KR101046110B1 - Method and apparatus for determining cycle time of passive optical network - Google Patents

Abstract

The present invention discloses a method and apparatus for determining a cycle time of a passive optical communication network. A cycle time determination method of a passive optical communication network according to the present invention comprises the steps of determining the propagation delay (T _pd ) and equalization round trip delay according to the distance information between the OLT and ONT; Determining a cycle time using the determined propagation delay and equalization round trip delay. According to the present invention, there is an effect of satisfying the limit range of the real-time traffic delay and the requirements of the real-time traffic and at the same time minimizing the performance degradation of the system due to the overhead overhead.

TDM-PON, G-PON, E-PON, OLT, ONT, Cycle Time, Equal Round Trip Delay, Propagation Delay

Description

Cycle time determining method and apparatus based on passive optical network

The present invention relates to a method and apparatus for determining a cycle time of a passive optical communication network, and more particularly, to a method for determining a cycle time of a TDM-PON such as a G-PON. The present invention relates to a method and apparatus for determining a cycle time for maximizing the transmission performance between an optical fiber terminal device (OLT) on the side of the office and the optical fiber subscriber device (ONT) on the subscriber side.

With the rapid increase in Internet traffic and the convergence of broadcasting and telecommunication services, the speed of communication networks is increasing rapidly. Among these technologies, Passive Optical Network (PON) technology provides high bandwidth to subscribers. In addition, since the OSP (OutSide Plant) is composed of only passive components, the introduction is spreading because it can significantly reduce the operating cost of the network.

1 is a block diagram of an embodiment of a TDM-PON according to the prior art. The TDM-PON shown in FIG. 1 includes a TDM-PON OLT 10, a light distribution / combiner 20, and a TDM-PON ONT ₁ to ONT _N. As shown in FIG. 1, the TDM-PON according to the prior art has an optical fiber terminal device (TDM-PON OLT) 10 on the side of the national company, and a optical fiber subscriber device (TDM-PON ONT, 20) on each subscriber side. Between the TDM-PON OLT 10 and the TDM-PON ONT 30 an optical splitter / combiner 20, for example a splitter, for optical signal distribution (optical signal power branching, optical signal power coupling). Include.

TDM-PON has a structure in which the TDM-PON ONT 20 of each subscriber side shares the optical fiber with the TDM-PON OLT 10 of the national company side by using a time division scheme, and B-standardized in ITU-T. PON, G-PON, and IEEE standardized E-PON are currently in use.

For example, a description will be given of a signal transmission method in the TDM-PON. First, in view of a downlink signal, the TDM-PON OLT 10 broadcasts traffic transmitted to each TDM-PON ONT 20. )do. A light splitter / combiner distributes or combines light, and an example of a light splitter / combiner is preferably a 1xN splitter that simply diverts optical power to a remote location. The splitter distributes the downlink signals received from the TDM-PON OLT 10 to N subscriber lines, and selectively receives only the frames allocated to itself by receiving the downlink signals sent to it from the TDM-PON ONT 20. It will be delivered to the subscriber.

In terms of an uplink signal, each TDM-PON ONT 20 assigns its own dedicated time slot to TDM-PON OLT through ranging and dynamic bandwidth allocation (DBA) processes. In the state previously allocated from (10), the uplink signal is transmitted only when the time slot assigned to the terminal arrives, and the uplink signal transmission is stopped when the slot is not its own slot. Each uplink signal from the TDM-PON ONT 20 is combined at a remote splitter and transmitted to the TDM-PON OLT 10.

In view of the above-described problems of the prior art, the present invention determines the cycle time according to the distance between the OLT and ONT of the passive optical network, that is, the transmission distance, thereby ensuring the requirements of the real time traffic while satisfying the limit range of the real time traffic delay. It is an object of the present invention to provide an apparatus and method for determining a cycle time that can minimize performance degradation of a system due to upward overhead.

