CN102629916B - A kind of EPON distribution method of dynamic bandwidth of improvement - Google Patents

Abstract

The invention provides an improved DBA algorithm to solve the problem of bandwidth allocation in the EPON system, which is characterized in that: first, the last bandwidth request and data frame in each cycle first sends the bandwidth request, so that the transmission can be used The data time is used to allocate bandwidth, so that the cycle loss is reduced. In the second aspect, a linear prediction coefficient is introduced to make up for data requests received during the waiting time for authorization. Finally, the bandwidth is allocated twice to make full use of the bandwidth fragments allocated once. Starting from the above three methods, cycle loss can be greatly reduced, bandwidth utilization can be improved, and service delay can be reduced.

Description

An Improved EPON Dynamic Bandwidth Allocation Method

technical field

The invention relates to the field of optical access networks, in particular to the use of a novel DBA algorithm to solve the problem of bandwidth allocation in an Ethernet optical access network (EPON) network.

Background technique

The EPON system was launched early, the technology is mature, and the corresponding equipment, chips, and industrial chain are sound. It is one of the main optical access network technologies at present. It has been used on a large scale in Japan, South Korea and other Asian countries, and it is gradually getting better in my country. The uplink and downlink bandwidth of EPON is 1Gbps, the downlink is accessed by broadcasting, and the uplink is accessed by TDMA.

EPON system is generally composed of optical line terminal (OLT), optical splitter (POS) and optical network unit (ONU). The OLT is the core of the EPON system, and the main allocation algorithm is implemented in it, which is responsible for allocating bandwidth to each user. POS is equivalent to the function of a switch, which mainly realizes the intercommunication and exchange of uplink and downlink messages; ONU is mainly used to buffer and store bandwidth requests of users. Because the uplink bandwidth of EPON is limited, the research on uplink bandwidth allocation algorithm has always been the core issue of EPON system.

At present, the main DBA algorithms are mainly based on two categories: one is based on the IPACT algorithm, and the other is based on the CPFCT algorithm. The IPACT algorithm is mainly based on the REPORT/GATE interaction mechanism. Whenever the OLT receives a bandwidth request REPORT from an ONU, it will immediately allocate a GATE. The difference between adjacent ONUs is only a guard time slot, so that the uplink bandwidth can be fully utilized. However, its polling cycle is not fixed and changes with the load. Under light load conditions, there will be a large number of REPORT/GATE frames, resulting in a waste of bandwidth. In addition, the polling period is not fixed, which will lead to unstable delay and delay jitter, which is intolerable for sensitive services such as EF services. The CPFCT algorithm is also based on the REPORT/GATE interaction mechanism. Unlike IPACT, the OLT does not immediately allocate a GATE if it does not receive a bandwidth request report from an ONU, but waits until all ONU report frames are collected, and allocates bandwidth uniformly. The CPFCT algorithm has a fixed polling cycle, and the delay and jitter are relatively constant. It has become the first choice of the dynamic bandwidth allocation algorithm. However, due to the time required for DBA, there is a certain cycle loss.

Therefore, researching a more ideal CPFCT dynamic bandwidth algorithm to make the cycle loss of the new CPFCT algorithm smaller is still a hot issue worthy of research.

Contents of the invention

In view of the above-mentioned analysis of the advantages and disadvantages of the current CPFCT dynamic algorithm, the purpose of the present invention is to provide an improved EPON dynamic bandwidth allocation method for bandwidth allocation of optical access networks.

The improved EPON dynamic bandwidth allocation method of the present invention is characterized in that:

(1) The last ONU in the EPON system sends the request first, and then sends the data;

(2) Data source prediction model;

(3) Secondary allocation of bandwidth.

in:

(1) The last ONU in the EPON system sends the request first, and then sends the data; it is used to collect all the requests in advance, and then use the time of data transmission to offset part of the data processing time, so that the cycle loss will inevitably be reduced and the bandwidth utilization rate will be reduced. Improve naturally.

(2) The data source prediction model is a linear prediction model used to predict the data source; during the time when the ONU sends the request to the OLT and the ONU receives the authorization sent by the OLT, the ONU is still receiving the user's request , in the original authorization request mechanism, this part of the request will not be processed until the next cycle, so the delay of this part of the request will be very large, but after the introduction of the data source prediction model, this part of the request can be partly in this part Periodic transmission, the delay is naturally reduced.

(3) Secondary allocation of bandwidth is used to re-allocate the once-allocated fragments; in the traditional dynamic allocation method, the received request is only allocated once, so that the bandwidth of the light-loaded ONU remains, and the bandwidth of the heavy-loaded ONU Insufficient bandwidth causes a waste of bandwidth. How to use the remaining bandwidth of light-loaded ONUs to make up for the insufficient bandwidth of heavy-loaded ONUs is the entry point for the introduction of secondary distribution.

