KR20090083634A - Enhanced onu activation methods for the g-pon based on g.984.3 - Google Patents

Abstract

An enhanced ONU activation method for the G-PON(Gigabit-Passive Optical Network) based on g.984.3 is provided to shorten the length of a time window that is established during the activation process. An OLT(Optical Line Termination) receives a message from an ONU(Optical Network Unit) which is in a serial-number-state. The OLT discriminates a random delay value based on the serial number of the message, and measures the return electric wave delay value with an ONU in the serial-number-state. The OLT estimates the position of the ONU based on the random delay value and the return electric wave delay value.

Description

Enhanced ONU Activation Methods for the G-PON Based on G.984.3

The present invention is to activate the ONU in the ITU-T G.984.3-based G-PON, when the activation process proceeds in the state of not knowing the advance distance information between the OLT and ONU, and in the state of knowing the advance distance information between the OLT and ONU The present invention relates to a method for reducing the length of time window opened during the activation process.

The advancement of the Internet has gone beyond low-speed services such as early e-mail and web browsing, such as video conferencing, IPTV (Internet Protocol Television), HDTV (High Definition TV), high-definition interactive games, and VoD (Video on Demand). It is evolving to provide broadband services. The Digital Subscriber Line (xDSL) technology, which accounts for a large portion of demand, provides speeds of several Mbps and even several tens of Mbps, but these services can be simultaneously delivered to subscribers in the most frequent evening hours. There is a lack of provision. As the number of users increases and the speed of speed increases, there is a need for a reorganization of the subscriber network structure. As a result, interest in FTTH (Fiber to the Home), which is the ultimate network structure, is drawing attention.

FTTH technologies for providing Triple Play Service (TPS) include AON (Active Optical Network) and PON (Passive Optical Network), but much research is being conducted on the latter, which is low in installation and maintenance costs. PON is further classified into TDMA (Time Division Multiple Access) and WDMA (Wavelength Division Multiple Access). The former is developed according to the domestic standard, while the latter is the worldwide standard. PON), E-PON (Ethernet PON), and G-PON (Gigabit capable PON).

Among them, G-PON is highly efficient and has the highest transmission rate among conventional TDMA PONs and can operate up to 2.5Gbps regardless of the protocol regardless of ATM or Ethernet.

Looking at the trends abroad, in North America, SBC, Bellsouth, and Verizon issued RFP (Requirement for Proposal) to build FTTP (Fiber to the Premise) using B-PON in June 2003, and from 2004 to 2008 Although the company has invested tens of trillion won to about 10 million subscribers, the company is continuing this attempt using G-PON rather than B-PON. North American PON standards typically include a separate wavelength to accommodate CATV (Community Antenna Television).

The Middle East has issued a technical request to build a subscriber network using PON of 2.4 / 1.2 Gbps at downlink and uplink rates from the beginning. Although G-PON provides the function to accommodate TDM, it is characterized by transmitting voice signal (VoIP) or line signal through Ethernet. In order to provide TPS, it must be able to accept IPTV signals and include a separate wavelength for analog TV processing.

In Korea, G-PON development and commercialization is relatively slow compared to E-PON and W-PON. However, G-PON has higher uplink and downlink bandwidth, higher efficiency and better interoperability than E-PON, and lower price than W-PON. Therefore, G-PON emerges as an alternative to next-generation subscriber network when timely commercialization is achieved. Doing.

Like other Time Division Multiple Access (TDMA) PONs, the Optical Line Termination (OLT) in G-PON performs a process to operate smoothly on the PON when a new Optical Network Unit (ONU) is connected. This process is called an activation process. . This process also includes a ranging process that measures distances and assigns equalization delays so that all ONUs are logically at the same distance. During this activation process, the OLT opens several time windows, where the ONU already activated is prohibited from transmitting data upward. Therefore, it is important to shorten the length of the time window as much as possible to provide bandwidth saving and smooth service for the activated ONU.

The present invention devised to solve the above problems is when activating the ONU in the ITU-T G.984.3-based G-PON, when the activation process in the state of not knowing the advance distance information between the OLT and ONU, OLT and ONU It is an object of the present invention to provide a method of reducing the length of a time window opened during an activation process when the activation process is performed while the prior distance information is known.