In order to achieve the above object of the present invention, the method for determining a cycle time of a passive optical communication network according to the present invention receives distance information between an OLT and an ONT, and propagates a delay (T) between the OLT and the ONT according to the input distance information. _pd ) and determining an equalization round trip delay T _{eqd that} is a difference between a time at which the OLT transmits an acknowledgment message to the ONT and a time at which the OLT receives data transmitted by the ONT receiving the acknowledgment message. ; And determining a cycle time using the determined propagation delay and equalization round trip delay.

In order to achieve the above object of the present invention, the apparatus for determining a cycle time of a passive optical communication network according to the present invention determines a propagation delay T _pd that determines a propagation delay T _pd between the OLT and the ONT according to the distance information between the OLT and the ONT. part; An equalization round trip delay determination unit for determining an equalization round trip delay T _{eqd which} is a difference between a time when the OLT transmits an acknowledgment message to the ONT and a time when the OLT receives data transmitted by the ONT receiving the acknowledgment message. ; And a cycle time determiner configured to determine a cycle time using the determined propagation delay and the equalized round trip delay.

The present invention also provides a computer-readable recording medium having recorded thereon a program for performing the above-described method for determining a cycle time of a passive optical communication network on a computer.

According to the present invention, by determining the cycle time according to the distance between the OLT and the ONT of the passive optical network, that is, the transmission distance, while satisfying the limit range of the real-time traffic delay while ensuring the requirements of the real-time traffic, This has the effect of minimizing performance degradation.

Hereinafter, a method and apparatus for determining a cycle time of a passive optical communication network according to the present invention and a recording medium on which a program for executing the method on a computer according to the present invention will be described in detail. In the following description and the accompanying drawings, substantially identical components are denoted by the same reference numerals, and thus redundant description will be omitted. In addition, in the following description of the present invention, if it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In TDM-PON, a typical passive optical network, the cycle time is the period during which all currently active ONTs are authorized to send data up once, or the period during which all ONTs inform OLT of their queue length information once and request the transmission of upstream data. Means. However, the cycle time can be defined differently according to the network system, and it is important to determine the optimal cycle time in consideration of various parameters because the performance of the system can be largely determined by how the cycle time is defined and used.

In general, cycle time is related to overhead and traffic latency. If the cycle time is shortened, there is an advantage that the delay is shortened for real-time traffic. However, since all ONTs send data upward in a short time, the overhead overhead is increased. On the other hand, if the cycle time is longer, the overhead overhead is reduced, but the delay for the real-time traffic is long. Therefore, it is desirable to keep the length of the cycle time as long as possible to ensure the delay requirement of the real-time traffic while reducing the overhead.

In the cycle time determining method of the present invention, the OLT transmits a propagation delay T _pd between the OLT and the ONT, the time at which the OLT transmits an acknowledgment message to the ONT, and the data transmitted by the ONT receiving the acknowledgment message. An equalization round trip delay T _eqd , which is a difference in the received time, is used.

2 shows a downward frame structure of a G-PON. The downlink frame shown in FIG. 2 includes a PDBd and a payload field. As shown in FIG. 2, the PCBd field includes a PSync, Ident, PLOAM, BIP, and PLend field, and the payload field includes an ATM cells section, a TDM & DATA fragments Over GEM section field. The US BW map (Upstream Bandwidth map) field in the downstream header can give all ONTs the opportunity to access upwards. In this case, one cycle time corresponds to the length of one frame time and the implementation can be simplified. However, according to Equation 1 below, the overhead reaches about 24% when N = 128.

[Equation 1]

Where N is the number of ONUs currently operating, R [Gbit / s] is the uplink rate, cycle time is C [s], G _B is the guard bit, and P _B is the preamble length ). If the cycle time is set to a simple frame length, there is a problem that the overhead becomes large. It is also the case of using an extension predecessor that causes a bigger problem. The use of extended predecessors occurs when the OLT instructs ONU to use a very long predecessor through a PLOAM message called Extended_Burst_Length when uplink synchronization is not possible. At this time, the overhead can be calculated by the following equation (2).

