* Results of revenue mobilization
By the end of 2016, Nghe An Provincial Forest Protection Fund had collected : 271,249 million VND, of which: 2012: 43,281 million VND, 2013: 44,336 million VND
SITUATION OF DVMTR MONEY COLLECTION OVER THE YEARS
69,261
70,000
64,963
60,000
50,000
40,000
30,000
20,000
10,000
0
43,281
44,336
49,408
Total revenue
Year Year Year Year 2012 2013 2014 2015 2016
(Year)
Million Dong
VND, 2014: 49,408 million VND, 2015: 69,261 million VND, 2016: 64,963 million VND. This revenue will be doubled in the coming years due to the unit price being adjusted according to the provisions of Decree 147/2016/ND-CP dated November 2, 2016 of the Government amending and supplementing a number of articles of Decree 99/2010/ND-CP. At the same time, expand revenue from industrial production establishments using water sources, tourism services benefiting from DVMTR, services providing spawning grounds, food sources and natural seeds, aquaculture, etc.
Chart 4.1. Revenue mobilization results over the years
* Disbursement results
Accumulated to the end of the 2016 disbursement plan, the BVPTR Fund has disbursed a total of 224,091 million VND. The disbursement results over the years are as follows: 2012: 17,564 million VND, 2013: 20,494 million VND, 2014: 27,336
million VND, 2015: 78,120 million VND, 2015: 80,576 million VND
TOTAL DVMTR EXPENDITURE OVER THE YEARS
90000.0
80000.0
Million Dong
70000.0
60000.0
50000.0
40000.0
30000.0
20000.0
10000.0
-
2012
2013
2014
2015
2016
Total cost
78120.209
80576.201
20494.018
27335.536
17563.501
Year
Chart 4.2. Disbursement situation over the years
* Impact on forest protection and development
In fact, along with the drastic solutions of the Government, the Provincial People's Committee and relevant parties, the policy of paying for forest environmental services has been effective, having a very positive impact on forest management, protection and development. Forests are better protected, violations of legal regulations on forest protection, development, forest fire prevention and fighting have gradually decreased over the years. In 2011, the number of forestry law violations in the province was 1,366 cases, in 2012 it was 1,267 cases, in 2013 it was 1,141 cases, in 2014 it was 856 cases, in 2015 it was 695 cases, in 2016 the number of violations decreased to only 275 cases (Data provided by Nghe An Forest Protection Department) .
NUMBER OF VIOLATIONS IN MANAGEMENT AND PROTECTION OVER THE YEARS
1,500
Number of cases
1,000
500
-
2011 2012 2013 2014 2015 2016
Number of violations
1,366
1,267
1,141
856
695
275
Year
Chart 4.3. Number of forestry law violations over the years
The policy has gradually contributed to stabilizing and ensuring forest area, maintaining forest cover, improving forest quality and contributing to improving the quality of the ecological environment. The area of BVR contracted tends to increase rapidly every year, affirming the expectations and trust of forest owners and people in the benefits that the policy brings specifically: In 2013, it was 47,034.72 ha, in 2014, it was 95,112.57 ha, in 2015, the total area of BVR contracted that had been recorded and paid was 228,106.85 ha (according to the results of the BR TKKT dossier approved by competent authorities and the area accepted) , by 2016, the total area of BVR contracted with records was: 274,600.97 ha
SUMMARY OF SERVICE PROVIDING AREA
OVER THE YEARS
274,600.9
228,106.85
95,112.57
47,034.72 47,034.72
300,000.00
Area (ha)
250,000.00
200,000.00
150,000.00
100,000.00
50,000.00
Chart 4.4. Area of DVMTR supply over the years
* Improve the livelihoods of forest workers
The results from the implementation of the forest environmental service payment policy have not only gradually raised the sense of responsibility of forest owners, increased the number of households contracted to protect forests, but also mobilized a large human resource for regular forest patrolling and protection. The number of forest owners benefiting from forest environmental service payments has increased each year, while the number of organizations, households and individuals participating in forest protection contracts has increased. Specifically: In 2012, the number of forest owners benefiting from forest environmental service payments was 3 forest owners who were organizations with 765 contracts; By 2016, the number of forest owners was 6,351 and the total number of contracts was 1,756, including 11 forest owners who were organizations, 51 commune People's Committees, 6,289 households, individuals and communities with long-term land allocation.
Thanks to the implementation of the policy, the average real income of households and individuals contracted to protect forests has gradually improved. As in the water basin
Hua Na/Cua Dat power plant, in 2015, each household contracted to protect 30 hectares of forest, the income from forest environmental services reached 12,000,000 million VND/household/year . Along with other income, forest environmental services have contributed to creating jobs, reducing poverty, improving livelihoods, helping people feel secure in their attachment to the forest, contributing to stabilizing political security, social order and safety in localities in mountainous and border areas.
4.1.3. Difficulties, problems and obstacles in the implementation process
- The implementation of the responsibility of declaring and paying the trust money of some facilities using DVMTR is still slow and not timely according to the prescribed schedule, affecting the accounting and unit price calculation.
- The large difference in payment prices between basins in the province has a significant impact on policy implementation. The payment prices for forest environmental services in some basins are very low (Khe Bo, Sao Va, Nam Pong, Nam On, Chi Khe...), leading to forest owners' hesitation and comparison. For basins with low payment prices, it is difficult to encourage people to actively protect and develop forests.