In order to achieve the above object, the present invention, in the process of reducing the time window performed in the OLT is activated through the connection with the ONU that does not know the mutual advance distance information, receiving a message transmitted from the ONU in the Serial-Number-state, Distinguishing a random delay value corresponding to each ONU by a serial number in the message; Measuring a round trip propagation delay value with the ONU in a Serial-Number-state; Estimating the position of the ONU based on the random delay value and the round trip propagation delay value; And assigning a pre-assignment delay value such that all ONUs have the same equalization reciprocation delay value.

식을 통하여 계산되며, 여기서 T_RTD는 Serial-Number-state에서 측정되는 왕복전파지연 값, T_rd는 ONU에서 생성되는 랜덤지연 값을 의미한다.Preferably, the propagation delay value T _pd is

Calculated by the equation, where T _RTD is the round trip propagation delay value measured in Serial-Number-state and T _rd is the random delay value generated in ONU.

식을 통하여 계산되며, 여기서 D는 ONU와 OLT 사이의 거리, T_pd는 ONU까지의 전파지연 값, V는 광케이블에서 신호의 전파 속도를 의미한다.In addition, the position estimate value of the ONU is

Calculated by the equation, where D is the distance between ONU and OLT, T _pd is the propagation delay value to ONU, and V is the propagation speed of the signal in the optical cable.

식을 통하여 계산되며, 여기서 T_eqd는 등화왕복 지연 값, T_pd는 ONU까지의 전파지연 값을 의미한다.In addition, the pre-allocation delay value T _pre is

Calculated by the equation, where T _eqd is the equalization reciprocation delay value and T _pd is the propagation delay value to ONU.

In addition, the pre-allocation delay value is transmitted to the ONU through an USB bandwidth map (USBWmap).

In addition, the present invention in the process of reducing the time window performed in the OLT is activated through the connection with the ONU knowing the mutual advance distance information, calculating the propagation delay value using the position information of the ONU known in advance; Calculating a round trip propagation delay value by doubling the calculated propagation delay value; And calculating a pre-allocation delay value based on the equalized round trip delay value specified in the specification.

식을 통하여 계산되며, 여기서 D는 ONU와 OLT 사이의 거리, V는 광케이블에서 신호의 전파 속도를 의미한다.Further, the propagation delay value T _pd is

Calculated by the equation, where D is the distance between ONU and OLT, and V is the speed of propagation of the signal in the optical cable.

식을 통하여 계산 되며, 여기서 T_eqd는 등화왕복 지연 값, T_pd는 ONU까지의 전파지연 값을 의미한다.In addition, the pre-allocation delay value T _pre is

Calculated by the equation, where T _eqd is the equalization reciprocation delay value and T _pd is the propagation delay value to ONU.

In addition, the pre-allocation delay value is delivered to the ONU through the pre-allocation delay field of the Upstream_Overhead message defined in the standard.

In addition, determining the window length in consideration of the protected area and the length of the frame transmitted in the ONU receiving the pre-allocation delay value is performed.

As described above, the present invention, when activating the ONU in the ITU-T G.984.3-based G-PON, when the activation process proceeds without knowing the advance distance information between the OLT and ONU, and the dictionary between the OLT and ONU When the activation process is performed while the distance information is known, a method of reducing the length of the time window opened during the activation process is provided.

In order to fully understand the present invention, the advantages of the operability of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In order for the new ONU to run smoothly on the G-PON, it must be activated. This includes a ranging process that allows the ONU to transmit data on the G-PON without collision. To perform this procedure, OLT and ONU exchange PLOAM (Physical Layer Operation, Administration and Maintenance) messages with flag fields of up and down frames. According to the specification, ONU has a total of eight states, and six states related to activation. When using a random delay, the use of the Serial_Number_Mask message is optional, so a schematic procedure of omitting it is shown in FIG.

1 is a diagram illustrating a data flow in an activation process of an ONU according to an embodiment of the present invention.

A state transition of the ONU will be described with reference to FIG. 1.

