KR20070030564A - An Adaptive Limited Bandwidth Allocation Scheme for EPON - Google Patents

Abstract

The present invention relates to a dynamic bandwidth allocation method for more efficiently distributing bandwidth allocated to users in an Ethernet Passive Optical Network (EPON) system. In consideration of each packet delay information, the dynamic maximum allocation bandwidth of each ONU in a specific cycle is determined and stored.When a bandwidth allocation request message is received from the ONU, the bandwidth requested by the ONU is compared with the stored maximum dynamic bandwidth. The bandwidth to be allocated to the ONU is determined according to the size of the case, and a gate message including the allocated bandwidth information is prepared and transmitted to the ONU.

Optical subscriber network, Ethernet PON, MAC protocol, dynamic band allocation

Description

Adaptive Limited Bandwidth Allocation Scheme for EPON

1 is a conceptual diagram of bandwidth allocation in a conventional limited scheme.

2 is a bandwidth allocation flowchart of a conventional limited scheme.

Figure 3 is a block diagram showing the configuration of the EPON system to which the present invention is applied.

4 is an explanatory diagram for explaining an uplink and a downlink transmission scheme between an OLT and an ONU in the EPON system of FIG.

5 is a flowchart illustrating a gate message operation procedure when an OLT allocates bandwidth to an ONU.

6 is a flowchart illustrating a procedure of operating a REPORT message when an OLT allocates bandwidth to an ONU.

7 is a conceptual diagram of dynamic band allocation in an EPON system in accordance with the present invention.

8 is a flowchart of a method for dynamic band allocation in an EPON system in accordance with the present invention.

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

11... OLT

12... Manual dispenser

13, 14, 15... ONU

16... PSTN

17... Internet

The present invention relates to dynamic band allocation in an Ethernet Passvie Optical Network (EPON) system, and more particularly, to a dynamic band allocation method in an EPON system for more efficiently distributing bandwidth allocated to users in an EPON system.

In general, Ethernet PON (EPON) is a next-generation optical subscriber network combining the PON technology and the Ethernet technology most widely used for the Internet connection among the optical optical network passive optical network (PON) technology. EPON has the advantages of scalability and economics of Ethernet technology, and because of its convenient management system, much research is being conducted as an optimal subscriber network technology for configuring Fiber To The Home (FTTH).

In EPON, a transmitting device (Optical Line Terminal, hereinafter abbreviated as "OLT") and multiple subscriber network devices (Optical Network Unit, hereinafter abbreviated "ONU") are configured in a tree form through a passive optical splitter. It is an optical subscriber network technology that can efficiently connect service providers with service providers. There are two types of data transmission in the EPON system: downlink transmission from OLT to ONU and uplink transmission from ONU to OLT. Downlink data transmission is performed by broadcasting to all ONUs connected to the OLT, and uplink data transmission is performed by unicasting with a plurality of ONUs allocated a shared bandwidth by TDMA (Time Division Multiple Access). Done. In particular, in uplink transmission, the OLT plays an important role in allocating shared bandwidth to each ONU. This is called dynamic bandwidth allocation (DBA). The dynamic band allocation scheme performed by the OLT in uplink transmission is an important factor in determining the efficiency of the EPON system.

In the conventional dynamic band allocation scheme, a fixed scheme (G. Kramer, B. Mukherjee, and G. Pesavento, “IPACT: a dynamic protocol for a scheme of allocating a fixed bandwidth at all times regardless of user traffic conditions similar to TDM schemes) an Ethernet PON (EPON), "IEEE Communications Magazine, Vol. 40, No. 2, 74-80, Feb. 2002.) and each ONU requests the bandwidth that the ONU wants to use, and the OLT requests the bandwidth requested by the ONU. Gated method (G. Kramer, B. Mukherjee, and G. Pesavento, "IPACT: a dynamic protocol for an Ethernet PON (EPON)," IEEE Communications Magazine, Vol. 40, No. 2, 74-80 , Feb. 2002.), and there is also a limited method that allocates the bandwidth below the maximum allocated bandwidth by comparing the bandwidth requested by the ONU with the maximum allocated bandwidth determined by the OLT. And there is a credit method that allocates bandwidth to ONU by adding a certain extra bandwidth to the bandwidth requested by ONU. Credit method is divided into Constant Credit method and Linear Credit method. The constant credit method determines the allocation bandwidth by adding the same extra bandwidth to the bandwidth requested by the ONU, and the linear credit method allocates the bandwidth by adding the extra bandwidth in proportion to the bandwidth requested by the ONU (G. Kramer, B. Mukherjee, and G. Pesavento, "IPACT: a dynamic protocol for an Ethernet PON (EPON)," IEEE Communications Magazine, Vol. 40, No. 2, 74-80, Feb. 2002.).

