In addition, the IPA technique allows organizations to identify attributes or their combinations that influence customer consumption behavior more or less. This is considered valuable information for developing marketing strategies in organizations as well as the process of forming useful management tools (Ford et al., 1991). The process of developing IPA is carried out through identifying attributes related to the quality assessment situation for a service. After consulting experts and managers (through focus group interviews), a list of quality attributes for evaluation is given. Next, the study will establish a questionnaire to collect information from customers to evaluate the importance of each attribute for providing service quality as well as to evaluate the level of implementation. By using the mean values to calculate the importance and implementation attributes as well as compare the mean differences of each quality attribute. For each attribute value obtained, it will be represented on a graph of 04 regions (importance and performance).
High
Maybe you are interested!
-
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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Solutions for tourism development in Tien Lang - 10
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- District People's Committees and authorities of communes with tourist attractions should support, promote, and provide necessary information to people, helping them improve their knowledge about tourism. Raise tourism awareness for local people.
*
* *
Due to limited knowledge and research time, the thesis inevitably has shortcomings. Therefore, I look forward to receiving guidance from teachers, experts as well as your comments to make the thesis more complete.
Chapter III Conclusion
Through the issues presented in Chapter II, we can come to some conclusions:
Based on the strengths of available tourism resources, the types of tourism in Tien Lang that need to be promoted in the coming time are sightseeing and resort tourism, discovery tourism, weekend tourism. To improve the quality and diversify tourism products, Tien Lang district needs to combine with local cultural tourism resources, at the same time combine with surrounding areas, build rich tourism products. The strengths of Tien Lang tourism are eco-tourism and cultural tourism, so developing Tien Lang tourism must always go hand in hand with restoring and preserving types of cultural tourism resources. Some necessary measures to support and improve the efficiency of exploiting tourism resources in Tien Lang are: strengthening the construction of technical facilities and labor force serving tourism, actively promoting and advertising tourism, and expanding forms of capital mobilization for tourism development.
CONCLUDE
I Conclusion
1. Based on the results achieved within the framework of the thesis's needs, some basic conclusions can be drawn as follows:
Tien Lang is a locality with great potential for tourism development. The relatively abundant cultural tourism resources and ecological tourism resources have great appeal to tourists. Based on this potential, Tien Lang can build a unique tourism industry that is competitive enough with other localities within Hai Phong city and neighboring areas.
In recent years, the exploitation of the advantages of resources to develop tourism and build tourist routes in Tien Lang has not been commensurate with the available potential. In terms of quantity, many resource objects have not been brought into the purpose of tourism development. In terms of time, the regular service time has not been extended to attract more visitors. Infrastructure and technical facilities are still weak. The labor force is still thin and weak in terms of expertise. Tourism programs and routes have not been organized properly, the exploitation content is still monotonous, so it has not attracted many visitors. Although resources have not been mobilized much for tourism development, they are facing the risk of destruction and degradation.
2. Based on the results of investigation, analysis, synthesis, evaluation and selective absorption of research results of related topics, the thesis has proposed a number of necessary solutions to improve the efficiency of exploiting tourism resources in Tien Lang such as: promoting the restoration and conservation of tourism resources, focusing on investment and key exploitation of ecotourism resources, strengthening the construction of infrastructure and tourism workforce. Expanding forms of capital mobilization. In addition, the thesis has built a number of tourist routes of Hai Phong in which Tien Lang tourism resources play an important role.
Exploiting Tien Lang tourism resources for tourism development is currently facing many difficulties. The above measures, if applied synchronously, will likely bring new prospects for the local tourism industry, contributing to making Tien Lang tourism an important economic sector in the district's economic structure.
