal, a WDM (Wavelength Division
Multiplexing) coupler (WDM) 6 that multiplexes wavelengths of
upstream data and downstream data, and a physical-layer processing
unit (PHY) 7 that realizes a physical interface function of an NNI
(Network Node Interface) with the network. The optical transceiver
5 includes an optical receiver (Rx: Receiver) 51 that performs a
reception process and an optical transmitter (Tx: Transmitter) 52
that performs a transmission process.
[0032] The ONU 10-1 includes a PON control unit 2 that performs a
process on the ONU side based on the PON protocol, a transmission
buffer (upstream buffer) 12 as a buffer that stores therein
transmission data (upstream data) to the OLT 1, a reception buffer
(downstream buffer) 13 as a buffer that stores therein reception
data (downstream data) from the OLT 1, an optical transceiver 14, a
WDM 15 that multiplexes wavelengths of upstream data and downstream
data, and physical-layer processing units (PHYs) 16-1 and 16-2 that
realize a physical interface function of an UNI (User Network
Interface) with the terminals 20-1 and 20-2, respectively.
[0033] The optical transceiver 14 includes an optical transmitter
(Tx: Transmitter) 141 that performs a transmission process and an
optical receiver (Rx: Receiver) 142 that performs a reception
process. The PHY 16-1 includes a receiving unit (Rx: Receiver)
161-1 that performs a reception process and a transmitting unit
(Tx: Transmitter) 162-1 that performs a transmission process, and
the PHY 16-2 includes a receiving unit (Rx: Receiver) 161-2 that
performs a reception process and a transmitting unit (Tx:
Transmitter) 162-2 that performs a transmission process.
[0034] Two terminals are connected to the ONU 10-1, however, the
number of the terminals is not limited thereto and can be any
number, and the physical-layer processing units (PHYs) are provided
to correspond to the number of the terminals. Moreover, in FIG. 1,
the configuration example of the ONU 10-1 is illustrated as
representative, however, the ONUs 10-2 and 10-3 also have the same
configuration as that of the ONU 10-1.
[0035] The PON control unit 2 of the OLT 1 performs a bandwidth
allocation of upstream data to give transmission permission to each
of the ONUs 10-1 to 10-3 so that transmission time periods do not
overlap with each other thereby preventing collision of
transmission data from the ONUs 10-1 to 10-3 in the same manner to
the conventional PON system. Any method can be used for this
bandwidth allocation, and, for example, it is possible to use a
Dynamic Bandwidth Allocation Algorithm described in ""HuhDynamic
Bandwidth Allocation Algorithm for Multimedia Services over
Ethernet (registered trademark) PONs", ETRI Journal, Volume 24,
Number 6, December 2002 p. 465 to p. 466 written by Su-il Choi and
Jae-doo".
[0036] Next, the overall operation of the OLT 1 and the ONUs 10-1
to 10-3 in the present embodiment is explained. The PON control
unit 2 stores downstream data (downstream communication data)
received from the network via the PHY 7 in the transmission buffer
4. When transmitting data from the OLT 1, the PON control unit 2
reads out the downstream data stored in the transmission buffer 4
and outputs it to the optical transceiver 5, the Tx 52 of the
optical transceiver 5 outputs the transmission data to the WDM 6 as
an optical signal, and the WDM 6 performs wavelength multiplexing
on the optical signal output from the optical transceiver 5 and
outputs it to the ONUs 10-1 to 10-3 via the subscriber line 30 as a
downstream signal. Moreover, when the PON control unit 2 transmits
a control message such as a transmission bandwidth allocation that
transmits an instruction of transmission permission, the PON
control unit 2 outputs the generated control message to the optical
transceiver 5 and thereafter the control message is transmitted to
the ONUs 10-1 to 10-3 in the same manner to downstream data. In the
PON system in FIG. 1, the WDMs 6 and 15 are used for performing
wavelength multiplexing, however, in the case of communication at a
single wavelength, the WDMs 6 and 15 are not necessary.
[0037] In the ONUs 10-1 to 10-3, when a downstream signal is
received from the OLT 1, the WDM 15 separates the downstream signal
to output it to the optical transceiver 14 and the Rx 142 of the
optical transceiver 14 converts the downstream signal into
downstream data of an electrical signal and outputs it to the PON
control unit 2. The PON control unit 2 stores the downstream data
output from the Rx 142 of the optical transceiver 14 in the
reception buffer 13. The PON control unit 11 reads out the
downstream data stored in the reception buffer 13 and outputs it to
both or one of the PHYs 16-1 and 16-2 depending on the destination
of the data. The PHYs 16-1 and 16-2 that received the downstream
data performs a predetermined process on the downstream data and
transmits it to the terminals 20-1 and 20-2 connected thereto.
[0038] On the other hand, when transmitting upstream data from the
ONUs 10-1 to 10-3, the PON control unit 11 stores the upstream data
obtained from the terminals 20-1 and 20-2 via the PHYs 16-1 and
16-2 in the transmission buffer 12. Then, the PON control unit 11
reads out the upstream data stored in the transmission buffer based
on transmission bandwidth from the OLT 1 and outputs it to the
optical transceiver 14. The Tx 141 of the optical transceiver 14
converts the upstream data into an optical signal (upstream signal)
and transmits it to the OLT 1 via the WDM 15 and the subscriber
line 30.
[0039] The PON control unit 2 of the OLT 1 stores the upstream data
received from the ONUs 10-1 to 10-3 via the subscriber line 30, the
WDM 6, and the Rx 51 of the optical transceiver 5 in the reception
buffer 3. Moreover, the PON control unit 2 reads out the upstream
data stored in the reception buffer 3 and outputs it to the network
via the PHY 7.
[0040] Moreover, in the ONUs 10-1 to 10-3, for the control message
from the OLT 1, the PON control unit 11 receives the control
message via the WDM 15 and the Rx 142 of the optical transceiver 14
and performs an operation based on the instruction of the control
message, generation of a response to the control message, and the
like.
[0041] Power-Saving Operation
[0042] Next, the power-saving operation of the PON system is
explained with reference to FIG. 2 as an example of a power-saving
operation of a communication system.