- The collection of fees for converting forest use to other purposes according to Decree No. 05/2008/ND-CP from 2012 and earlier still faces many difficulties. At the same time, Circular 26/2015/TT-BNNPTNT dated July 29, 2015 stipulates that replacement forest planting can only be arranged for protective and special-use forests, which is very difficult, affecting the progress of replacement forest planting.
4.1.4. General assessment and lessons learned
4.1.4.1. General assessment
- On the activities of the BVPTR Fund
The Fund for Protection and Development of Forests has implemented the policy of payment for forest environmental services well in the province. However, the organizational model and operation methods are not unified and synchronized from the central to local levels, so some contents are directed by many agencies at the same time, so there is sometimes overlap in direction and management. In addition, the implementation of the autonomy mechanism is not unified and there is no similarity between financial autonomy and autonomy in organization and operation, so the role of the Fund has not been fully promoted.
- About DVMTR payment policy
After 5 years of implementation, the Payment for Forest Environmental Services Policy in Nghe An province has achieved many positive results and valuable lessons learned during the process.
implementation process. The implementation results show that this is a correct policy and consistent with the practice of forest protection and sustainable forest development in Nghe An in particular and the whole country in general. The policy has gradually entered life, linking the interests of forest environmental service users and forest protectors, creating a sustainable economic link between users and suppliers of forest environmental services. Most of the cadres and people in the area receiving payment for forest environmental services have a deep understanding of the meaning and importance of implementing the policy, seeing the responsibilities and rights of service providers through forest protection and the increasingly improved forest protection work.
4.1.4.2. Lessons learned
- The role of local authorities and people's cooperation are very important in implementing the policy of payment for forest environmental services;
- Propaganda work to raise awareness of the significance of the policy on payment for forest environmental services is very necessary and plays a very important role in determining the success in organizing the implementation of the task of collecting and spending money for forest environmental services. Therefore, it is necessary to promote propaganda, dissemination and fully disseminate the policy content to relevant agencies and organizations, especially those who have the right and obligation to implement the policy on payment for forest environmental services;
- The statistical classification of subjects that must pay for forest environmental services, determining forest area and forest status for each forest owner who is paid for forest environmental services is a very important step in implementing the policy of paying for forest environmental services. In order to have a basis for paying for forest environmental services to forest owners and subjects providing forest environmental services quickly, the work of reviewing and preparing design documents for forest protection contracts must be implemented promptly and accurately;
- There needs to be synchronous and drastic coordination between all levels and sectors in assigning tasks and organizing the implementation and synchronous deployment of the payment mechanism and system for forest environmental services at all levels from province, district, and commune to suit the conditions of each locality, which is necessary to carry out the payment for forest environmental services;
- It is necessary to strengthen inspection and supervision of payment activities, forest protection organization, mechanisms, management and use, and content related to the payment policy for forest environmental services;
- As a new operating model and new policy, it is necessary to regularly research and advise on amending and supplementing regulations and instructions to suit local realities.
(Attached with Appendix 01: Summary of policy implementation indicators in Nghe An province).
4.2. Current status of payment for forest environmental services in Que Phong district, Nghe An province
4.2.1. Procedure for implementing payment for forest environmental services
To implement the policy, the People's Committee of Que Phong district has established a Steering Committee to deploy and implement the policy of payment for forest environmental services in the district, headed by the Chairman of the People's Committee of the district. Along with the provincial forest environmental service payment system, in Que Phong, forest environmental services are paid by the provincial Forest Protection Fund through 2 focal points:
- Payment through forest owners who are organizations: Pu Hoat Nature Reserve Management Board makes payments to forest protection contracted units, organizations, households, and household groups for the area under the management of the Management Board.
Protected forests
- Payment through district-level payment organization: Assign Que Phong Forest Protection Department as the focal agency for payment of forest environmental services at district level to make payment for the forest area managed by households, individuals, village/hamlet communities and the Commune People's Committee.
Company using DVMTR
Central Fund for Protection and Development
Forest owner is an organization
Company using DVMTR
Provincial Fund for Forest Protection and Development
District level payment organization (District Forest Protection Department)
Contracted households
Forest owners are households, individuals, village and hamlet communities.
Commune People's Committee
Protected forests
Figure 4.2. Payment diagram for forest environmental service entrustment
4.2.2. Conditions for implementing the DVMTR payment policy
4.2.2.1. Determining the subjects that must pay and the level of payment for DVMTR
Up to now, Que Phong district has identified the subjects that must pay for forest environmental services, including hydropower plants inside and outside the province that use forest environmental services in the area, including 05 plants that have signed contracts to entrust payment for forest environmental services, of which Chau Thang hydropower plant has completed construction and has a plan to generate electricity in the first quarter of 2017, and 06 facilities are under construction. This is a very favorable condition for implementing the policy of paying for forest environmental services in Que Phong district.
