Optical line terminal and optical network unit

• US 8,929,737 B2
• Filed: 02/19/2010
• Issued: 01/06/2015
• Est. Priority Date: 02/24/2009
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Kani, Jun-ichi, Kubo, Ryogo, Otaka, Akihiro
• Primary Examiner(s): Curs, Nathan
• Assistant Examiner(s): LAMBERT, DAVID W
• Application Number:
  US13/148,462
• Publication Number:
  US 20110318008A1
• Time in Patent Office: 1,782 Days
• Field of Search: None
• US Class Current: 398/72
• CPC Class Codes: H04B 10/25 Arrangements specific to fibre transmission
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04L 12/12 Arrangements for remote connection or disconnection of substations or of equipment thereof
• CPC Class Codes: H04Q 11/0067 Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
• CPC Class Codes: H04Q 2011/0079 Operation or maintenance aspects
• CPC Class Codes: H04Q 2011/0083 Testing; Monitoring
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

An optical line terminal which includes an observing unit that observes information of any one or all of an arrival interval of frames, an instantaneous bandwidth under use of a flow, a queue length of a queue temporarily storing the frames, and a traffic type, and a stop determining unit that dynamically determines a sleep time to be a period in which a sleep state where partial functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit. The ONU is entered into a sleep state, immediately after communication ends, after a predetermined waiting time passes from when the communication ends, or after a waiting time determined on the basis of the information passes from when the communication ends.

Claims

1. An optical line terminal in an optical network in which the optical line terminal (OLT) and an optical network unit (ONU) communicate with each other through an optical fiber transmission path, the OLT including:

an observing unit that observes information of an arrival interval of frames transmitted to the ONU or frames received from the ONU, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the ONU, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the ONU of a sleep state entering request and the sleep time is transmitted to the ONU immediately after communication with the ONU ends, after a predetermined time passes from when the communication with the ONU ends, or after a time determined on the basis of the information passes from when the communication with the ONU ends,

wherein a maximum value and a minimum value are set for the sleep time, and the ONU is maintained in a normal state in the case of at least one of the case where the arrival interval of the frames obtained by the observing unit is smaller than a threshold value of the arrival interval of the frames, the case where the instantaneous bandwidth under use is greater than a threshold value of the instantaneous bandwidth under use, and the case where the queue length is greater than a threshold value of the queue length,

wherein the ONU is entered into the sleep state where the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, where the instantaneous bandwidth under use is equal to or smaller than the threshold value of the instantaneous bandwidth under use, or where the queue length is equal to or smaller than the threshold value of the queue length,

wherein the sleep time is set to a value between the maximum value and the minimum value,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

2. The optical line terminal of claim 1, wherein an average value of information obtained during a past predetermined period is used in at least one of the information of the arrival interval of the frames, the instantaneous bandwidth under use, and the queue length.

3. An optical network unit in an optical network in which an optical line terminal (OLT) and the optical network unit (ONU) communicate with each other through an optical fiber transmission path, the optical network unit including:

an observing unit that observes information of an arrival interval of frames transmitted to the ONU or frames received from the OLT, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the OLT, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the OLT;

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit; and

a sleep unit that stops the non-used functions to enter into a sleep state,

wherein a sleep state entering request and the sleep time are recognized using a control signal received from the OLT and the optical network unit is entered into the sleep state by the sleep unit immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the optical network unit returns to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th 1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

an one of the calculated sleep times is determined as the sleep time.

4. A method of controlling a sleep state of an optical network unit in an optical network in which an optical line terminal (OLT) and the optical network unit (ONU) communicate with each other through an optical fiber transmission path, the method including:

a step that the OLT observes information of an arrival interval of frames transmitted to the ONU or frames received from the ONU, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the ONU, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the ONU;

a step that the OLT dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing;

a step that the OLT transmits a control signal to notify the ONU of a sleep state entering request and the sleep time to the ONU immediately after communication with the ONU ends, after a predetermined time passes from when the communication with the ONU ends, or after a time determined on the basis of the information passes from when the communication with the ONU ends;

a step that the ONU recognizes the sleep state entering request and the sleep time using the control signal received from the OLT; and

a step that the ONU enters into the sleep state immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes from when the control signal is received, and return to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

5. An optical network system, including:

one optical line terminal (OLT) and one optical network unit (ONU), wherein the OLT performs point-to-point communication with the ONU through an optical fiber transmission path,

the OLT including;

an observing unit that observes information of an arrival interval of frames transmitted to the ONU or frames received from the ONU, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the ONU, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the ONU of a sleep state entering request and the sleep time is transmitted to the ONU immediately after communication with the ONU ends, after a predetermined time passes from when the communication with the ONU ends, or after a time determined on the basis of the information passes from when the communication with the ONU ends,

the ONU including;

a sleep unit that stops non-used functions to enter into a sleep state,

wherein a sleep state entering request and a sleep time to be a period in which the sleep state is maintained are recognized using a control signal received from the OLT and the optical network unit is entered into the sleep state by the sleep unit immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the optical network unit returns to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

6. An optical network system, including:

one optical line terminal (OLT) and a plurality of optical network units (ONU),

wherein the OLT performs point-to-multi-point communication with the plurality of ONUs through an optical fiber transmission path,

wherein the plurality of ONUs includes a first ONU,

the OLT including;

an observing unit that observes information of an arrival interval of frames transmitted to the first ONU or frames received from the first ONU, an instantaneous bandwidth under use of a flow transmitted to the first ONU or a flow received from the first ONU, and a queue length of a queue temporarily storing the frames transmitted to the first ONU or a queue temporarily storing the frames received from the first ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the first ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the first ONU of a sleep state entering request and the sleep time is transmitted to the first ONU immediately after communication with the first ONU ends, after a predetermined time passes from when the communication with the first ONU ends, or after a time determined on the basis of the information passes from when the communication with the first ONU ends,

the first ONU including;

a sleep unit that stops non-used functions to enter into a sleep state, wherein a sleep state entering request and a sleep time to be a period in which the sleep state is maintained are recognized using a control signal received from the OLT, and the first ONU is entered into the sleep state by the sleep unit immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the first ONU returns to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