&Quot; (2) "

According to Equation 2, the ratio of overhead reaches (150 × 128) / 19,440 '' 99%. Even in this extreme situation, if the cycle time is two or three times longer than one frame time, the overhead is reduced to 1/2 or 1/3. Therefore, it is important to increase the cycle time as much as possible while satisfying the delay of the real-time traffic.

3 is a block diagram illustrating an apparatus for determining a cycle time of a passive optical communication network according to an embodiment of the present invention. The cycle time determining apparatus 100 illustrated in FIG. 3 includes a distance information input unit 110, a distance section determination unit 120, a propagation delay determination unit 130, an equalization round trip delay determination unit 140, and a cycle time determination unit ( 150). The cycle time determining apparatus of this embodiment may be mounted inside the OLT or as a separate external device, and is characterized by determining the cycle time according to the transmission distance.

The distance information input unit 110 receives distance information between the OLT and the ONT.

The distance section determiner 120 determines a distance section to which the distance between the OLT and ONT belongs among predetermined distance sections using the distance information between the OLT and the ONT.

The propagation delay determiner 130 determines a propagation delay T _pd between the OLT and the ONT according to the determined distance section. Propagation delay here means a delay time for transmitting the information transmitted from the OLT to the ONT.

Equalization round trip delay determination unit 140 equalization round trip delay (T _{eqd) that} is the difference between the time when the OLT transmits the approval message to the ONT and the time when the OLT receives the data transmitted by the ONT receiving the approval message. Is determined. Here, the equalization round trip delay refers to the time it takes for the data sent by the ONT receiving the grant to arrive at the OLT immediately after the OLT sends a grant (see FIG. 4).

The cycle time determiner 150 determines the cycle time using the determined propagation delay and the equalized round trip delay. In particular, the cycle time determiner 150 further determines the cycle time in consideration of the limit delay time T _max , which is a time that can be delayed after the data to be transmitted is received in the ONT, until the data is received in the OLT. It is desirable to decide.

4 is a reference diagram for describing a cycle time according to an embodiment of the present invention. 4 illustrates a report, grant, and data transmission procedure between the OLT and the ONT. Where C is the cycle time and T _f Is one frame time (125 ms), T _eqd is an equalized round trip delay, T _d is an equalization delay, and T _pd is a propagation delay.

Here, the equalization round trip delay is the time from immediately after the OLT sends a grant message until the data sent by the ONT receiving the grant message arrives at the OLT. Equalization round trip delay includes propagation delay due to downlink transmission, approval processing time of ONT, equalization delay, and propagation delay due to uplink transmission. In FIG. 4, the processing time of the ONT is omitted, and the equalization round trip delay is preferably kept constant for all ONTs even when the distance between the OLT and the ONT is different. In order to keep the equalization round trip delay constant, it is necessary to adjust the equalization delay of the distant ONT and to make the equalization delay of the distant ONT large through a ranging procedure. Typically, the equalization round trip delay is 250 ms if the maximum distance between OLT and ONT is within 0 to 20 Km (100 ms propagation delay) and 650 if it is within 40 to 60 Km (300 ms propagation delay) according to international standards. ms is preferred.

4 illustrates an example of determining a cycle time in consideration of a worst case delay situation according to an embodiment of the present invention. The greatest time delay when real-time data arrives at a certain ONU, for example, when ONT sends a report message to the OLT side immediately before data from the subscriber arrives at the ONT. to be. In this case, in order to transmit the report message related to the arrived data, a time corresponding to one cycle time is required.

If ONT sends the queue's information as a report message at the next cycle time, the transmitted report message arrives at the OLT after experiencing a propagation delay (T _pd ). Considering the case where the time delay is maximum, report messages arriving at the OLT require another cycle time before the ONT can be scheduled. This is because OLT requires processing time for scheduling together with report messages from other ONTs.

After the scheduling is completed, the OLT transmits an acknowledgment message to the corresponding ONT through a US BW map (Upstream Bandwidth map) in a downlink frame as shown in FIG. 2. The acknowledgment message sent to ONT arrives until ONT and the equalization round trip delay time elapses. If the OLT has scheduled the ONT to send the last data in providing the grant, another cycle time is required. That is, after all, the worst case delay may be expressed by Equation 3 below.