Initial-state S100 is a process of powering ONU and acquiring synchronization through a downlink frame. When the synchronization is obtained, the LOS / LOF alarm is dismissed and transitioned to (S200). Standby-state (S200) is a state waiting for the Upstream_Overhead message, and immediately after reception receives the switch (S300). The power-setup-state S300 starts by generating a request to adjust the transmission optical output of the ONU at the OLT, and the ONU in this state adjusts the output optical power. The ONU sends a Power-Setup transmission according to the request generated by the OLT based on the output optical power information of the Upstream_Overhead message received three times. At this time, in order to prevent collision of uplink messages sent by ONUs in a similar position, the message is transmitted after a random delay time has elapsed. Serial-Number-state (S400) starts by generating a Serial_Number request in the OLT. On request, the ONU sends a Serial_Number_ONU message with its serial number and a random delay value waited for transmission. Upon receiving this message, the OLT obtains the serial number and random delay value, and assigns the ONU-ID by sending an Assign_ONU-ID message to the ONU that sent the valid serial number. The Ranging-state (S500) sends a Serial_Number_ONU message in response to the ranging request of the OLT. The OLT measures the distance from the difference between the request point and the response point, calculates the equalization delay, and notifies the ONU via a Ranging-Time message. In the operation state (S600), the ONU transitions the above states and is activated. ONUs in this state can transmit data up to the bandwidth allocated by the OLT. Upstream data transmission is prohibited if other ONUs require activation.

According to the above procedure, a time window is opened a total of four times, in which ONUs which are already activated (in S600) are prohibited from transmitting data upwards at that time. In this process, if the length of time window is long, bandwidth consumption is increased and it can be a fatal flaw for ONUs carrying real-time traffic. Accordingly, the present invention proposes an improved activation process in order to provide a smooth service to an already activated ONU. The first algorithm can be activated by opening a very short time window of the second two out of four times when the prior distance between OLT and ONU is unknown. Each time, a short time window is opened to enable ONU.

The first algorithm proposed is to improve the ONU activation process when the OLT does not know the location information of the ONU. The ONU in the serial-number-state specifies a random delay value when transmitting data upward. This value can be used to improve the ONU activation process by reducing the total time window length.

In the OLT receiving a message transmitted from the ONU in the serial-number-state, the random delay value corresponding to each ONU can be distinguished by the serial number in the message. In addition, OLT can measure round trip propagation delay value in serial-number-state. Therefore, the position of the ONU can be estimated based on the information obtained from the ONU in this state. Assuming the uplink and downlink transmission rate is 2.48832 Gbps, the process of determining the pre-allocation delay value by estimating the location of the ONU is as follows. First, the variables used in the present invention are defined as follows.

V is the propagation speed of the signal in the optical cable (about 2c / 3, c is the speed of light), D is the distance between ONU and OLT, T _pd is the propagation delay to ONU, T _rd is the random delay generated by ONU, T _RTD is the round trip propagation delay value measured in the Serial-Number-state, T _eqd is the equalization reciprocal delay value, and Tpre is the pre-allocation delay value.

2 is a diagram illustrating propagation delay measurement in a serial-number-state according to an embodiment of the present invention.

Referring to FIG. 2, the time elapses from when the Serial_Number request is generated in the OLT until the response of the ONU arrives in the OLT. In the serial-number-state, the OLT can obtain a propagation delay and T _pd to a corresponding ONU by using the T _RTD value and the random delay value as shown in Equation 1 below.

Using the propagation delay, T _pd obtained from this equation, the actual distance of the ONU can also be estimated as in Equation 2 below.

In G-PON, T _eqd has a delay value of about 5 frames (a logical distance of 60 km or more). Therefore, in order to have the same T _eqd for all ONUs, T _pre and T _eqd have the following equation (3).

As a result, the pre-allocation delay of Equation 4 below is obtained from Equations 1 and 3 above.

The pre-allocation delay (equalization delay of the predicted ONU) obtained through the above process is transmitted through the USBWmap (Upstream Bandwidth Map) when ranging is requested in Ranging-state. USBWmap is defined in G.984.3 and is a field used to control bandwidth allocation of ONU.

3 is a view showing the structure of a USBWmap according to an embodiment of the present invention.

Referring to FIG. 3, the Sstart portion represents a time at which the ONU starts data transmission, and the Sstop represents an end time. These two parts can be used to control the allocated bandwidth of the ONU. Since the USBWmap always exists in the header portion of the G-PON frame, it does not need to be transmitted separately for the improved activation process disclosed in the present invention.

