KR101051205B1 - Apparatus and method for determining cycle time for transmitting data in optical subscriber network - Google Patents

Abstract

The present invention relates to a cycle time determining apparatus and method for determining a cycle time for data transmission in consideration of the transmission efficiency of the link and delay for real-time traffic in a composite passive optical subscriber network. The present invention provides a grouping unit for grouping at least two subscriber-side terminal devices in consideration of distance information between a station-side device connected to an optical subscriber network service provider and a subscriber-side terminal device connected to an optical subscriber network service user; A ranging processor configured to perform ranging on all the subscriber-side terminal devices belonging to the generated subscriber-side terminal device group when the subscriber-side terminal device group including the at least one subscriber-side terminal device is generated from the grouping; And a cycle time determination unit for determining a cycle time for data transmission for each generated subscriber-side terminal device group. According to the present invention, the delay of the data packet can be shortened and the data transmission performance of the optical subscriber network system can be improved.

hybrid PON, cycle time, WDM-TDM, grouping, ranging, equalization round-trip delay, packet delay

Description

Apparatus and method for determining cycle time for data transmission in optical network}

The present invention relates to an apparatus and method for determining a cycle time for transmitting data in an optical subscriber network. More specifically, the present invention relates to a cycle time determining apparatus and method for determining a cycle time in consideration of a transmission efficiency of a link and a delay for real-time traffic in a hybrid PON.

Today, with the accelerated deployment of high-definition IPTV and the emergence of three-dimensional TVs, operators of passive optical networks (PONs) operate with broadband bandwidths of up to gigahertz (GHz) and long-distance transmissions of more than 100 km. There is a need for optimization.

Therefore, studies have been made to overcome the branch rate limitation problem and the transmission distance limitation problem of the conventional time division multiplexing (TDM) -PON. Recently, research on Wavelength Division Multiplexing (WDM) -TDM PON incorporating time division multiplexing for one wavelength is in progress. WDM-TDM PON can increase the number of branches per optical cable from the previous 64 minutes to more than 256 quarters, and the transmission distance can be increased from the existing 20 km to more than 100 km. In addition, it is possible to configure a wide area network to reduce the number of telephone companies. Thus, the study of hybrid passive PON such as WDM-TDM PON is expected to accelerate further in the future.

In addition to the fundamental problems to be solved at the physical layer, such as optical power, optical transceiver, optical amplifier, and FEC, to construct a wide area subscriber network, a plan for efficiently designing a media access control (MAC) at a transmission convergence (TC) layer is also included. Should be considered. The reason is that the transmission efficiency of the link is compatible with the delay for the real-time traffic.

In the conventional passive optical subscriber network, ranging of all ONUs was performed by determining the cycle time from the ONU located at the longest distance from the optical line terminal (OLT) for the entire optical network unit (ONU) constituting the network. . Thus, ONUs located close to the OLT have a long delay. One way to solve this problem is to reduce the cycle time. However, this method is another problem in that the ONUs frequently transmit data with fixed physical layer overhead in a short period upwards, so that the occupancy ratio of the overhead for the entire period is increased, thereby degrading the link transmission efficiency. Generates.

The present invention has been made to solve the above problems, by grouping the ONUs located at a similar distance from the OLT and determine the cycle time to obtain the maximum link efficiency while satisfying the maximum allowable delay for each group It is an object of the present invention to provide an apparatus and method for determining a cycle time for data transmission in an optical subscriber network which shortens the delay of a data packet.

The present invention has been made in order to achieve the above object, at least two of the subscriber side in consideration of the distance information between the subscriber station terminal connected to the subscriber station device connected to the optical subscriber network service provider; A grouping unit for grouping the terminal device; A ranging processor configured to perform ranging on all the subscriber-side terminal devices belonging to the generated subscriber-side terminal device group when the subscriber-side terminal device group including the at least one subscriber-side terminal device is generated from the grouping; ; And a cycle time determination unit for determining a cycle time for data transmission for each of the generated subscriber-side terminal device groups.

Preferably, the grouping unit is a time required to receive a response message for the approval message from the subscriber station terminal device after transmitting the approval message for approving the network connection to the subscriber station terminal device to the subscriber station terminal device; Grouping the subscriber station terminal by dividing the distance information including a multiple of the cycle time.

Preferably, the cycle time determiner determines the cycle time to be equal to the equalization round trip delay of the generated subscriber-side terminal group. More preferably, the cycle time determining unit takes into account the maximum propagation delay between the subscriber station terminal device and the subscriber station terminal device and the maximum packet delay of the subscriber station terminal device located at the longest distance from the subscriber station device. Determine.

Preferably, the grouping unit, if it finds a subscriber-side terminal device that does not belong to the subscriber-side terminal device group, a round trip delay calculation unit for calculating a round trip delay of the found subscriber-side terminal device; A round trip delay size comparison unit for comparing the calculated round trip delay with a maximum round trip delay value of the subscriber station terminal group; And generate the subscriber-side terminal group including the found subscriber-side terminal if the calculated round-trip delay is greater than the round-trip delay maximum, and if the calculated round-trip delay is less than or equal to the round-trip delay maximum. And a subscriber station terminal unit processing unit which associates the subscriber station terminal unit with the subscriber station terminal group having the maximum round trip delay value.