Table 4.2. List of hydropower plants using DVMTR in Que Phong district
TT
Factory name | Management and operation company | House Construction Site machine | Plant capacity (MW) | DVMTR payment time | |
I. Hydropower plants have signed contracts to entrust payment of forest environmental services | |||||
1 | Cua Dat Hydropower Plant | Vinaconex Energy Investment and Development Joint Stock Company | Xuan Cam Commune, Thuong Xuan District, Thanh Hoa | 100 | 2013 |
2 | Hydroelectric Hua Na | Joint Stock Company Hua Na Hydropower Plant | Dong Van Commune, Que Phong | 180 | 2013 |
3 | Hydroelectric Ban Coc | Hydropower Joint Stock Company Que Phong | Chau Kim Commune, Que Phong | 18 | 2011 |
4 | Hydroelectric Sao Va | LLC Sao Va Hydropower Plant | Muong Noc Commune, Que Phong district | 3 | 2011 |
5 | Hydroelectric Chau Thang | Prime Joint Stock Company Que Phong | Chau Thon Commune, Que Phong district | 14 | Quarter II/2017 |
III. Hydroelectric plants under construction in the district | |||||
1 | Hydroelectric Quang River | Development Corporation Son Vu Energy | Chau Thon Commune, Que Phong district | 12 | Under construction build |
2 | Hydroelectric Village | Development Corporation Son Vu Energy | Chau Thon Commune, Que Phong district | 27 | Under construction build |
3 | Hydroelectric Crane Label | Za Hung Joint Stock Company | Que Son Commune, Que Phong district | 59 | Under construction build |
4 | Hydroelectric Dong Van | Hydropower Joint Stock Company Dakrong | Dong Van Commune, Que Phong district | 28 | Under construction build |
5 | Tien Hydropower Wind | Prime Joint Stock Company Que Phong | Tien Phong Commune, Que Phong district | 6 | Under construction build |
6 | Hydroelectric Nam Giai | Hydropower Joint Stock Company Nghe An Oil and Gas | Nam Giai Commune, Que Phong district | 4 | Under construction build |
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Evaluation of the effectiveness of the Forest Environmental Services Payment Policy on forest management and protection, improving people's lives in the Cua Dat Hydropower Plant Basin in Thanh Hoa province, period from 2012-2016 - 13 -
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low. The EF PHB requires a sufficiently large number of output ports to provide low delay, low loss, and low jitter.
EF PHBs can be implemented if the output ports bandwidth is sufficiently large, combined with small buffer sizes and other network resources dedicated to EF packets, to allow the routers service rate for EF packets on an output port to exceed the arrival rate λ of packets at that port.
This means that packets with PHB EF are considered with a pre-allocated amount of output bandwidth and a priority that ensures minimum loss, minimum delay and minimum jitter before being put into operation.
PHB EF is suitable for channel simulation, leased line simulation, and real-time services such as voice, video without compromising on high loss, delay and jitter values.
Figure 2.10 Example of EF installation
Figure 2.10 shows an example of an EF PHB implementation. This is a simple priority queue scheduling technique. At the edges of the DS domain, EF packet traffic is prioritized according to the values agreed upon by the SLA. The EF queue in the figure needs to output packets at a rate higher than the packet arrival rate λ. To provide an EF PHB over an end-to-end DS domain, bandwidth at the output ports of the core routers needs to be allocated in advance to ensure the requirement μ > λ. This can be done by a pre-configured provisioning process. In the figure, EF packets are placed in the priority queue (the upper queue). With such a length, the queue can operate with μ > λ.
Since EF was primarily used for real-time services such as voice and video, and since real-time services use UDP instead of TCP, RED is generally
not suitable for EF queues because applications using UDP will not respond to random packet drop and RED will strip unnecessary packets.
2.2.4.2 Assured Forwarding (AF) PHB
PHB AF is defined by RFC 2597. The purpose of PHB AF is to deliver packets reliably and therefore delay and jitter are considered less important than packet loss. PHB AF is suitable for non-real-time services such as applications using TCP. PHB AF first defines four classes: AF1, AF2, AF3, AF4. For each of these AF classes, packets are then classified into three subclasses with three distinct priority levels.
Table 2.8 shows the four AF classes and 12 AF subclasses and the DSCP values for the 12 AF subclasses defined by RFC 2597. RFC 2597 also allows for more than three separate priority levels to be added for internal use. However, these separate priority levels will only have internal significance.
PHB Class
PHB Subclass
Package type
DSCP
AF4
AF41
Short
100010
AF42
Medium
100100
AF43
High
100110
AF3
AF31
Short
011010
AF32
Medium
011100
AF33
High
011110
AF2
AF21
Short
010010
AF22
Medium
010100
AF23
High
010110
AF1
AF11
Short
001010
AF12
Medium
001100
AF13
High
001110
Table 2.8 AF DSCPs
The AF PHB ensures that packets are forwarded with a high probability of delivery to the destination within the bounds of the rate agreed upon in an SLA. If AF traffic at an ingress port exceeds the pre-priority rate, which is considered non-compliant or “out of profile”, the excess packets will not be delivered to the destination with the same probability as the packets belonging to the defined traffic or “in profile” packets. When there is network congestion, the out of profile packets are dropped before the in profile packets are dropped.
When service levels are defined using AF classes, different quantity and quality between AF classes can be realized by allocating different amounts of bandwidth and buffer space to the four AF classes. Unlike
EF, most AF traffic is non-real-time traffic using TCP, and the RED queue management strategy is an AQM (Adaptive Queue Management) strategy suitable for use in AF PHBs. The four AF PHB layers can be implemented as four separate queues. The output port bandwidth is divided into four AF queues. For each AF queue, packets are marked with three “colors” corresponding to three separate priority levels.