The improved EPON dynamic bandwidth allocation method described above is characterized in that:

(1) The existing total bandwidth is Among them, T _cycle is the polling cycle, T _guard is the guard time slot, N is the number of ONUs, R is the data transmission rate, and the uplink and downlink bandwidth of EPON is 1Gbps, that is, 1/8GBps.

(2) The guaranteed bandwidth of the i-th ONU is Where Wi is the service level weight of the ONU.

(3) The allocated bandwidth of the three services (EF, AF, BE) of the i-th ONU is

(4) Secondary allocation of bandwidth; ONUs with light loads will have excess bandwidth. In order to make full use of this part of bandwidth, secondary allocation of bandwidth can be carried out, and this part of bandwidth can be allocated to heavy-loaded ONUs, thereby improving bandwidth utilization. . The remaining bandwidth after the first allocation is B _excess =∑B″i;

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; BE</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{{\mathrm{<span\; class="notranslate">\; BE</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{{\mathrm{<span\; class="notranslate">\; AF</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{{\mathrm{<span\; class="notranslate">\; BE</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; excess</span>}}<span\; class="notranslate">\; .</span>$

The above-mentioned improved EPON dynamic bandwidth allocation method is characterized in that: the allocated bandwidth of the three services (EF, AF, BE) of the i-th ONU: The allocated bandwidth for EF services is in Indicates the EF service request bandwidth, It is the request coefficient generated in the process of waiting for allocation, and T _wait is the time from sending the request to the time before the OLT sends the authorization for the EF service.

(1) The remaining bandwidth of the i-th ONU after removing the EF service is

A. Under light load conditions, ie

The allocated bandwidth for the AF service is in Indicates the requested bandwidth of the AF service.

The allocated bandwidth for BE services is in Indicates the requested bandwidth of the BE service.

The remaining bandwidth after allocating the three services is

B. Heavy load conditions, i.e.

The bandwidth allocated to the AF service for the first time is $G_{i1}^{\mathrm{AF}}=\mathrm{MIN}\{(1+\&PartialD;)*R_i^{\mathrm{AF}},B_i^{\&prime;}\};$

The bandwidth allocated for the BE service for the first time is

The unallocated bandwidth of the AF service is

The unbatched bandwidth of BE services is

The improved EPON dynamic bandwidth allocation method described above is characterized in that:

(1) Light load ONU, namely The ONU whose EF service is allocated bandwidth is The allocated bandwidth for its AF service is The allocated bandwidth of its BE service is $G_i^{\mathrm{BE}}=(1+\&PartialD;)*R_i^{\mathrm{BE}};$

(2) Heavy load ONU, namely The ONU whose EF service is allocated bandwidth is The allocated bandwidth for its AF service is The allocated bandwidth of its BE service is $G_i^{\mathrm{BE}}=G_{i1}^{\mathrm{BE}}+G_{i2}^{\mathrm{BE}}.$

Outstanding substantive features and remarkable progress of the present invention are:

(1) The last ONU adopts the scheduling mechanism of reporting the request first and sending data, which can use the time of data transmission to offset part of the processing time, so that the cycle loss is reduced, and the bandwidth utilization rate has been improved to a certain extent.

(2) Introduce the data source linear prediction model, so that the data received between the ONU sending the request to the OLT and the ONU obtaining the OLT authorization can be authorized in this cycle, thereby reducing the delay of this part of the data and reducing the service delay There is some help.

(3) The secondary allocation of bandwidth enables the remaining bandwidth of the primary allocation to be reused, which is conducive to the improvement of bandwidth utilization.

Description of drawings

Fig. 1 is a schematic diagram of the EPON system of the present invention.

Fig. 2 is an algorithm sequence diagram of the present invention.

Fig. 3 is a flowchart of an OLT node.

Fig. 4 is a flowchart of an ONU node.

Figure 5 is a comparison of the bandwidth utilization of the three algorithms under light load.

Figure 6 is a comparison of the bandwidth utilization of the three algorithms under heavy load.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings, but the scope of the present invention is not limited in any way.

1. Simplified Block Diagram

As shown in Figure 1, a simple EPON system is composed of an optical line terminal (OLT), an optical splitter (PoS), and 16 optical user ports (ONU).

Fig. 2 is a simple sequence diagram of the present invention. To simplify the process, only the scheduling process of two ONUs is shown in this sequence diagram. The first ONU transmits data to the OLT according to the normal data first and then the Report frame; the second ONU sends the Report frame first, and then sends the data. After receiving the Report frame, the OLT allocates time slots uniformly. The polling period is 2ms.