&Quot; (3) "

Here, T _max is the limit delay time that can be delayed until data is received from the ONT to the OLT. According to Equation 3, the cycle time C = ( T _max - T _pd - T _eqd ) / 3 can be expressed. For example, real-time data, such as voice, requires a separate echo canceller if the round trip delay exceeds 20 ms on one node. However, to avoid installing an echo canceller, it is desirable to limit the delay time to 2 ms or less on one node. . Therefore, the limit delay time is T _max It is desirable to limit ≤ 2 ms (16T _f ). In this case, the cycle time C is limited to the range of the following equation (4).

&Quot; (4) "

In addition, the cycle time is T _f It cannot be smaller than Because, when referring to the structure of the downlink frame shown in Figure 2, the approval is made through the US BW map and the cycle time means a period that can provide the grant to all ONT at least once, which can be implemented in less than one frame Because it is not.

Propagation delay and equalization round trip delay depend on the distance between ONT and OLT. When ONT is 0 to 20 Km away from OLT, propagation delay is up to 100ms (0.8T _f ) and equalization round trip delay is up to 250ms (2T) _f ) is preferred. In consideration of this, Equation 4 may be expressed by Equation 5 below.

[Equation 5]

When the ONT is 20 to 40 Km away from the OLT, propagation delays of up to 200 ms (1.6T _f ) and equalization round trip delays of up to 450 ms (3.6T _f ) are preferred. That is, the cycle time of the ONT belonging to the distance section 20 ~ 40km is preferably determined within the range of the following equation (6).

[Equation 6]

T _f ≤ C ≤ 3.6T _f

ONT is in the range of 40 ~ 60 Km from the OLT, the propagation delay is up to 300ms (2.4T _f), equalized round trip delay is preferably between 650ms (5.2T _f). That is, the cycle time of ONT belonging to a distance section of 40 ~ 60km is preferably determined within the range of equation (7).

[Equation 7]

That is, when the distance between the OLT and the ONT is far, the overhead is increased to maintain the delay of the real-time traffic within a range below the limit value, and the length of the cycle time is shortened when the distance is short. It is preferable.

As represented by Equations 5 to 7, the cycle time in the distance section 0 ~ 20km is C = 4.4 T _f , the cycle time in the 20 ~ 40km distance section is C = 3.6T _f , 40 ~ 60km in the distance section The cycle time is preferably set to C = 2.8 T _f .

5 is a flowchart illustrating a cycle time determination method of a passive optical communication network according to an embodiment of the present invention. FIG. 5 includes the following steps performed in time series in the cycle time determining apparatus 100, and descriptions of the common items described above will be omitted.

In step 210, the distance information input unit 110 receives distance information between the OLT and the ONT.

In step 220, the distance section determiner 120 determines the distance section to which the distance between the OLT and the ONT belongs using the received distance information. For example, the observed distance may be divided into a 0 to 20 km distance section, a 20 to 40 km distance section, and a 40 to 60 km distance section, and the section information to which the observed distance belongs may be input as the distance information. This embodiment is an example in which the distance section determination unit is adopted as a separate component. However, when the distance information is input in the form of predetermined distance section information in step 210, the cycle time may be determined without using the distance distance section determination unit.

In operation 230, the propagation delay determiner 130 determines a propagation delay T _pd according to the distance section determined in operation 220.

In step 240, the equalization round trip delay determination unit 140 determines the equalization round trip delay T _eqd according to the distance section determined in step 220. In this case, the equalization round trip delay means a difference between a time when the OLT transmits an acknowledgment message to the ONT and a time when the OLT receives data transmitted by the ONT receiving the acknowledgment message.

In step 250, the cycle time determiner 150 determines the cycle time using the propagation delay and the equalized round trip delay determined in steps 230 and 240. In particular, the cycle time determiner may determine the cycle time in Equations 3 to 7.