In addition to the 32 DSCP 1 groups defined in Table 2.8, 21 DSCPs have been standardized as follows: one for PHB EF, 12 for PHB AF, and 8 for CSCP. There are 11 DSCP 1 groups still available for other standards.
2.2.5.Example of Differentiated Services
We will look at an example of the Differentiated Service model and mechanism of operation. The architecture of Differentiated Service consists of two basic sets of functions:
Edge functions: include packet classification and traffic conditioning. At the inbound edge of the network, incoming packets are marked. In particular, the DS field in the packet header is set to a certain value. For example, in Figure 2.12, packets sent from H1 to H3 are marked at R1, while packets from H2 to H4 are marked at R2. The labels on the received packets identify the service class to which they belong. Different traffic classes receive different services in the core network. The RFC definition uses the term behavior aggregate rather than the term traffic class. After being marked, a packet can be forwarded immediately into the network, delayed for a period of time before being forwarded, or dropped. We will see that there are many factors that affect how a packet is marked, and whether it is forwarded immediately, delayed, or dropped.
Figure 2.12 DiffServ Example
Core functionality: When a DS-marked packet arrives at a Diffservcapable router, the packet is forwarded to the next router based on
Per-hop behavior is associated with packet classes. Per-hop behavior affects router buffers and the bandwidth shared between competing classes. An important principle of the Differentiated Service architecture is that a routers per-hop behavior is based only on the packets marking or the class to which it belongs. Therefore, if packets sent from H1 to H3 as shown in the figure receive the same marking as packets from H2 to H4, then the network routers treat the packets exactly the same, regardless of whether the packet originated from H1 or H2. For example, R3 does not distinguish between packets from h1 and H2 when forwarding packets to R4. Therefore, the Differentiated Service architecture avoids the need to maintain router state about separate source-destination pairs, which is important for network scalability.
Chapter Conclusion
Chapter 2 has presented and clarified two main models of deploying and installing quality of service in IP networks. While the traditional best-effort model has many disadvantages, later models such as IntServ and DiffServ have partly solved the problems that best-effort could not solve. IntServ follows the direction of ensuring quality of service for each separate flow, it is built similar to the circuit switching model with the use of the RSVP resource reservation protocol. IntSer is suitable for services that require fixed bandwidth that is not shared such as VoIP services, multicast TV services. However, IntSer has disadvantages such as using a lot of network resources, low scalability and lack of flexibility. DiffServ was born with the idea of solving the disadvantages of the IntServ model.
DiffServ follows the direction of ensuring quality based on the principle of hop-by-hop behavior based on the priority of marked packets. The policy for different types of traffic is decided by the administrator and can be changed according to reality, so it is very flexible. DiffServ makes better use of network resources, avoiding idle bandwidth and processing capacity on routers. In addition, the DifServ model can be deployed on many independent domains, so the ability to expand the network becomes easy.
Chapter 3: METHODS TO ENSURE QoS FOR MULTIMEDIA COMMUNICATIONS
In packet-switched networks, different packet flows often have to share the transmission medium all the way to the destination station. To ensure the fair and efficient allocation of bandwidth to flows, appropriate serving mechanisms are required at network nodes, especially at gateways or routers, where many different data flows often pass through. The scheduler is responsible for serving packets of the selected flow and deciding which packet will be served next. Here, a flow is understood as a set of packets belonging to the same priority class, or originating from the same source, or having the same source and destination addresses, etc.
In normal state when there is no congestion, packets will be sent as soon as they are delivered. In case of congestion, if QoS assurance methods are not applied, prolonged congestion can cause packet drops, affecting service quality. In some cases, congestion is prolonged and widespread in the network, which can easily lead to the network being frozen, or many packets being dropped, seriously affecting service quality.
Therefore, in this chapter, in sections 3.2 and 3.3, we introduce some typical network traffic load monitoring techniques to predict and prevent congestion before it occurs through the measure of dropping (removing) packets early when there are signs of impending congestion.
3.1. DropTail method
DropTail is a simple, traditional queue management method based on FIFO mechanism. All incoming packets are placed in the queue, when the queue is full, the later packets are dropped.
Due to its simplicity and ease of implementation, DropTail has been used for many years on Internet router systems. However, this algorithm has the following disadvantages:
− Cannot avoid the phenomenon of “Lock out”: Occurs when 1 or several traffic streams monopolize the queue, making packets of other connections unable to pass through the router. This phenomenon greatly affects reliable transmission protocols such as TCP. According to the anti-congestion algorithm, when locked out, the TCP connection stream will reduce the window size and reduce the packet transmission speed exponentially.
− Can cause Global Synchronization: This is the result of a severe “Lock out” phenomenon. Some neighboring routers have their queues monopolized by a number of connections, causing a series of other TCP connections to be unable to pass through and simultaneously reducing the transmission speed. After those monopolized connections are temporarily suspended,
Once the queue is cleared, it takes a considerable amount of time for TCP connections to return to their original speed.
− Full Queue phenomenon: Data transmitted on the Internet often has an explosion, packets arriving at the router are often in clusters rather than in turn. Therefore, the operating mechanism of DropTail makes the queue easily full for a long period of time, leading to the average delay time of large packets. To avoid this phenomenon, with DropTail, the only way is to increase the routers buffer, this method is very expensive and ineffective.