In the enhanced activation process, the values of Sstart and Sstop become the data transmission start time and the transmission end time considering the equalization delay. Since Sstart and Sstop are each 2 bytes in size, the counter can range from 0 to 65,535. However, the equalization delay range required by G-PON is 0 to 5 in frame unit, 1,555,200 in bit unit and 194,400 even in byte unit. Therefore, the length of a 2-byte field is not enough to indicate the resolution in bytes.

Solving this problem and recognizing the support of the proposed algorithm between OLT and ONU while reconfiguring the above ONU activation process is as follows. The procedure is the same (S100), and when the OLT sends an Upstream_Overhead message downward in S200, it marks whether the algorithm is supported by marking a bit reserved for use in the tenth octet. In S300, when ONU sends a PLOAMu message, ONU_ID = 255 is used in a general case, but ONU_ID = 254 if an improved algorithm is used. In step S400, when the OLT receives the Serial_Number_ONU message, the OLT calculates T _pre based on Equations 1 and 4 with random delays specified in the 11th and 12th octets. At (S500), the OLT converts the calculated value into 4 byte unit resolution instead of 1 byte unit, records it in the Sstart and Sstop fields of FIG. 3, performs a ranging request to the ONU, and immediately starts a timer. do. If the ONU supports the algorithm, the Serial_Number_ONU message will be sent by referring to T _pre of the field. Otherwise, the ONU will be ignored. When a message arrives from the ONU, the OLT stops running the timer, calculates the exact equalization delay from the time spent, and notifies the ONU of the final equalization delay (Equalization Delay, EqD) via the Ranging_Time message.

Above, we have seen an improved ONU activation process that opens up a short time window in Ranging-state if the distance between OLT and ONU is unknown. In this case, if the distance between the OLT and the ONU to be activated is known contrary to the conditions of the above algorithm, look at the activation process of the ONU. If the OLT knows the location information of the ONU to be activated, the OLT can continue to provide services by allocating bandwidth to the ONU which is already activated while proceeding with the activation process for the ONU. This is shown in FIG. 4.

4 is a diagram illustrating a ranging time measurement process when a distance of an ONU is known according to an embodiment of the present invention.

Referring to FIG. 4, in order to proceed with the activation process, the OLT must determine a pre-equalization delay value based on the distance information of the ONU. The methods for determining the pre-equalization delay value are as follows. However, variables used here should be used together with the previously defined variables.

The OLT can obtain propagation delay and T _pd values based on the position information of the ONU known in advance and Equation 2 as shown in Equation 5 below.

The reciprocating propagation delay value is obtained by doubling the propagation delay value obtained through Equation 5 above. Once the round trip propagation delay value is obtained, the pre-allocation delay value can be calculated based on the equalized round trip delay value specified in the specification, which is the same as Equation 4 above.

The pre-allocation delay value obtained according to the above procedure is communicated to the ONU before the ONU activation process begins. The method does not use the USBWmap proposed above, but passes it to the ONU through the pre-allocation delay field of the Upstream_Overhead message defined in the standard.

The pre-allocation delay field consists of 2 bytes, which represents an equalization delay with a resolution of 32 bytes. The Upstream_Overhead message is the first message received from the OLT in the initial phase of ONU's activation, so it can be assigned a pre-allocation delay value before the ONU begins the activation process. As a result, the activation process as shown in FIG. 4 may proceed.

After the predelay allocation value has been determined and notified to the ONU, the OLT shall determine the length of the frame transmitted in the ONU and the window length taking into account the protected area. Since the preallocation delay passed to ONU is in 32 byte units, the window length to be opened must consist of an integer multiple of 32 bytes. In the process of activating the ONU, the window length opened in each state may vary according to the length of the frame transmitted upward. The window lengths opened in each state are as follows.

The ONU must be transitioned to the Power-Setup-state to transmit the first frame upwards. The transmitted frame consists of 120 bytes of PLSu, 13 bytes of PLOAMu, and 12 bytes of PLOu. It has a length of about 152 bytes. The OLT determines the window length by considering this frame length and the length of the guard time. The length of the guard section is determined by the accuracy of the distance information known in advance. Normally, the OLT will determine the time window length by an integer multiple of 32 bytes, taking into account the resolution of the preallocation delay. Therefore, the length of time window opened in Power-Setup-state is 32 (2n + 5). And if ONU is in Serial-Number-state and Ranging-state, ONU transmits frame composed of Serial_Nimber_ONU message and PLOu. The length of the window for transmitting this frame can be calculated as follows. The message contains 13 bytes of pure length and 12 bytes of PLOu in the header, resulting in a frame length of only 25 bytes. And, considering the laser on-off time, it is about 32 bytes. However, no matter how accurate the length of the optical cable between the OLT and the ONU, the error from the actual length cannot be regarded as zero. Therefore, if the OLT allows an error in multiples of bytes to the left and right of the position recognized, the length of the window including the error can be regarded as 32 (2n + 1) (n is an integer).