Preferably, the cycle time determining unit allocates at least two bands during the cycle time to at least one subscriber station terminal located further than a predetermined criterion in the subscriber station terminal group when determining the cycle time.

Preferably, the cycle time determination device further comprises a distance measuring unit for measuring the distance between the station-side device and the subscriber-side terminal device included in the distance information.

Preferably, the cycle time determination device is provided on an optical path connecting the station-side device and the subscriber-side terminal device in a passive optical network combining different division multiplexing schemes.

In addition, the present invention (a) grouping at least two of the subscriber-side terminal device in consideration of the distance information between the station-side device connected to the optical subscriber network service provider and the subscriber-side terminal device connected to the optical subscriber network service user; ; (b) when a group of subscriber station terminals including at least one of the subscriber station terminals is generated from the grouping, ranging of all the subscriber station terminals belonging to the generated subscriber station terminal groups; step; And (c) determining a cycle time for data transmission for each of the generated subscriber-side terminal groups.

Preferably, the step (a) may be performed until the office-side device transmits an acknowledgment message for approving network access to the subscriber-side terminal device until it receives a response message for the approval message from the subscriber-side terminal device. The subscriber station terminal is grouped by dividing the distance information including the time required by a unit of a multiple of the cycle time.

Preferably, the step (c) determines the cycle time with the same size as the equalized round trip delay of the generated subscriber-side terminal group. More preferably, the step (c) may include the cycle in consideration of the maximum propagation delay between the subscriber station terminal device and the subscriber station terminal device and the maximum packet delay of the subscriber station terminal device located at the furthest distance from the subscriber station device. Determine the time.

Preferably, the intermediate steps of steps (a) and (b) may include (aa) a round trip delay of the found subscriber station terminal device if it finds a subscriber station device which does not belong to the subscriber station terminal device group. Calculating; (ab) comparing the calculated round trip delay with a maximum round trip delay value of the subscriber station terminal group; And (ac) if the calculated round trip delay is greater than the round trip delay maximum value, create a subscriber side terminal device group including the found subscriber side terminal device, and the calculated round trip delay is less than the round trip delay maximum value. If the same, joining the found subscriber station to a group of subscriber station terminals with the round trip delay maximum.

Advantageously, step (c) allocates at least two bands during said cycle time to at least one subscriber-side terminal device located further than a predetermined criterion in said subscriber-side terminal device group when determining said cycle time. .

The present invention can achieve the following effects by grouping ONUs located at a similar distance from the OLT and determining the cycle time for each group. First, it is possible to shorten the delay of the data packet, and at the same time to ensure the requirements of the real-time traffic while satisfying the maximum allowable delay required by the service. In addition, it is possible to obtain maximum link efficiency and to prevent performance degradation of the optical subscriber network system due to upward overhead. Second, it is possible to smoothly implement wireless telephony services such as real-time two-way TV service sensitive to packet delay, such as IPTV or 3D TV, and Voice over Internet Protocol (VoIP). Third, when the transmission distance is longer than 100km, the data transmission performance between the telephone company side and the subscriber side can be further improved than before, and more efficient ranging can be realized in the composite passive optical subscriber network system.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even if displayed on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

1 is a block diagram schematically illustrating an apparatus for determining a cycle time for data transmission in an optical subscriber network system. According to FIG. 1, the cycle time determining apparatus 100 includes a distance measuring unit 110, a grouping unit 120, a ranging processor 130, and a cycle time determining unit 140.

Prior to describing the present embodiment with reference to FIG. 1, first, parameters to be applied to the present embodiment are defined.

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

In general, cycle time is related to overhead and traffic latency. If the cycle time is shortened, the delay is shortened for real-time traffic. However, since all ONUs send data upward in a short time, the overhead overhead is increased. On the other hand, if the cycle time is increased, 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 following, some parameters are defined for better understanding of the present embodiment.

C: cycle time

In the TDMA PON, the cycle time means a period in which a requestor of a band is allowed to send data (band request signal or user data) up once to the corresponding OLT. Here, the subjects requesting the band may be referred to as respective ONUs in the case of the E-PON, and correspond to individual Alloc-IDs (Allocation Identification) in the case of the G-PON. The reason for this is that in case of E-PON, request information for all traffic queues is contained in one band request signal (Report PDU) at once. In case of G-PON, multiple Alloc-IDs are defined for each ONU for each traffic. This is because they can request bands in separate burst units. In any case, this cycle time can be implemented as a variable or constant value, and the latter is usually preferred due to the simplicity of implementation.

D _L : logical reach

T _rt : maximum round trip time (RTT)

T _pd : maximum propagation delay

TDM-PON uses a technique that allows logically different distances to appear to be logically at the same distance so that they do not collide when sending data upwards. The position arranged in this way is called logical distance D _L. This value is equal to or greater than the distance of the ONU farthest from the OLT. Therefore, in this embodiment, the time taken for the optical signal to shuttle this logical distance through the optical cable will be referred to as the maximum round trip delay T _rt . This corresponds to twice the maximum propagation delay T _pd . That is, T _rt = 2T _pd .

T _d ⁱ : equalized delay for the i th ONU

T _eqd : equalized round trip delay

When receiving data grants from OLT to prevent data collisions, the near ONU will wait longer before sending data, while the longer ONU will wait before sending data. Shorten. The wait value just before transmission of these ONUs is called equalization delay. The equalization delay is a value assigned to each ONU after the OLT is measured by a procedure called ranging when registering ONUs.

After all, even for ONUs at different distances, the time it takes for data to arrive upwards immediately after OLT grants is the same for all ONUs. This is called equalization round trip delay. This value should have a value greater than the time it takes to round the logical distance, i.e. the maximum round trip delay. Before ranging, the equalization round trip delay value is determined in advance according to the maximum distribution distance of the ONU or the specification of the PON. When performing ranging, the OLT measures the round trip delay of each ONU and subtracts the individual round trip delay value from the equalization round trip delay value to obtain the equalization delay.

Hereinafter, the present embodiment will be described in earnest with reference to FIG. 1.

In this embodiment, the cycle time determination apparatus 100 groups subscriber side optical network units (ONUs) located at a similar distance from the telephone line optical line terminal (OLT) and satisfies the maximum allowable delay for each group. The cycle time for obtaining the maximum link efficiency can be determined to shorten the delay of the data packet than before.

In general, as the transmission distance is extended, the cycle time length must be shortened to guarantee the delay for the real-time traffic. In this case, the reduced cycle time reduces the transmission efficiency of the link. Therefore, in order to construct a wide area network, it is very important to determine the optimal cycle time for obtaining the maximum link efficiency within the limit of guaranteeing the delay of traffic. The cycle time determination apparatus 100 according to the present embodiment groups the ONUs located at a similar distance from the OLT and determines the cycle time for obtaining the maximum link efficiency while satisfying the maximum allowable delay for each group. Applicable to subscriber networks.

In this embodiment, the cycle time determination apparatus 100 is applied to a hybrid passive PON system. The hybrid passive optical subscriber network system is a passive optical subscriber network system that combines a plurality of different multiplexing schemes. For example, a WDM-TDM PON that combines a time division multiplexing scheme for one wavelength is an example. At this time, applicable TDM PON includes E-PON (Ethernet PON) or G-PON (Gigabit Ethernet PON).

The distance measuring unit 110 measures a distance to the OLT for each ONU provided in the passive optical subscriber network system. Since the OLT performs such a distance measuring function, the distance measuring unit 110 may not be provided in the cycle time determining device 100. When the distance measuring unit 110 is not provided, the grouping unit 120 receives the distance measurement value from the OLT.

The grouping unit 120 performs a function of grouping ONUs provided in the passive optical subscriber network system. The grouping unit 120 considers the distance information from the OLT for each ONU when grouping the ONUs. The distance information from the OLT of each ONU includes the time it takes from the ONU to send a response message after the OLT has sent a message that it has granted network access to the ONU. The grouping unit 120 receives the distance information to group the ONUs. Preferably, the grouping unit 120 divides the distance information into cycle time units applied to the system to group ONUs.

In general, in order to reduce packet delay, the TDM-PON has to reduce the cycle time, and even the smallest packet delay is three times the maximum propagation delay. Moreover, when the length of the cycle time is shortened, the proportion of overhead occupies becomes large, resulting in a problem that the efficiency of the link is lowered. In this embodiment, ONUs are grouped to solve this problem. Thus, if the ranging is performed for each ONU group after grouping the ONUs, the equalization delay of the ONUs and the equalization round-trip delay of the ONU groups can be further reduced. If both equalization delay and equalization round trip delay are further reduced than before, not only can the packet delay be reduced, but the efficiency of the link can be increased.

The reason why the packet delay is reduced will be described below. 2 is a reference diagram for describing various methods of calculating an equalization delay, and is provided to help an understanding that the equalization delay is reduced according to the present embodiment.

The method of calculating the equalization delay is a first method of determining the equalization round trip delay based on the maximum communicable distance provided by the optical subscriber network system, and the ONU located the furthest distance from the OLT among the ONUs existing in the optical subscriber network system. A second method for determining an equalization round trip delay based on the reference, and a third method for determining an equalization round trip delay based on the selected ONU.

Among the first to third methods, the least desirable method in consideration of the packet delay aspect is the first method in which the maximum communication distance provided by the optical subscriber network system is a logical distance. According to the first method, the equalization delay of the i th ONU is larger than that of the second and third methods with T _d ⁱ = T _DL , and the equalization round trip delay is also maximized. Since the second method makes a logical distance from the currently active ONUs to the ONU (Nth ONU in FIG. 4) located farthest from the OLT, the equalization delay of the i-th ONU (T _d ⁱ = T _DN). ) Is greater than that of the first method. In either the first or second method, the equalization round-trip delay is constant, so if the OLT provides an acknowledgment, the timing of the upstream traffic arrival is constant for all ONUs.

On the other hand, since the third method determines the equalization round trip delay on the basis of self (selected ONU), the equalization delay of the i th ONU becomes T _d ⁱ = 0 (i = 1, 2,..., N). Therefore, although the third method has a minimum equalization delay than the first method or the second method, and the equalization round trip delay varies depending on the position of the selected ONU, this also has a smaller value than the first method or the second method.