REFERENCES
1. Nhuan Ha, Trinh Minh Hien, Tran Phuong, Hai Phong - Historical and cultural relics, Hai Phong Publishing House, 1993
2. Hai Phong City History Council, Hai Phong Gazetteer, Hai Phong Publishing House, 1990.
3. Hai Phong City History Council, History of Tien Lang District Party Committee, Hai Phong Publishing House, 1990.
4. Hai Phong City History Council, University of Social Sciences and Humanities, VNU, Hai Phong Place Names Encyclopedia, Hai Phong Publishing House. 2001.
5. Law on Cultural Heritage and documents guiding its implementation, National Political Publishing House, Hanoi, 2003.
6. Tran Duc Thanh, Lecture on Tourism Geography, Faculty of Tourism, University of Social Sciences and Humanities, VNU, 2006
7. Hai Phong Center for Social Sciences and Humanities, Some typical cultural heritages of Hai Phong, Hai Phong Publishing House, 2001
8. Nguyen Ngoc Thao (editor-in-chief, Tourism Geography, Hai Phong Publishing House, two volumes (2001-2002)
9. Nguyen Minh Tue and group of authors, Hai Phong Tourism Geography, Ho Chi Minh City Publishing House, 1997.
10. Nguyen Thanh Son, Hai Phong Tourism Territory Organization, Associate Doctoral Thesis in Geological Geography, Hanoi, 1996.
11. Decision No. 2033/QD – UB on detailed planning of Tien Lang town, Hai Phong city until 2020.
12. Department of Culture, Information, Hai Phong Museum, Hai Phong relics
- National ranked scenic spot, Hai Phong Publishing House, 2005. 13. Tien Lang District People's Committee, Economic Development Planning -
Culture - Society of Tien Lang district to 2010.
14.Website www.HaiPhong.gov.vn
APPENDIX 1
List of national ranked monuments
STT
Name of the monument
Number, year of decisiondetermine
Location
1
Gam Temple
938 VH/QĐ04/08/1992
Cam Khe Village- Toan Thang commune
2
Doc Hau Temple
9381 VH/QĐ04/08/1992
Doc Hau Village –Toan Thang commune
3
Cuu Doi Communal House
3207 VH/QĐDecember 30, 1991
Zone II of townTien Lang
4
Ha Dai Temple
938 VH/QĐ04/08/1992
Ha Dai Village –Tien Thanh commune
APPENDIX II
STT
Name of the monument
Number, year of decision
Location
1
Phu Ke Pagoda Temple
178/QD-UBJanuary 28, 2005
Zone 1 - townTien Lang
2
Trung Lang Temple
178/QD-UBJanuary 28, 2005
Zone 4 – townTien Lang
3
Bao Khanh Pagoda
1900/QD-UBAugust 24, 2006
Nam Tu Village -Kien Thiet commune
4
Bach Da Pagoda
1792/QD-UB11/11/2002
Hung Thang Commune
5
Ngoc Dong Temple
177/QD-UBNovember 27, 2005
Tien Thanh Commune
6
Tomb of Minister TSNhu Van Lan
2848/QD-UBSeptember 19, 2003
Nam Tu Village -Kien Thiet commune
7
Canh Son Stone Temple
2160/QD-UBSeptember 19, 2003
Van Doi Commune –Doan Lap
8
Meiji Temple
2259/QD-UBSeptember 19, 2002
Toan Thang Commune
9
Tien Doi Noi Temple
477/QD-UBSeptember 19, 2005
Doan Lap Commune
10
Tu Doi Temple
177/QD-UBJanuary 28, 2005
Doan Lap Commune
11
Duyen Lao Temple
177/QD-UBJanuary 28, 2005
Tien Minh Commune
12
Dinh Xuan Uc Pagoda
177/QD-UBJanuary 28, 2005
Bac Hung Commune
13
Chu Khe Pagoda
177/QD-UBJanuary 28, 2005
Hung Thang Commune
14
Dong Dinh
2848/QD-UBNovember 21, 2002
Vinh Quang Commune
15
President's Memorial HouseTon Duc Thang
177/QD-UBJanuary 28, 2005
NT Quy Cao
Ha Dai Temple
Ben Vua Temple
Tien Lang hot spring
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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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Analysis of factors affecting customer satisfaction with the quality of FiberVNN fiber optic internet service of Can Tho Telecom - 2 -
Results of Regression Model Analysis with Two Independent Variables Service and Interbank
PART I

Level of importance
FOCUS ON DEVELOPMENT
High importance Low implementation level PART III
DEVELOPMENT RESTRICTIONS
Low importance
Low level of implementation
PART II
KEEP MAINTAINING
High level of importance
High level of performance
PART IV
REDUCE INVESTMENT
Low importance
High level of performance
Low Implementation Level High
Table 1.1: IPA model analyzes the importance and performance level of services
case- Martilla, James (1997)
Its results will indicate the priority of quality attributes to take actions to improve them (Slack, 1991). The four areas in the IP graph are evaluated as follows:
Quadrant 1 (Development Focus): Service quality attributes in this area are considered very important to customers, but the level of performance of the service provider is very poor. This result suggests that service management should pay attention to these attributes, focusing on developing the level of service provision to satisfy customer needs.
