"Social capital in production and business development, creating strong motivation and dynamic and effective management mechanisms for state-owned enterprises, promoting the true ownership role of workers and shareholders, and strengthening social supervision of enterprises, ensuring harmony of interests of the state, enterprises and workers" [36].
Thus, the equitization of state-owned enterprises also has a very important goal of creating conditions for enterprises to make profits. Because of the confusion that the goal of enterprises is only a matter of ownership, many people, including leaders and managers, do not care about the goal of making profits. The ability of enterprises to make profits is closely linked to expanding production, creating more jobs, increasing products for the market, and increasing budget payments. Increasing budget revenue is the only way for the State to increase welfare for workers. If we emphasize ownership, not only will the goal of profit not be achieved, but the goal of welfare for workers will also be meaningless. This is an expensive lesson that we have had to pay for in the decades of the economy operating under a centralized planning mechanism.
The implementation of the form of multiple ownership for enterprises in the process of equitization of state-owned enterprises is essentially the elimination of the “ownerless” state in these enterprises. Depending on the nature and characteristics of the type of enterprise, the state can hold controlling shares in a few special enterprises or only participate in shares at the necessary level. The important thing is to build on the basis of premises and feasible forecasts so that effective solutions can be proposed to improve competitiveness and truly effective business.
The implementation of state capital divestment in state-owned enterprises also means increasing the mobilization of investors with potential capital and business conditions to participate in buying shares, along with employees in enterprises to enhance the responsibility of management, production and business organization with the responsibility of owning assets in enterprises. In Thanh Hoa province, due to the characteristics of the
Enterprises formed from the equitization of state-owned enterprises in the area mostly have very small state capital sources, so it is necessary to apply the form of expanding production scale by issuing more shares.
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Current Status of Inspection and Examination of State-Owned Enterprise Activities in Dak Lak Province -
Key Solutions to Solve Socio-Economic Problems During and After Equitization of Enterprises in the Transport Industry -
Establishment of State-owned Enterprise and Shareholding Agency. -
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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Socio-Economic Impacts of Tourism Activities
4.1.2.3. Solve emerging socio-economic problems on the basis of enhancing publicity, transparency and establishing the principle of harmonization of interests .
In many cases, the conflict of interest associated with the equitization process of SOEs is revealed as a socio-economic problem that can hinder and negatively impact this process due to the lack of openness and transparency in the equitization method. For example, when land or many other assets of SOEs are publicly and transparently valued through a competitive auction mechanism, attracting many participants, when information related to the assets is widely published, then certainly negative and abusive factors in the valuation of the above assets have less chance to arise, and state assets are therefore less likely to be lost. When the equitization process of a certain SOE only takes place in a closed manner within the leaders and labor collective of the enterprise, the possibility of the enterprise's value being undervalued through the enterprise's stock price being held at a low level is very likely to occur. Outside investors have the potential to become new shareholders, which can bring new life to the enterprise in terms of both talent and financial resources that have been hindered. Therefore, publicity and transparency must become the principle to prevent and handle socio-economic problems associated with the equitization process of SOEs.

As analyzed, conflicts of interest are inevitable in the process of converting the form and ownership structure from a state-owned enterprise to a joint stock company. To prevent and limit opposition arising from this conflict, in addition to propaganda and publicity, it is necessary to apply the principle of maximum harmonization of the interactions of interests between relevant economic entities. To a certain extent, it is possible to use appropriate forms of compensation for those who suffer losses, especially those who are in difficulty and in a disadvantaged position. For example, workers who are "redundant" are such people. In
In this case, the state, for the long-term social benefit, must be responsible for "compensating" them appropriately in various forms, avoiding the situation where, due to short-term budget difficulties, state agencies tend to shift responsibility to equitized enterprises. Former SOE leaders who have worked for a long time and have been attached to the enterprise can also be considered for compensation. However, when the damage suffered by some people working in former SOEs is linked to their "privileged and advantageous" position, in principle, the state and society do not need to "compensate". In this case, the appropriate handling principle is propaganda and publicity.