Band allocation schemes that have been proposed in the prior art cause many problems depending on the traffic characteristics occurring in the ONU. In the case of the Gated method, the bandwidth allows all bandwidths as desired. Therefore, there is a disadvantage in that bandwidth is unfairly allocated between ONUs and a specific ONU monopolizes the bandwidth. In addition, the fixed method of allocating fixed bandwidth allocates bandwidth equally to each ONU, so the number of subscribers that can be supported is limited, and it is difficult to flexibly cope with the rapidly changing traffic due to the lack of dynamic bandwidth allocation capability.

In addition, the limited method has a maximum bandwidth that can be allocated to each ONU, so that the bandwidth can be flexibly allocated for the rapidly changing traffic. However, there is a problem in supporting services such as constant bit rate (CBR) due to irregularity of cycle time.

And the credit method allocates the extra bandwidth to the ONU in order to flexibly cope with the traffic change, but it has the disadvantage of unnecessary bandwidth waste and longer cycle time for the small traffic request.

The limited method of the various band allocation methods as described above is described in more detail as follows.

1 is a conceptual diagram of bandwidth allocation in a conventional limited scheme.

As shown here, in the limited scheme, each ONU has the same maximum allocated bandwidth (Wmax) (504 and 505). The sum of the maximum allocated bandwidths of the N ONUs is called the total maximum allocated bandwidth N * Wmax (503), which is equal to cycles t-1 and t, which are one period of the transmission bandwidth from ONU 1 to ONU N (501,502). If the requested bandwidth of the ONU i is smaller than the maximum allocated bandwidth (Wmax), the allocated bandwidth allocates all of the bandwidth requested by the ONU i (506). However, if the requested bandwidth of ONU i is larger than the maximum allocated bandwidth (Wmax) of ONU i, the allocated bandwidth of ONU i is limited to the maximum allocated bandwidth (Wmax) (507). That is, if the bandwidth request exceeds the maximum allocated bandwidth, the excess portion 508 is not allocated.

2 is a flowchart of a bandwidth allocation in the conventional limited scheme.

The OLT checks whether a request message (request message) requesting bandwidth allocation is received from the ONU (S511). When the request message arrives from the ONU, the OLT analyzes the request bandwidth information included in the message and converts the request bandwidth information into the corresponding ONU. The maximum allocation bandwidth is compared (S512). If the requested bandwidth is smaller than the maximum allocated bandwidth, the allocated bandwidth allocates all of the bandwidth requested by the corresponding ONU (S513). However, if the request bandwidth is larger than the maximum allocated bandwidth of the ONU, the bandwidth allocated to the ONU is limited to the maximum allocated bandwidth (S514). The OLT transmits the allocated bandwidth information determined through this algorithm to the ONU using a GATE message (S515).

As described in more detail the problems of the limited method as follows.

1) Lack of elastic dynamic bandwidth allocation: In the limited scheme, there is a maximum allocation bandwidth (Wmax) predetermined by the OLT when performing bandwidth allocation to the ONU. The maximum allocated bandwidth is the bandwidth that the OLT can allocate the most to a particular ONU. Therefore, even if the traffic changes drastically, bandwidth allocation beyond the maximum allocated bandwidth is impossible.