2. Specific examples of structural schemes

As shown in Figure 3, after receiving the data packet, the OLT first judges whether it is from the ONU or from its own interrupt. If it comes from itself, it will format the data packet and send it. If it comes from ONU, judge the type of data packet, if it is a discover_req frame, create a register frame and send it; if it is a report frame, create a GATE frame and send it; if it is a register_ack frame, record the round-trip time RTT.

As shown in Figure 4, after the ONU receives the data packet, it judges whether it is from the OLT or from its own interrupt. If it is itself, it will format the data packet and store it for sending; if it is from the OLT, it will be judged to be a discover frame. , GATE frame, or register frame, if it is a discover frame, create a register_req frame and send it; if it is a GATE frame, send data, and create a report frame; if it is a register frame, create a register_ack frame and send it.

With the aid of simulation software, an EPON optical access network with 18 nodes as shown in Figure 1 is established according to the algorithm proposed by the present invention. The performance comparison charts of the new algorithm and the classic IPACT and CPFCT algorithms are obtained. As can be seen from Figures 5 and 6, the new algorithm is superior to IPACT and CPFCT algorithms in terms of delay, in terms of bandwidth utilization, it is second only to IPACT under light loads, and is superior to IPACT and CPFCT algorithms under heavy loads.

Application example: In order to solve different business needs, the telecommunications department divides the user's business into three categories: voice, video, and information. Among them, the voice belongs to the EF type service, which is sensitive to delay and jitter, and there should be no too much delay, otherwise the communication quality will not be high; the video belongs to the AF type service, which has certain requirements on the delay; the information belongs to the BE type, and the delay is not too large Require. The three business priorities are high, medium and low. At present, the access network technology with better commercialization and broadband is EPON. In order to realize the scheduling of the three services, the EPON system can use this algorithm. Compared with other algorithms, after simulation, it has higher bandwidth utilization and better performance. low latency.

The above are the embodiments of the present invention. According to the disclosed content of the present invention, some similarities and alternatives that those skilled in the art can obviously think of should fall into the protection scope of the present invention.

Claims (1)

1. the EPON distribution method of dynamic bandwidth improved, is characterized by:

(1) last ONU in EPON system, first sends request, rear transmission data;

(2) data source forecast model;

(3) bandwidth secondary is distributed;

In described EPON system, last ONU, first sends request, rear transmission data; For collecting all requests in advance, recycling transmits the time of data, offsets a part of data processing time, reduces cycle loss, improves bandwidth availability ratio;

Described data source forecast model is a kind of linear prediction model, for predicting data source; Send request at ONU to OLT and receive the mandate of OLT transmission during this period of time to ONU, ONU is also receiving the request of user, and the requested part of this part sent in this cycle, reduces time delay;

Described bandwidth secondary is distributed, for carrying out sub-distribution again to the fragment of primary distribution; Utilize the remaining bandwidth of underload ONU, the bandwidth making up heavy duty ONU is not enough;

In the EPON distribution method of dynamic bandwidth of above-mentioned improvement:

(1) existing total bandwidth is B= ; Wherein for polling cycle, for protection time slot, for the number of ONU, R is data transmission rate, and EPON upstream and downstream bandwidth is 1Gbps, i.e. 1/8GBps;

(2) i-th ONU ensure that bandwidth is B _i= ; Wherein it is the grade of service weight of ONU;

The bandwidth that three kinds of business (EF, AF, BE) of (3) i-th ONU are assigned with is , , ; The bandwidth that wherein EF business is assigned with is, = (1+ ); Wherein represent EF service request bandwidth, = for waiting request coefficient produced in process to be allocated, for EF business sends the time before authorizing from transmiting a request to OLT;

(4) i-th ONU remove EF business remaining bandwidth and are = ;

(5) secondary distribution of bandwidth; Underloaded ONU has bandwidth left, in order to make full use of this part bandwidth, can carry out the secondary distribution of bandwidth, gives heavy duty ONU by this part allocated bandwidth, thus improves the utilance of bandwidth;

Distributing remaining bandwidth through first time is = ;

AF business by the bandwidth of secondary distribution is = ;

BE business by the bandwidth of secondary distribution is = ;

In formula,

A. under light load condition, namely ( ) (1+ ) <

The bandwidth that AF business is assigned with is =(1+ ) * ; Wherein for the bandwidth on demand of AF business;

The bandwidth that BE business is assigned with is =(1+ ) * ; Wherein for the bandwidth on demand of BE business;

After distributing three kinds of business, remaining bandwidth is = ;

B. in heavy duty situation, namely ( ) (1+ ) >

The bandwidth that AF business first time is assigned with is =MIN{ (1+ ) * , ;

The bandwidth that BE business first time is assigned with is =MIN{0, ;

The bandwidth that AF business is not assigned with is = ;

The bandwidth that BE business is not assigned with is = ;

Underload ONU and heavy duty ONU is defined as follows: