KR100657122B1 - Dynamic bandwidth allocation method for transmitting upstream data in ethernet passive optical network - Google Patents

Abstract

The present invention relates to dynamic bandwidth allocation (DBA) based on SLA in uplink TDMA MAC, which is a core technology in Ethernet passive optical subscriber network (E-PON). In E-PON, several ONUs share one optical fiber by TDMA for uplink transmission, and there is a need for a method of dynamically allocating an uplink bandwidth to each ONU while preventing data collision between ONUs. This algorithm provides a solution to the problem of starvation which can occur when the maximum cycle time exceeded or the maximum cycle time is strictly observed in the DBA algorithm. In addition, the method of determining the transmission start time of the ONU in allocating the upper bandwidth also describes the GRANT scheduling.

Description

DYNAMIC BANDWIDTH ALLOCATION METHOD FOR TRANSMITTING UPSTREAM DATA IN ETHERNET PASSIVE OPTICAL NETWORK}

1 is a general diagram of an Ethernet passive optical subscriber network.

2 is a flowchart illustrating an example of a dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network according to the present invention;

3 is a flow chart showing the modified calculation form of FIG.

4 is a diagram illustrating a calculation process of REMNANT_TIME applying sliding cycle time in the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive optical network (hereinafter referred to as a PON), and more particularly to an optical network unit (ONU) in an Ethernet passive optical network (hereinafter referred to as an EPON). The present invention relates to a dynamic bandwidth allocation method for uplink data transmission.                         

X-Digital Subscriber Line (xDSL), Hybrid Fiber Coax (HFC), Fiber To The Building (FTTB), Fiber To The Curb (FTTC), and Fiber To (FTTH) The Home) and various network structures are proposed, and among these various network structures, FTTx structure can be divided into active FTTx and passive FFTx depending on the presence of outdoor active equipment. Among them, PON is a passive FTTx method, which has a point-to-multipoint topology by passive elements, and a single optical fiber is shared by several ONUs, which reduces the use of fiber optics and eliminates outdoor active elements. It is proposed as a way to implement economical optical subscriber network by reducing maintenance costs.

The above-described PON refers to a single optical line termination device (hereinafter referred to as 'OLT') and a plurality of optical subscriber network devices (ONUs) of 1: N optical distribution network (ODN). By using), it is an optical subscriber network structure that forms a distributed topology of a tree structure.

As shown in FIG. 1, the E-PON has a tree structure in which one OLT 100 corresponds to 1: N through a plurality of ONUs (O1, O2, O3) and passive devices. In downlink transmission from the OLT 100 to ONU (O1, O2, O3), data transmitted from the OLT 100 is broadcast to all ONUs (O1, O2, O3), and this method is based on the existing Ethernet. Since it is almost the same as in E-PON, the media sharing problem does not occur. On the other hand, in the uplink transmission from the ONU (O1, O2, O3) to the OLT 100, the ONU (O1) because a plurality of ONU (O1, O2, O3) is connected from the passive element to the OLT (100) through one optical fiber In order to perform uplink transmission without collision between O2 and O3, a Time Division Multiple Access Medium Access Control (TDMA MAC) protocol is required to access a medium while avoiding time overlap.

The simplest uplink bandwidth allocation method is to assign a fixed timeslot to each ONU (O1, O2, O3) to avoid collisions between ONU (O1, O2, O3). In this method, however, the ONU (O1, O2, O3) without uplink data continues to occupy the band, thereby causing unnecessary bandwidth waste. Since the amount of traffic that ONU (O1, O2, O3) wants to send is variable over time and has a burst characteristic, it is necessary to allocate uplink dynamically accordingly to prevent unnecessary waste of upband and reduce transmission delay time. .

Reference numerals U1, U2, and U3 denote user terminals connected to the respective ONUs O1, O2, and O3.

An object of the present invention, which has been created to meet the above-described demands, is to provide a dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network essential for EPON implementation.

Dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network according to an embodiment of the present invention for achieving the above object, Ethernet passive optical subscriber network including a plurality of ONU (Optical Network Unit) ( E-PON: Dynamic Bandwidth Allocation (DBA) method for uplink data transmission of an optical network unit (ONU) of an Ethernet Passive Optical Network (EU), the length of an uplink bandwidth desired from a specific ONU (called ONUi) A first step of, when receiving a band allocation request message including information REQi, comparing it with a maximum usable time length CREDITi guaranteed by a service level agreement (SLA); And as a result of the comparison in the first step, if the desired uplink bandwidth use time satisfies the SLA and is less than the guaranteed available time length, the OLT requests uplink available time GRANTi by the time requested by the ONUi. Determining a second step; Characterized in that it comprises a dynamic bandwidth allocation method for uplink data transmission, characterized in that consisting of.

According to another aspect of the present invention, a dynamic bandwidth for uplink data transmission of an optical network unit (ONU) of an Ethernet passive optical network (E-PON) including a plurality of optical network units (ONU) In the Dynamic Bandwidth Allocation (DBA) method, when a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (hereinafter referred to as ONUi), the bandwidth allocation request message is transmitted to a service level agreement (SLA). Comparing the guaranteed maximum usable time length CREDITi by the first step; A second step of determining an available time (REMNANT_TIME) for traffic processing of the specific ONU; And a third step of finally determining an uplink available time GRANTi using a parameter (WFi) related to the distribution of the excess band determined by the SLA and the maximum available time length (CREDITi). A dynamic bandwidth allocation method for uplink data transmission is provided.

According to another aspect of the present invention, a dynamic bandwidth for uplink data transmission of an optical network unit (ONU) of an Ethernet passive optical network (E-PON) including a plurality of optical network units (ONU) In the Dynamic Bandwidth Allocation (DBA) method, when a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (hereinafter referred to as ONUi), the bandwidth allocation request message is transmitted to a service level agreement (SLA). Comparing the guaranteed maximum usable time length CREDITi by the first step; A second step of determining whether there is a pre-calculated available time (REMNANT_TIME) for traffic processing of a specific ONU; A third step of determining an available time (REMNANT_TIME) for traffic processing of the specific ONU if there is no pre-calculated available time in the second step; A fourth step of finally determining an upward band available time (GRANTi) using a parameter (WFi) related to the distribution of the surplus band determined by the SLA and the maximum available time length (CREDITi); And a fifth step of calculating a usable time in advance using the available time REMNANT_TIME calculated in the third step. The dynamic bandwidth allocation method for uplink data transmission is provided.

Hereinafter, a dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.                     

For convenience of explanation, it is assumed that the distance between the OLT and several ONUs is the same.

2 is a flowchart illustrating a dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network according to the present invention. Before the description, the terms are defined as follows.

A. How to Determine the GRANT Length

REQi = Upband transmit desired time requested by ONUi (O1, O2, O3 ...) to OLT (100)

GRANTi = Uplink transmittable time that OLT (100) grants to ONUi (O1, O2, O3 ...) and informs ONUi (O1, O2, O3 ...) of the transmission start time and available time length. . The exchange of REQi and GRANTi uses MPCP (Multi Point Control Protocol) defined in IEEE 802.3ah, and each ONU (O1, O2, O3 ...) is uplinked once by round robin for one cycle time. And receive the corresponding GRANTi. Transmission of REQi is done by sending MPCP Ethernet Frame at the end of upstream data transmission, and GRANTi is sent by sending MPCP Ethernet Frame at the end of downlink data transmission.

MIN_GRANTi = time to statically allocate to ONUi (O1, O2, O3 ...) for one cycle regardless of REQi, determined by the initial SLA.

CREDITi = guaranteed transferable time that is always available for one cycle of cycle to ONUi (O1, O2, O3 ...), as determined by SLA.

MAX_CYCLE_TIME = The maximum time period in which all ONUs (O1, O2, O3 ...) receive at least one uplink transmission opportunity to provide services that require minimum latency guarantees such as audio, video, or leased lines. Normally, when providing POTS service, the delay condition is satisfied by setting MAX_CYCLE_TIME within 2 msec.