2) Cycle Time Irregularity: In the limited method, the cycle time is kept constant because the fixed bandwidth allocation is made when the ONU's requested bandwidth exceeds the maximum allocated bandwidth, whereas the cycle time is irregular when the requested bandwidth is below the maximum allocated bandwidth. Done. Irregularities in cycle time cause problems in providing smooth QoS for real-time services.

3) Insufficient ability to maintain fairness between delays between ONUs: In case of the limited method, dynamic bandwidth allocation may be limited due to user's traffic change, but there is no ability to control delay fairness between ONUs.

The present invention has been proposed to solve the problems of the lack of dynamic bandwidth allocation capability, the lack of real-time service support due to the irregular cycle time, the lack of delay fairness between ONUs, which occurs when the conventional limited bandwidth allocation,

It is an object of the present invention to provide a dynamic band allocation method in an EPON system for more efficiently distributing bandwidth allocated to users in an EPON system.

Another object of the present invention is to provide a dynamic bandwidth allocation method in an EPON system that considers packet delay information of each ONU (Optical Network Unit) and improves flexible dynamic bandwidth allocation capability by using a flexible variable maximum allocation bandwidth. To provide.

It is still another object of the present invention to provide a dynamic bandwidth allocation method in an EPON system that facilitates real-time service support by minimizing fluctuation in total cycle time and provides delay fairness control capability between ONUs.

Dynamic band allocation method in the EPON system according to the present invention for achieving the above object,

Determining a cycle in the OLT and determining and storing a dynamic maximum allocation bandwidth for each ONU in a specific cycle in consideration of packet delay information for each ONU when the cycle starts;

When receiving a bandwidth allocation request message from the ONU, comparing the bandwidth requested by the ONU with the stored dynamic maximum allocation bandwidth and determining a bandwidth to be allocated to the ONU according to the magnitude;

And generating a gate message including the determined bandwidth information and transmitting the same to the ONU.

First, the present invention solves all the problems caused by band allocation in the conventional limited scheme through the following concept.

)을 사용한다. 동적 최대 할당 대역폭은 N개의 ONU에게 주어진 최대 할당 대역폭의 합을 기반으로 제공된다.(

)는 각 ONU의 트래픽 상황과 ONU간 지연상황을 고려하여 각 ONU에게 동적으로 할당된다. 따라서 동적 최대 할당 대역폭을 사용한 적응적 리미티드 방식은 고정 최대 할당 대역폭을 사용하는 종래의 리미티드 방식에 비해 더욱더 탄력적으로 대역 할당이 가능하다.1) Improved elastic dynamic bandwidth allocation: Dynamic maximum allocation bandwidth that varies with traffic conditions and ONU packet delay (

). The dynamic maximum allocation bandwidth is provided based on the sum of the maximum allocation bandwidths given to the N ONUs.

) Is dynamically allocated to each ONU in consideration of traffic conditions of each ONU and delay conditions between ONUs. Therefore, the adaptive limited scheme using the dynamic maximum allocation bandwidth is more flexible than the conventional limited scheme using the fixed maximum allocation bandwidth.

2) Improved regularity of cycle time: In the conventional limited scheme, the maximum allocated bandwidth that can be allocated to each ONU is fixed, so that if there is less traffic in a specific ONU, the overall cycle time is irregular. However, in the adaptive limited method, the maximum allocation bandwidth is variable, and a large amount of bandwidth is allocated to the ONU with many waiting packets, thereby reducing the variation in the total cycle time. Therefore, the adaptive limited method facilitates real-time service support.

3) Delay Fairness Control Ability between ONUs: The conventional limited scheme uses a fixed independent maximum allocated bandwidth for each ONU. When a lot of traffic is generated in a specific ONU, the packet delay of a specific ONU increases rapidly. However, in the adaptive limited method, the maximum allocated bandwidth is calculated for each ONU in proportion to the weighted average packet delay for each ONU. Therefore, the adaptive limited method can control the fairness of the average packet delay of each ONU.

3 illustrates an example of a configuration of an EPON to which the present invention is applied and driven.