4.1.2.4. Viewing the completion and improvement of the quality of market institutions to create a favorable and healthy business environment for all enterprises as an effective method to handle socio-economic issues arising in the process of equitization of state-owned enterprises.
Many socio-economic problems arising in the process of equitization of SOEs become difficult to solve due to the weakness or absence of corresponding market institutions. For example, asset valuation or enterprise valuation becomes difficult and vulnerable to abuse partly because markets related to the trading, buying and selling of high-end products and services such as the stock market, the debt buying and selling market, the market for intellectual property, brands or other intangible goods as well as the land market have not yet been born or are just developing, are still incomplete, and operate unhealthy due to the absence of appropriate regulations and regulatory standards. Therefore, continuing to develop and improve these markets is not only necessary to continue promoting the development of the market economy in Vietnam in general, but also a way to prevent and solve many long-term socio-economic problems arising in the process of equitization of SOEs in the future.
Discrimination between SOEs and other types of enterprises, as analyzed, not only promotes fear of equitization but also distorts the business environment, distorts market signals, and causes inefficient allocation of common social resources. This situation not only discourages SOEs from enhancing their competitiveness but also prevents the healthy development of other types of enterprises, including equitized enterprises. Therefore, continuing to improve the general business environment to create a level playing field for all enterprises is necessary, as well as handling issues arising in the equitization process. It needs to be done in the direction of: creating equal favorable conditions for all enterprises in entering the market, accessing resources such as land, credit, accessing information and public services; minimizing informal costs in relations with public agencies; enhance market competitiveness, on the basis of minimizing barriers to market entry as well as eliminating the "artificial" monopoly position of some enterprises (such as some current economic groups, for example)
4.2. Some solutions to limit and solve socio-economic problems arising in the process of equitization of state-owned enterprises in Thanh Hoa in the coming years
4.2.1. Innovating valuation methods along with improving skills and professional ethics of the team of staff valuing corporate assets
4.2.1.1. Innovation in business valuation methods
Enterprise valuation (determining enterprise value) in equitization is a very important task and has a decisive impact on the success of converting state-owned enterprises into joint stock companies. The essence of the equitization process of state-owned enterprises is the process of transferring ownership. Therefore, it requires the value of existing state capital in the enterprise to be accurately valued.
Prevent loss and corruption of state assets in state-owned enterprises, attract social capital to invest in enterprises.
Currently, Thanh Hoa province is implementing enterprise valuation according to two methods of determining enterprise value prescribed by the State, which are the asset method and the discounted cash flow method. Determining enterprise value according to these methods has proven to be ineffective in practice due to its subjectivity, leading to inaccurate results that do not reflect the true value of the enterprise. In many cases, incorrect valuation of enterprise assets has led to conflicts of interest between the State and investors. If the enterprise is valued lower than its true value, the State suffers a loss (loss of assets) and the share buyers benefit; if the enterprise is valued higher than its true value, the opposite situation will occur, that is, the State benefits and the share buyers suffer a loss. In both cases, the equitization process is more difficult, because until the harmony of interests is resolved, it will not attract the attention of investors, especially potential investors. In addition, low enterprise valuation also leads to a large difference between the value of shares transferred at the enterprise after equitization and the initial value of shares, giving rise to negative phenomena such as buying and selling shares by hand, or selling preferential shares such as: 25 A Joint Stock Company, Hoang Hoa Trading Joint Stock Company...
The most obvious manifestation of inaccurate valuation of state-owned enterprise assets is in the stock market. Specifically, there have been some enterprises whose economic potential is not considered strong, but their stock indexes have still increased very high on the stock market, thanks to not including the value of land use rights in the enterprise value when equitizing (only calculating the annual land rental value according to the long-term contract signed in advance). Meanwhile, the land use value can become a super-profitable value in the capital business of the equitized enterprise. Not including the value of land use rights in the enterprise value when equitizing is the same as
This means that the State has lost the right to receive the "differential rent" arising from land use rights; and the managers and operators of enterprises after equitization will of course receive that "rent".
