Social services are currently not yet available to the majority of workers in this area. The network providing social services for workers in general and workers in the KTPNN sector in particular in Ho Chi Minh City is not really widespread but is only the efforts of individual local authorities. In addition, there are many factors affecting the ability of workers in the KTPNN sector to use social services.
3.3.1. The impact of team capacity factors on social work services
3.3.1.1. Capacity of staff providing social work services
Social services are important because they create favorable conditions for individuals, families, and groups of migrant workers in need of help to be able to solve the problems they are facing; meet the needs and enhance social functions to prevent, intervene, and restore migrant workers to better integrate into the social community at their destination.
The research results show that there are many factors that are assessed to affect the ability to access social services of migrant workers. Depending on the characteristics of the needs of migrant workers, resources and service capacity of the districts, the ability to use social services is different, each factor affecting the service is not the same such as: The factor of the team of social workers has the strongest influence on their ability to access social services. The migrant workers in the KTNNN area really need social services to ensure the quality of life at their place of residence. Vulnerable groups in general and migrant workers in particular often face many social problems, they often feel inferior, passive and rarely seek assistance activities. Some previous research results have also shown that the effective provision of social services requires a team of service providers who are well-trained from professional schools [29]; [66].
The research results also show that the capacity of service providers is one of the factors that strongly affects the ability to access social services of migrant workers in the KTPNN sector with the average = 3.75. Social work is a newly developed profession in Vietnam, not yet known by many people. Most communes/wards in Ho Chi Minh City currently do not have professional social workers, but are mainly performed by semi-professional staff. The staff providing social services to support migrant workers in the locality are often part-time, part-time staff, women's union staff or different departments and branches. Depending on each problem of migrant workers, social workers provide different social services such as: temporary residence registration by the local police, social security-related issues are supported by the cultural staff of the ward. Therefore, they do not have much time.
to support but only focus on the field they are in charge of. In addition, these officers rarely participate or have never participated in a training course on social work. Therefore, it has a significant impact on service provision for workers in this area.
Table 3.13. Immigrant workers' perceptions of factors affecting social work services
TT
Factors affecting social services for migrant workers | Average | DLC | Rank | |
1 | Capacity of staff providing social services | 3.75 | 0.69 | 1 |
2 | Media information about local social services | 3.71 | 0.89 | 2 |
3 | Resources/network providing social services | 3.66 | 0.89 | 3 |
4 | Characteristics of migrant workers | 3.61 | 0.94 | 4 |
5 | Facilities | 3.48 | 0.72 | 5 |
6 | Policies and laws for migrant workers | 3.42 | 0.76 | 6 |
DTBC | 3.61 | 0.82 |
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Identify Rating Levels and Rating Scales
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of the islanders. Therefore, this indicator will be divided into two sub-indicators:
a1. Natural tourism attractiveness a2. Cultural tourism attractiveness
b. Tourist capacity
The two island communes in Quan Lan have different capacities to receive tourists. Minh Chau Commune is home to many standard hotels and resorts, attracting high-income domestic and international tourists. Meanwhile, Quan Lan Commune has many motels mainly built and operated by local people, so the scale and quality are not high, and will be suitable for ordinary tourists such as students.
c. Time of exploitation of Quan Lan Island Commune:
Quan Lan tourism is seasonal due to weather and climate conditions and festivals only take place on certain days of the year, specifically in spring. In Quan Lan commune, the period from April to June and from September to November is considered the best time to visit Quan Lan because the cultural tourism activities are mainly associated with festivals taking place during this time.