In general, the EPON has a structure in which one OLT 11 and a plurality of ONUs 13, 14, and 15 are connected in a tree form through a passive coupler 13, which is a passive optical device. In EPON, the OLT 11 is mainly located at a telephone station or a head-end and plays a role similar to that of a Digital Subscriber Line Access Multiplex (DSLAM) device that controls DSL or cable modem services. The mission of the OLT 11 in EPON is to broadcast downlink traffic signals to EPON service subscribers in a broadcast manner, and to control and aggregate the upstream traffic signals transmitted from the ONUs 13, 14, and 15 according to their priorities. It is passed to a transmission network such as the Internet 17 or a public telephone network (PSTN) 16. In EPON, the ONUs 13, 14, and 15 receive optical signals, convert them into Ethernet frames of electrical signals, and deliver them to end users 18, 19, and 20 to provide various services, or vice versa. The data to be transmitted from 20) is converted into an optical signal and transmitted to the OLT 11.

4 is an explanatory diagram for explaining an uplink and a downlink transmission method between an OLT and an ONU in the EPON system of FIG. 3.

In the case of downlink transmission, the OLT 11 transmits the downlink data 21 to the ONUs 13, 14, and 15 in a broadcast manner. The broadcasted data is transmitted to the end users 18, 19, and 20 by the ONU 13, 14, and 15 selecting only data suitable for themselves through a unique ID. On the other hand, in the case of uplink transmission, the OLT 11 analyzes the request bandwidth information of the REPORT message arriving from the ONU 13, 14, and 15, determines the allocated bandwidth by the dynamic band allocation algorithm, and records the bandwidth information in the GATE message. To the ONU (13, 14, 15) in a unicast manner. The ONUs 13, 14, and 15 cause the OLT 11 to transmit uplink data 22 by the allocated bandwidth specified in the GATE message.

5 and 6 illustrate a GATE message operation procedure which is a procedure required when an OLT allocates bandwidth to an ONU and a REPORT message operation procedure which is a procedure required when an ONU requests bandwidth from an OLT in accordance with the present invention.

First, the Gate message procedure of FIG. 5 will be described.

(1) From the MAC Control Client 312, the OLT 311 receives a request for generating a GATE message to be sent to a specific ONU 326. In this case, the GATE message includes a transmission start time 313 and a transmission length 314.

(2) Since the OLT 311 and the ONU 326 exchange data in a TDMA manner, synchronization is required to avoid collisions. To this end, when the GATE message is transferred from the MAC control client 312 to the MAC control unit 315, the clock register 316 of the MAC control unit 315 stores time information recorded in a time slot of the GATE message. Will be updated.

(3) The GATE message passes through the MAC layer 317 and the PHY layer 318 of the OLT 311, the MAC control unit of the ONU 324 via the PHY layer 319 and the MAC layer 320 of the ONU 324 ( 321).

(4) The MAC controller 321 receiving the GATE message synchronizes the time information with the OLT 311 through the transmission start time 322, the transmission stop time 323, and the clock register 324 of the GATE message. . The processed GATE message then enters the MAC control client 325.

(5) Upon receiving the GATE message, the ONU 326 generates MA_DATA.request 327 and transmits an Ethernet frame through the uplink data transmission path 328. The MA_DATA.request 327 includes Ethernet frame data transmitted using the allocated band and information of a REPORT message to be requested next.

Next, the REPORT message operation procedure of FIG. 6 is as follows. The REPORT message is sent from the ONU 410 to the OLT 423. The REPORT message may be sent automatically at the request of the OLT 423.

(1) The REPORT message is generated at the MAC control client 411 of the ONU 410. The generated REPORT message contains information about the start time 412 and the end time 413.

(2) The REPORT message is sent to the MAC control unit 414, which is the next lower layer, to synchronize the time information with the OLT in the clock register 415. In the REPORT message, information on the amount of timeslots to be transmitted next is recorded, which is determined by the amount of packets waiting in the transmission queue of each ONU.