In this embodiment, since the equalization delay and the equalization round trip delay are determined using the third method, the packet delay can be minimized. This may be a reason for grouping ONUs located at a similar distance from the OLT through the grouping unit 120. In this embodiment, the group is determined according to the location where the ONU is present, and the grouping criterion is determined by how many times of the cycle time the response takes from immediately after the OLT is approved.

This will be described with reference to FIG. 1 again.

The ranging processor 130 performs the ranging for each ONU group after grouping the ONUs. The ranging method of the ranging processor 130 may be performed as follows, for example.

First, in the first step, the individual round trip delay for each ONU is obtained from the distance measurement to each ONU belonging to the OLT and ONU groups. Subsequently, in the second step, the equalization delay of each ONU is calculated by subtracting the individual round trip delay of each ONU from the equalized round trip delay set for each ONU group.

3 is a view comparing the conventional ranging method and the ranging method according to the present embodiment. Referring to FIG. 3A, when a new ONU group 300 is added to an optical subscriber network system, ranging is performed again on all ONUs. As a result, there is a problem in that packet delay of ONUs belonging to the existing ONU group 310 is long. However, in the present embodiment, since the ONUs are grouped as shown in FIG. 3 (b), ranging may be performed for each ONU group or only for the ONUs belonging to the new ONU group 300. In this case, since ONUs belonging to the existing ONU group 310 do not perform ranging again, the packet delay is maintained as it is, and thus the packet delay may be increased.

On the other hand, ONUs not belonging to the ONU group may be newly discovered in the optical subscriber network system. In this case, the round trip delay value of the ONU is first calculated, and then it is determined whether the calculated round trip delay value is smaller than the maximum round trip delay value for the entire ONU. If the round trip delay value of the newly discovered ONU is smaller than the maximum value, the ONU belongs to a specific ONU group in consideration of the round trip delay value. On the other hand, if the round trip delay value of the newly discovered ONU is greater than the maximum value, the new ONU group is created including the ONU.

In the present embodiment, such a function is performed by the grouping unit 120. In this case, when the grouping unit 120 finds an ONU that does not belong to the ONU group, the grouping unit 120 calculates a round trip delay of the found ONU, and a round trip delay size comparing the calculated round trip delay with the maximum round trip delay of the ONU group. A comparator, and an ONU group including the found ONU if the calculated round trip delay is greater than the round trip delay maximum value, and if the calculated round trip delay is less than or equal to the round trip delay maximum value, the found ONU is the round trip delay maximum value. It may include an ONU processing unit to belong to the ONU group having a value.

In the present embodiment, the ranging method is not limited to the above. For example, it is also possible to perform as follows. First, in the first step, an equalization delay value is allocated in advance between ONUs belonging to the ONU group, and the window length is determined according to the error range of the distance. The equalization delay value assigned in advance can take into account the distance between the OLT and the corresponding ONU, the transmission rate of the uplink frame, the speed of the light, the response time of the ONU, and the window length is the distance between the OLT and the ONU, the transmission rate of the uplink frame, The propagation speed of signals in optical cables can be considered. Then, in the second step, the equalization delay value of ONUs belonging to the ONU group is calculated. The equalization delay value at this time may take into account the time when the OLT transmits the ranging approval message to the ONU, the time when the OLT receives the response message of the ONU to the ranging approval message, and the pre-assigned equalization delay value.

On the other hand, the passive optical subscriber network system in this embodiment is provided with at least one OLT. In this case, the OLT may be defined as an optical subscriber network provider device connected to the optical subscriber network service provider as an optical line terminal. In this embodiment, such OLT is understood as a (telephone) national side device of a concept including a central office terminal (COT). On the other hand, there are usually a plurality of ONUs connected to one OLT. The ONU may be defined as an optical subscriber terminal or an optical subscriber network user device to which an optical subscriber network service user connects as a subscriber indoor terminal. In the present embodiment, such an ONU is understood as a subscriber side terminal having a concept including a remote terminal (RT), an optical network terminal (ONT), and the like.

This will be described with reference to FIG. 1 again.

The cycle time determination unit 140 determines the cycle time for obtaining the maximum link efficiency while satisfying the maximum allowable delay of traffic for each ONU group when ranging is completed for each ONU group. Preferably, the cycle time determiner 140 determines the cycle time to be equal to the equalization round trip delay of the ONU group. More preferably, the cycle time determiner 140 determines the cycle time in consideration of the maximum propagation delay between the OLT and the ONU and the maximum packet delay of the ONU located at the furthest distance from the OLT. The cycle time determiner 140 determines the cycle time as follows.

In December 2003, FSAN, a neighboring organization of the ITU-T SG15 Q2 standardization activity, began discussing the Next Generation Access (NGA), which explores the evolution of subscriber networks since the current G-PON. NGA's requirements include wide area subscriber networks with 100 km transmission distance, high subscriber rate optical subscriber transmission, and increased bandwidth to 1 GB / s per subscriber.

NGAs feature long range, high bandwidth, and high branch rates. If ITU-T supports the target 100km, only the maximum round trip delay will have 1ms. This means that the equalized round trip delay is 1 ms or more. Therefore, consider how much delay is incurred when going through a request, acknowledgment, or transmission process for traffic that requires real-time processing. In particular, channel zapping time in IPTV corresponds to real-time traffic that must guarantee strict QoE without having a fixed rate. If a complex procedure such as a channel change had to be done in 0.43 seconds, then in the optical subscriber network, the time from ONU to request to transmission would have to be done within a few ms.