Quadrant 2 (Continue to Maintain): Attributes in this quadrant are considered very important to customers and the service provider has also performed very well. Service delivery managers should continue to maintain and develop this strength.
Quadrant 3 (Limited Development): Attributes in this quadrant are considered to have low performance and are not important to customers. Service providers should limit resources to develop these attributes.
Quadrant IV (Reducing Investment): Attributes that fall in this quadrant
considered unimportant to customers, but the supplier's performance is very good. It can be seen that the current excessive investment is useless. Service supply managers should use this resource to focus on developing other attributes.
Through this chart, the organization will know the priority of quality attributes to take actions to improve them (Slack 1991). In addition, the chart can also provide a useful guide for forming the organization's marketing strategy (Burns, 1986). So far, the importance and performance analysis has been applied in a number of different service sectors such as: Tourism (Bush & Ortinqu, 1986; Evans & Chon, 1990; Uysal et al., 1991; Martin 1995); Healthcare (Cunningham & Gaeth, 1989; Nitse & Bush, 1993); Education (Alberty & Mihailik, 1989); Banking (Ennew et al., 1993).
1.2. Practical basis
1.2.1.Some features of the real estate market
1.2.1.1.Real estate market in Vietnam
Over the past 10 years, the Vietnamese real estate market has experienced many ups and downs, but above all, it has been a spectacular re-heating after a period of freezing in most of the implementation of the Party and State's policies and guidelines on economic development.
socialist market, in the past 10 years, the real estate market has developed in terms of scale, quantity, product structure, investment capital and market participants.
Currently, the whole country has been implementing 5,000 projects, with a total investment capital of more than 4.5 billion VND (3 times higher than in 2009). The number of apartments has grown strongly. According to 2010 data, Hanoi's population reached about 6.6 million people, the whole market had more than 20,000 townhouses, apartments were mainly old apartments, estimated at about 73,000 units. By 2019, Hanoi's population reached 8.1 million people, about 46,000 townhouses and more than 300,000 apartments.
In addition to commercial housing, there are also social housing, industrial real estate, tourist real estate (villas, tourist apartments), offices, and commercial centers for rent. By the end of 2019, out of a total of 5,000 housing projects, there were more than 1,000 social housing projects; there were 326 industrial parks, about 30,000 tourist accommodation establishments; there were 6 million square meters of offices for rent (nearly tripled in 2009).
Like a cyclical law, the real estate market over the past 10 years has gone through stages of development: fever - freezing - stagnation - recovery and growth again.
Specifically, the period 2009 - 2010 was a period of hot development of the market, most real estate segments grew hotly mainly due to credit easing.
The period 2011 - 2013 was a period of stagnation and freezing, due to banks tightening capital sources and credit standards for real estate loans; considering real estate a non-production sector.