− No QoS guarantee: With the DropTail mechanism, there is no way to prioritize important packets to be transmitted through the router earlier when all are in the queue. Meanwhile, with multimedia communication, ensuring connection and stable speed is extremely important and the DropTail algorithm cannot satisfy.
The problem of choosing the buffer size of the routers in the network is to “absorb” short bursts of traffic without causing too much queuing delay. This is necessary in bursty data transmission. The queue size determines the size of the packet bursts (traffic spikes) that we want to be able to transmit without being dropped at the routers.
In IP-based application networks, packet dropping is an important mechanism for indirectly reporting congestion to end stations. A solution that prevents router queues from filling up while reducing the packet drop rate is called dynamic queue management.
3.2. Random elimination method – RED
3.2.1 Overview
RED (Random Early Detection of congestion; Random Early Drop) is one of the first AQM algorithms proposed in 1993 by Sally Floyd and Van Jacobson, two scientists at the Lawrence Berkeley Laboratory of the University of California, USA. Due to its outstanding advantages compared to previous queue management algorithms, RED has been widely installed and deployed on the Internet.
The most fundamental point of their work is that the most effective place to detect congestion and react to it is at the gateway or router.
Source entities (senders) can also do this by estimating end-to-end delay, throughput variability, or the rate of packet retransmissions due to drop. However, the sender and receiver view of a particular connection cannot tell which gateways on the network are congested, and cannot distinguish between propagation delay and queuing delay. Only the gateway has a true view of the state of the queue, the link share of the connections passing through it at any given time, and the quality of service requirements of the
traffic flows. The RED gateway monitors the average queue length, which detects early signs of impending congestion (average queue length exceeding a predetermined threshold) and reacts appropriately in one of two ways:
− Drop incoming packets with a certain probability, to indirectly inform the source of congestion, the source needs to reduce the transmission rate to keep the queue from filling up, maintaining the ability to absorb incoming traffic spikes.
− Mark “congestion” with a certain probability in the ECN field in the header of TCP packets to notify the source (the receiving entity will copy this bit into the acknowledgement packet).
Figure 3. 1 RED algorithm
The main goal of RED is to avoid congestion by keeping the average queue size within a sufficiently small and stable region, which also means keeping the queuing delay sufficiently small and stable. Achieving this goal also helps: avoid global synchronization, not resist bursty traffic flows (i.e. flows with low average throughput but high volatility), and maintain an upper bound on the average queue size even in the absence of cooperation from transport layer protocols.
To achieve the above goals, RED gateways must do the following:
− The first is to detect congestion early and react appropriately to keep the average queue size small enough to keep the network operating in the low latency, high throughput region, while still allowing the queue size to fluctuate within a certain range to absorb short-term fluctuations. As discussed above, the gateway is the most appropriate place to detect congestion and is also the most appropriate place to decide which specific connection to report congestion to.
− The second thing is to notify the source of congestion. This is done by marking and notifying the source to reduce traffic. Normally the RED gateway will randomly drop packets. However, if congestion
If congestion is detected before the queue is full, it should be combined with packet marking to signal congestion. The RED gateway has two options: drop or mark; where marking is done by marking the ECN field of the packet with a certain probability, to signal the source to reduce the traffic entering the network.
− An important goal that RED gateways need to achieve is to avoid global synchronization and not to resist traffic flows that have a sudden characteristic. Global synchronization occurs when all connections simultaneously reduce their transmission window size, leading to a severe drop in throughput at the same time. On the other hand, Drop Tail or Random Drop strategies are very sensitive to sudden flows; that is, the gateway queue will often overflow when packets from these flows arrive. To avoid these two phenomena, gateways can use special algorithms to detect congestion and decide which connections will be notified of congestion at the gateway. The RED gateway randomly selects incoming packets to mark; with this method, the probability of marking a packet from a particular connection is proportional to the connections shared bandwidth at the gateway.
− Another goal is to control the average queue size even without cooperation from the source entities. This can be done by dropping packets when the average size exceeds an upper threshold (instead of marking it). This approach is necessary in cases where most connections have transmission times that are less than the round-trip time, or where the source entities are not able to reduce traffic in response to marking or dropping packets (such as UDP flows).
3.2.2 Algorithm
This section describes the algorithm for RED gateways. RED gateways calculate the average queue size using a low-pass filter. This average queue size is compared with two thresholds: minth and maxth. When the average queue size is less than the lower threshold, no incoming packets are marked or dropped; when the average queue size is greater than the upper threshold, all incoming packets are dropped. When the average queue size is between minth and maxth, each incoming packet is marked or dropped with a probability pa, where pa is a function of the average queue size avg; the probability of marking or dropping a packet for a particular connection is proportional to the bandwidth share of that connection at the gateway. The general algorithm for a RED gateway is described as follows: [5]
For each packet arrival
Caculate the average queue size avg If minth ≤ avg < maxth
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Qos Assurance Methods for Multimedia Communications
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low. The EF PHB requires a sufficiently large number of output ports to provide low delay, low loss, and low jitter.
EF PHBs can be implemented if the output port's bandwidth is sufficiently large, combined with small buffer sizes and other network resources dedicated to EF packets, to allow the router's service rate for EF packets on an output port to exceed the arrival rate λ of packets at that port.
