KR101294516B1 - Method and apparatus for burst mode clock and data recovery - Google Patents

Abstract

An optical line terminal for recovering packet data and a clock from an optical signal including a silent period is disclosed. The optical telephony terminal may receive packet data and a clock from at least one optical network unit. Even in a silent period in which the optical network unit does not transmit packet data, the optical line terminal proposed in the present invention can successfully recover the clock.

Description

Burst Mode Clock and Data Recovery Apparatus and Method {METHOD AND APPARATUS FOR BURST MODE CLOCK AND DATA RECOVERY}

The following embodiments relate to a burst mode clock and data recovery technique applied to an optical line transmission (OLT) in an optical subscriber network, particularly a passive optical subscriber network.

A passive optical network is a 1: N star topology in which a plurality of optical network units (ONUs) are connected to one OLT through a splitter (RN). The data transmitted from the OLT to the ONU is a continuous signal broadcast to a plurality of ONUs, and each ONU extracts and processes data corresponding to itself.

On the other hand, in case of transmitting data from ONU to OLT, to prevent collision between ONU data, OLT notifies time to ONU through DBA (Dynamic bandwidth algorithm) and ONU transmits data to OLT only within the allotted time. do. Therefore, data transmitted from the OLT to the ONU is a continuous signal, but data transmitted from the ONU to the OLT has a signal of a discontinuous burst.

One object of exemplary embodiments is to provide an optical line terminal for extracting and restoring a clock from fast burst mode packet data transmitted from an ONU to an OLT in a passive optical subscriber network.

Another aspect of the exemplary embodiments aims to provide an optical line terminal which maintains a clock by inserting a dummy clock into a silent section without data.

According to one side of the exemplary embodiments, a receiving unit for receiving optical signals including packet data, respectively, from a plurality of optical network units (ONU), a power recovery unit for recovering the power of the received optical signals equally And an optical line terminator (OLT) including a data insertion unit for inserting dummy data in a time interval when the packet data does not exist among the received optical signals.

According to yet another aspect of an exemplary embodiment, a receiver for receiving an optical signal including packet data from an optical network unit (ONU), a dummy data generator for generating dummy data synchronized with the packet data; There is provided an optical line terminal including a dummy data insertion unit for inserting the dummy data in a time interval in which the packet data does not exist among the optical signals.

According to yet another aspect of the exemplary embodiments, a transmission unit for transmitting an optical signal including the packet data to the optical line terminal, the optical signal is dummy data in the time interval in which the packet data of the optical signal does not exist There is provided an optical network unit into which is inserted.

According to one aspect of exemplary embodiments, an optical line terminal is provided for extracting and restoring a clock from fast burst mode packet data transmitted from an ONU to an OLT in a passive optical subscriber network.

According to yet another aspect of the exemplary embodiments, an optical line terminal is provided which maintains a clock by inserting a dummy clock into a silent section without data.

1 is a view showing the structure of a passive optical subscriber network according to an exemplary embodiment.
2 is a diagram briefly illustrating burst mode packet data according to an exemplary embodiment.
3 is a diagram illustrating a structure of an optical line terminal according to an exemplary embodiment.
Fig. 4 is a diagram showing the structure of an optical line terminal according to another exemplary embodiment.
Fig. 5 is a diagram showing the structure of an optical line terminal according to another exemplary embodiment.
Fig. 6 is a diagram showing the structure of another optical network unit in yet another exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the structure of a passive optical subscriber network according to an exemplary embodiment.

Referring to FIG. 1, a plurality of ONUs 120 and 130 may transmit packet data and a clock to an OLT using an optical subscriber network. Packets and clocks transmitted by the respective ONUs 120 and 130 are included in the same optical signal and transmitted.

The optical signals 121, 122, and 123 transmitted by the ONUs 120 and 130 are transmitted to the splitters RN and 140. The channels from the respective ONUs 120 and 130 to the splitter 140 are composed of optical cables. The distances from the respective ONUs 120 and 130 to the splitter 140 may be different from each other, so that the optical signals 121, 122, and 123 transmitted by the ONUs 120 and 130 may experience different transmission losses. That is, the magnitudes of the optical signals received by the splitter 140 may be different from each other.

