U.S. patent number 9,270,406 [Application Number 14/085,609] was granted by the patent office on 2016-02-23 for communication method, optical communication system, station-side optical-line terminal apparatus, and user-side optical-line terminal apparatus.
This patent grant is currently assigned to Mitsubishi Electric Corporation. The grantee listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Yukio Hirano, Hiroaki Mukai.
United States Patent |
9,270,406 |
Hirano , et al. |
February 23, 2016 |
Communication method, optical communication system, station-side
optical-line terminal apparatus, and user-side optical-line
terminal apparatus
Abstract
A communication method of an optical communication system in
which a user-side optical-line terminal apparatus (ONU) is
connected to a station-side optical-line terminal apparatus (OLT)
by an optical fiber includes allocating by the OLT to the ONY a
transmission bandwidth for transmitting a response signal in a
tentative wake-up period in a sleep mode in which a transmission
function of the ONU is activated in the tentative wake-up period
and deactivated in a sleep period. The method also includes
transmitting a transmission bandwidth notification to the ONU, and
transmitting, to the ONU, a notification of the sleep period in
which deactivation of the transmission function is allowed.
Inventors: |
Hirano; Yukio (Tokyo,
JP), Mukai; Hiroaki (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Mitsubishi Electric Corporation
(Tokyo, JP)
|
Family
ID: |
44672519 |
Appl.
No.: |
14/085,609 |
Filed: |
November 20, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140079396 A1 |
Mar 20, 2014 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
13395145 |
|
8687960 |
|
|
|
PCT/JP2010/002054 |
Mar 24, 2010 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J
14/0238 (20130101); H04B 10/272 (20130101); H04J
14/0282 (20130101); H04J 14/0227 (20130101); H04J
14/0247 (20130101); H04J 14/0267 (20130101); H04Q
11/0067 (20130101); H04J 14/0252 (20130101); H04J
14/0258 (20130101); H04Q 2011/0079 (20130101) |
Current International
Class: |
H04J
14/00 (20060101); H04J 14/02 (20060101); H04B
10/272 (20130101); H04Q 11/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2005-151150 |
|
Jun 2005 |
|
JP |
|
2007-274534 |
|
Oct 2007 |
|
JP |
|
2008-244583 |
|
Oct 2008 |
|
JP |
|
2009-171424 |
|
Jul 2009 |
|
JP |
|
2009-260970 |
|
Nov 2009 |
|
JP |
|
Other References
Haran, O., et al., "ONU power-save annex," PMC-Sierra Inc., pp.
1-10, (Apr. 2008). cited by applicant .
International Search Report Issued May 11, 2010 in PCT/JP10/02054
Filed Mar. 24, 2010. cited by applicant .
Office Action mailed Aug. 6, 2013, in Japanese Patent Application
No. 2012-220548 (with English-language translation). cited by
applicant .
Extended European Search Report mailed Oct. 31, 2013, in European
Patent Application No. 10848313.2. cited by applicant .
ITU-T, "Gigabit-capable Passive Optical networks (G-PON):
Transmission Convergence layer specification," Amendment 1,
G.984.3, Feb. 2009. cited by applicant .
Editors G.984.3, "White Paper: Means and impact of GPON power
conservation," ITU-T Draft, Dec. 2008. cited by applicant .
Communication pursuant to Article 94(3) EPC filed Jan. 14, 2015, in
Application No. 10 848 313.2-1851. cited by applicant .
U.S. Appl. No. 14/095,962, filed Dec. 3, 2013, Mukai, et al. cited
by applicant .
International Telecommunication Union, "GPON power conservation",
ITU-T Telecommunication Standardization Sector of ITU, Series G,
Supplement 45, Total 44 pages, (May 2009). cited by applicant .
Mangin, Christopher and Mukai, Hiroaki, "Type B Optical Link
Protection", Draft Contribution to IEEE 1904.1, TF3,Total 7 pages,
(Server Date Oct. 18, 2010), XP17737894A. cited by applicant .