4 shows the relationship between cycle time and equalization round trip delay. Since the maximum distance that E-PON and G-PON actually support is only 10km ~ 20km, the round trip delay is 100㎲ ~ when applying the normal light speed of 200,000km / s in the optical cable. 200 ㎲. In this case, the equalization round trip delay is further added to the processing time of the ONU at this time.

Cycle times vary from implementation to vendor, but range from 0.75ms to 2ms. In the case where the logical distance is short (D _L1 ), C≥T _rt1 holds, and in the opposite case (D _L2 ), C≤T _rt2 holds. The equalization round-trip delay must be a multiple of the cycle time because the upstream data comes up during the next cycle if the grant is issued in one cycle. Accordingly, in the former case, T _eqd1 = C is established, and in the latter case, T _eqd2 = 2C. Combining both cases, the following equation can be derived.

(a) T _eqd = nC

(b) (n-1) C≤T _rt ≤nC

As a result, the longer the distance supported by FIG. 2, the longer the maximum round trip delay, and even if this value is only slightly longer than the length of the cycle time, the equalized round trip delay is increased by a multiple of the cycle time, resulting in a significant delay.

If you want to reduce the delay while keeping the supported distance, you can consider reducing the cycle time, but this leads to a decrease in link efficiency as described above. The reason for this is as follows. Shortening the cycle time shortens the frequency of sending data upward in terms of the ONU, thus reducing the delay of real-time traffic. On the other hand, if ONUs frequently send data with a fixed physical layer overhead in a short period upward, the occupation rate of overhead for the entire period becomes high, resulting in a decrease in link efficiency. Conversely, lengthening the cycle time increases link efficiency but inevitably lengthens the delay.

5 shows a request (ⓑ), grant (ⓒ), and data transfer (ⓓ) for traffic (ⓐ) arriving at an ONU at a certain time to determine the relationship between cycle time and maximum delay, according to an embodiment of the present invention. The maximum delay from going through the process and arriving at the OLT is shown. The OLT starts the next cycle after the scheduling time by the DBA mechanism has elapsed after collecting all ONU reports. Thus, the cycle time observed in the ONU and the cycle time observed in the OLT are shifted by the scheduling time T _sch .

The greatest time delay when real-time data arrives at a certain ONU is, for example, when the ONU sends a report message to the OLT side just before data from the subscriber arrives at the ONU. In this case, one more cycle time is required to transmit the report message relating to the arrived data.

If the ONU sends the information in the queue 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, the report message arriving at the OLT needs another cycle time before the ONT is scheduled. The reason for this is that OLT must also take into account the processing time it takes to collect and report messages from other ONUs as well.

The OLT sends an acknowledgment message to the ONU after completing the scheduling. The ONU sends the data to the OLT after receiving the acknowledgment message, which takes the equalization round trip time. As mentioned in Equation 1, the equalized round trip delay has a value of nC (where n ≧ 1) depending on the maximum round trip delay range. If the OLT has scheduled the ONU to send the last data in providing the grant, another cycle time is required. Considering this situation, the packet delay T _pk that ONU _i may experience can be derived as follows.

T _pk = 3C + T _pd + T _eqd = (n + 3) C + T _pd

Since the equalization round trip delay includes the maximum propagation delay, that is, T _eqd > 2T _pd , the following equation can be derived even if the value of the cycle time approaches zero.

It can be seen from Equation 3 that the packet delay is always more than three times the propagation delay.

If the distance between the OLT and the ONU is 100 km, the packet delay can be considered to be about 1.5 ms. If the packet delay is to be limited to T _pk ≤ T _max , the following equation may be derived by substituting Equation 2 into this condition.

In the above, T _max is the maximum packet delay of the ONU located farthest from the OLT.

The following inequality can be obtained by combining Equation 4 with the equation derived from the relationship between the two equations T _rt = 2T _pd and (n-1) C≤T _rt ≤nC.

To solve the above equation and simply summarize, it can be expressed as follows.

In the above, [x] is a maximum integer not exceeding x. Given T _max and T _pd , Equation 6 can be used to find the minimum value of n. If the minimum value of n is substituted into Equation 4, the maximum value of C can be obtained. The maximum value of C at this time becomes the optimum cycle time.

As described above, if the cycle time determiner 140 determines the cycle time for each ONU group, the maximum link efficiency may be obtained while satisfying the maximum allowable delay of traffic.

The cycle time determining apparatus 100 according to the present embodiment groups data by grouping ONUs located at a similar distance from the OLT and determining a cycle time for obtaining maximum link efficiency while satisfying a maximum allowable delay for each group. The delay of the packet is shortened than before. This will be described in detail below.

6 is a diagram illustrating scheduling of a scheme having a fixed cycle time with a variable equalization delay according to the present embodiment. The following description refers to FIG. 6.

First, the ONUs in group 1 have a distance between 0 and C _v / 2 if the RTT value is C and ignores T _res . Where v is the propagation speed of light in the optical cable, which is 200,000 km / s. Therefore, the position value d of the ONU belonging to the group k has a range of ((k-1) C _v / 2) ≤d <(kC _v / 2).