[0043] (d1)-(d2) & (u1)-(u2) Communication in Normal Operation
State
[0044] FIG. 2 illustrates a sequence after a process such as the
discovery is finished and communication in a normal communication
state (Normal mode) is started. FIG. 2 illustrates only one ONU 10,
however, in practice, the OLT 1 communicates with a plurality of
the ONUs 10 by the similar method. In the PON system, in an
upstream communication (uplink), a transmission bandwidth is
allocated to a plurality of the ONUs 10 by time-division
multiplexing communication. The OLT 1 transmits a grant signal
(Grant), which specifies a transmission bandwidth Bw and grants
communication, to the ONU 10 for controlling this time-division
multiplexing. The transmission bandwidth can also be referred to as
a transmission time, so that, in other words, the OLT 1 allocates
the transmission time to the ONU 10 and transmits the grant signal
to the ONU 10. The Grant includes information from which each ONU
10 can be identified, a communication start time, and a
communication end time (or communication duration).
[0045] The ONU 10 transmits upstream data (Data) in a specified
bandwidth specified by this Grant. The OLT 1 receives the upstream
data in the transmission bandwidth Bw, and performs data relay to
an upper-level device that is present on a core network side and
also detects a communication failure with the ONU 10. When the
upstream data is not transmitted in the specified transmission
bandwidth Bw, the OLT 1 determines that abnormality occurs in the
ONU 10 corresponding to this transmission bandwidth. This
communication failure monitoring is described later.
[0046] (d3)-(d8) & (u3)-(u8) Communication in Power-Saving
State
[0047] When the ONU 10 becomes possible to communicate in the
power-saving state or needs communication in the power-saving
state, the ONU 10 notifies the OLT 1 of transition to the
power-saving state. Any request signal can be used for this
notification, and, for example, a Dying_Gasp signal is
transmitted.
[0048] When this notification is received, the OLT 1 detects that
the ONU 10 enters into the power-saving state and pauses bandwidth
allocation to the ONU 10 for a predetermined period (sleep time).
In this communication method, any value can be set as the sleep
time, however, it is difficult to maintain a normal link for a long
period such as one hour basis, so that, for example, a short period
such as millisecond is specified.
[0049] When the ONU 10 transitions to the power-saving state, the
ONU 10 turns off the laser power of the Tx 141 of the optical
transceiver 14 to control to an off-state. At this time, the ONU 10
does not perform power cut of the Rx 142 of the optical transceiver
14 and continues reception of a control signal and downstream data
from the OLT 1. On the other hand, the OLT 1 also does not transmit
the Grant to the ONU 10 transitioned to the power-saving state,
however, transmits other control signal and downstream data. In
FIG. 2, the power-supply state of the Tx 141 of the ONU 10 is
indicated by "ON" and "OFF" on the right side of the ONU sequence.
In the power-saving state, i.e., the sleep mode, on and off of the
power are intermittently repeated for this period. The period
indicated by "OFF" is a stop period during which the laser power of
the Tx 141 is stopped. Between intermittent stop periods, the ONU
10 wakes up the Tx 141 to generate a tentative wake-up time
(Tentative wake-up time). The "Sleep time" is a predetermined time
length and, in this example, specifies absolute time of the stop
period based on the start time of a bandwidth update cycle. In FIG.
2, the "Sleep time" and the "OFF" period do not match. This is
because the ONU 10 that transmitted upstream data cuts power supply
without waiting for the next bandwidth update cycle. Other
embodiments are not limited to this example and, it is applicable
to cause the "Sleep time" and the "OFF" period to match.
[0050] The OLT 1 measures the sleep time for each ONU 10 and
transmits the Grant to the ONU 10 after elapse of the sleep time
(d6). This Grant is transmitted to tentatively wake up the ONU 10
in the power-saving state. When the ONU 10 receives the Grant from
the OLT 1 in this tentative wake-up time, the ONU 10 tentatively
supplies laser power to the Tx 141 of the optical transceiver 14
even during operation in the power-saving state to cause the Tx 141
to be in an on-state. Because the end time of the sleep time is
known, the ONU 10 can cause the power to be in an on-state without
waiting for notification of a bandwidth allocation from the OLT 1.
When the ONU 10 maintains the power-saving state, the ONU 10
retransmits the sleep request as explained in the above (u3) and
turns off the laser power of the Tx 141 of the optical transceiver
14 to transition to the power-saving state (u6).
[0051] The OLT 1 monitors the bandwidth allocated to the ONU 10 in
the power-saving state and detects whether the request signal is
normally transmitted. At this time, when the signal is not normally
transmitted from the ONU 10 in the power-saving state, the OLT 1
determines that a failure occurs in a communication path of an
uplink or the ONU 10 itself and issues an alarm. This operation at
the time of occurrence of a failure is described later with
reference to FIG. 5.
[0052] (d9)-(d10) & (u9)-(u10) Communication at the time
Power-saving Release
[0053] In the ONU 10, when release of the power-saving state is
needed, such as in a case where transmission of a large amount of
data is needed, the ONU 10 requests release of the power-saving
state in the tentative wake-up time after the sleep time. This
release of the power-saving state can be performed by the ONU 10
transmitting a specific signal, however, can be realized, for
example, by transmitting valid upstream data in a specified
bandwidth. The power-saving state is released by transmitting valid
upstream data, so that a bandwidth of transmission data in which
transmission bits are saved can be effectively used.
[0054] The OLT 1 monitors the bandwidth allocated to the ONU 10 in
the power-saving state after the timing (d9) and performs failure
detection in the similar manner to the operation after the above
(d6). At the same time, when the ONU 10 transmits a power-saving
request, the OLT 1 maintains an operation in the power-saving state
with respect to the ONU 10, however, when a release request of the
power-saving state is received as above, an operation in the
power-saving state is released and an operation for normal
operation is started with respect to the ONU 10.
[0055] According to the above operation, the OLT 1 can allow a
power-saving operation by the ONU 10 while maintaining a link to
the ONU 10, and at the same time, can detect occurrence of a
failure at an early stage even if a failure occurs in a
communication with the ONU 10 that normally does not transmit data.