7. An optical network system, including:

one optical line terminal (OLT) and an optical network unit (ONU),

wherein the OLT performs point-to-point communication with the ONU through an optical fiber transmission path,

the OLT including;

an observing unit that observes information of an arrival interval of frames transmitted to the ONU or frames received from the ONU, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the ONU, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the ONU of a sleep state entering request and the sleep time is transmitted to the ONU immediately after communication with the ONU ends, after a predetermined time passes from when the communication with the ONU ends, or after a time determined on the basis of the information passes from when the communication with the ONU ends,

the ONU including;

a sleep unit that stops non-used functions to enter into a sleep state, wherein a sleep state entering request and a sleep time to be a period in which the sleep state is maintained are recognized using a control signal received from the OLT and the ONU is entered into the sleep state by the sleep unit, immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the ONU returns to a normal state after the sleep time passes,

wherein when the arrival interval of the frames obtained b the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2″

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

8. An optical network system, including:

an optical line terminal (OLT) and a plurality of optical network units (ONU),

wherein the OLT performs point-to-multi-point communication with the plurality of ONUs through an optical fiber transmission path,

wherein the plurality of ONUs includes a first ONU,

the OLT including;

an observing unit that observes information of an arrival interval of frames transmitted to the first ONU or frames received from the first ONU, an instantaneous bandwidth under use of a flow transmitted to the first ONU or a flow received from the first ONU, and a queue length of a queue temporarily storing the frames transmitted to the first ONU or a queue temporarily storing the frames received from the first ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the first ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the first ONU of a sleep state entering request and the sleep time is transmitted to the first ONU immediately after communication with the first ONU ends, after a predetermined time passes from when the communication with the first ONU ends, or after a time determined on the basis of the information passes from when the communication with the first ONU ends,

the first ONU including;

a sleep unit that stops non-used functions to enter into a sleep state, wherein a sleep state entering request and a sleep time to be a period in which the sleep state is maintained are recognized using a control signal received from the OLT and the first ONU is entered into the sleep state by the sleep unit immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the first ONU returns to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein, when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.

9. An optical network system, including:

an optical line terminal (OLT) and an optical network unit (ONU),

wherein the OLT performs point-to-point communication with the ONU through an optical fiber transmission path,

the OLT including;

an observing unit that observes information of an arrival interval of frames transmitted to the ONU or frames received from the ONU, an instantaneous bandwidth under use of a flow transmitted to the ONU or a flow received from the ONU, and a queue length of a queue temporarily storing the frames transmitted to the ONU or a queue temporarily storing the frames received from the ONU; and

a calculating unit that dynamically determines a sleep time to be a period in which a sleep state where non-used functions of the ONU are stopped is maintained, on the basis of the information obtained by the observing unit,

wherein a control signal to notify the ONU of a sleep state entering request and the sleep time is transmitted to the ONU immediately after communication with the ONU ends, after a predetermined time passes from when the communication with the ONU ends, or after a time determined on the basis of the information passes from when the communication with the ONU ends,

the ONU including;

a sleep unit that stops non-used functions to enter into a sleep state,

wherein a sleep state entering request and a sleep time to be a period in which the sleep state is maintained are recognized using a control signal received from the OLT and the ONU is entered into the sleep state by the sleep unit immediately after the control signal is received, after a predetermined time passes from when the control signal is received, or after a time designated by the OLT passes, and the ONU returns to a normal state after the sleep time passes,

wherein, when the arrival interval of the frames obtained by the observing unit is equal to or greater than the threshold value of the arrival interval of the frames, the sleep time is calculated using following equations;

T1=Tmin+(Tmax−

Tmin)*f(p)

f(p)=(1−

(Th1/p)) or

f(p)=(p−

Th1)/(Th1′

−

Th1),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th1 indicates the threshold value of the arrival interval of the frames, p indicates the arrival interval of the frames, and Th1′

indicates the maximum threshold value of the arrival interval of the frames,

wherein when the instantaneous bandwidth under use obtained by the observing unit is equal to or smaller than the threshold value of the instantaneous bandwidth under use, the sleep time is calculated using following equations;

T1−

Tmin+(Tmax−

Tmin)*f(B)

f(B)=(1−

(B/Th2)) or

f(B)=(Th2−

B)/(Th2−

Th2′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th2 indicates the threshold value of the instantaneous bandwidth under use, B indicates the instantaneous bandwidth under use, and Th2′

indicates the minimum threshold value of the instantaneous bandwidth under use, and

wherein, when the queue length obtained by the observing unit is equal to or smaller than the threshold value of the queue length, the sleep time is calculated u in following equations;

T1=Tmin+(Tmax−

Tmin)*f(q)

f(q)=(1−

(q/Th3)) or

f(q)=(Th3−

q)/(Th3−

Th3′

),

T1 indicates the sleep time, Tmin indicates the minimum value of the sleep time, Tmax indicates the maximum value of the sleep time, Th3 indicates the threshold value of the queue length, q indicates the queue length, and Th3′

indicates the minimum threshold value of the queue length, and

any one of the calculated sleep times is determined as the sleep time.