The splitter 140 transmits the received optical signals 141, 142, and 143 to the OLT 110.

The OLT 110 may receive the optical signals 141, 142, and 143 via the splitter 140, and recover the packet data and the clock included in the received optical signals 141, 142, and 143.

In general, an optical receiving device used in an optical network uses a PD and a TIA / LIA (Transimpedence amplifier / Limiting amplifier) for photoelectric conversion and an optical network to extract a clock from a transmitted optical signal and align packet data with the extracted clock. A clock and data recovery (CDR) device is needed.

As shown in FIG. 1, when there is no data to be transmitted by each of the ONUs 120 and 130, an uplink signal from the ONUs 120 and 130 to the OLT 110 has a silent period. In the silent period, the ONUs 120 and 130 do not transmit any signal to the OLT 110. In this case, the OLT 110 cannot even receive the clock from the ONUs 120 and 130, and the general CDR cannot keep the clock. Therefore, the OLT 110 should use a burst mode CDR capable of quickly recovering a clock even in a silent period.

2 is a diagram briefly illustrating burst mode packet data according to an exemplary embodiment.

Referring to the optical signal 210 transmitted by the ONU, each ONU may have a guard time to prevent collisions between packet data, and may have a silent period when there is no upstream data.

Referring to the optical signal 220 received by the splitter, the transmission loss of the optical signal 221 transmitted by the first ONU is rather small. However, the transmission loss of the optical signal 223 transmitted by the second ONU is relatively large. In the silent section 222, no ONU transmits the optical signal.

OLT recovers the power of the received optical signal. When the power of each optical signal is restored, the power of the optical signal 231 transmitted by the first ONU and the optical signal 233 transmitted by the second ONU are the same. There is no optical signal in the silent section 232.

The OLT recovers the data packet 240 and clock 243 from the restored power optical signal. The recovered data packet 240 includes a packet 241 transmitted by the first ONU and a packet 242 transmitted by the second ONU. The recovered data packet 240 includes a silent section, but the recovered clock 243 does not include a silent section.

That is, the OLT should recover the clock even in a section where no signal is received from the ONU.

OLT may use a general-purpose PLL CDR or an oversampling PLL. When the OLT uses a general-purpose PLL CDR, it is difficult to recover the clock because the phase difference due to the distance difference between each ONU and the loop time to recover in the silent period are very large. When the OLT uses an oversampling CDR, the oversampling burst mode CDR should maintain 4 to 8 times the oversampling rate when the input data is a high speed signal of 2.5 Gbps or more. The design of CDRs operating at such high bandwidths is not only difficult but also very expensive and therefore difficult to apply.

3 is a diagram illustrating a structure of an optical line terminal according to an exemplary embodiment.

Referring to FIG. 3, the optical line terminal includes a power recovery unit 320, a burst adaptation block 330, a CDR 340, and a MAC 350. The block 310 including the burst adaptation block 310 and the CDR 340 extracts a clock by converting the received signal in the burst mode as a general received signal.

The power recovery unit 320 recovers optical signals having different optical power into electrical signals of a predetermined size. According to one side, the electrical signal 360 recovered by the power recovery unit 320 may not have any signal in the silent period. In this case, the general CDR cannot extract the clock.

The burst adaptation block 330 inserts dummy data into a silent section in which no packet data exists. According to one side, the dummy data and the packet data may be synchronized, in this case, the generation speed of the dummy data may match the transmission speed of the packet data.

The signal 370 in which the dummy data is inserted in the silent period is not a received signal in a burst mode, but has a form similar to a general received signal. Therefore, even when the general CDR 340 is used, the CDR 340 can easily recover the packet data and the clock from the signal 370 in which dummy data is inserted in the silent period. Here, the CDR 340 may restore the packet data and the clock by using a general phase locked loop (PLL) or delay locked loop (DLL) scheme.