Furthermore, the ONU 10 can suppress power consumption by stopping
supply of laser power to the Tx 141 of the optical transceiver 14,
and, even in a communication necessary for failure monitoring, the
ONU 10 can suppress power consumption by decimated Grant compared
with the case where transmission of any signal is forced every
bandwidth update cycle.
[0056] A transmission bandwidth allocation cycle is a cycle in
which the OLT 1 notifies of allocation of a transmission bandwidth
and allocates the transmission bandwidth to the ONU 10. The above
decimated Grant is the Grant, which has an allocation interval of a
transmission bandwidth longer than the time when the ONU 10 is
operated in a normal state, in the ONU 10 in the power-saving
state.
[0057] The transmission bandwidth allocation cycle allocated to the
ONU 10 in the power-saving state can be determined by any method,
and, as an example, the transmission bandwidth allocation cycle can
be set to have a value matching a detection time T of an MPCP
(Multi-Point Control Protocol) timeout alarm. If the transmission
bandwidth allocation cycle is set longer than the time of the MPCP
timeout, the ONU 10 in the sleep mode lasts into this MPCP timeout,
so that the OLT 1 sets the transmission bandwidth allocation cycle
to the time equal to or less than the MPCP timeout. Moreover, if a
transmission period is provided to the ONU 10 a plurality of times
(n times) but cannot be received even once and this is determined
as the MPCP timeout, unnecessary alarm and the like can be
suppressed. Therefore, for example, when the MPCP timeout is set to
T milliseconds, the OLT 1 sets the transmission bandwidth
allocation cycle to T/n milliseconds.
[0058] Moreover, because the link between the OLT 1 and the ONU 10
is maintained, power consumption can be reduced even while user
terminals continue communication with each other.
[0059] Details of Communication Control of OLT
[0060] Next, details of the communication process of the OLT 1 are
explained with reference to FIG. 3.
[0061] FIG. 3 illustrates the process of the PON control unit 2
(PON controller) of the OLT 1. First, the PON control unit 2
specifies the ONUs 10 to which a transmission bandwidth of an
uplink needs to be allocated based on a list (ActiveONUList) of the
ONUs 10, which are discovered by the discovery and to which a link
is provided, and allocates a transmission bandwidth to each ONU 10
(Step S1). At this time, for example, when a transmission bandwidth
for one cycle is divided into N, an identifier ID of a
corresponding ONU 10 is given as id.sub.bw=ONU[bw], bw=1, 2, . . .
, N.
[0062] In the ActiveONUList, the ONU 10 in the power-saving state
is excluded, so that the PON control unit 2 can perform a dynamic
bandwidth allocation so that a transmission bandwidth is not
allocated to the ONU 10 in the power-saving operation by referring
to this list.
[0063] Next, the PON control unit 2 collects the Grant and
downstream data in a frame and controls the optical transceiver 5
to transmit this frame to the ONU 10 (Step S2). The Grant and the
downstream data can be transmitted with the same frame or can be
transmitted with different frames.
[0064] Next, the PON control unit 2 performs a reception process of
each transmission bandwidth received by the Rx 51 by the following
steps (Step S3).
[0065] First, the PON control unit 2 specifies the ONU 10 allocated
to the next transmission bandwidth (Step S4). At this time, the Rx
51 of the optical transceiver 5 performs reception of an uplink
concurrently, and the PON control unit 2 reads data received by the
Rx 51 into a built-in memory or the like for processing (Step S5).
The PON control unit 2 checks the type of the received upstream
signal (Step S6), and when there is no valid signal, the process
proceeds to Step S17, when the request signal (Dying_gasp) for the
power-saving state is detected, the process proceeds to Step S12,
and when the signal is other data signals or the like, the process
at Step S7 is performed.
[0066] At Step S7, the PON control unit 2 checks the ONU 10 of the
transmission source of the received data, and when this ONU 10 is
not included in the ActiveONUList, the PON control unit 2 adds the
ONU 10 to the ActiveONUList. The OLT 1 detects that the ONU 10
releases the power-saving state by the ONU 10 in the power-saving
state transmitting normal data.
[0067] The received data includes a bandwidth request from the ONU
10, and the PON control unit 2 reads the bandwidth request from the
received frame, and associates it with the identifier (ID) of the
ONU 10 for the next bandwidth allocation at Step S1 and records
this bandwidth request in a memory (Step S8). The bandwidth request
is expressed by a stored amount of data (occupancy) in the transmit
buffer 12 of the ONU 10 or the like. The method in which the ONU 10
transmits a report on the occupancy of the transmit buffer 12 and
the OLT 1 performs the dynamic bandwidth allocation based on this
report is called an SR-DBA (status reporting DBA). The bandwidth
request does not need to be performed explicitly, and it is
possible that the OLT 1 adjusts a bandwidth to be allocated with
respect to a bandwidth allocated to the ONU 10 by monitoring a data
amount actually transmitted by the ONU 10. This is called a TM-DBA
(traffic-monitoring DBA). At Step S8, traffic monitoring by this
TM-DBA can be performed.
[0068] Next, the PON control unit 2 transmits the received data
stored in the receive buffer 3 to the network via the PHY 7 (Step
S9).
[0069] The PON control unit 2 always monitors a communication state
of an uplink to each ONU 10. If an expected frame cannot be
received at the timing at which the ONU 10 transmits a frame, an
alarm signal called a LOSi (Loss of signal for ONUi) is output.
This alarm signal is an alarm necessary for network management,
and, when the LOSi is generated, this is notified to a network
operator and the network operator performs measures against failure
based on this LOSi. Step S10 is a process of clearing a failure
count for this LOSi. The LOSi is a signal that is output when a
signal cannot be received, for example, four times continuously
from an i-th ONU 10 and a true failure is determined, and the
failure count is a variable that counts the number of continuous
times of this non-receipt. The PON control unit 2 performs count-up
of the count of the LOSi at Step S17 described later.