Minh Chau island commune:
Tourism exploitation time is all year round, because this is a place with a number of tourist attractions with diverse ecosystems such as Bai Tu Long National Park Research Center, Tram forest, Turtle Laying Beach, so besides coming to the beach for tourism and vacation in the summer, Minh Chau will attract research groups to come for tourism combined with research at other times of the year.
d. Sustainability
The sustainability of ecotourism sites in Quan Lan and Minh Chau communes depends on the sensitivity of the ecosystems to climate changes.
landscape. In general, these tourist destinations have a fairly high level of sustainability, because they are natural ecosystems, planned and protected. However, if a large number of tourists gather at certain times, it can exceed the carrying capacity and affect the sustainability of the environment (polluted beaches, damaged trees, animals moving away from their habitats, etc.), then the sustainability of the above ecosystems (natural ecosystems, human ecosystems) will also be affected and become less sustainable.
e. Location and accessibility
Both island communes have ports to take tourists to visit from Van Don wharf:
- Quan Lan – Van Don traffic route:
Phuc Thinh – Viet Anh high-speed boat and Quang Minh high-speed boat, depart at 8am and 2pm from Van Don to Quan Lan, and at 7am and 1pm from Quan Lan to Van Don. There are also wooden boats departing at 7am and 1pm.
- Van Don - Minh Chau traffic route:
Chung Huong high-speed train, Minh Chau train, morning 7:30 and afternoon 13:30 from Van Don to Minh Chau, morning 6:30 and afternoon 13:00 from Minh Chau to Van Don.
f. Infrastructure
Despite receiving investment attention, the issue of infrastructure and technical facilities for tourism on Quan Lan Island is still an issue that needs to be resolved because it has a direct impact on the implementation of ecotourism activities. The minimum conditions for serving tourists such as accommodation, electricity, water, communication, especially medical services, and security work need to be given top priority. Ecotourism spots in Minh Chau commune are assessed to have better infrastructure and technical facilities for tourism because there are quite complete and synchronous conditions for serving tourists, meeting many needs of domestic and foreign tourists.
3.2.1.4. Determine assessment levels and assessment scales
Corresponding to the levels of each criterion, the index is the score of those levels in the order of 4, 3, 2, 1 decreasing according to the standard of each level: very attractive (4), attractive (3), average (2), less attractive (1).
3.2.1.5. Determining the coefficients of the criteria
For the assessment of DLST in the two communes of Quan Lan and Minh Chau islands, the students added evaluation coefficients to show the importance of the criteria and indicators as follows:
Coefficient 3 with criteria: Attractiveness, Exploitation time. These are the 2 most important criteria for attracting tourists to tourism in general and eco-tourism in particular, so they have the highest coefficient.
Coefficient 2 with criteria: Capacity, Infrastructure, Location and accessibility . Because the assessment area is an island commune of Van Don district, the above criteria are selected by the author with appropriate coefficients at the average level.
Coefficient 1 with criteria: Sustainability. Quan Lan has natural and human-made ecotourism sites, with high biodiversity and little impact from local human factors. Most of the ecotourism sites are still wild, so they are highly sustainable.
3.2.1.6. Results of DLST assessment on Quan Lan island
a. Assessment of the potential for natural tourism development
For Minh Chau commune:
+ Natural tourism attractiveness is determined to be very attractive (4 points) and the most important coefficient (coefficient 3), so the score of the Attractiveness criterion is 4 x 3 = 12.
+ Capacity is determined as average (2 points) and the coefficient is quite important (coefficient 2), then the score of Capacity criterion is 2 x 2 = 4.
+ Exploitation time is long (4 points), the most important coefficient (coefficient 3) so the score of the Exploitation time criterion is 4 x 3 = 12.
+ Sustainability is determined as sustainable (4 points), the important coefficient is the average coefficient (coefficient 1), so the score of the Sustainability criterion is 4 x 1 = 4 points
+ Location and accessibility are determined to be quite favorable (2 points), the coefficient is quite important (coefficient 2), the criterion score is 2 x 2 = 4 points.
+ Infrastructure is assessed as good (3 points), the coefficient is quite important (coefficient 2), then the score of the Infrastructure criterion is 3 x 2 = 6 points.