IEEE P 1904.1, "Service iteroperability in Ethernet Passive Optical
Networks (SIEPON)", pp. 9-1 to 9-18,(Aug. 2010), XP17739757A. cited
by applicant .
Draft Amendment to IEEE Std. 802.3-2008, IEEE 802.3zv 10G-EPON Task
Force, IEEE Draft P802.3av/D1.3, Section 93. Multipoint MAC
Control, (Apr. 2008). cited by applicant .
Office Action issued Jul. 31, 2015 in Vietnamese Patent Application
No. 1-2012-01562 (with English translation). cited by applicant
.
Office Action issued Nov. 2, 2015 in European Patent Application
No. 10 848 313.2. cited by applicant.
|
Primary Examiner: Tran; Dzung
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
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.
Claims
The invention claimed is:
1. A communication method of an optical communication system in
which a user-side optical-line terminal (ONU) apparatus is
connected to a station-side optical-line terminal (OLT) apparatus
by an optical fiber, comprising: allocating, by the OLT to the ONU,
a transmission bandwidth for transmitting a response signal in a
tentative wake-up period in a sleep mode in which a transmission
function of the ONU is activated in the tentative wake-up period
and deactivated in a sleep period, and transmitting a transmission
bandwidth notification to the ONU; and transmitting, to the ONU, a
notification of the sleep period in which deactivation of the
transmission function is allowed.
2. The communication method according to claim 1, wherein the ONU
stops power supply to a laser of an optical transmitter in the
sleep period.
3. The communication method according to claim 1, wherein the OLT
transmits, to the ONU, a signal that grants the ONU permission to
transition to the sleep mode.
4. The communication method according to claim 1, wherein when the
sleep mode is continued after the sleep period, the ONU in the
sleep mode transmits a signal requesting transition to the sleep
mode with respect to the transmission bandwidth notification.
5. The communication method according to claim 1, wherein the OLT
causes a transmission bandwidth allocation cycle with respect to
the ONU in the sleep mode to be longer than a transmission
bandwidth allocation cycle with respect to the ONU not in the sleep
mode.
6. An optical communication system in which a user-side
optical-line terminal (ONU) apparatus is connected to a
station-side optical-line terminal (OTL) apparatus by an optical
fiber, wherein the OLT includes: an optical transceiver connected
to the optical fiber, and a control device that allocates to the
ONU a transmission bandwidth for transmitting a response signal in
a tentative wake-up period in a sleep mode in which a transmission
function of an optical transmitter of the ONU is activated in the
tentative wake-up period and deactivated in a sleep period, and
transmits, to the ONU, a notification of the sleep period in which
deactivation of the transmission function is allowed.
7. The optical communication system according to claim 6, wherein
the ONU stops power supply to a laser of the optical transmitter in
the sleep period.
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 the sleep period, the ONU in
the sleep mode transmits a signal requesting transition to the
sleep mode with respect to the transmission bandwidth
notification.
10. The optical communication system according to claim 6, wherein
the control device causes a transmission bandwidth allocation cycle
with respect to the ONU in the sleep mode to be longer than a
transmission bandwidth allocation cycle with respect to the ONU not
in the sleep state.
11. A user-side optical-line terminal apparatus of an optical
communication system in which a user-side optical-line terminal
apparatus and a station-side optical-line terminal apparatus are
connected by an optical fiber, comprising: an optical transceiver
connected to the optical fiber; and a control device that, when a
transmission bandwidth is allocated by the station-side
optical-line terminal apparatus in a sleep mode, causes the optical
transceiver to transmit a response signal to the station-side
optical-line terminal apparatus, wherein the control device
deactivates, in the sleep mode, a transmission function of the
optical transceiver in a sleep period according to a notification
received from the station-side optical-line terminal apparatus and
activates, in the sleep mode, the transmission function of the
optical transceiver to transmit the response signal in the
transmission bandwidth in a tentative wake-up period after the
sleep period.
12. The user-side optical-line terminal apparatus according to
claim 11, wherein the optical transceiver stops power supply to a
laser of the optical transceiver in the sleep period.