[0070] When the process at Step S10 is finished, the PON control
unit 2 returns to the top of the loop process at Step S3 for
processing the next bandwidth. This loop process is a process of
repeating the process for the bw-th bandwidth from 1-th to
N-th.
[0071] Next, the process in the case where the OLT 1 receives the
sleep request (Dying_Gasp) at Step S6 is explained.
[0072] In this embodiment, there are two types of the Dying_Gasp.
One is Dying_Gasp (0) that is output when the ONU 10 disconnects a
link and turns off the power and the other one is Dying_Gasp (1)
that is output by the ONU 10 as the sleep request. The Dying_Gasp
signal has a format containing a signal identifier indicating the
Dying_Gasp signal, an ID of the ONU 10, and a flag (option)
indicating the sleep request. The PON control unit 2 checks whether
the received Dying_Gasp signal is the sleep request at Step S12,
and in the case of the sleep request, i.e., the Dying_Gasp (1)
signal, the process proceeds to the process at Step S13.
[0073] At Step S12, the PON control unit 2 detects that the ONU 10
is transitioned to the power-saving state and records this.
Specifically, the PON control unit 2 performs a process of
excluding the ID of the ONU 10 from the ActiveONUList that is an
allocation target list of a transmission bandwidth. Moreover, the
PON control unit 2 sets a timer of the sleep time with respect to
the i-th ONU 10 for measuring a power-saving period (Step S14).
This sleep time can be the time stored in the OLT 1 in advance or
the time calculated based on a communication status, or a specific
time can be obtained from the ONU 10 and this value can be set as
the sleep time. Moreover, any method can be used for measurement of
the sleep time as long as the power-saving period can be determined
and the measurement can be performed also by measuring a relative
time lapse counted up or counted down according to a predetermined
elapsed time or by absolute time monitoring specifying absolute
time of a clock. Next, the PON control unit 2 moves to the above
upstream-data reception process (Step S9) and repeats the similar
process. If the specification is such that upstream data can also
be transmitted in the same bandwidth (or frame) together with the
Dying_Gasp (1), there is an advantage that even in the state where
the ONU 10 completes data transmission leaving only a small piece
of data in the transmit buffer 12, the ONU 10 can immediately enter
into the power-saving state. On the other hand, in the state
capable of the power-saving state, because the ONU 10 does not have
upstream data in many cases, the specification can be such that,
when the sleep request is received, a process for upstream data of
this frame is not performed.
[0074] On the other hand, at Step S12, when the PON control unit 2
determines that the Dying_Gasp (0) is received, the PON control
unit 2 detects the state that the power of the ONU 10 is turned off
(Step S15), and performs a process of removing the ONU 10 from the
ActiveONUList and deleting information and resources of the link
allocated to the ONU 10. At this time, the OLT 1 transmits a
Deactivate signal (Deactivate_ONU-ID) indicating disconnection of
the link and instructing to discard all information, such as link
information, to the ONU 10. Upon reception of this signal, the ONU
10 turns off the power of the optical transceiver 14. When this
process is finished, the PON control unit 2 returns to the process
at Step S3 again to process the next bandwidth.
[0075] Step S17 is a process in the case where a valid signal is
not received in the transmission bandwidth allocated to the ONU 10
at Step S6, and the PON control unit 2 detects a communication
failure by this process. In the system having the power-saving mode
in which the ONU 10 is in the power-saving state simply by turning
off the power of the Tx 141 of the transceiver, the ONU 10 in the
power-saving state does not, by necessity, transmit upstream data
and the like, so that the OLT 1 cannot detect a failure. In this
embodiment, the OLT 1 tentatively allocates a transmission
bandwidth also to the ONU 10 in the power-saving operation and the
ONU 10 tentatively turns on the power of the Tx 141 after the sleep
time and transmits a frame. Therefore, at Step S6, a communication
failure of an upstream link can be detected by determining whether
the ONU 10 transmits a frame in the allocated transmission
bandwidth. When a frame cannot be received in the bandwidth, the
PON control unit 2 counts up the variable LOS[i] that counts the
number of times of non-receipt with respect to the i-th ONU 10.
[0076] When the variable LOS[i] reaches a predetermined number of
times LOS_Max (for example, four), the PON control unit 2
determines that communication abnormality occurs in the upstream
link of the ONU 10 and issues the above alarm LOSi (Step S19).
Moreover, the PON control unit 2 moves to the process at Step S16
and disconnects the link. On the other hand, when the variable
LOS[i] has not reached the LOS_Max, the PON control unit 2 does not
issue the alarm and returns to the process (Step S3) for the next
bandwidth.
[0077] After performing the above process for all transmission
bandwidths in one bandwidth update cycle, the PON control unit 2
checks whether there is the ONU 10 in which the sleep time expires
for each ONU 10 in the power-saving operation. If the ONU 10 in
which the sleep time expires is detected, the ID thereof is added
to the ActiveONUList for tentatively waking up the ONU 10 (Step
S20). With this process, the monitoring operation of the ONU 10 in
the power-saving operation explained at Steps S17 to S19 becomes
possible. Moreover, when the ONU 10 maintains the power-saving
state, the sleep request is returned by using the transmission
bandwidth allocated at Step S1, so that the ONU 10 can continue the
operation in which power consumption is suppressed again while
maintaining the link.
[0078] Next, the PON control unit 2 determines whether to continue
the operation in the next bandwidth update cycle, and when the
operation is continued, the process returns to the process at Step
S1 and the above operation is resumed.
[0079] Details of Communication Control of ONU
[0080] Next, details of the communication process of the ONU 10 are
explained with reference to FIG. 4.
[0081] FIG. 4 is a flowchart illustrating the communication control
performed by the PON control unit 11 of the ONU 10. The
communication control is roughly broken down into a downlink
reception control (Steps S30 to S33) and an uplink transmission
control (S35 to S51).