However, during the scheduling time T _sch , the OLT performs scheduling for the arrival to arrive after one cycle time 1C for the group 1, and performs scheduling for the arrival to arrive after kC for the group k. Therefore, the maximum packet delay of the i-th ONU (ONU _i ) belonging to the group k is determined by Equation 2 as follows.

T _pk ^k = (k + 3) C + T _pd

According to the related art, n is determined by the farthest ONU, whereas Equation 7 shows that the differential is applied according to the position of the ONU. Therefore, it is not necessary to bear long packet delays until all ONUs to which small delays can be applied. In addition, as shown in the figure, it is a feature of the present embodiment that the delayed group can be somewhat reduced by scheduling the farthest group to which the longest delay is to be applied first.

If there are n groups managed by the OLT and the distances are uniformly distributed, the average of the maximum packet delays can be obtained from Equation 7 as follows.

Comparing Equation 8 and the conventional E [T _pk ] = (n + 3) C + T _pd , it can be seen that the packet delay is reduced by (n-1) C / 2 in the method according to the present embodiment. . This indicates that the greater the difference in distance between the nearest ONU and the furthest ONU, the greater the gain. In addition, when most ONUs are in close proximity and only one ONU is located far away, in the conventional method, the packet delay is increased due to one remote ONU, whereas the packet delay is changed in the method according to the present embodiment. Notify

On the other hand, the cycle time determiner 140 allocates at least two bands to at least one ONU located farther than a predetermined reference when determining the cycle time for the ONU group. For example, if there are 10 ONUs in the ONU group, 8 of which are located between 10km and 15km, and the other 2 are located between 15km and 20km, two farthest will have 2 bands at cycle time. To allocate times.

In this embodiment, if the bandwidth is allocated in the determination of the cycle time, the overhead can be further reduced. This part will be described below.

Suppose that there are currently 64 ONUs, 63 of which are at 68km and the other at 100km, which limits the maximum delay of packets to 2.0ms for all ONUs.

According to the conventional method, a cycle time is obtained, which is C = 0.15ms due to one unit located at 100 km. Overhead headers are calculated as follows.

In the method according to this embodiment, the ONU at 68 km belongs to group 3 (n = 3), and the ONU at 100 km belongs to group 7 (n = 7). In this case, the delay can be reduced compared to the conventional method, but the cycle time is still C = 0.15ms, and the overhead is 9.1%.

However, if the cycle time is calculated only for 63 ONUs in close proximity, C = 0.2767ms. Thus, this cycle time is maintained, but the remote ONU is allocated two bands within this cycle time. Then, since the actual cycle time provided to the remote ONU is C ₆₄ = 0.2767 / 2 = 0.1384ms, the value is smaller than the maximum delay time of the packet of 2.0ms, and the overhead is calculated as follows.

The reason for N + 1 in the numerator is that the 64th ONU is subject to the overhead of physical layer 2 at one cycle time (C = 0.2767ms). Comparing the two overheads, the method according to the present embodiment shows that the overhead is reduced by about 1/2 compared to the conventional method, and the delay is further reduced.

Next, a cycle time determination method for shortening a delay time of a data packet in an optical subscriber network system will be described. 7 is a flowchart illustrating a method of determining a cycle time for data transmission in an optical subscriber network system according to the present embodiment. The following description refers to FIG. 7.

First, the distance measuring unit 110 measures the distance to the OLT for each ONU provided in the optical subscriber network system (S700). Afterwards, the grouping unit 120 groups the ONUs in consideration of the distance between the OLT and the ONU (S710). Thereafter, the ranging processor 130 performs ranging for each ONU group (S720). The ranging method is to avoid collisions between ONUs belonging to the ONU group, and to obtain individual round trip delays for each ONU from a distance measurement between the OLT and the ONU. Calculating the equalization delay of each ONU by subtracting the individual round trip delay.

When ranging is completed for each ONU group, the cycle time determination unit 140 determines a cycle time for obtaining maximum link efficiency while satisfying a maximum allowable delay of traffic for each ONU group (S730). See the foregoing for how to determine the cycle time.

8 is a graph comparing the average value of the maximum packet delay according to the conventional method with the average value of the maximum packet delay according to the present embodiment. The following description refers to FIG. 8.

In the conventional method, since the maximum packet delay is fixed at 2 ms, the packet has a constant value regardless of the distance. However, in this embodiment, the first type and the second type are classified according to whether the distribution of ONUs is uniform.

The first type is a case where all ONUs are uniformly distributed within a given distance. Here, it can be seen that there is no performance difference from the conventional method up to 44 km. The reason is that up to 44 km is calculated as n = 1, since the result of Equation 2 and the result of Equation 8 are the same. On the other hand, for more than 44 km, the ONU within 40 km has a much lower delay, and after 40 km, the ONU shows better performance because it follows the existing delay value.

The second type is a case where the distribution of ONUs is nonuniform. This is assuming an extreme situation that can cause a great loss when following the conventional method. For example, suppose there are 64 ONUs in the optical subscriber network system, 63 of which are located close to the OLT, with an approximate propagation delay of 0, and the other of which are located at 100 km. In this non-uniform distribution, it can be seen that the method according to the present embodiment has the maximum average delay reduced by half compared to the conventional method. In this case, increasing the cycle time to increase the efficiency of the link and sending the data to the furthest ONU two times in one cycle time will achieve the two purposes of improving the efficiency of the link and reducing the delay value. .