(3) The REPORT message is passed through the MAC layer 416 of the ONU 410 and the PHY layer 417, and the MAC control unit 420 of the OLT 423 via the PHY layer 418 MAC layer 419 of the OLT 412. To enter.

(4) The MAC control unit 420 synchronizes the time synchronization stored by the clock register 415 of the ONU 410 of the REPORT message, and uses this time to round the round trip time between the ONU 410 and the OLT 423. Trip Time: RTT) 421 is calculated.

(5) The REPORT message that matches the time synchronization signal with the RTT 421 for the ONU 410 is transmitted to the MAC control client 422, which is the next higher layer.

7 shows a conceptual diagram of bandwidth allocation in an adaptive limited method according to the present invention.

)(602)을 결정한다.The adaptive limited method takes into account the packet delay information for each ONU in cycle t-1 (601) and the maximum allocated bandwidth for each ONU in cycle t (609).

(602).

)(602)에 따라 각 ONU가 전송한 패킷 지연 정보를(603) 고려하여 사이클 t에 적용할 (

)를 아래와 같은 수학식에 의거하여 계산한다(605). 이때 (

)계산은 새로운 사이클이 시작되는 시점에서 수행된다(604).Dynamic maximum allocated bandwidth for each ONU in cycle t-1 (601)

According to (602), the packet delay information transmitted by each ONU is taken into consideration and applied to cycle t (

) Is calculated based on the following equation (605). At this time (

The calculation is performed 604 at the beginning of a new cycle.

)은 아래의 수학식1과 같다.In the adaptive limited scheme, the total maximum allocated bandwidth (

) Is shown in Equation 1 below.

= 리미티드 Max이다.Where N = Number of ONUs,

= Limited Max.

First, an average packet delay time for each ONU is calculated (606). For the i-th ONU, it is calculated by Equation 2 as follows.

는 t-2까지의 i번째 ONU의 평균 패킷 지연시간을 나타내고,

Denotes the average packet delay time of the i th ONU up to t-2,

은 t-1에서의 i번째 ONU의 패킷 지연시간을 나타낸다.

Denotes the packet delay time of the i-th ONU at t-1.

In addition, avg_delay [t-1] of all ONUs is calculated by Equation 3 as follows (607).

)을 다음과 같은 수학식4에 의해 결정한다(608).Dynamic maximum allocation bandwidth for each ONU using avg_delay [t-1] determined above (

) Is determined by Equation 4 as follows (608).

)은 사이클 t의 각 ONU별 최대 할당 대역폭(

)로 적용된다. This process determines the dynamic maximum allocation bandwidth (

) Is the maximum allocated bandwidth for each ONU in cycle t (

Is applied.

)를 사용하여 전체 사이클 시간의 변동폭을 최소화하였다.Through this algorithm, the adaptive limited scheme is more flexible than the conventional limited scheme, and the packet delay fairness control between ONUs can be controlled by differentiating the bandwidth allocation according to the packet delay for each ONU. Adaptively variable (

) To minimize fluctuations in overall cycle time.

8 is a flowchart illustrating a dynamic band allocation method of an adaptive limited method according to the present invention.

)을 할당하기 위한 알고리즘을 수행한다(S612). ONU별 최대 할당 대역폭(

) 알고리즘은 상기 서술한 바와 같다. 이와 같이 할당된

을 각 ONU에게 적용하기 위하여 OLT내에 저장한다(S613). 만약 사이클이 이미 시작되었다면 해당 사이클에 적용될

는 이미 결정된 상태이며, ONU로부터 전송된 Request 메시지 수신을 대기한다.As shown therein, the OLT checks the starting point S611 of the cycle t to determine the maximum allocated bandwidth for each ONU to be used in the cycle t.

In step S612, an algorithm for allocating the algorithm is performed. Maximum allocated bandwidth per ONU (

) Algorithm is as described above. Assigned like this

Is stored in the OLT to apply to each ONU (S613). If a cycle has already started, it will be applied to that cycle.

Is already determined and waits for the request message sent from the ONU.