The MAC 350 processes the data using the clock and the data recovered from the CDR 340. According to one side, the MAC 350 may determine the exact start time and the end time of the silent section using the higher layer information included in the recovered data. In this case, the MAC 350 may generate a control signal to control the operations of the power recovery unit 320 and the burst adaptation block 330.

For example, the burst adaptation block 330 may receive a control signal from the MAC 350 and insert dummy data only from the start point of the silent section to the end point of the silent section.

In addition, the power recovery unit 320 may receive a control signal from the MAC 350, may not operate at the end of the silent section from the start of the silent section.

Fig. 4 is a diagram showing the structure of an optical line terminal according to another exemplary embodiment.

Referring to FIG. 4, the optical line terminal includes a power recovery unit 420, a signal processing module 410, and a MAC 350. According to one side, the signal processing module 410 may include a dummy data generator 410, a switch 440, and a CDR 450, as shown in FIG. 4.

Since the recovery unit 420 and the MAC 350 shown in FIG. 4 operate similarly to those of FIG. 3, a detailed description thereof will be omitted.

The dummy data generator 410 generates dummy data synchronized with the packet data. According to one side, the dummy data generator 410 may receive a reference clock and generate a dummy clock synchronized with the packet data based on the reference clock.

The switch 440 generates the dummy data from the dummy data generator 410 and receives the power signal restored from the power restorer 420. The switch 440 may transmit the power restored electrical signal to the CDR 450 in a time section other than the silent section, and transmit dummy data to the CDR 450 in the silent section.

Fig. 5 is a diagram showing the structure of an optical line terminal according to another exemplary embodiment.

Referring to FIG. 5, the optical line terminal 500 includes a receiver 510, a power recovery unit 520, a data insertion unit 530, a data and clock recovery unit 540, and a MAC 550.

The receiver 510 receives an optical signal including packet data from a plurality of optical network units (ONUs). The received optical signal suffers transmission loss proportional to the distance from each optical network unit. Thus, the power of the received optical signal may be different for each optical network unit.

According to one side, each optical signal may include packet data and a clock. Packet data included in the optical signal may be distinguished from each other in time using a guard time period.

Each optical network unit transmits an optical signal only when there is data to transmit to the optical line terminal 500. Accordingly, the optical signal received by the receiver 510 may include a silent period in which no optical network unit transmits data.

The power recovery unit 520 modulates the received optical signal to generate an electrical signal corresponding to the received optical signal. In this case, the power of the electrical signal may be the same power regardless of the optical network unit that transmitted the optical signal. That is, the power recovery unit 520 may restore the power loss due to transmission loss by generating an electrical signal corresponding to the power of the power signal and a time position of the electrical signal corresponding to the time position of the optical signal. Since the temporal position of the electrical signal corresponds to the temporal position of the optical signal, the silent section in the optical signal is the same as the silent section in the electrical signal.

Although not shown in FIG. 5, the optical line terminal 500 may include a dummy data generator. The dummy data generator generates dummy data synchronized with the packet data. That is, the generation speed of dummy data may match the transmission speed of packet data.

The data insertion unit 530 inserts dummy data into a silent section in which no packet data exists among electrical signals. When the dummy data is inserted, the electrical signal has a continuous form 370, and the data and clock recovery unit 540 having a general structure can easily recover the packet data and the clock transmitted by the optical network unit from the electrical signal. According to one side, the data and clock recovery unit 540 may restore the packet data and the clock by using a phase lock loop (PLL) or a delay lock loop (DLL).

The MAC 550 extracts higher layer information from the recovered packet data. The higher layer information may include accurate silent section information in the optical signal transmitted from the optical network unit. If the MAC 550 can determine the exact start time and the end time of the silent section, the MAC 550 may generate a control signal for controlling the power recovery unit 520 or the data insertion unit 530.

For example, the power recovery unit 520 may not operate in the silent period according to the control signal. In addition, the data insertion unit 520 transmits the dummy data to the data and clock recovery unit 540 in the silent period, and restores the data and clock the electrical signal recovered by the power recovery unit 520 in the non-silent period. And transmit to unit 540.

Fig. 6 is a diagram showing the structure of another optical network unit in yet another exemplary embodiment.