Next, an example in which the cycle time determination device 100 is applied to the optical subscriber network system will be described. 9 is a conceptual diagram of an optical subscriber network system having a cycle time determining apparatus. The following description refers to FIG. 9.

First, the configuration of the optical subscriber network system 900 will be described.

The optical subscriber network system 900 includes a hybrid PON OLT 910, a hybrid PON ONU 920, an arrayed waveguide grating (AWG) 930, an optical splitter / combiner 940, and a cycle time determination device ( 100). Hybrid PON OLT 910 and hybrid PON ONU 920 are composed of TDM-PON MACs 911, WDM-PON transmitters 912, and WDM-PON receivers 913. The wavelength branch combiner 930 performs a function of multiplexing / demultiplexing the WDM-PON wavelength. In the present embodiment, the hybrid PON OLT 910 may include the wavelength branch combiner 930. The optical splitter / combiner 940 is a device for TDM-PON optical signal distribution, and performs functions such as optical signal power branching and optical signal power combining. The light splitter / combiner 940 has, for example, a 1 × N splitter that simply branches the optical power to a remote location.

Next, operation of the optical subscriber network system 900 will be described.

In this embodiment, the optical subscriber network system 900 is composed of a WDM-TDM composite passive optical communication network. WDM-PON bundles and transmits multiple TDM-PONs at the WDM wavelength, increasing the branching rate per optical cable and enabling long-distance transmissions over 100km. In the actual subscriber section communication, up and down communication is performed through the same TDMA scheme as the TDM-PON.

Referring to the signal transmission method in the TDM-PON, the hybrid-PON OLT 910 broadcasts the traffic transmitted to each hybrid-PON ONU 920 in terms of downlink signals. The optical splitter / combiner 940 distributes or combines the light, distributes the downlink signal received from the hybrid-PON OLT 910 to N subscriber lines, and the downlink signal transmitted from the hybrid-PON ONU 920 to itself. Receive and selectively transmit it to the subscriber during the time allocated to itself.

In terms of an uplink signal, a plurality of ONUs 920 connected to the same wavelength branch combiner 930 may have its own dedicated time slot (RBA) through ranging and dynamic bandwidth allocation (DBA) processes. In a state in which a slot is previously allocated from an OLT corresponding MAC 911, when an allocated time slot arrives, the uplink signal is transmitted, and when the slot is not its own slot, the uplink signal is stopped. The uplink signal from each hybrid-PON ONU 920 is combined in the optical splitter / combiner 940 and transmitted to the hybrid-PON OLT 910.

The cycle time determining apparatus 100 has such a configuration and is provided between the hybrid PON OLT 710 and the hybrid PON ONU 720 in the optical subscriber network system 700 operated as described above, and thus, FIGS. 1 to 8. Reference to the above-described function is performed.

With the rise of IPTV services, interest in quality of experience (QoE) has increased. In particular, the effects of delay on QoE are enormous when retransmitting terrestrial waves in real time through IPTV. Ultimately, it will never be an easy problem to provide a constant delay variation when hundreds of channels at home and abroad are pouring down in real time. In addition, satisfying QoE comparable to analog TV is one of important issues when frequent channel zapping is required upward.

Although a reference value of several hundred ms (0.43 seconds or less) has been suggested as a user-friendly channel change time, the channel change time actually depends on the Internet Group Multicasting Protocol (IGMP) response time of access equipment, L3 switches, routers, etc. The difference is very large depending on the equipment. Eventually, the protocol processing time will be the main factor in order to satisfy the channel change time, so the packet delay in the access device should be almost negligible, that is, several ms or less.

Therefore, in the WDM-TDM hybrid passive optical network, delay is considered to be a very important factor among various quality of service. In consideration of this, the cycle time determining apparatus 100 according to the present embodiment proposes a method for determining an optimal cycle time when the subscriber transmission distance is extended to 100 km in the H-PON, and an efficient ranging method and When allocating the band in the MAC, we will propose a way to minimize the average delay by grouping according to the location of the subscriber.

The above description is merely illustrative of the technical idea of the present invention, and various modifications, changes, and substitutions may be made by those skilled in the art without departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

The present invention is characterized by facilitating long-distance transmission of 100 km or more by grouping ONUs located at a similar distance from the OLT and determining a cycle time for each group to shorten the delay of the data packet. The present invention further improves data transmission performance, thereby enabling smooth implementation of wireless telephony services such as real-time interactive TV service sensitive to packet delay such as IPTV or 3D TV, and Voice over Internet Protocol (VoIP).

1 is a block diagram schematically illustrating an apparatus for determining a cycle time for data transmission in an optical subscriber network system.

2 is a reference diagram for describing various methods of calculating an equalization delay.

3 is a view comparing the conventional ranging method and the ranging method according to the present embodiment.

4 shows the relationship between cycle time and equalization round trip delay.

5 is a diagram for determining a relationship between a cycle time and a maximum delay according to the present embodiment.

6 is a diagram illustrating scheduling of a scheme having a fixed cycle time with a variable equalization delay according to the present embodiment.