This means that packets with PHB EF are considered with a pre-allocated amount of output bandwidth and a priority that ensures minimum loss, minimum delay and minimum jitter before being put into operation.
PHB EF is suitable for channel simulation, leased line simulation, and real-time services such as voice, video without compromising on high loss, delay and jitter values.
Figure 2.10 Example of EF installation
Figure 2.10 shows an example of an EF PHB implementation. This is a simple priority queue scheduling technique. At the edges of the DS domain, EF packet traffic is prioritized according to the values agreed upon by the SLA. The EF queue in the figure needs to output packets at a rate higher than the packet arrival rate λ. To provide an EF PHB over an end-to-end DS domain, bandwidth at the output ports of the core routers needs to be allocated in advance to ensure the requirement μ > λ. This can be done by a pre-configured provisioning process. In the figure, EF packets are placed in the priority queue (the upper queue). With such a length, the queue can operate with μ > λ.
Since EF was primarily used for real-time services such as voice and video, and since real-time services use UDP instead of TCP, RED is generally
not suitable for EF queues because applications using UDP will not respond to random packet drop and RED will strip unnecessary packets.
2.2.4.2 Assured Forwarding (AF) PHB
PHB AF is defined by RFC 2597. The purpose of PHB AF is to deliver packets reliably and therefore delay and jitter are considered less important than packet loss. PHB AF is suitable for non-real-time services such as applications using TCP. PHB AF first defines four classes: AF1, AF2, AF3, AF4. For each of these AF classes, packets are then classified into three subclasses with three distinct priority levels.
Table 2.8 shows the four AF classes and 12 AF subclasses and the DSCP values for the 12 AF subclasses defined by RFC 2597. RFC 2597 also allows for more than three separate priority levels to be added for internal use. However, these separate priority levels will only have internal significance.
PHB Class
PHB Subclass
Package type
DSCP
AF4
AF41
Short
100010
AF42
Medium
100100
AF43
High
100110
AF3
AF31
Short
011010
AF32
Medium
011100
AF33
High
011110
AF2
AF21
Short
010010
AF22
Medium
010100
AF23
High
010110
AF1
AF11
Short
001010
AF12
Medium
001100
AF13
High
001110
Table 2.8 AF DSCPs
The AF PHB ensures that packets are forwarded with a high probability of delivery to the destination within the bounds of the rate agreed upon in an SLA. If AF traffic at an ingress port exceeds the pre-priority rate, which is considered non-compliant or “out of profile”, the excess packets will not be delivered to the destination with the same probability as the packets belonging to the defined traffic or “in profile” packets. When there is network congestion, the out of profile packets are dropped before the in profile packets are dropped.
When service levels are defined using AF classes, different quantity and quality between AF classes can be realized by allocating different amounts of bandwidth and buffer space to the four AF classes. Unlike
EF, most AF traffic is non-real-time traffic using TCP, and the RED queue management strategy is an AQM (Adaptive Queue Management) strategy suitable for use in AF PHBs. The four AF PHB layers can be implemented as four separate queues. The output port bandwidth is divided into four AF queues. For each AF queue, packets are marked with three “colors” corresponding to three separate priority levels.
In addition to the 32 DSCP 1 groups defined in Table 2.8, 21 DSCPs have been standardized as follows: one for PHB EF, 12 for PHB AF, and 8 for CSCP. There are 11 DSCP 1 groups still available for other standards.
2.2.5.Example of Differentiated Services
We will look at an example of the Differentiated Service model and mechanism of operation. The architecture of Differentiated Service consists of two basic sets of functions:
Edge functions: include packet classification and traffic conditioning. At the inbound edge of the network, incoming packets are marked. In particular, the DS field in the packet header is set to a certain value. For example, in Figure 2.12, packets sent from H1 to H3 are marked at R1, while packets from H2 to H4 are marked at R2. The labels on the received packets identify the service class to which they belong. Different traffic classes receive different services in the core network. The RFC definition uses the term behavior aggregate rather than the term traffic class. After being marked, a packet can be forwarded immediately into the network, delayed for a period of time before being forwarded, or dropped. We will see that there are many factors that affect how a packet is marked, and whether it is forwarded immediately, delayed, or dropped.
Figure 2.12 DiffServ Example
Core functionality: When a DS-marked packet arrives at a Diffservcapable router, the packet is forwarded to the next router based on
Per-hop behavior is associated with packet classes. Per-hop behavior affects router buffers and the bandwidth shared between competing classes. An important principle of the Differentiated Service architecture is that a router's per-hop behavior is based only on the packet's marking or the class to which it belongs. Therefore, if packets sent from H1 to H3 as shown in the figure receive the same marking as packets from H2 to H4, then the network routers treat the packets exactly the same, regardless of whether the packet originated from H1 or H2. For example, R3 does not distinguish between packets from h1 and H2 when forwarding packets to R4. Therefore, the Differentiated Service architecture avoids the need to maintain router state about separate source-destination pairs, which is important for network scalability.
Chapter Conclusion
Chapter 2 has presented and clarified two main models of deploying and installing quality of service in IP networks. While the traditional best-effort model has many disadvantages, later models such as IntServ and DiffServ have partly solved the problems that best-effort could not solve. IntServ follows the direction of ensuring quality of service for each separate flow, it is built similar to the circuit switching model with the use of the RSVP resource reservation protocol. IntSer is suitable for services that require fixed bandwidth that is not shared such as VoIP services, multicast TV services. However, IntSer has disadvantages such as using a lot of network resources, low scalability and lack of flexibility. DiffServ was born with the idea of solving the disadvantages of the IntServ model.