The total score for evaluating DLST in Minh Chau commune according to 6 evaluation criteria is determined as: 12 + 4 + 12 + 4 + 4 + 6 = 42 points
Similar assessment for Quan Lan commune, we have the following table:
Table 3.3: Assessment of the potential for natural ecotourism development in Quan Lan and Minh Chau communes
Attractiveness of self-tourismof course
Capacity
Mining time
Sustainability
Location and accessibility
Infrastructure
Result
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
CommuneMinh Chau
12
12
4
8
12
12
4
4
4
8
6
8
42/52
Quan CommuneLan
6
12
6
8
9
12
4
4
4
8
4
8
33/52
b. Assessment of the potential for humanistic tourism development
For Quan Lan commune:
+ The attractiveness of human tourism is determined to be very attractive (4 points) and the most important coefficient (coefficient 3), so the score of the Attractiveness criterion is 4 x 3 = 12.
+ Capacity is determined to be large (3 points) and the coefficient is quite important (coefficient 2), then the score of the Capacity criterion is 3 x 2 = 6.
+ Mining time is average (3 points), the most important coefficient (coefficient 3) so the score of the Mining time criterion is 3 x 3 = 9.
+ Sustainability is determined as sustainable (4 points), the important coefficient is the average coefficient (coefficient 1), so the score of the Sustainability criterion is 4 x 1 = 4 points.
+ Location and accessibility are determined to be quite favorable (2 points), the coefficient is quite important (coefficient 2), the criterion score is 2 x 2 = 4 points.
+ Infrastructure is rated as average (2 points), the coefficient is quite important (coefficient 2), then the score of the Infrastructure criterion is 2 x 2 = 4 points.
The total score for evaluating DLST in Quan Lan commune according to 6 evaluation criteria is determined as: 12 + 6 + 6 + 4 + 4 + 4 = 36 points.
Similar assessment with Minh Chau commune we have the following table:
Table 3.4: Assessment of the potential for developing humanistic eco-tourism in Quan Lan and Minh Chau communes
Attractiveness of human tourismliterature
Capacity
Mining time
Sustainability
Location and accessibility
Infrastructure
Result
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Point
DarkMulti
Quan CommuneLan
12
12
6
8
9
12
4
4
4
8
4
8
39/52
Minh CommuneChau
6
12
4
8
12
12
4
4
4
8
6
8
36/52
Basically, both Minh Chau and Quan Lan localities have quite favorable conditions for developing ecotourism. However, Quan Lan commune has more advantages to develop ecotourism in a humanistic direction, because this is an area with many famous historical relics such as Quan Lan Communal House, Quan Lan Pagoda, Temple worshiping the hero Tran Khanh Du, ... along with local festivals held annually such as the wind praying ceremony (March 15), Quan Lan festival (June 10-19); due to its location near the port and long exploitation time, the beaches in Quan Lan commune (especially Quan Lan beach) are no longer hygienic and clean to ensure the needs of tourists coming to relax and swim; this is also an area with many beautiful landscapes such as Got Beo wind pass, Ong Phong head, Voi Voi cave, but the ability to access these places is still very limited (dirt hill road, lots of gravel and rocks), especially during rainy and windy times; In addition, other natural resources such as mangrove forests and sea worms have not been really exploited for tourism purposes and ecotourism development. On the contrary, Minh Chau commune has more advantages in developing ecotourism in the direction of natural tourism, this is an area with diverse ecosystems such as at Rua De Beach, Bai Tu Long National Park Conservation Center...; Minh Chau beach is highly appreciated for its natural beauty and cleanliness, ranked in the top ten most beautiful beaches in Vietnam; Minh Chau commune is also home to Tram forest with a large area and a purity of up to 90%, suitable for building bridges through the forest (a very effective type of natural ecotourism currently applied by many countries) for tourists to sightsee, as well as for the purpose of studying and researching.