7 is a flowchart illustrating a method of determining a cycle time for data transmission in an optical subscriber network system according to the present embodiment.

8 is a graph comparing the average value of the maximum packet delay according to the conventional method with the average value of the maximum packet delay according to the present embodiment.

9 is a conceptual diagram of an optical subscriber network system having a cycle time determining apparatus.

<Explanation of symbols for the main parts of the drawings>

100: cycle time determination device 110: distance measuring unit

120: grouping unit 130: ranging processing unit

140: cycle time determination unit 900: optical subscriber network system

910: Hybrid PON OLT 911: TDM-PON MAC

912: WDM-PON Transmitter 913: WDM-PON Receiver

920: Hybrid PON ONU 930: Wavelength Divider Coupler

940: Light Distribution / Combiner

Claims (14)

A grouping unit for grouping at least two of said subscriber-side terminal devices in consideration of distance information between a station-side device connected to an optical subscriber network service provider and a subscriber-side terminal device connected to an optical subscriber network service user; A ranging processor configured to perform ranging on all the subscriber-side terminal devices belonging to the generated subscriber-side terminal device group when the subscriber-side terminal device group including the at least one subscriber-side terminal device is generated from the grouping; ; And Cycle time determination unit for determining the cycle time for data transmission for each of the generated subscriber-side terminal device group Cycle time determination device comprising a. The method of claim 1, The grouping unit includes a time required for the terminal device to receive a response message for the approval message from the subscriber terminal device after transmitting the approval message for approving the network connection to the subscriber terminal device. And grouping the subscriber-side terminal device by dividing distance information into multiples of the cycle time. The method of claim 1, And the cycle time determiner determines the cycle time to have the same magnitude as the equalized round trip delay of the generated subscriber-side terminal group. The method of claim 1, The grouping portion, A round trip delay calculator configured to calculate a round trip delay of the found subscriber station when the subscriber station is located in the subscriber station terminal group; A round trip delay size comparison unit for comparing the calculated round trip delay with a maximum round trip delay value of the subscriber station terminal group; And If the calculated round trip delay is greater than the round trip delay maximum value, create a subscriber side terminal group including the found subscriber side terminal device, and if the calculated round trip delay is less than or equal to the round trip delay maximum value, Subscriber terminal device processing unit which associates the subscriber terminal device with the subscriber terminal device group having the maximum round trip delay value. Cycle time determination device comprising a. The method of claim 1, And the cycle time determining unit allocates at least two bands during the cycle time to at least one subscriber station terminal located farther than a predetermined criterion in the subscriber station terminal group when determining the cycle time. Time determination device. The method of claim 3, wherein The cycle time determining unit determines the cycle time in consideration of the maximum propagation delay between the subscriber station terminal device and the subscriber station terminal device and the maximum packet delay of the subscriber station terminal device located at the longest distance from the subscriber station device. A cycle time determination device. The method of claim 1, Distance measuring unit for measuring the distance between the terminal device and the subscriber station terminal included in the distance information The cycle time determination device further comprises. The method of claim 1, And the cycle time determining device is provided on an optical fiber path connecting the station-side device and the subscriber-side terminal device in a passive optical network combining different division multiplexing schemes. (a) grouping at least two subscriber-side terminal devices in consideration of distance information between a station-side device connected to an optical subscriber network service provider and a subscriber-side terminal device connected to an optical subscriber network service user; (b) when a group of subscriber station terminals including at least one of the subscriber station terminals is generated from the grouping, ranging of all the subscriber station terminals belonging to the generated subscriber station terminal groups; step; And (c) determining a cycle time for data transmission for each of the generated subscriber-side terminal groups; Cycle time determination method comprising a. The method of claim 9, In the step (a), the time required for the office-side device to transmit an acknowledgment message for approving network access to the subscriber-side terminal device and to receive a response message for the approval message from the subscriber-side terminal device is determined. And grouping the subscriber station terminal by dividing the distance information by a unit of a multiple of the cycle time. The method of claim 9, In the step (c), the cycle time determination method is characterized in that the cycle time is determined to have the same magnitude as the equalized round trip delay of the generated subscriber-side terminal device group. The method of claim 9, The intermediate step of step (a) and (b), (aa) calculating a round-trip delay of the found subscriber-side terminal if the subscriber-side terminal is not included in the subscriber-side terminal group; (ab) comparing the calculated round trip delay with a maximum round trip delay value of the subscriber station terminal group; And (ac) if the calculated round trip delay is greater than the round trip delay maximum value, create a subscriber side terminal group including the found subscriber side terminal device, and if the calculated round trip delay is less than or equal to the round trip delay maximum value, Assigning the found subscriber station to a group of subscriber station terminals having the maximum round trip delay value; Cycle time determination method comprising a. The method of claim 9, In the step (c), the band is allocated at least twice during the cycle time to at least one subscriber-side terminal device located farther than a predetermined criterion in the subscriber-side terminal device group when determining the cycle time. How to determine cycle time. The method of claim 11, In step (c), the cycle time is determined in consideration of the maximum propagation delay between the subscriber station terminal device and the subscriber station terminal device and the maximum packet delay of the subscriber station terminal device located at the longest distance from the subscriber station device. A cycle time determination method characterized by the above-mentioned.

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