DiffServ follows the direction of ensuring quality based on the principle of hop-by-hop behavior based on the priority of marked packets. The policy for different types of traffic is decided by the administrator and can be changed according to reality, so it is very flexible. DiffServ makes better use of network resources, avoiding idle bandwidth and processing capacity on routers. In addition, the DifServ model can be deployed on many independent domains, so the ability to expand the network becomes easy.
Chapter 3: METHODS TO ENSURE QoS FOR MULTIMEDIA COMMUNICATIONS
In packet-switched networks, different packet flows often have to share the transmission medium all the way to the destination station. To ensure the fair and efficient allocation of bandwidth to flows, appropriate serving mechanisms are required at network nodes, especially at gateways or routers, where many different data flows often pass through. The scheduler is responsible for serving packets of the selected flow and deciding which packet will be served next. Here, a flow is understood as a set of packets belonging to the same priority class, or originating from the same source, or having the same source and destination addresses, etc.
In normal state when there is no congestion, packets will be sent as soon as they are delivered. In case of congestion, if QoS assurance methods are not applied, prolonged congestion can cause packet drops, affecting service quality. In some cases, congestion is prolonged and widespread in the network, which can easily lead to the network being "frozen", or many packets being dropped, seriously affecting service quality.
Therefore, in this chapter, in sections 3.2 and 3.3, we introduce some typical network traffic load monitoring techniques to predict and prevent congestion before it occurs through the measure of dropping (removing) packets early when there are signs of impending congestion.
3.1. DropTail method
DropTail is a simple, traditional queue management method based on FIFO mechanism. All incoming packets are placed in the queue, when the queue is full, the later packets are dropped.
Due to its simplicity and ease of implementation, DropTail has been used for many years on Internet router systems. However, this algorithm has the following disadvantages:
− Cannot avoid the phenomenon of “Lock out”: Occurs when 1 or several traffic streams monopolize the queue, making packets of other connections unable to pass through the router. This phenomenon greatly affects reliable transmission protocols such as TCP. According to the anti-congestion algorithm, when locked out, the TCP connection stream will reduce the window size and reduce the packet transmission speed exponentially.
− Can cause Global Synchronization: This is the result of a severe “Lock out” phenomenon. Some neighboring routers have their queues monopolized by a number of connections, causing a series of other TCP connections to be unable to pass through and simultaneously reducing the transmission speed. After those monopolized connections are temporarily suspended,
Once the queue is cleared, it takes a considerable amount of time for TCP connections to return to their original speed.
− Full Queue phenomenon: Data transmitted on the Internet often has an explosion, packets arriving at the router are often in clusters rather than in turn. Therefore, the operating mechanism of DropTail makes the queue easily full for a long period of time, leading to the average delay time of large packets. To avoid this phenomenon, with DropTail, the only way is to increase the router's buffer, this method is very expensive and ineffective.
− No QoS guarantee: With the DropTail mechanism, there is no way to prioritize important packets to be transmitted through the router earlier when all are in the queue. Meanwhile, with multimedia communication, ensuring connection and stable speed is extremely important and the DropTail algorithm cannot satisfy.
The problem of choosing the buffer size of the routers in the network is to “absorb” short bursts of traffic without causing too much queuing delay. This is necessary in bursty data transmission. The queue size determines the size of the packet bursts (traffic spikes) that we want to be able to transmit without being dropped at the routers.
In IP-based application networks, packet dropping is an important mechanism for indirectly reporting congestion to end stations. A solution that prevents router queues from filling up while reducing the packet drop rate is called dynamic queue management.
3.2. Random elimination method – RED
3.2.1 Overview
RED (Random Early Detection of congestion; Random Early Drop) is one of the first AQM algorithms proposed in 1993 by Sally Floyd and Van Jacobson, two scientists at the Lawrence Berkeley Laboratory of the University of California, USA. Due to its outstanding advantages compared to previous queue management algorithms, RED has been widely installed and deployed on the Internet.
The most fundamental point of their work is that the most effective place to detect congestion and react to it is at the gateway or router.
Source entities (senders) can also do this by estimating end-to-end delay, throughput variability, or the rate of packet retransmissions due to drop. However, the sender and receiver view of a particular connection cannot tell which gateways on the network are congested, and cannot distinguish between propagation delay and queuing delay. Only the gateway has a true view of the state of the queue, the link share of the connections passing through it at any given time, and the quality of service requirements of the
traffic flows. The RED gateway monitors the average queue length, which detects early signs of impending congestion (average queue length exceeding a predetermined threshold) and reacts appropriately in one of two ways:
− Drop incoming packets with a certain probability, to indirectly inform the source of congestion, the source needs to reduce the transmission rate to keep the queue from filling up, maintaining the ability to absorb incoming traffic spikes.
− Mark “congestion” with a certain probability in the ECN field in the header of TCP packets to notify the source (the receiving entity will copy this bit into the acknowledgement packet).