Figure 3.1: Thenmala Forest Bridge (India) Source: https://www.thenmalaecotourism.com/(August 21, 2019)
3.2.2. Using SWOT matrix to evaluate Quan Lan island tourism
General assessment of current tourism activities of Quan Lan island is shown through the following SWOT matrix:
Table 3.5: SWOT matrix evaluating tourism activities on Quan Lan island
Internal agent
Strengths- There is a lot of potential for tourism development, especially natural ecotourism and humanistic ecotourism.- The unskilled labor force is relatively abundant.- resource environmentunpolluted, still
Weaknesses- Poorly developed infrastructure, especially traffic routes to tourist destinations on the island.- The team of professional staff is still weak.- Tourism products in general
quite wild, originalintact
general and DLST in particularalone is monotonous.
External agents
Opportunity- Tourism is a key industry in the socio-economic development strategy of the province and Van Don economic zone.- Quan Lan was selected as a pilot area for eco-tourism development within the framework of the green growth project between Quang Ninh province and the Japanese organization JICA.- The flow of tourists and especially ecotourism in the world tends toincreasing
Challenge- Weather and climate change abnormally.- Competition in tourism products is increasingly fierce, especially with other localities in the province such as Ha Long, Mong Cai...- Awareness of tourists, especially domestic tourists, about ecotourism and nature conservation is not high.
Through summary analysis using SWOT matrix we see that:
To exploit strengths and take advantage of opportunities, it is necessary to:
- Diversify products and service types (build more tourism routes aimed at specific needs of tourists: experiential tourism immersed in nature, spiritual cultural tourism...)
- Effective exploitation of resources and differentiated products (natural resources and human resources)
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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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Research Model of Factors Impacting Work Motivation of Tour Guide Team in Binh Dinh Province -
Developing the team of social work lecturers in universities in Vietnam at present - 29 -
Developing the team of social work lecturers in universities in Vietnam at present - 1

(Source: Actual survey data).
Qualitative research data shows that service providers must have the necessary knowledge and skills in social work to approach and identify problems, plan treatment, and connect with service resources to help clients solve their problems and move towards a more useful life. A LĐ, Invalids and Social Affairs officer said: “Consultation activities for workers in the KTPNN area are mainly sharing to relieve stress for them. In reality, when workers in the KTPNN area encounter psychological crises, social workers with knowledge of social work cannot provide consultation, treatment, or intervention, but need to refer workers to experts in this field. Therefore, social workers must be trained, fostered, and coached in knowledge and skills in social work ”. (LĐ, Invalids and Social Affairs officer, District 12).
After the Government issued Decision 32, the Project on Developing Social Work Profession has created a positive change in the awareness of Party committees, authorities at all levels and society about the social work profession. Currently, provinces and cities across the country have developed plans and allocated funds to implement the Project and have established nearly 40 centers providing social work services at provincial and district levels; a number of social work consulting offices in districts and hundreds of consulting points in communities, hospitals; schools; increasing the total number of facilities related to providing social work services.
The current social work service network has 418 facilities, with a total of 30,000 staff working at the facilities and networks at the commune/ward level [60].
The capacity of the staff providing social services is assessed through the following indicators: Knowledge, skills, attitudes, and seniority in the profession. These factors directly and indirectly affect the process of providing social services to workers in the KTPNN sector in localities. The research results in Table 3.14 show that one of the indicators of professional qualifications is knowledge and professional skills with the average score of 4.06, corresponding to 20.9% of opinions saying it is very influential and 49.3% saying it is influential on the ability of workers in this sector to access social services.
Table 3.14. Perceptions of service staff influencing the likelihood of using social work services
TT
Staff providing social services (F4) | Answer options (%) | Average | DLC | |||||
Absolutely right. | Mostly yes | Confused | Partly so. | Not true. | ||||
1 | Service providers trained in basic knowledge and skills in social work will have a plan. Provide better service | 29.0 | 49.3 | 20.7 | 1.0 | 0.0 | 4.06 | 0.73 |
2 | Service providers with good attitude and passion for work will have experience. in the process of providing services | 8.1 | 28.3 | 63.3 | 0.2 | 0.0 | 3.44 | 0.64 |
DTBC | 3.75 | 0.69 | ||||||
(Source: Actual survey data).