Referring to FIG. 6, the optical network unit 600 includes a transmitter 610.

The transmitter 610 transmits an optical signal including packet data and a clock to the optical line terminal 630. According to one side, not only the optical network unit 600, but also the second optical network unit 620 transmits an optical signal to the optical line terminal 630. According to one side, the transmitter 610 may transmit the packet data divided by the time using a guard time interval.

Each optical network unit 600, 620 transmits an optical signal only when there is data to transmit. Therefore, the time period in which neither optical network unit 600 or 620 has data to be transmitted becomes a silent period.

According to one side, the signal transmitted to the optical line terminal 630 is converted into an electrical signal. The electrical signal has a silent section in the same time section as the silent section of the optical signal. Dummy data may be inserted in the silent section of the electrical signal.

According to one side, the packet data and the clock transmitted by the transmitter 610 may be restored from the electrical signal into which the dummy data is inserted.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

110: optical line terminal (OLT)
120, 130: optical network unit 120, 130
140: splitter

Claims (16)

A receiving unit for receiving optical signals including packet data from a plurality of optical network units (ONUs), respectively;
A power recovery unit for recovering an electrical signal having a constant power corresponding to the received optical signals; And
Data insertion unit for inserting the dummy data in the time interval in which the packet data does not exist in the recovered electrical signal
Including
The packet data is divided in time using a guard time interval (OLT: Optical Line Terminator). The method of claim 1,
And the optical signal includes a clock received from the optical network unit. delete A receiving unit for receiving optical signals including packet data from a plurality of optical network units (ONUs), respectively;
A power recovery unit for recovering an electrical signal having a constant power corresponding to the received optical signals; And
Data insertion unit for inserting the dummy data in the time interval in which the packet data does not exist in the recovered electrical signal
Including
And a generation rate of the dummy data coincides with a transmission rate of the packet data. A receiving unit for receiving optical signals including packet data from a plurality of optical network units (ONUs), respectively;
A power recovery unit for recovering an electrical signal having a constant power corresponding to the received optical signals;
A data insertion unit for inserting dummy data in a time interval in which the packet data does not exist among the recovered electrical signals; And
A MAC for determining a time interval in which the packet data does not exist and generating a control signal according to the determination result
/ RTI >
And the data insertion unit inserts the dummy data in accordance with the control signal. The method of claim 5,
And the power of the electrical signal is a preset power level. The method of claim 5,
Data and clock recovery unit for recovering the packet data and the clock received from the optical network unit from the electrical signal into which the dummy data is inserted
Optical line terminal further comprising. The method of claim 7, wherein
And the data and clock recovery unit restores the packet data and the clock by using a phase lock loop (PLL) or a delay lock loop (DLL). A receiving unit for receiving an optical signal including packet data from an optical network unit (ONU);
A dummy data generator configured to generate dummy data synchronized to the packet data;
A dummy data insertion unit for inserting the dummy data in a time section in which the packet data does not exist among the optical signals; And
MAC for determining the time interval without the packet data, and generates a control signal according to the determination result
/ RTI >
And the data insertion unit inserts the dummy data in accordance with the control signal. 10. The method of claim 9,
Data and clock recovery unit for recovering the packet data and the clock received from the optical network unit from the optical signal into which the dummy data is inserted
Optical line terminal further comprising. delete 10. The method of claim 9,
And the data and clock recovery unit transmits the restored packet data and clock to the MAC. 10. The method of claim 9,
Power recovery unit for restoring the power of the received optical signal to a predetermined power level
Further comprising:
And the dummy data insertion unit inserts the dummy data into the optical signal from which the power is restored. Transmission unit for transmitting the optical signal including the packet data to the optical line terminal
Lt; / RTI >
The optical signal is converted into an electrical signal, dummy data is inserted in a time interval in which the packet data does not exist among the electrical signals,
The transmitting unit transmits the packet data by dividing the packet data in time using a guard time period. 15. The method of claim 14,
The transmission unit transmits the clock by including the clock,
And the packet data and the clock are recovered from the optical signal into which the dummy data is inserted. delete

Images