As described above, the present invention is a passive optical communication network, in particular, TDM-PON-based optical network systems such as B-PON, E-PON, G-PON, etc. OLT and ONT even in the situation that the transmission distance between the OT is extended more than 20Km many connected to the OLT It is effective in minimizing the performance degradation of the system due to upward overhead while ensuring the ONT requirements of real time traffic.

On the other hand, the cycle time determination method in the passive optical communication network of the present invention can be implemented in a computer-readable code on a computer-readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored.

Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like, which may also be implemented in the form of carrier waves (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, codes, and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

The present invention has been described above with reference to preferred embodiments. Those skilled in the art will understand that the present invention can be embodied in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown not in the above description but in the claims, and all differences within the scope should be construed as being included in the present invention.

The present invention provides a method and apparatus for determining a cycle time of a passive optical network to minimize performance degradation of the system due to upward overhead in an optical network system such as B-PON, E-PON, and G-PON based on TDM-PON. Suitable for

1 is a block diagram of an embodiment of a TDM-PON according to the prior art.

2 shows a downward frame structure of a G-PON.

3 is a block diagram illustrating an apparatus for determining a cycle time of a passive optical communication network according to an embodiment of the present invention.

4 is a reference diagram illustrating a cycle time concept according to an embodiment of the present invention.

5 is a flowchart illustrating a cycle time determination method of a passive optical communication network according to an embodiment of the present invention.

Claims (10)

In the cycle time determination method of a passive optical communication network, a) receiving distance information between the OLT and the ONT, and propagating delay T _pd between the OLT and the ONT according to the input distance information, the time at which the OLT transmits an acknowledgment message to the ONT, and the acknowledgment message. Determining an equalization round trip delay (T _eqd ), which is a difference between a time at which the OLT receives data transmitted by the received ONT; And b) determining a cycle time using the determined propagation delay and equalization round trip delay. The method of claim 1, In the step b), after the data to be transmitted is received in the ONT, the cycle time is further determined in consideration of the limit delay time (T _max ), which is a _delayable time until the data is received in the OLT. Cycle time determination method of a passive optical network. The method of claim 1, wherein step a) Determining a distance section to which the distance between the OLT and the ONT belongs among predetermined distance sections using the distance information between the OLT and the ONT; The propagation delay and the equalized round trip delay is determined in accordance with the distance interval cycle time determination method of a passive optical network. 3. The method of claim 2, The cycle time (C) is a cycle time determination method of a passive optical network, characterized in that represented by the following equation. [Equation] C = (T _max -T _pd -T _eqd ) / 3 Where T _max is the limit delay time and T _eqd Is the equalization round trip delay, and T _pd is the propagation delay. 3. The method of claim 2, The cycle time (C) is a cycle time determination method of a passive optical network, characterized in that represented by the following equation. [Equation] T _f ≤ C ≤ (16T _f -T _pd -T _eqd ) / 3 Where T _f is the length of the frame, T _max is the limit delay time, and T _eqd Is the equalization round trip delay and T _pd is the propagation delay. 3. The method of claim 2, If the data to be transmitted includes voice data, And the threshold delay time is determined depending on whether or not the echo component is required according to the delay of the voice data. A computer-readable recording medium having recorded thereon a program for performing the cycle time determining method according to any one of claims 1 to 6 on a computer. A propagation delay determining unit configured to determine a propagation delay T _pd between the OLT and the ONT according to distance information between an OLT and an ONT; An equalization round trip delay determination unit for determining an equalization round trip delay T _{eqd that} is a difference between a time at which the OLT transmits an acknowledgment message to the ONT and a time at which the OLT receives data transmitted from the ONT receiving the acknowledgment message. ; And And a cycle time determiner configured to determine a cycle time by using the determined propagation delay and the equalized round trip delay. The method of claim 8, The cycle time determiner determines the cycle time by further considering a limit delay time T _max , which is a delay time after the data to be transmitted is received at the ONT, until the data is received at the OLT. Cycle time determination device of a passive optical network. The method of claim 8, And the distance information between the OLT and ONT is information on a distance section to which the distance between the OLT and ONT belongs among predetermined distance sections.

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