A well-trained social worker will be more confident and effective in assisting clients, and conversely, if the social worker lacks knowledge and skills, he or she will be more confused in assisting activities. This is consistent with the comments of the project leader who said: “ For a social worker, enthusiasm and dedication are not enough, they must be trained and nurtured to have the knowledge and skills to work with each specific client. In addition, each client often encounters many problems at the same time, which cannot be solved by the social worker alone, but requires the participation of many sectors. If the social worker has the knowledge and skills in the process of assisting clients,
It is easier for the owner to approach and accompany the family to assess, identify problems and comply with principles and professional ethics. (E&D Project Leader in District 8).
In reality, there is still a huge contradiction between the demand for human resources in social work and the recruitment policy. Some communes/wards do not have recruitment targets or have difficulty recruiting. On the other hand, the network of facilities providing social work services has just been formed, mainly in the field of labor, invalids and social affairs. The staff, employees and collaborators are still small or have not been trained or fostered in professional skills in social work, so they cannot promote their professional skills in providing social work services to workers in the KTPNN area. This issue is also reflected in the opinion of a ward leader: "Most of our commune/ward staff have not been trained or fostered, or if they have, they have very little training in social work. They are very enthusiastic in their work, but they only rely on their many years of experience to solve problems, so the effectiveness of assistance is not high." (Leader of BTĐ B ward, Binh Tan district).
Through the analysis of the above results, it can be seen that the staff working in communes/wards have not met practical requirements, most of them have not been trained in social work or have very little formal training in social work knowledge and skills. This is an ongoing problem not only in Ho Chi Minh City but also in localities across the country. This result affirms the role of social workers in terms of professional qualifications and attitudes towards the profession, which has a profound impact on the effectiveness of using social work services of workers in the KTPNN sector as well as on the reputation of the facilities and localities providing social work services. Therefore, it is necessary to continue to train and provide them with knowledge and skills in identifying problems, assessing needs as well as planning to provide social work services so that workers in the KTPNN sector can have a more stable life.
The results of in-depth interviews show that the quality of social services for workers in the KTPNN area is greatly influenced by the service providers. The fact that service providers are trained and professionally fostered in social work helps them master the methods, skills, ways as well as principles of action and professional ethics to ensure that the service provision process is guaranteed. The Ward leader said: " Ward staff who are not trained in social work will encounter many difficulties in the process of providing services to workers in the KTPNN area, because they often have multiple needs that need assistance. Without knowledge and skills, staff will not understand the psychology, aspirations, assess the problems and needs to plan the provision, connect, and refer workers in the KTPNN area to the necessary services to solve their problems." (Labor of DHT Ward, District 12).
For social service providers who have not been trained in knowledge and skills in social work, it greatly affects the provision of services to people in the community. In addition, the current network of social service providers in the community is not diverse, there is a lack of specialized support services, the socialization is not high and does not meet the needs of people using the service. Therefore, social service providers cannot demonstrate their role in mobilizing and connecting resources to support workers in the KTPNN sector to solve their problems. For facilities with professionally trained staff, service provision will be better. This is an issue that needs to be noted when the Social Work Development Project is entering its final stage with the goals gradually being completed.
The pilot construction of the model of the Center for providing social work services; training, retraining, and improving skills and expertise for the team of cadres, civil servants, employees, and social work collaborators, especially in the community, has not brought about the expected results. Previous research results have also shown that, according to regulations, social work workers work according to the principles of action such as putting the interests of clients first; respecting the right to self-determination; focusing on strengths, taking advantage of available resources of clients to promote empowerment and responsibility for social work professional activities, while ensuring the provision of appropriate and quality social work services to clients [15].