[0082] Downlink Reception Control
[0083] First, the reception control of a downlink is explained. The
Rx 142 of the optical transceiver 14 receives a downlink frame
transmitted from the OLT 1 and records this received data in the
receive buffer 13. The PON control unit 11 monitors the frame
received by the optical transceiver 14 (Step S30) and extracts
transmission bandwidth information of the uplink from header
information included in the frame (Step S31). The transmission
bandwidth information includes information from which the ONU 10 as
an allocation target can be specified and information from which a
transmission start time and a transmission end time can be
specified.
[0084] Moreover, the PON control unit 11 extracts a payload portion
from the reception frame and outputs it to an upper-layer
processing unit (Step S32). This process is a process for
transmitting data received in an upper protocol suitable for the
terminals 20-1, 2 connected to the ONU 10. Next, the PON control
unit 11 determines whether to end the reception control and turn
off the power, and when reception is continued without turning off
the power, the process returns to Step S30 and the above reception
control is continued.
[0085] Uplink Transmission Control
[0086] Next, the transmission control of an uplink is
explained.
[0087] The PON control unit 11 waits for allocation (Grant) of a
transmission bandwidth from the OLT 1 at Step S35. When a
transmission bandwidth is allocated, the PON control unit 11
supplies power to the Tx 141 of the optical transceiver 14 to set
to a laser-power-on state (Step S36). This process is necessary,
particularly, when returning from the power-saving state, so that
if the ONU 10 is in operation in a normal operation state and the
Tx 141 is already in an on-state, the process of starting power
supply does not need to be performed again.
[0088] The PON control unit 11 instructs power supply to the Tx 141
before the actual start time of a transmission bandwidth and at
least the time period for the Tx 141 of the optical transceiver 14
to wake up and optical output to be stabilized in advance. The
bandwidth update cycle of this embodiment is an extremely short
cycle and transition from the power-saving state to the tentative
wake-up state (Tentative wake-up) is extremely short time and is
performed frequently. Accordingly, when the Tx 141 wakes up
immediately before a transmission time without considering behavior
of optical output at the time of waking up the Tx 141, effects,
such as a non-receivable state and deterioration of an error rate,
occur in the OLT 1. Thus, as shown in FIG. 4, when allocation of a
transmission bandwidth is detected, the PON control unit 11 starts
power supply to the Tx 141. Thereafter, other operations such as a
frame generating operation are performed and transmission of a
frame by the PON control unit 11 is actually performed at the
subsequent Step S46.
[0089] Next, the PON control unit 11 detects a data storing state
in the transmit buffer 12 and an operation state of connected
equipment, such as the terminals 20-1 and 20-2, on the downstream
side (Step S37) and determines whether to transition to the
power-saving state (Sleep mode) (Step S38). For example, when the
OLT 1 determines that the data storing state in the transmit buffer
is a no-data state or is such that only a small amount of data of a
predetermined threshold or less is stored in a predetermined period
and there is room in the transmit buffer, the OLT 1 determines to
transition to the power-saving state. In the power-saving state, an
uplink is maintained, so that the ONU 10 needs to focus on the
point that it is possible to transmit data in a relatively small
bandwidth with respect to the capacity of the transmit buffer and a
transmission rate of a communication line. Moreover, other examples
of the criteria for the ONU 10 to transition to the power-saving
state include (1) a power state of each terminal and the number of
on-state terminals or the number of terminals responsive to
communication, (2) whether transition of all of connected terminals
(in the present embodiment, the terminals 20-1 and 20-2) to the
power-saving state is detected, for example, by a method such as an
LPI reception defined in IEEE802.3az, and the like.
[0090] When it is determined that the ONU 10 does not transition to
the power-saving state, the PON control unit 11 generates a
transmission payload based on transmission data stored in the
transmit buffer (Step S39). This payload is data that is processed
and generated in an upper layer. Next, in order to secure a
transmission bandwidth of the next cycle, a status report is
generated based on the data occupancy of the transmit buffer 12 and
the like (Step S40). The report is generated, for example, by the
PON control unit 11 expressing a ratio of data actually stored in
the buffer with respect to a buffer size instructed by a protocol
such as an OMCI (Optical Network Unit Management and Control
Interface) and encoding this ratio by a predetermined encoding
method. The status can be generated based on any criteria as long
as communication traffic of an uplink is recognized. Moreover, when
the TM-DBA is used, this report is not necessary.
[0091] On the other hand, when transitioning to the power-saving
state, the PON control unit 11 records information (flag)
indicating transition to the power-saving state in a built-in
memory for transitioning to the power-saving state at Step S48
described later. Moreover, the PON control unit 11 generates the
Dying_Gasp (1) signal that is the sleep request (Step S51).
[0092] At Step S41, the PON control unit 11 determines whether to
turn off the power of the ONU 10. In the case of turning off the
power, in order to insert the Dying_Gasp (0) into a transmission
frame and transmit it to the OLT 1, the PON control unit 11
generates this signal (Step S42). When the power is turned off,
power supply to the optical transceiver 14 including the Rx 14 is
stopped and the ONU 10 becomes a state in which both transmission
and reception are not possible. Accordingly, the PON control unit
11 actually turns off the power after Step S49 at which necessary
transmission processes are finished.
[0093] The PON control unit 11 collects various signals generated
at the above steps and generates a frame that accommodates them
(Step S44). At this time, the PON control unit 11 generates a frame
header (Step S43) and inserts it into the frame.
[0094] When generation of the frame is finished, the PON control
unit 11 waits until the transmission start time specified in the
transmission bandwidth information extracted at Step S31 (Step S45)
and starts transmission of the frame (Step S46). When transmission
of the frame is finished, the PON control unit 11 determines
whether to transition to the power-saving state (Sleep mode) (Step
S47), and in the case of transitioning to the power-saving state,
the PON control unit 11 stops power supply to the Tx 141 (Step
S48). Specifically, the PON control unit 11 can cause the Tx 141 to
transition to the power-saving state by transmitting an electrical
signal, such as a power-down and a shut-down, to the Tx 141 of the
optical transceiver 14. With this process, the PON control unit 11
generates an intermittent transmission stop period (stop period of
the transmitting unit) in the sleep mode.
[0095] Finally, the PON control unit 11 determines whether to turn
off the power or to be on standby for the next transmission (Step
S49), and in the case of turning off the power, the PON control
unit 11 turns off the power of the optical transceiver 14 and the
like and ends the process. When the Dying_Gasp (0) signal is not
correctly transmitted to the OLT 1 due to a single communication
error, unnecessary alarm is issued frequently in the OLT 1, so that
the power can be turned off after transmitting the Dying_Gasp (0)
signal a plurality of times before turning off the power. In this
case, the PON control unit 11 counts the number of times of
transmission of the Dying_Gasp (0) signal at Step S49 and controls
to return to the process at Step S35 until reaching a predetermined
number of times. On the other hand, when the PON control unit 11
determines not to turn off the power, the PON control unit 11
returns to Step S35 and repeats the processes similar to the
above.
[0096] Operation at the time of Occurrence of Failure
[0097] Next, the operation of the communication system when a
communication failure occurs is explained.
[0098] FIG. 5 is a sequence diagram illustrating the case where a
communication failure occurs in the ONU 10 in operation in the
power-saving state. The ONU 10 transitions to the power-saving
state after the transmission timing (u3), and thereafter, receives
a large amount of transmission data from the terminal 20-1 and
tries to return from the power-saving state after the timing (u4).
If a communication failure occurs in the upstream communication
path 30, data transmission cannot be performed. Because the OLT 1
knows that the ONU 10 turns off the power of the Tx 141 of the
optical transceiver 14 and does not transmit data, temporary
absence of an uplink communication is not abnormal when viewed from
the OLT 1 and the OLT 1 cannot detect occurrence of abnormality.
However, in the communication system in this embodiment, while
suppressing an upstream communication of the ONU 10 during the
sleep time, a transmission bandwidth is tentatively allocated to
the ONU 10 in the power-saving state after the sleep time (d6).
Therefore, the OLT 1 can detect whether there is communication
abnormality (Loss of Signal for ONUi) in a link to the ONU 10 in
the power-saving state by monitoring the bandwidth allocated at
(d6).
[0099] In the example in FIG. 5, when there is no response signal
from the ONU 10 in the bandwidth Bw allocated at the timing (d6),
the bandwidth Bw is allocated to the same ONU 10 also at the
following timing (d7), so that bandwidth monitoring is performed
twice in total and the LOSi alarm is output based on the second
bandwidth monitoring result. This bandwidth allocation does not
need to allocate in the continuous bandwidth update frequencies and
can be transmitted intermittently. Moreover, the number of times of
monitoring can also be set to any number.
[0100] The OLT 1 that output the alarm LOSi disconnects a link to
the ONU 10 and notifies the ONU 10 of that effect by outputting the
Deactivate_ONU-ID three times. The ONU 10 that received the
Deactivate_ONU-ID detects disconnection of the link and needs to
discard stored information on the link and stop data transmission.
Thereafter, the ONU 10 transitions to a communication standby state
(standby mode) from the OLT 1.
[0101] After the link is disconnected, for the ONU 10 to reconnect
to the OLT 1, the ONU 10 responds to a discovery request
transmitted from the OLT 1 and registers itself in the OLT 1. The
OLT 1 registers the ONU 10 by the discovery and does not allocate a
transmission bandwidth to the ONU 10 until a link is
established.
[0102] Operation at the time of Power-off
[0103] Next, the operation when the ONU 10 turns off the power is
explained.
[0104] FIG. 6 is a sequence diagram explaining the case where the
ONU 10 turns off the power after the power-saving state. The ONU 10
performs an operation in the power-saving state until the timing
(u8), however, for example, when a user performs an operation to
turn off the power of the ONU 10, there arises the necessity of
starting an operation of turning off the power in the ONU 10. At
this time, if the ONU 10 turns off the power immediately from the
power-saving state, the OLT 1 cannot detect this and issues the
LOSi. Therefore, the ONU 10 waits until bandwidth allocation after
the sleep time (d9) and transmits the
[0105] Dying Gasp (0) signal to the OLT 1 (u9), and thereafter,
turns off the power.
[0106] On the other hand, the OLT 1 can also recognize that a
communication failure with the ONU 10 occurs or the ONU 10 has not
returned from the sleep state by receiving the Dying_Gasp (0)
signal, so that unnecessary alarm output can be prevented.
[0107] Variable Setting of Sleep Time and Acknowledgement
[0108] FIG. 7 illustrates a sequence of a communication method of
determining the sleep time in the power-saving state by signaling.
When outputting the sleep request, the ONU 10 specifies the sleep
time that is set according to the communication state of itself and
outputs it to the OLT 1. For example, when there is no upstream
data, the ONU 10 sets the sleep time long, and, in the case of an
extremely small bandwidth or when intermittent communication
continues, the ONU 10 sets the sleep time short (however, the ONU
10 is transitioned to the power-saving state). In this manner, the
ONU 10 can output the sleep request with the sleep time changed
according to the communication state of the ONU 10 (u3).
[0109] On the other hand, the OLT 1 also can set the sleep time
according to the request from the ONU 10 and a network condition
such as a maximum delay condition. When the sleep request is
received from the ONU 10, this OLT 1 determines whether the sleep
state can be granted, and determines a sleep time that can be
granted while considering the requested sleep time and transmits
the acknowledgement signal (Acknowledgement) with respect to the
sleep request together with this sleep time (d4). It is applicable
that the OLT 1 does not notify of transmission bandwidth allocation
to the ONU 10 together with the acknowledgement signal.
[0110] The ONU 10 does not transition to the power-saving state
until receiving the acknowledgement signal and transitions to the
power-saving state after receiving the acknowledgement signal. In
this manner, false recognition of the state with the OLT 1 does not
occur by waiting for the acknowledgement signal, enabling to
suppress the situation in which the OLT 1 erroneously issues an
alarm. Moreover, the ONU 10 can operate in the power-saving state
during the granted sleep time, so that reduction of power
consumption and balance of communication can be appropriately
adjusted according to the communication state.