The period 2014 - 2019 is the period of recovery and development of the real estate market, because during this period the State has issued many suitable mechanisms and open policies to control and facilitate the development of the market. However, since the end of 2019, there have been signs of stagnation in some segments due to imbalance in supply and demand and credit conditions.
( Source: baoxaydung.com.vn) In 2020, although the real estate market has risks of slowing down, in general, with positive factors of the macro economy, this market still has basic development.
stable development
The real estate market in the first months of 2020 faced countless difficulties and challenges. While legal policies have not been resolved, the Covid-19 pandemic has once again pushed the market into a "difficult situation". According to records, most real estate businesses have been clearly affected, crowded events such as marketing promotion (PR), sales have been canceled....
Some real estate businesses have changed their business plans, effectively applying technology in their business strategies such as:
✓ Deploy sales apps
✓ Use ads with videos, 3D scanning
✓ Livestream broker to introduce products to customers to support buyer partners.
The real estate market is in a gradual decline and has not yet reached its peak. There are still many bright spots to expect the market to recover if the epidemic is soon completely controlled.
How does Covid 19 affect Vietnam real estate?
Difficulty:
The resurgence of Covid-19 has severely affected the progress of ongoing projects. This is a huge challenge because if the investor has a project that is on schedule, they still have to pay the contractor. If the cash flow is slowed down due to customers' payment interruptions, the investor will have a very difficult time.
This situation had not been resolved when, in early 2020, the Covid-19 pandemic struck, causing an unprecedented decline in market transactions.
Statistics show that in the first quarter of 2020, new supply and consumption were the lowest since 2015; about 800/1,000 trading floors nationwide have temporarily suspended operations; a series of real estate brokers lost their jobs...
Businesses face more cash flow difficulties if the launch event is postponed or market demand drops sharply.
Solution:
To overcome the above difficulties, many solutions have been proposed since the beginning of 2020. Social housing projects that are being implemented but have capital problems will work with the State Bank to find solutions to support loans.
The State will regulate by increasing incentives for businesses participating in the low-cost commercial apartment segment with an area of less than 75m2 and a price of less than 20 million VND/m2. It is expected that in the third quarter of 2020, a draft Resolution will be submitted to the Government. If this resolution is issued, it will help the market develop stably and harmoniously.
On the business side: Change the payment schedule according to contractual obligations with customers. This is also the solution of many real estate development businesses to find ways to share difficulties with customers. Thus, businesses have accepted to reduce profits to maintain stable housing prices after the Covid-19 pandemic.
Promoting technology application and investment in real estate: By applying technology, customers can know information about the project, visit the apartment through virtual reality with just a smartphone, at the same time helping customers save time, creating flexibility, initiative for customers and limiting contact with crowds during the epidemic season. This is a factor promoting online transactions in the real estate sector.
(Source: batdongsanoline.vn)
Real estate market in the first months of 2021:
According to the Department of Housing and Real Estate Market Management, real estate prices in 2020 and the first two months of 2021 continued to increase, with some areas and projects increasing by over 10% compared to the beginning of 2020.
This parameter is a picture of the overall market assessment, but in reality, in the first 2 months of 2021, the real estate market in many localities experienced local land fever with increases of up to several tens of percent, even a few percent such as: Luong Son (Hoa Binh), Gia Vien (Ninh Binh), Thu Duc (Ho Chi Minh City), Hon Quan (Binh Phuoc).
The increase in real estate prices in 2020 despite the difficult situation of the pandemic has given investors confidence and the market growth picture in 2021, especially when bottlenecks are cleared and the macroeconomic picture appears with brighter colors.
Mr. Nguyen Van Dinh, Vice President and General Secretary of the Vietnam Real Estate Brokers Association, commented that the real estate market has had an amazing recovery. State prices are forecast to continue to increase as the market growth cycle has not ended.
end. In 2021, house prices will continue to increase by about 10% compared to 2020. (Source: baochinhphu.vn)
1.2.1.2.Real estate market in Thua Thien Hue
Number of real estate projects doubled
According to statistics from the Department of Construction of Thua Thien Hue province, since 2016, the real estate market in Hue has recorded remarkable developments. Especially in 2018 and 2019, the market entered a period of explosion in both the number of projects and products.