In addition to professional competence, the awareness and attitude of service providers also have a great impact on service quality. To implement these principles well, social workers must have basic knowledge of social work, in the process of providing services, social workers must strictly comply with professional standards and ethics, enhance professional development as well as develop self-awareness to be able to provide appropriate social work services, ensuring quality for workers in the KTPNN sector.
The results of in-depth interviews also show that the factor of the service staff has an impact on social services for migrant workers in the KTPNN area. The effective provision of social services for migrant workers requires a team of professionals, experience, enthusiasm and professional ethics working in communes/wards. A social worker at a service provider said: “Staff providing services for migrant workers who are trained in knowledge and skills in social work will be able to apply appropriate intervention methods, follow the correct procedures, choose appropriate approaches and implement the principles of action well in the service provision process, contributing to the effectiveness of migrant workers. However, the majority of social workers and collaborators in communes/wards currently do not have methods and skills to provide services suitable for the
NLĐNC. On the other hand, some of them hold concurrent positions, so they have not focused on their expertise, and the effectiveness of providing services to NLĐNC in the KTPNN area is not high." (NVCTXH, District 12).
Good attitude towards the job is also one of the manifestations of service providers, with the average score = 3.4, corresponding to 8.1% of employees saying that it is very influential and 28.3% saying it is influential on social services for employees in the KTPNN area. A number of commune/ward staff who have not been trained in social work knowledge work based on the experiences they have accumulated during their work, or those who come later learn from those who come earlier, or mainly work from their heart, which is also one of the factors affecting social services. This makes the effectiveness of providing social services for employees in localities low, lacking sustainability, failing to meet current practical needs and the process of international integration. Some previous studies also show that the role of social workers is very important in ensuring the quality and professionalism of social services. “ The understanding of social work practice of social workers greatly affects service delivery. If they are not social workers, they cannot ensure that the process of accompanying them follows the social work process and it is difficult to accept and respect clients, but will do things for them, because supporting them takes more time than doing it directly…” [128, p. 66].
The results of the in-depth interviews show that the attitude towards the profession has a great influence on social services. A labor, invalids and social affairs officer said: “I have been involved in this work for more than ten years, most of the support work for the subjects is done based on experience and what I think is right, but in reality, I have not learned anything about social work, so I do not know what skills to use, what plans to make for the subjects, so the support effectiveness is not high”. (Labor, invalids and social affairs officer, District 8). In addition, because some staff are too confident in their many years of work, they often tend to impose their opinions on clients and do not respect the clients' right to self-determination in solving their problems, leading to ineffective service provision. Thus, the attitude towards the profession also has a significant influence on the effectiveness of using social services with workers in the KTPNN sector. However, a good attitude towards the profession leads to a more favorable relationship in mobilizing and connecting resources for clients. On the other hand, when working with social workers, social workers need to have a good grasp of their psychosocial characteristics to establish a good professional relationship and follow the rules and professional ethics, which will make it easier to identify problems and assess needs and plan to help clients use social services effectively.
To meet the requirements of the new era, the provision of social services also needs to change to train human resources to provide high-quality social services, meet social needs, and serve the development of the social work industry. According to
The report of the Department of Labor, Invalids and Social Affairs of Ho Chi Minh City said that in recent years, the implementation of Project 32 in the area has achieved many remarkable results. The Department of Home Affairs and the Department of Labor, Invalids and Social Affairs of Ho Chi Minh City in coordination with Campus II, the University of Labor and Social Affairs organized 38 training courses from basic to advanced, providing professional training for 4,574 trainees who are officials in the sector or working in the field of social work, including some members of the Steering Committee for the implementation of Project 32 of Ho Chi Minh City, employees of social organizations, social work officials at district, commune, ward levels, officials of unions, religious organizations, teachers of primary, secondary and high schools, medical staff at ward/commune levels [34]. Therefore, many communes/wards have created conditions for employees to participate in training courses and study specialized courses in social work to continuously improve the quality of providing social work services and gradually affirm their position and role in society, becoming an effective approach to deal with and solve many social problems.