이하일 경우 할당 대역폭은 ONU가 요청하는 대역폭 전부를 할당해 준다(S616). 그러나 요청 대역폭이 최대 할당 대역폭 이상일 경우, 할당 대역폭을 최대 할당대역폭으로 제한한다(S617). When the OLT receives the request message transmitted from the ONU, it analyzes it (S614) and calculates a bandwidth to be allocated to the ONU (S615). If the bandwidth requested by the ONU is the dynamic maximum allocated bandwidth

If less than the allocated bandwidth allocates all the bandwidth requested by the ONU (S616). However, if the request bandwidth is greater than or equal to the maximum allocation bandwidth, the allocation bandwidth is limited to the maximum allocation bandwidth (S617).

The OLT transmits the allocated bandwidth information to the ONU using the GATE message (S618).

According to the present invention described above, by applying the adaptive limited method has an advantage that can support more efficient and stable band allocation than the conventional limited method.

In addition, it is possible to solve the problem of the existing limited method by setting the maximum allocation bandwidth that is adaptively variable according to the traffic situation, it is effective to improve the performance of the EPON, and to provide a more stable service to the user There is an advantage.

Claims (8)

In a method in which an optical line terminal (OLT) and a plurality of optical network units (ONU) allocate a band to a subscriber in an EPON system configured in a tree form through a passive optical splitter, Determining a dynamic maximum allocation bandwidth for each ONU in a specific cycle in consideration of the packet delay information for each ONU when the cycle is started by checking the cycle in the OLT; Receiving a bandwidth allocation request message from the ONU, comparing the bandwidth requested by the ONU with the determined dynamic maximum allocation bandwidth and determining a bandwidth to be allocated to the ONU according to the magnitude; And a third step of creating a gate message including the determined allocated bandwidth information and transmitting the same to the ONU. The method of claim 1, wherein the dynamic maximum allocation bandwidth is set based on a sum of the maximum allocation bandwidths given to the N ONUs. The method according to claim 1, wherein the packet delay information for each ONU is calculated by the following Equation. Equation

In the above,

Denotes the average packet delay time of the i th ONU up to t-2,

Denotes the delay time of the packet delay time of the i-th ONU at t-1, and α is a constant between 0 and 1. FIG. 4. The method of claim 3, wherein the packet delay time for each ONU is calculated by the following Equation. Equation

The method of claim 1, wherein the dynamic maximum allocation bandwidth for each ONU is calculated based on Equation (1) below. Equation

The method of claim 1, wherein the determination of the bandwidth to allocate to the ONU of the second step, The request bandwidth included in the bandwidth allocation request message transmitted from the ONU is compared with the determined dynamic maximum allocation bandwidth, and when the request bandwidth is less than or equal to the dynamic maximum allocation bandwidth, all the bandwidths requested by the ONU are allocated. Dynamic bandwidth allocation method in the EP system, characterized in that if the maximum allocation bandwidth or more limit the allocation bandwidth to the maximum allocation bandwidth. 2. The method of claim 1, wherein a large amount of bandwidth is allocated to a large number of ONUs waiting for the determination of the maximum allocation bandwidth to reduce the variation in the total cycle time. In a method in which an optical line terminal (OLT) and a plurality of optical network units (ONU) allocate a band to a subscriber in an EPON system configured in a tree form through a passive optical splitter, Determining a dynamic maximum allocation bandwidth for each ONU in a specific cycle in consideration of the packet delay information for each ONU when the cycle is started by checking the cycle in the OLT; When receiving a bandwidth allocation request message from the ONU, comparing the bandwidth requested by the ONU with the determined dynamic maximum allocation bandwidth; Allocating all bandwidths requested by the ONU when the bandwidth requested from the ONU is equal to or less than the dynamic maximum allocated bandwidth; Determining an allocation bandwidth by limiting the allocation bandwidth to the maximum allocation bandwidth when the bandwidth requested from the ONU is equal to or larger than the maximum allocation bandwidth; And creating a gate message including the determined bandwidth information and transmitting the same to the ONU.

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