Correctly valuing an enterprise before equitization will help avoid losses and problems arising in post-equitization enterprises. However, valuing an enterprise is difficult. Including the value of land use rights in the assets of an enterprise before equitization as above is just a specific example. Valuing an enterprise often encounters other difficulties, such as valuing technology, especially used technology; valuing brands and business advantages - intangible assets with great value but very difficult to determine the price, etc. However, no matter how difficult it is, we must try to fully calculate the assets of state-owned enterprises into the value of the enterprise before equitization. Absolutely do not remove any part of the assets from the value of an equitized enterprise.
To objectively and accurately value enterprises, on the one hand, the province must start from the basis of State regulations, but on the other hand, it must be based on the practical conditions of the equitization process of State-owned enterprises in the area, taking into account domestic and foreign experience, to apply other more effective valuation forms. Specifically:.
+ To create more objectivity in calculating enterprise value, the province needs to use many different methods, including promoting the public auction method instead of valuation by relatively closed councils; at the same time, it is necessary to give more power to localities in choosing methods of selling shares such as: auction, agreement or underwriting. It is necessary to establish and use independent councils to evaluate or appraise the assets of enterprises as a basis for determining the initial starting price for auction instead of using state management agencies. Transfer the authority to determine this starting price (currently undertaken by the head of the provincial administrative agency) to the above independent councils.
It is important to note that only by determining the value of an enterprise through the market mechanism and letting the market regulate can the true value of the enterprise be reflected. Doing so will not only avoid the loss of state capital, but also make it more acceptable to shareholders. In cases where the market is not yet complete or fully developed, using independent organizations or consultants with appropriate expertise instead of organizations and individuals whose motives and interests are tied to the transfer of ownership of public assets or who do not have appropriate expertise will ensure that the valuation process becomes more objective and less susceptible to abuse.
+ Innovate the method of determining enterprise value on the basis of expanding and promoting economic measures and limiting and narrowing administrative measures. In addition to correctly and fully calculating the value of all types of assets of the enterprise, it is necessary to include the values of intangible assets such as: land use rights value, brand value, business advantages, management capacity, and workers' skills in the enterprise value when equitizing.
The province needs to pay attention to linking the innovation of enterprise valuation methods with the method of selling shares of equitized enterprises; linking the equitization process with listing shares on the stock market. Having the right policies for employees so that they can confidently participate in the equitization process. At the same time, there must be a plan to attract good experts to evaluate assets, in order to correctly determine the actual value of assets. Promoting the role of enterprise representatives in determining enterprise value according to market principles, so that the seller (the State) and the buyer (shareholder representatives) can negotiate with each other about assets and prices. The State should switch from the Council for determining enterprise value with an imposing nature to auctioning enterprise assets.
4.2.1.2. Improve the capacity and professional ethics of the valuation staff
Equitization of state-owned enterprises is essentially the sale of state capital in enterprises to the market, so how to properly value enterprises is important.
extremely important role. Obviously, when the State organizes the sale of its capital, the primary concern is to whom to sell to and how much to sell, that is, it must sell at a "good price" to preserve State capital. If the price is set high, it will be difficult to sell, and if the price is set low, the State will lose capital.
The difficulty of valuing a business is not only due to objective factors such as the qualifications and skills of the valuator; but also subjective factors such as the poor ethics and qualities of the valuator team, who only aim at personal gain. There have even been cases where officials undervalue the value of the business and then buy back those assets to sell outside, collecting the difference.
This reality is posing a requirement for Thanh Hoa province to improve the skills and professional ethics of the staff of enterprise valuation when equitizing. Improving the capacity of valuation and assessing the value of assets of enterprises is of particular importance in handling the complex issues arising in this process. Currently, the staff of enterprise valuation in Thanh Hoa province have not yet received specialized training courses, so they are still confused in handling situations during valuation. The most basic solution to this problem is to form a team of professional, core appraisers who are formally trained in asset valuation, especially real estate and brand valuation.
In order to conduct good valuation, in addition to the specialized staff, the province also needs to build a team of assistants for price appraisers. These are people who are not yet appraisers (not yet issued a card), but play an important role in assisting appraisers in collecting data and initial work, or supporting appraisal reports. These people are considered as the "reserve army" for the team of skilled appraisers (issued with a card) in the future.




![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 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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