[0111] In the above explanation, both the ONU 10 and the OLT 1
transmit the sleep time, alternatively, only any one of the
apparatuses can transmit the sleep time for enabling to adjust the
sleep time. Moreover, the communication system can use a sequence
with no acknowledgement signal.
Second Embodiment
[0112] The second embodiment is an embodiment in which a
transmission bandwidth is allocated also to the ONU 10 in the
power-saving state (sleep mode) to reduce delay of a sleeping
upstream. The hardware configuration of the communication system is
similar to the above communication system explained in FIG. 1.
[0113] FIG. 8 is a sequence illustrating a communication method of
this embodiment. In FIG. 8, as is apparent from the transmission
timings (d4), (d5), (d7), and (d8) of the OLT 1, in this
embodiment, the OLT 1 allocates a transmission bandwidth also to
the ONU 10 in the sleep mode different from the sequence in FIG. 2.
Accordingly, the ONU 10 can release the sleep mode without waiting
for the end of the sleep mode and transition to the normal mode to
resume transmission of upstream data.
[0114] On the other hand, in terms of alarm monitoring, the ONU 10
in the sleep mode transmits or does not transmit a frame at its own
decision, so that a device is needed. Therefore, the OLT 1 monitors
a transmission bandwidth allocated to the ONU 10 in the sleep mode,
however, masks the count of the LOSi for alarm monitoring to
perform control not to output an alarm even if a valid signal
cannot be received in this transmission bandwidth. The alarm
monitoring state of the Loss of Signal is indicated by "ON"
(monitoring valid) and "MASK" (monitoring invalid) on the left side
in FIG. 8. From this drawing, it is found that alarm monitoring of
the Loss of Signal is "MASKed" during the sleep time.
[0115] Details of Communication Control of OLT
[0116] Next, details of the communication process of the OLT 1 is
explained with reference to FIG. 9.
[0117] FIG. 9 illustrates the process of the PON control unit 2 of
the OLT 1. In FIG. 9, the same reference letters as those in FIG. 3
illustrate the same or corresponding processes in FIG. 3. In FIG.
3, the PON control unit 2 controls not to allocate a transmission
bandwidth to the ONU 10 in the power-saving state at Step S1 and
Step S13. On the other hand, in the control in FIG. 9, the PON
control unit 2 allocates a transmission bandwidth also to the ONU
10 in the sleep mode at Step S60. It is considered that a necessary
transmission bandwidth of the ONU 10 in operation in the sleep mode
is small, so that the PON control unit 2 allocates a transmission
bandwidth smaller than the ONU 10 in the normal mode.
[0118] At Step S61, the type of an upstream signal is identified,
and the PON control unit 2 detects the sleep request by a PLOAM
(Physical Layer OAM operations, Administrations and Maintenance)
message instead of the Dying_Gasp (1) signal. In the sleep request,
an identifier (identifier of a link to the ONU 10 is also
available) with which the ONU 10 can be specified and an identifier
of the message type indicating that the PLOAM message is the sleep
request are included. The sleep request can be the Dying_Gasp (1)
signal in the similar manner to the first embodiment. When the
sleep request is included in the received upstream signal, the PON
control unit 2 detects that the ONU 10 transitions to the sleep
mode at Step S13, however, at this time, the ONU 10 does not need
to be removed from the allocation target of a transmission
bandwidth as described above.
[0119] Moreover, in the bandwidth bw at Step S61, when it is
determined that there is no valid received signal, the PON control
unit 2 detects whether the ONU 10 allocated to the bandwidth is in
the sleep mode by checking a timer ti at Step S62. Then, when the
PON control unit 2 determines that the ONU 10 is in the sleep mode,
the PON control unit 2 masks the alarm process (Steps S17 to 19)
and moves to Step S11 to perform a process for the next
transmission bandwidth.
[0120] As above, the OLT 1 includes means for preventing a false
alarm of failure monitoring by allowing not to transmit a frame to
the ONU 10 in the sleep mode while allocating a transmission
bandwidth to the ONU 10 in the sleep mode.
[0121] Details of Communication Control of ONU
[0122] Next, details of the communication process of the ONU 10 is
explained with reference to FIG. 10.
[0123] FIG. 10 is a flowchart illustrating the communication
control performed by the PON control unit 11 of the ONU 10. In FIG.
10, the same reference letters as those in FIG. 4 illustrate the
same or corresponding processes in FIG. 4. In the communication
control in FIG. 10, even if a transmission bandwidth is allocated
in the sleep mode, the ONU 10 does not transmit data by using the
transmission bandwidth in the sleep mode (Steps S70 and S71).
Therefore, the ONU 10 does not need to wake up the Tx 141 and thus
can save power consumption. Moreover, at Step S70, the PON control
unit 11 determines whether there is transmission data, and when
there is transmission data even in the sleep mode, the PON control
unit 11 performs the transmission process following Step S36.
Therefore, in the ONU 10 that employs the communication method
described in FIG. 10, the sleep mode can be released before the
sleep time expires and transmission delay in the sleep mode can be
reduced.
[0124] At Step S72, the PON control unit 11 generates the sleep
request using the PLOAM message instead of the Dying_Gasp (1)
signal in FIG. 4. On the other hand, at Step S73, a normal
Dying_Gasp signal is generated as the Dying_Gasp signal at the time
of power-off.
[0125] Operation at the time of Occurrence of Failure
[0126] Next, the operation of the communication system when a
communication failure occurs is explained.
[0127] FIG. 11 is a sequence diagram illustrating the case where a
communication failure occurs in the ONU 10 in operation in the
power-saving state. At the timings (d1), (d2), (d5), and (d6) in
the sleep mode, failure monitoring is masked and thus the LOSi is
not erroneously detected. On the other hand, when a failure occurs
in an uplink after the transmission timing (u4) of the ONU 10, the
OLT 1 detects a failure of the LOSi in the transmission bandwidth
Bw allocated at the transmission timings (d6) and (d7) of the OLT 1
and outputs the alarm LOSi.
[0128] Operation at the time of Power-off
[0129] Next, the operation when the ONU 10 turns off the power is
explained.