A Labour, Invalids and Social Affairs officer said: “ In the past, the locality has created conditions for me to participate in training courses and improve my knowledge about social work and I am currently attending a part-time class in social work organized by the Department of Labour, Invalids and Social Affairs in collaboration with the University of Labour and Social Affairs, so I know the support methods and how to make a plan to help clients.” (Law, Invalids and Social Affairs officer, District 12). This shows that if officers are trained and improved their knowledge about social work more, the effectiveness of using social work services in the community will be improved.
The staff of commune/ward departments have not been trained and fostered in social work, so in the process of providing services, they do not fully understand the psychology, aspirations, working methods as well as the right attitude towards migrant workers. In addition, they are responsible for many tasks at the same time, so they are not fully devoted to supporting migrant workers, so they have difficulty mobilizing and finding quality resources, coordinating with departments/sectors, and organizations to organize programs and activities to provide, connect, and refer migrant workers to access services to solve their problems. Due to limited capacity, social workers cannot help migrant workers overcome their difficulties. These activities do not take place regularly but are only carried out according to the movement, focusing on holidays and Tet.
In reality, love for people and dedication are only necessary but not sufficient conditions to ensure the professionalism of staff in providing social work services in the community. This professionalism can only be achieved through training, coaching, and fostering for social work staff in communes/wards with full knowledge and skills in social work as well as necessary specialized and complementary knowledge.
This will have a significant impact on the attitude of social workers when working with migrant workers and help them clearly understand their roles and work responsibly in the process of performing their tasks, connecting and referring clients to necessary resources with appropriate intervention plans and promoting the implementation of programs/activities to meet social needs to enhance the effectiveness of the social service delivery system for migrant workers in the KTPNN sector.
3.3.1.2. Correlation between social worker capacity and social work services
The results of the correlation analysis in Table 3.15 show that the factor of social worker capacity is strongly correlated with the implementation of social work services for workers in the non-state sector (with p value < 0.01). In general, the correlation level of the factor of social worker capacity to each social work service is different. The correlation level of this factor with consulting and advisory services (r= -0.460**, p<0.00) and vocational training, employment and livelihood support referral services (r= 0.416**, p<0.00) has a strong correlation, on the contrary, services supporting access to public education; supporting information on safe accommodation and connecting resources have a weaker correlation. This shows that when the factors of social worker capacity change, it will lead to changes in the direction of increasing or decreasing the ability to access social work services for workers in the non-state sector.
Through multivariate linear regression analysis (R 2 , F –Test) with p value <0.000 for
It can be seen that all 05 factors included in the model are suitable, the independent variables: staff; Service communication; Resources/network; Characteristics of employees; Policy and legal mechanisms all affect social services. Specifically in this case, 05 independent variables included in the model can explain the variation of the dependent variable: social services with employees working in the KTPNN sector (R 2 = 49.7%; p = 0.00), the rest is due to variables outside the model that the thesis has not had the conditions to analyze and random errors.
(see appendix 3.3.1.2).
The factors included in the model affecting social services are not the same. Specifically: the factor of social service staff capacity has a Beta coefficient of -0.461 and p = 0.000 < 0.001. This shows that this factor affects social services and when other factors remain unchanged, the factor of social service staff capacity (knowledge, skills, attitudes, ...) changes, leading to a change in the dependent variable (C7 - social services) by 21.1% (R 2 = 0.211; p < 0.001). At the same time
Through the F test in the ANOVA table, the value (sig) of the F test is 0.000 < 0.05 (Appendix 3.3.2.1). In addition, the capacity, awareness, and attitude of the staff providing social services also have a significant impact on the service of connecting resources for the NLĐNC. Because social workers need to clearly understand where the resources are in the community.


![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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