“The Southeast area of Hue City is considered the center of the market when the number of projects has increased at an unprecedented rate. For example, in An Van Duong area, there were only 32 projects in 2015, but now it has increased to 64 projects. Not only that, with the development of the tourism and service industry in recent times, the real estate market in Thua Thien Hue has now started to 'heat up' again" - Mr. Nguyen Phuoc Buu Hung - Deputy Director of the Department of Construction of Thua Thien Hue province - said.
Not only tourism real estate projects but also commercial housing development projects and urban development investment projects are developing equally. According to data from the Department of Construction of Thua Thien Hue province, currently, the whole province has 10 commercial housing development projects and urban development projects that have been approved for investment, and are being implemented with a land area of about 230.1 hectares, along with about 7,146 apartments, equivalent to about 2.032 million square meters of floor space. Some large real estate projects attracting demand such as: Phu My Thuong urban area, Phu My An urban area, Manor Crown complex, Joyal Park project, Thuy Van Complex phase 2 project, ... have promoted the development of the market here.
In particular, the real estate market in Thua Thien Hue has recorded the excitement of the land segment after a long period of stagnation. “While land in the North and Northwest is quite quiet, the South and Southeast of the province are bustling. Land prices in new residential projects have “warmed up” due to the increasing demand for residential land. The growth of the land market in this area has created a spillover effect for the development of land projects in neighboring districts and towns,” Mr. Hung shared.
According to Mr. Hung, the reason why the southern area and land in planning areas have become the focus of the land market is because the initial technical infrastructure in these areas has been fully invested, and the orientation of moving the administrative center of Hue City to the South has pushed the market up.
From an investment perspective, many real estate project investors in Thua Thien Hue said that an important factor contributing to the recent revival of the Thua Thien Hue real estate market is that the caution of Hue people has decreased, helping them see opportunities and have much higher confidence in the real estate market than before.
“This is reflected in a series of projects from land to social housing, mid-range and high-end apartments that all have owners right after being opened for sale or auctioned,” said Mr. Quan, an investor.
Price doubled compared to before
Although people are still cautious, the increase in population size in the area has boosted the demand for real estate in the southern and southeastern areas of Thua Thien Hue province. Not only that, the change in tastes and the trend of improving the quality of life of residents has created a bustling atmosphere in this southeastern area.
Record land prices in the planning area of Xuan Phu, Thanh Thuy, Thuy Van, Phu
Vang,… has had strong changes, even the price has doubled compared to before. “If before the price of land on the main road of the Xuan
"The price of land in Phu Chi was only 16 million VND/m2, but now it has increased to 35 million VND/m2. In the planning area of Thuy Thanh, Thuy Van, the price has increased from 7-8 million VND/m2 to 12-16 million VND/m2 or the land in the planning area of Vinh Ve, Phu Vang has increased from 3 million VND/m2 to 5.5 million VND/m2.... This shows that not only the value of real estate has increased significantly but also represents an investment opportunity for the market" - Deputy Director of the Department of Construction of Thua Thien Hue province said.
Assessing the reasons for the strong growth in real estate prices, the leader of the Thua Thien Hue Department of Construction said that in order to create conditions for market development, the provincial Department of Construction authorized the Thua Thien Hue Real Estate Association to organize exams to grant real estate brokerage practice certificates in the province and up to now, real estate brokerage activities have been put into order, complying with the provisions of the Law on Real Estate Business and the Law on Housing.
“In addition, the orientation of developing Hue city into one of the major cities of Vietnam by 2025 is one of the growth poles that creates development momentum for the real estate market of Thua Thien Hue. In particular, according to the orientation at



![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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