GUARANTEED_TIME = Sum of all CREDITi

SHARED_TIME = MAX_CYCLE_TIME-GUARANTEED_TIME

OVER_GRANTi = max (GRANTi-CREDITi, 0)

UNDER_GRANTi = min (GRANTi, CREDITi)

GRANTi = UNDER_GRANTi + OVER_GRANTi

REMNANT_TIME = SHARED_TIME-Sum of previous N-1 ONU OVER_GRANTs

= SHARED_TIME-Sum {j = i-(N-1) to i-1} (OVER_GRANTj)

(In the above formula, i-(N-1) is shorthand for i- (N-1) mod N, and the mod N operation is used because of repeated cycles without any further explanation.)

WFi = Weighted Fairness usage factor of REMNANT_TIME (0 <WFi <1)

As shown in FIG.

In step (1), for uplink transmission, ONUi (O1, O2, O3 ...) requests OLT 100 to allow uplink transmission through REQi. REQi contains data transfer time according to the buffer status of ONUi (O1, O2, O3 ...).

In step (2), the OLT 100 checks whether the REQi of ONUi (O1, O2, O3 ...) conforms to the service level agreement (SLA). If REQi satisfies SLA and is less than CREDITi                     

In step (3), OLT 100 allocates GRANT for the time requested by ONUi (O1, O2, O3 ...).

GRANTi = REQi

The process in step (4) is explained. If REQi exceeds MAX_GRANTi, granting ONUi (O1, O2, O3 ...) up to MAX-GRANTi does not violate SLA. However, if there is a surplus band remaining by other ONUs, the surplus band may be allocated to the best effort. If REQi is greater than CREDITi, it is determined by REMNANT_TIME whether additional band allocation is possible. REMNANT_TIME is a time obtained by subtracting the total OVER_GRANT time used by N-1 ONUs prior to ONUi in SHARED_TIME, and represents the maximum time that ONUi can use within a range in which the sliding cycle time does not exceed MAX_CYCLE_TIME. Therefore, REMNANT_TIME of ONUi (O1, O2, O3 ...) can be calculated as follows.

REMNANT_TIME = SHARED_TIME-Sum {j = i (N-1) to i-1} OVER_GRANTj

In addition, REMNANT_TIME can be calculated in advance as shown in step (6) of FIG. 3 by using the previously calculated REMNANT_TIME without having to calculate each time in order to reduce the convenience of implementation and the time delay between REQ and GRANT.

REMNANT_TIME = REMNANT_TIME-OVER_GRANT i + OVER_GRANT i + 1

Where GRANT i + 1 represents the GRANT value of ONUi + 1 in the previous cycle.

In step 5, WFi is an SLA parameter for the distribution of the redundant band and has a value between 0 and 1. If WFi is 0, ADD_TIME cannot be used at all. If 1, all the excess bands at that moment are used by ONUi GREEDY. Properly defining WFi can provide fair distribution of burst traffic. For example, WFi = 1 / N means that all ONUs (O1, O2, O3 ...) are evenly divided in the surplus band. Alternatively, if WFi = 0.5, it means that up to 50% of the surplus band can be used by ONUi. WFi is determined by SLA. Accordingly, the GRANTi allocated to ONUi is determined as follows.

GRANTi = min (CREDITi + WFi * REMNANT_TIME, REQi)

In step 7, the process moves to step 1 to proceed to the next ONU.

3 is a flowchart illustrating a modified calculation form of FIG. 2. The same parts as in FIG. 2 will be omitted. For convenience of description, the same step display will be used in the same part as FIG. 2.

In FIG. 3, unlike in FIG. 2, in the process of determining REQi and CREDITi in step 2, if REQi exceeds MAX_GRANTi, it is first determined whether there is a pre-calculated REMNANT_TIME as in step 8. If there is no pre-calculated REMNANT_TIME, steps (4) and (5) in FIG. 2 are performed to obtain REMNANT_TIME and GRANTi. However, if there is a pre-calculated REMNANT_TIME, step 5 of obtaining GRANTi using the pre-calculated REMNANT_TIME without performing step (4) of FIG. 2 is performed. After step (5) iteratively calculates REMNANT_TIME in advance through the following equation as described above.

REMNANT_TIME = REMNANT_TIME-OVER_GRANT i + OVER_GRANT i + 1                     

Where GRANT i + 1 represents the GRANT value of ONUi + 1 in the previous cycle.

The calculated value can be used without having to calculate REMNANT_TIME every time.

B. Grant Scheduling Method

Method A describes the method of determining the length of grant. Here, a method of determining an uplink transmission start time of ONUi is described.

The OLT 100 may precompute the arrival time t1 of the last bit of data coming from ONUi-1. The arrival time t2 of the first bit of data coming from the ONUi must be after t1 + guard band time. If the round trip time of the OLT and ONUi is RTTi, the ONUi must start transmission at time t3 = t2-RTTi so that the upstream first bit of ONUi arrives at time t2. To do this, the OLT must send a grant before time t4 = t2-(RTTi + ONU processing time).

However, even if the REQi has not been received from ONUi or received, GRANTi may not be able to be sent before t4 due to the GRANTi scheduling time. In this case, t2 and t3 are also delayed by the time exceeding t4.

As described above, the dynamic bandwidth allocation method for uplink data transmission in an Ethernet passive optical subscriber network according to an embodiment of the present invention reduces variable uptime delay by reducing cycle time when the amount of uplink data is small using variable cycle time. In addition, by applying the sliding cycle time concept, the cycle time does not exceed MAX_CYCLE_TIME in any case.                     

In addition, the present invention is not assigned to other ONUs even if ONUi is not used. Therefore, when a GRANTi (fixed bandwidth) is allocated beyond MIN_GRANTi, a time fixed exclusively for ONUi, ONU always guarantees a constant speed or more. In addition to providing services, support for Guaranteed Bandwidth allows QoS to be guaranteed by allowing GRANTi to be used at any time within the CREDITi range for one cycle time.

In addition, the present invention introduces SHARED_TIME and REMNANT_TIME to allow the previous ONUs to use unused surplus time within one sliding cycle time. In particular, in the calculation of REMNANT_TIME, REMNANT_TIME can be additionally used by ONUi under the condition that the start and end of cycle time is not fixed and the sliding cycle time from ONUi-N + 1 to ONUi should not exceed MAX_CYCLE_TIME every time. Calculations allow instantaneous traffic to be sent during this time, providing extended bandwidth.

Next, an example of bandwidth setting according to an SLA contract according to an embodiment of the present invention will be described in detail.

Example of upstream bandwidth setting for each ONU (downlink bandwidth can be set by Ethernet-specific characteristics and is not related to the present invention)

Example 1)

Fixed bandwidth: 4 Mbps (E1 dedicated line + BcN video call)

Guaranteed bandwidth: 12 Mbps (Two-way video service for DTV + high speed internet)                     

Non-guaranteed extended bandwidth: 400Mbps (Efficient acceptance of burst traffic such as P2P, FTP, etc. by users running private servers)

MAX_CYCLE_TIME = 2 msec, Number of ONU N = 32,

If GUARD_TIME = 1 usec

MIN_GRANTi = 2 msec * 4Mbps / 1Gbps = 8 usec to provide fixed bandwidth

MAX_GRANTi = 2 msec * 12 Mbps / 1 Gbps = 24 usec to provide guaranteed bandwidth

GUARANTED_TIME = 32 * (1 + 8 + 24) = 1056 usec

SHARED_TIME = 2000 1056 = 944 usec and the maximum bandwidth by this is 944/2000 * 1 Gbps = 472 Mbps

Therefore, if WFi = 0.85, non-guaranteed extended bandwidth of 400Mbps is possible.

If 31 ONUs are idle, the total time used by ONUi is 8 + 24 + 944 * 0.85 = 834.4 usec and the total guard band time is 64 usec. We can see that (834.4 + 64) = 92.8%.

Example 2)

Fixed bandwidth: 4 Mbps (E1 dedicated line + BcN video call)

Guaranteed bandwidth: 20 Mbps (Two-way video service for DTV + high speed internet)

Non-guaranteed extended bandwidth: 100Mbps (effective acceptance of burst traffic such as P2P and FTP by users who operate private servers)

MAX_CYCLE_TIME = 2 msec, Number of ONU N = 32,                     

If GUARD_TIME = 1usec

MIN_GRANTi = 2 msec * 4Mbps / 1Gbps = 8 usec to provide fixed bandwidth

MAX_GRANTi = 2 msec * 20Mbps / 1Gbps = 40 usec to provide guaranteed bandwidth

GUARANTED_TIME = 32 * (1+ 8 + 40) = 1568usec

SHARED_TIME = 2000-1568 = 432usec and the maximum bandwidth due to this is 432/2000 * 1Gbps = 216 Mbps

Therefore, if WFi = 0.47, non-guaranteed extended bandwidth 100Mbps is possible.

If 31 ONUs are idle, the total time used by ONUi is 8 + 40+ 432 * 0.47 = 251 usec and the total guard band time is 64 usec. We can see that (251 + 64) = 80%.

On the other hand, due to the time of ON / OFF, MPCP message, etc. of the laser diode during ONU transmission, there is a certain GUARD_TIME between transmissions between ONUs, and a total of N GUARD_TIMEs exist during one CYCLE_TIME. Accordingly, utilization of uplink bandwidth is

Calculated as (CYCLE_TIME-N * GUARD_TIME) / CYCLE_TIME.

Therefore, if CYCLE_TIME is reduced, the transmission delay is reduced but the utilization is lowered. This phenomenon becomes a problem when the number of ONU is large. For example, if MAX_CYCLE_TIME is 2 msec, GUARD_TIME is 1 usec, and the number of ONU is 32, MAX_GRANT = 2000/32 -1 = 61.5 usec unless SHARED_TIME is set. If one of 32 ONUs is idle at a given time, the maximum efficiency of one ONU can be (61.5 usec) / (61.5 usec + 32 * 1 usec) = 0.66, about 660 Mbps to be. If GUARD_TIME is increased for physical implementation reasons, the efficiency is further reduced. This low efficiency is because the ratio of GUARD_TIME becomes relatively large when CYCLE_TIME decreases.

However, according to the dynamic bandwidth allocation method for uplink data transmission of the Ethernet passive optical subscriber network according to the present invention, MAX_GRANT is set to 40 usec for each ONU, and SHARED_TIME = 2000-40 * 32-1 * 32 = 688 usec. Assuming that WFi = 1, the upward utilization of ONU is (40 usec + 688 usec) / (728 usec + 32 * 1 usec) = 0.957, which is close to 950 Mbps. Therefore, when using the present invention, it is possible to maximize the utilization (Utilization) through the efficient distribution of unused bandwidth.

According to the dynamic bandwidth allocation method for the uplink data transmission of the Ethernet passive optical subscriber network according to the present invention, it is possible to reduce the transmission delay time while minimizing unnecessary waste of the uplink band by dynamically allocating the uplink band according to the traffic amount of the ONU. It is possible to provide a dynamic bandwidth allocation method for uplink data transmission of an Ethernet passive optical subscriber network.

On the other hand, the present invention is not limited to the above-described embodiment, but can be modified and modified within the scope not departing from the gist of the present invention, such modifications and changes should be regarded as belonging to the following claims. will be.

Claims (9)

Dynamic Bandwidth Allocation (DBA) method for uplink data transmission of an Optical Network Unit (ONU) of an Ethernet Passive Optical Network (E-PON) including a plurality of optical network units (ONUs) To When a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (referred to as ONUi), it is compared with a maximum usable time length (CREDITi) guaranteed by a service level agreement (SLA). A first step of making; And As a result of the comparison in the first step, if the desired uplink bandwidth use time satisfies the SLA and is less than the guaranteed available time length, the OLT obtains an uplink available bandwidth GRANTi by the time requested by the ONUi. Determining a second step; dynamic bandwidth allocation method for uplink data transmission. Dynamic Bandwidth Allocation (DBA) method for uplink data transmission of an Optical Network Unit (ONU) of an Ethernet Passive Optical Network (E-PON) including a plurality of optical network units (ONUs) To When a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (hereinafter referred to as ONUi), the maximum allocation time length (CREDITi) guaranteed by a service level agreement (SLA) is received. A first step of comparing; A second step of determining an available time (REMNANT_TIME) for traffic processing of the specific ONU; And And a third step of finally determining an uplink available time GRANTi using a parameter (WFi) related to the distribution of the excess band determined by the SLA and the maximum available time length (CREDITi). A dynamic bandwidth allocation method for uplink data transmission. Dynamic Bandwidth Allocation (DBA) method for uplink data transmission of an Optical Network Unit (ONU) of an Ethernet Passive Optical Network (E-PON) including a plurality of optical network units (ONUs) To When a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (hereinafter referred to as ONUi), the maximum allocation time length (CREDITi) guaranteed by a service level agreement (SLA) is received. A first step of comparing; A second step of determining whether there is a pre-calculated available time (REMNANT_TIME) for traffic processing of a specific ONU; A third step of determining an available time (REMNANT_TIME) for traffic processing of the specific ONU if there is no pre-calculated available time in the second step; A fourth step of finally determining an upward band available time (GRANTi) using a parameter (WFi) related to the distribution of the surplus band determined by the SLA and the maximum available time length (CREDITi); And And a fifth step of calculating a usable time in advance using the available time (REMNANT_TIME) calculated in the third step. The method of claim 2, The available time (REMNANT_TIME) is determined by the following equation Dynamic bandwidth allocation method for uplink data transmission. REMNANT_TIME = SHARED_TIME-Sum {j = i-(N-1) to i-1} (OVER_GRANTj) OVER_GRANTi = max (GRANTi CREDITi, 0) Where N is the total number of ONUs, i is an integer greater than or equal to 1 and less than or equal to N, and i- (N-1) is short for i- (N-1) mod N for convenience. The method of claim 3, wherein The available time (REMNANT_TIME) in the fifth step is determined by the following equation. Dynamic bandwidth allocation method for uplink data transmission. REMNANT_TIME = REMNANT_TIME-OVER_GRANTi + OVER_GRANTi + 1 Here, OVER_GRANTi + 1 represents the OVER_GRANT value of ONUi + 1 in the previous cycle. The method of claim 2, In the fourth step, the final uplink bandwidth available time is determined by the following equation, Dynamic bandwidth allocation method for uplink data transmission. GRANTi = min {CREDITi + WFi * REMNANT_TIME, REQi} Dynamic Bandwidth Allocation (DBA) method for uplink data transmission of an Optical Network Unit (ONU) of an Ethernet Passive Optical Network (E-PON) including a plurality of optical network units (ONUs) To When a band allocation request message including uplink bandwidth use time length information (REQi) is received from a specific ONU (hereinafter referred to as ONUi), the maximum allocation time length (CREDITi) guaranteed by a service level agreement (SLA) is received. A first step of comparing; A second step of determining whether there is a pre-calculated available time (REMNANT_TIME) for traffic processing of a specific ONU; In the second step, if there is a pre-calculated available time, it is finalized by using the parameter about the distribution of the surplus band determined by the SLA and the maximum usable time length CREDITi with the time. A third step of determining an uplink available time GRANTi; And And a fourth step of repeating the available time calculation in advance by using the available time (REMNANT_TIME) calculated in the second step. The method of claim 7, wherein In the third step, the final uplink bandwidth available time is determined by the following equation, wherein the REMNANT TIME is the available time calculated in advance by the fifth step. Assignment method. GRANTi = min {CREDITi + WFi * REMNANT_TIME, REQi} The method of claim 1, wherein the arrival time of the first bit of data coming from the ONUi is after t2, where t2 = t1 (the arrival time of the last bit of data coming from the ONUi-1) + guard band time, The ONUi starts transmitting at time t3 = t2-RTTi (round trip time of the OLT and ONUi) so that the uplink data first bit of the ONUi arrives at the time t2, and the OLT is time t4 = t2 (RTTi). + ONU processing time) Dynamic bandwidth allocation method for uplink data transmission, characterized in that the grant is sent before.

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