13. The user-side optical-line terminal apparatus according to
claim 11, 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.
14. The user-side optical-line terminal apparatus according to
claims 11, wherein in 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.
15. The user-side optical-line terminal apparatus according to
claim 11, wherein the control device causes a transmission
bandwidth allocation cycle in the sleep mode to be longer than a
transmission bandwidth allocation cycle not in the sleep mode.
16. A station-side optical-line terminal apparatus of an optical
communication system in which a user-side optical-line terminal
apparatus and a station-side optical line terminal apparatus are
connected an optical fiber, comprising: an optical transceiver
connected to the optical fiber; and a control device that allocates
to a user optical-line terminal apparatus a transmission bandwidth
for transmitting a response signal in a tentative wake-up period in
a sleep mode in which a transmission function of an optical
transmitter of the user-side optical-line terminal apparatus is
activated in the tentative wake-up period and deactivated in a
sleep period in the sleep mode, and transmits a transmission
bandwidth notification to the user-side optical-line terminal
apparatus, and transmits, to the user-side optical-line terminal
apparatus, a notification of the sleep period in which deactivation
of the transmission function of the optical transmitter is
allowed.
17. The station-side optical-line terminal apparatus according to
claim 16, 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.
18. The station-side optical-line terminal apparatus according to
claim 16, wherein the control device causes a transmission
bandwidth allocation cycle with respect to the user-side
optical-line terminal apparatus in the sleep mode to be longer than
a transmission bandwidth allocation cycle with respect to the
user-side optical-line terminal apparatus not in the sleep
mode.
19. A control device of a user-side optical-line terminal apparatus
of an optical communication system in which a user-side
optical-line terminal apparatus and a station-side optical-line
terminal apparatus are connected by an optical fiber, wherein: the
control device controls an optical transceiver of the user-side
optical-line terminal apparatus and causes the optical transceiver
to transmit a response signal to the station-side optical-line
terminal apparatus, and when a transmission bandwidth is allocated
by the station-side optical-line terminal apparatus in a sleep
mode, the control device deactivates a transmission function of the
user-side optical-line terminal apparatus in a sleep period
according to a notification received from the station-side
optical-line terminal apparatus and activates the transmission
function to transmit the response signal in the transmission
bandwidth in a tentative wake-up period after the sleep period.
20. The control device according to claim 19, wherein the control
device causes power supply to a laser of the optical transceiver to
be stopped in the sleep period.
21. The control device according to claim 19, 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.
22. The control device according to claim 19, wherein in 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.
23. A control device of a station-side optical-line terminal
apparatus of an optical communication system in which a user-side
optical-line terminal apparatus and a station-side optical-line
terminal apparatus are connected by an optical fiber, wherein: the
control device allocates to the user-side optical-line terminal
apparatus a transmission bandwidth for transmitting a response
signal in a tentative wake-up period in a sleep mode in which a
transmission function of an optical transmitter of the user-side
optical-line terminal apparatus is activates in the tentative
wake-up period and deactivated in a sleep period, and transmits a
transmission bandwidth notification to the user-side optical-line
terminal apparatus, and transmits, to the user-side optical-line
terminal apparatus, a notification of the sleep period in which
deactivation of the transmission function is allowed.
24. The control device according to claim 23, 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.
25. The control device according to claim 23, wherein 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 not in the sleep mode.
Description
FIELD
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
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.
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.
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
Patent Literature 1: Japanese Patent Application Laid-open No.
2007-274534
SUMMARY
Technical Problem
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
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.
According to another aspect of 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 sleep mode in the sleep
period and transmitting a transmission bandwidth notification to
the ONU; (d) the ONU, to which the transmission bandwidth
notification is transmitted, 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.
According to still another aspect of 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.
According to still another aspect of 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 optical transceiver of the
station-side optical-line terminal apparatus.
According to still another aspect of 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 station-side optical-line terminal apparatus when a
transmission bandwidth is allocated by the station-side
optical-line terminal apparatus 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.
According to still another aspect of 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
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
FIG. 1 is a configuration diagram illustrating a configuration of a
communication system according to an embodiment of the present
invention.