Figure 3. 1 RED algorithm
The main goal of RED is to avoid congestion by keeping the average queue size within a sufficiently small and stable region, which also means keeping the queuing delay sufficiently small and stable. Achieving this goal also helps: avoid global synchronization, not resist bursty traffic flows (i.e. flows with low average throughput but high volatility), and maintain an upper bound on the average queue size even in the absence of cooperation from transport layer protocols.
To achieve the above goals, RED gateways must do the following:
− The first is to detect congestion early and react appropriately to keep the average queue size small enough to keep the network operating in the low latency, high throughput region, while still allowing the queue size to fluctuate within a certain range to absorb short-term fluctuations. As discussed above, the gateway is the most appropriate place to detect congestion and is also the most appropriate place to decide which specific connection to report congestion to.
− The second thing is to notify the source of congestion. This is done by marking and notifying the source to reduce traffic. Normally the RED gateway will randomly drop packets. However, if congestion
If congestion is detected before the queue is full, it should be combined with packet marking to signal congestion. The RED gateway has two options: drop or mark; where marking is done by marking the ECN field of the packet with a certain probability, to signal the source to reduce the traffic entering the network.
− An important goal that RED gateways need to achieve is to avoid global synchronization and not to resist traffic flows that have a sudden characteristic. Global synchronization occurs when all connections simultaneously reduce their transmission window size, leading to a severe drop in throughput at the same time. On the other hand, Drop Tail or Random Drop strategies are very sensitive to sudden flows; that is, the gateway queue will often overflow when packets from these flows arrive. To avoid these two phenomena, gateways can use special algorithms to detect congestion and decide which connections will be notified of congestion at the gateway. The RED gateway randomly selects incoming packets to mark; with this method, the probability of marking a packet from a particular connection is proportional to the connection's shared bandwidth at the gateway.
− Another goal is to control the average queue size even without cooperation from the source entities. This can be done by dropping packets when the average size exceeds an upper threshold (instead of marking it). This approach is necessary in cases where most connections have transmission times that are less than the round-trip time, or where the source entities are not able to reduce traffic in response to marking or dropping packets (such as UDP flows).
3.2.2 Algorithm
This section describes the algorithm for RED gateways. RED gateways calculate the average queue size using a low-pass filter. This average queue size is compared with two thresholds: minth and maxth. When the average queue size is less than the lower threshold, no incoming packets are marked or dropped; when the average queue size is greater than the upper threshold, all incoming packets are dropped. When the average queue size is between minth and maxth, each incoming packet is marked or dropped with a probability pa, where pa is a function of the average queue size avg; the probability of marking or dropping a packet for a particular connection is proportional to the bandwidth share of that connection at the gateway. The general algorithm for a RED gateway is described as follows: [5]
For each packet arrival
Caculate the average queue size avg If minth ≤ avg < maxth
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Source: Department of Industry and Trade, Nghe An Province Forest Protection and Development Fund)
4.2 .2.2. Determining the amount of DVMTR payment over the years
By the end of 2016, there were 04 facilities using forest environmental services in Que Phong district that signed contracts to entrust and pay for forest environmental services, with a total revenue of 80,033,549,286 VND, an average of 20 billion VND per year (accounting for over 30% of the total revenue of the whole province) . This amount will increase nearly 2 times in 2017 and the following years and will increase steadily over the years due to the emergence of new facilities using forest environmental services and the increase in the unit price of commercial electricity for hydropower production facilities to 36 VND/KWh, and commercial water for clean water production and supply facilities to 52 VND/m3 according to the provisions of Decree 147/2016/ND-CP.
dated November 2, 2016 of the Government. This is a stable and sustainable source of funding for forest management, protection and development in the area.
Table 4.3. Summary of commission payments from facilities using DVMTR
TT
Hydropower Name | Total revenue | 2013 | 2014 | 2015 | 2016 | |
1 | Hua Na | 48,556,426,980 | 5,183,742,000 | 12,851,856,000 | 17,455,446,320 | 13,065,382,660 |
2 | Dat Door | 25,860,000,000 | 3,000,000,000 | 5,900,000,000 | 10,460,000,000 | 6,500,000,000 |
3 | Sao Va | 810.394.210 | 190,842,950 | 193,830,940 | 173,886,560 | 251,833,760 |
4 | Ban Coc | 4,806,728,096 | 1,162,653,090 | 1,313,682,560 | 1,064,542,560 | 1,265,849,886 |
Total | 80,033,549,286 | 9,537,238,040 | 20,259,369,500 | 29,153,875,440 | 21,083,066,306 | |
Source: Nghe An Provincial Forest Protection and Development Fund) The data in the table above shows that after 4 years of implementing the policy of paying for forest environmental services in the district (2013-2016), in general, the facilities using forest environmental services have fully paid to the Forest Protection and Development Fund. However, in the first years of implementing the policy, some facilities using forest environmental services have not had a high awareness of the responsibility of enterprises to society, while there are no sanctions for implementation, so there is still a situation of procrastination and arrears lasting over the years. To date, the Government has issued Decree No. 40/2015/ND-CP dated April 27, 2015 amending and supplementing a number of articles of Decree No. 157/2013/ND-CP dated November 11, 2013 of the Government regulating administrative sanctions for violations of forest management, forest development, forest protection and forest product management. Including the content of sanctioning violations of regulations on payment of DVMTR, so by the end of the 2015 and 2016 planning years, there is no longer any basis.