Hereinafter, the comparison between the ONU activation process defined in ITU-T G.984.3 and the window length created during the ONU activation process using the above-described algorithm is compared.

First, the contents of the standard draft of ITU-T G.984.3 are as follows. The length of one frame of the G-PON is defined as 125 μs, and the length T _f of one frame is 38,880 (19,440) bytes when the uplink frame rate is 2.48832 (1.24416) Gbps. During the activation process, the OLT prohibits data transmission upward to the previously activated ONU, and opens a time window corresponding to a length of about two frames to send a PLOAM message to the newly registered ONU.

As shown in Fig. 1, a total of eight frames will be consumed since at least four windows are opened until one ONU is successfully activated.

If it is assumed that the number of ONUs to be activated is N and there are no conflicts between PLOAM messages sent by all ONUs participating in the activation in the time windows opened at S300 and S400, only two windows 4T _f are opened. If all the ONUs can go to (S500). In S500, since each ONU-ID is assigned, individual equalization delay measurements are performed. Since then, two time windows are opened for each ONU, consuming 4NT _f . Finally, the total lead time based on the standard, T _{G .984,} is _given by the following equation.

On the other hand, when using the first algorithm described above, the length of time window required in (S500) depends on the length of the PLOAM message and how long to allocate the guard interval. As mentioned above, it is assumed to be 32 bytes considering all overheaders (PLOu and laser on-off time) for sending 13 bytes of Serial_Number_ONU messages. The size of the guard interval is, and determines the reliability, whether the propagation delay measured in the above equation (1), the total length of a time window consisting of a message before and after the fold in the 32-byte integers, respectively, and the opening including the information frame is T _w = 32 (2n + 1). Since two reduced time windows are opened for each ONU, N total time required, T _{Algo I} based on the first algorithm, is obtained as shown in Equation 7 below.

Finally, the time window length established in the second algorithm can be opened elastically according to the length of the frame transmitted upward by the ONU in each state of the activation process. In S300, a frame of 152 bytes is transmitted, so a window of 32 (2n + 5) bytes is opened once, and in (S400), a window of 32 bytes is transmitted, so that an opened window is 32 (2n + 1) bytes. Open it once. In addition, the 32 byte frame is also transmitted in (S500), so that the window of 32 (2n + 1) bytes is opened in the same way as in (S400), but in (S500), since the ONU transmits twice upward, the window of the above length is 2 It will be opened. Therefore, the total N times, T _{Algo II} , based on the second algorithm are given by Equation (8).

Hereinafter, using the equations 6 to 8 obtained above, the total required length is converted into byte units according to the window length of the scheme proposed in the standard, the two algorithms proposed in the present invention, and the number of ONUs to be activated in application. Compare. In case of G.984, however, it is assumed that all ONU messages are received without conflict in Power-Setup and Serial-Number states.

5 is a diagram illustrating a time window length when n = 2 according to an embodiment of the present invention.

Referring to FIG. 5, when the error of the position information of the ONU recognized by the OLT (that is, n = 2) is a byte, window sizes for various algorithms may be compared. In this error, when the uplink rate is 2.48832 (1.24416) Gbits / s, the distance corresponds to the error of ± 0.041 (± 0.082) Km of the actual optical cable.

In the above figure, in the case of G.984.3, as N increases, the window length increases almost in proportion. In Algorithm I, however, there is almost no change as N increases, so the proposed method is advantageous as N increases. Algorithm II is basically more advantageous than Algorithm I when N is small, but the difference decreases as N increases. This is because the difference of 4 frames is large when N is small when Equations 7 and 8 are compared.

Next, consider the case where the error of the optical cable occurs extremely.

6 is a diagram illustrating a time window length when n = 256 according to an embodiment of the present invention.

Referring to FIG. 6, when the error of position information of the ONU recognized by the OLT is ± 8192 bytes (that is, n = 256) bytes, the size of the window required in each case may be known. This is a distance corresponding to an error of ± 5.27 (± 10.34) Km of the actual optical cable when the uplink rate is 2.48832 (1.24416) Gbits / s. Given that the service distance of the PON is 20 Km, if the error is ± 10.34 Km, it means that the extreme state without knowing the location information at all.

In Fig. 6, Algorithm I still shows superior performance compared to G.984.3. However, as N increases, the difference in performance still increases, but the gap decreases as compared with FIG. 5. This is because of the large window length due to the uncertainty of the position. Comparing Algorithm I and II, the performance is reversed based on N = 5. Algorithm II uses a small window length based on Algorithm I at (S300) and (S400), but the disadvantage is that N increases as the power setup is done separately.

Overall, it is shown that any algorithm can reduce bandwidth by about 50% to 90% over traditional methods. In particular, the proposed algorithm shows better performance as the number of ONUs increases. And if the distance information is correct in the proposed second algorithm, it shows that ranging can be done with less than 1% of the window length suggested in the standard. Therefore, when there are many ONUs already activated and a few new ONUs are to be registered, the activation process can be performed without affecting ONUs in service.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a view showing a data flow in the activation process of the ONU according to an embodiment of the present invention.

2 is a diagram illustrating propagation delay measurement in a serial-number-state according to an embodiment of the present invention.

3 is a view showing the structure of a USBWmap according to an embodiment of the present invention.

4 is a diagram illustrating a ranging time measurement process when a distance of an ONU is known according to an embodiment of the present invention.

5 is a diagram illustrating a time window length when n = 2 according to an embodiment of the present invention.

6 is a diagram illustrating a time window length when n = 256 according to an embodiment of the present invention.

Claims (10)

In the process of reducing the time window performed in the OLT activated through connection with ONU that does not know mutual advance distance information, Receiving a message transmitted from an ONU in a Serial-Number-state, and distinguishing a random delay value corresponding to each ONU by a serial number in the message; Measuring a round trip propagation delay value with the ONU in a Serial-Number-state; Estimating the position of the ONU based on the random delay value and the round trip propagation delay value; And Improved ONU activation method for G.984.3 based G-PON comprising assigning a pre-allocation delay value such that all ONUs have the same equalization reciprocal delay value. The method of claim 1, The propagation delay value T _pd is

Calculated by the equation, where T _RTD is the round trip propagation delay value measured in the Serial-Number-state and T _rd is the random delay value generated in the ONU. Way. The method of claim 1, The position estimate of the ONU is

Calculated from the equation, where D is the distance between ONU and OLT, T _pd is the propagation delay value to ONU, and V is the improved ONU for G-PON based on G.984.3, which is the propagation speed of the signal on the optical cable. Activation method. The method of claim 1, The pre-allocation delay value T _pre is

Calculated by Equation, where Teqd is equalization reciprocal delay value and T _pd is propagation delay value to ONU. The method of claim 1, The pre-assignment delay value is transmitted to the ONU via an upstream bandwidth map (USBWmap). In the process of reducing the time window performed in the OLT activated through the connection with the ONU knowing the mutual prior distance information, Calculating a propagation delay value using position information of the ONU known in advance; Calculating a round trip propagation delay value by doubling the calculated propagation delay value; And An improved method of enabling ONU for G-PON based on G.984.3 comprising calculating a pre-allocation delay value based on an equalized round trip delay value specified in the specification. The method of claim 6, The propagation delay value T _pd is

Calculated from the equation, where D is the distance between ONU and OLT, and V is the G.984.3-based G-PON's improved method for activating G-PON. The method of claim 6, The pre-allocation delay value T _pre is

Calculated by the equation, where T _eqd is the equalization reciprocal delay value and T _pd is the propagation delay value to ONU. The method of claim 6, An improved method for enabling ONUs for G-PON based on G.984.3, where the preallocation delay value is passed to the ONU through the preallocation delay field of the Upstream_Overhead message defined in the standard. The method of claim 6, Determining a window length in consideration of a length of a frame and a protection zone transmitted in an ONU having received the pre-allocation delay value, and the method of activating the ONU for the G-PON based on G.984.3.

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