[0130] FIG. 12 is a sequence diagram explaining the case where the
ONU 10 turns off the power after the power-saving state. The ONU 10
performs an operation in the power-saving state until the timing
(u8), however, for example, when a user performs an operation to
turn off the power of the ONU 10, there arises the necessity of
starting an operation of turning off the power in the ONU 10. At
this time, if the ONU 10 turns off the power immediately from the
power-saving state, the OLT 1 cannot detect this and issues the
LOSi. Therefore, the ONU 10 waits until bandwidth allocation after
the sleep time (d9) and transmits the Dying_Gasp signal to the OLT
1 (u9), and thereafter, turns off the power. On the other hand, the
OLT 1 can also recognize that a communication failure with the ONU
10 occurs or the ONU 10 has not returned from the sleep state by
receiving the Dying_Gasp signal, so that unnecessary alarm output
can be prevented.
[0131] Variable Setting of Sleep time and Acknowledgement
[0132] FIG. 13 illustrates a sequence of a communication method of
determining the sleep time in the power-saving state by signaling
in the similar manner to FIG. 7. When outputting the sleep request,
the ONU 10 specifies the sleep time that is set according to the
communication state of itself and outputs it to the OLT 1. For
example, when there is no upstream data, the ONU 10 sets the sleep
time long, and, in the case of an extremely small bandwidth or when
intermittent communication continues, the ONU 10 sets the sleep
time short (however, the ONU 10 is transitioned to the power-saving
state). In this manner, the ONU 10 can output the sleep request
with the sleep time changed according to the communication state of
the ONU 10 (u3).
[0133] On the other hand, the OLT 1 also can set the sleep time
according to the request from the ONU 10 and a network condition
such as a maximum delay condition. When the sleep request is
received from the ONU 10, this OLT 1 determines whether the sleep
state can be granted, and determines a sleep time that can be
granted while considering the requested sleep time and transmits
the acknowledgement signal (Acknowledgement) with respect to the
sleep request together with this sleep time (d4). It is applicable
that the OLT 1 does not notify of transmission bandwidth allocation
to the ONU 10 together with the acknowledgement signal.
[0134] The ONU 10 does not transition to the power-saving state
until receiving the acknowledgement signal and transitions to the
power-saving state after receiving the acknowledgement signal. In
this manner, false recognition of the state with the OLT 1 does not
occur by waiting for the acknowledgement signal, enabling to
suppress the situation in which the OLT 1 erroneously issues an
alarm. Moreover, the ONU 10 can operate in the power-saving state
during the granted sleep time, so that reduction of power
consumption and balance of communication can be appropriately
adjusted according to the communication state.
[0135] In the above explanation, both the ONU 10 and the OLT 1
transmit the sleep time, however, only any one of the apparatuses
can transmit the sleep time for enabling to adjust the sleep time.
Moreover, a sequence with no acknowledgement signal can also be
used.
[0136] Explicit Release of Sleep Mode by PLOAM Message
[0137] In the above first and second embodiments, when returning
from the power-saving state (sleep mode) to the normal mode, the
ONU 10 performs data transmission, which is not accompanied with
the sleep request, in the allocated bandwidth. The OLT 1 detects
that the ONU 10 transitions to the normal mode by receiving this
data transmission, however, the ONU 10 and the OLT 1 can perform
this power-saving state (sleep mode) by using an explicit sleep
release request using the PLOAM Message. The flowchart of FIG. 14
illustrates the communication control of the OLT 1 that processes
this explicit Sleep release request. In FIG. 14, the same reference
letters as those in FIG. 9 illustrate the same or corresponding
processes in FIG. 9.
[0138] The Step S62 in FIG. 14 is a process of determining whether
the sleep request received by the OLT 1 is the transition request
or the release request. The format of the PLOAM Message can be any
format. For example, the sleep request includes an identifier
(identifier of a link to the ONU 10 is also available) with which
the ONU 10 can be specified, an identifier of the message type
indicating that the PLOAM message is the sleep request, and a flag
indicating any one of transition/release. This flag is a flag
indicating whether the sleep request requests transition to the
sleep mode or to the requests release. Moreover, as another
example, a method of allocating the identifier of the message type
to be distinguishable between transition/release instead of the
flag is considered. Release of the sleep mode is explicitly
performed in this manner, so that both the ONU 10 and the OLT 1 can
recognize transition and release of the sleep mode more surely and
therefore the process becomes more reliable. Moreover, if a
handshake method of returning the Acknowledgement signal to release
of the sleep mode is employed, reliability of the communication
system is further improved.
[0139] The embodiments of this invention are explained above. This
invention is not limited to these embodiments and any modifications
can be made as long as the modification is within the scope of this
invention. For example, the communication system to which this
communication method is applied does not need to be the PON system,
and can be also applied to an optical communication system using an
active element. Moreover, it is possible to apply to a
communication system that communicates between terminals by using
electrical signals without being limited to an optical
communication.
[0140] The communication system or the communication method of this
invention is an excellent communication system firstly capable of
suppressing power consumption. Accordingly, the effect of the
invention is obtained that it is possible to use even if a failure
monitoring function is removed from the above embodiments and power
consumption can be suppressed even in this case. Moreover, as a
second additional effect, there is a feature that failure
monitoring can be performed while maintaining a link in the
communication system in which power consumption is suppressed.
INDUSTRIAL APPLICABILITY
[0141] This invention is suitable for a communication method and a
communication system that need power saving.
REFERENCE SIGNS LIST
[0142] 1 OLT
[0143] 2 PON CONTROL UNIT
[0144] 3, 13 RECEIVE BUFFER
[0145] 4, 12 TRANSMIT BUFFER
[0146] 5, 14 OPTICAL TRANSCEIVER
[0147] 6 WDM
[0148] 7 PHY
[0149] 10-1 to 10-3 ONU
[0150] 11 PON CONTROL UNIT
[0151] 20-1, 20-2 TERMINAL
[0152] 30 SUBSCRIBER LINE
[0153] 40 SPLITTER
[0154] 51, 142, 161-1, 161-2 Rx
[0155] 52, 141, 162-1, 162-2 Tx
* * * * *