FIG. 2 is a sequence diagram illustrating a communication method
according to a first embodiment of the present invention.
FIG. 3 is a flowchart illustrating a communication control of an
OLT according to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating a communication control of an
ONU according to the first embodiment of the present invention.
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.
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.
FIG. 7 is a sequence diagram illustrating a communication method
(modified example) according to the first embodiment of the present
invention.
FIG. 8 is a sequence diagram illustrating a communication method
according to a second embodiment of the present invention.
FIG. 9 is a flowchart illustrating a communication control of an
OLT according to the second embodiment of the present
invention.
FIG. 10 is a flowchart illustrating a communication control of an
ONU according to the second embodiment of the present
invention.
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.
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.
FIG. 13 is a sequence diagram illustrating a communication method
(modified example) according to the second embodiment of the
present invention.
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
Hardware Configuration
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.
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.
The ONU 10-1 includes a PON control unit 11 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.
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.
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.
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".
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.
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 11.
The PON control unit 11 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.
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.
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.
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.
Power-saving Operation
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.
(d1)-(d2) & (u1)-(u2) Communication in Normal Operation
State
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).
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.
(d3)-(d8) & (u3)-(u8) Communication in Power-Saving State
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.
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.
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.
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).
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.
(d9)-(d10) & (u9)-(u10) Communication at the time Power-saving
Release
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.
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.
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.
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
transmitssion bandwidth longer than the time when the ONU 10 is
operated in a normal state, in the ONU 10 in the power-saving
state.
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.
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.
Details of Communication Control of OLT
Next, details of the communication process of the OLT 1 are
explained with reference to FIG. 3.
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.
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.
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.
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).
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.
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.
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.
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).
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.
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.
Next, the process in the case where the OLT 1 receives the sleep
request (Dying_Gasp) at Step S6 is explained.
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.
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.
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.
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.
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.
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.
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.
Details of Communication Control of ONU
Next, details of the communication process of the ONU 10 are
explained with reference to FIG. 4.
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).
Downlink Reception Control
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.
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.
Uplink Transmission Control
Next, the transmission control of an uplink is explained.
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.
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.
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.
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.
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).
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 142 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.
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.
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.
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.
Operation at the time of Occurrence of Failure
Next, the operation of the communication system when a
communication failure occurs is explained.
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).
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.
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.
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.
Operation at the time of Power-off
Next, the operation when the ONU 10 turns off the power is
explained.
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
Dying Gasp (0) 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 (0)
signal, so that unnecessary alarm output can be prevented.
Variable Setting of Sleep Time and Acknowledgement
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).
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.
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.
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
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.
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.
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.
Details of Communication Control of OLT
Next, details of the communication process of the OLT 1 is
explained with reference to FIG. 9.
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.
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.
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 S19) and
moves to Step S11 to perform a process for the next transmission
bandwidth.
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.
Details of Communication Control of ONU
Next, details of the communication process of the ONU 10 is
explained with reference to FIG. 10.
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.
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.
Operation at the time of Occurrence of Failure
Next, the operation of the communication system when a
communication failure occurs is explained.
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.
Operation at the time of Power-off
Next, the operation when the ONU 10 turns off the power is
explained.
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.
Variable Setting of Sleep time and Acknowledgement
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).
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.
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.
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.
Explicit Release of Sleep Mode by PLOAM Message
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 the release of 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.
The Step S64 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.
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.
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
This invention is suitable for a communication method and a
communication system that need power saving.
REFERENCE SIGNS LIST
1 OLT
2 PON CONTROL UNIT
3, 13 RECEIVE BUFFER
4, 12 TRANSMIT BUFFER
5, 14 OPTICAL TRANSCEIVER
6 WDM
7 PHY
10-1 to 10-3 ONU
11 PON CONTROL UNIT
20-1, 20-2 TERMINAL
30 SUBSCRIBER LINE
40 SPLITTER
51, 142, 161-1, 161-2 Rx
52, 141, 162-1, 162-2 Tx
* * * * *