and I became shipowners' civil liability insurance or shipowners' civil liability insurance and compensation is no longer correct and no longer necessary.
3.1.3. Nature of the Association
In the course of business, the shipowner or charterer is responsible for losses caused by the use of the ship for operations that cause damage to others. According to international law, the shipowner's civil liability (the shipowner's liability) includes liability to compensate third parties, liability for the goods carried and the people on board.
When a ship owner participates in hull insurance under the conditions of insurance for civil liability caused by collision, the hull insurance is responsible for compensating ¾ of that civil liability. Thus, the ship owner must bear the remaining civil liability. Therefore, in the early 18th century, ship owners joined together and established the “Protection Clubs”. This club was established to insure ¼ of the liability for collision that hull insurance did not cover. At the same time, the club also insured 100% of the liability for death and injury to officers, passengers and crew…
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Details of the General P&I Premium Increase of the Associations -
P&I insurance activities for Vietnamese shipping companies - 12 -
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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Accounting for production costs and product pricing of P&G Advertising and Trading Company Limited - 1 -
Corresponding Techniques for Task Type T 1 Μ , T 1 P , T 1 2
3.1.4. Organizational structure of the Association
P&I Club is a legal entity. Each club consists of a number of members who are ship owners from countries around the world.

The highest authority of the association is the Board of Directors. This board decides
regulations, policies, and compensation settlement for members.
The body assisting the Board of Directors can be organized in two forms: Board of Directors and Management Board.
The Board of Directors is elected by the Board of Directors and the Chairman is usually the shipowner with the largest fleet in the association. Therefore, the daily work is not handled equally and objectively, often tending to favor the shipowners with the larger fleet.
The management board consists of a chairman and several vice chairmen. The management board is staffed by competent people hired by the Board of Directors. The daily working method is more fair and reasonable.
3.1.5. Management of the Association
The P&I insurance association operates on the basis of balanced income and expenditure. In essence, the association's fee calculation method is an accounting method between the association and its members on the basis of mutual support to balance the association's income and expenditure. The association's main sources of income are insurance premiums and investment interest. Insurance premiums are contributed annually by members. Investment interest includes all interest from all forms of investment from the association's idle capital. These sources of income are used to cover expenses during the year. Expenses include: Expenses for compensation for losses of members, compensation expenses for other members in the International group, reinsurance costs for losses exceeding the retention level of the association and the group, and administrative management costs. In addition to the above expenses, the association also takes into account the loss in value of premium payments. Due to the complexity of the risks that the association accepts insurance for, in
In the business year, there are losses that have to wait several years for a court or arbitration decision. Only when all expenses in the business year have been paid do members have data to allocate the costs that must be contributed by members for that year.
The management of a P&I insurance club is essentially based on the shipowners through an elected board, or board of directors. The board of directors will decide policies on coverage, indemnity, and premium contributions.
The board of directors assigns responsibility and authorizes within a certain limit to the board of directors or management board to handle daily tasks or compensation cases under 100,000 USD. In addition, the board of directors also uses a network of representatives in other countries to grasp information, changes in laws... of other countries to help the board of directors handle them promptly and in accordance with the law.
The operation of the P&I club is based on the principle of mutual balance of income and expenditure, which means that all expenses such as compensation for losses, management expenses, and member assistance expenses are contributed by the club's members.
The Association also assists members in litigation and disputes, provides new information, and trains professional staff.
According to the rules, the association does not allow ship owners to mortgage or transfer P&I insured vessels to others without the association's consent. The validity of the insurance contract will terminate when the member dies, becomes bankrupt or becomes insane (according to specific regulations).
3.1.6. Association membership and insurance period
a. Joining the association and related issues
Any person wishing to join the club must apply for membership within a specified period and must provide all the required information and specifications. If the vessel is accepted for insurance, the information and specifications provided in the application form form part of the contract of insurance. The information provided must be true to the best of the member's knowledge and reasonable diligence. The club may refuse to accept any member's application for membership without giving any reason, whether the applicant is already a member of the club or not. Upon acceptance of the application, the member will be issued with a Certificate of Entry. This certificate will state the name of the member and his rights in respect of the vessel entered into the club, the time and date of commencement of insurance, and the terms and conditions of the accepted insurance. If a shipowner enters into a P&I insurance scheme with multiple vessels (fleet enter), the liability of any member for both the fleet and the club will be treated as if all the vessels of the fleet entered into the club by the same member.
b. Change and supplement insurance conditions
Unless otherwise notified, the insurance conditions for the following fiscal year shall remain the same as the current fiscal year. However, the insurance conditions may be amended at any time and shall take effect at the beginning of the following fiscal year.
If the association wishes to change the terms for the next financial year, it must notify the members before 12 noon (GMT) on 20 February, and the contract will continue.
subject to renegotiated terms, otherwise the coverage will terminate at the end of the current financial year.
c. End of insurance
When wishing to terminate coverage for the following financial year, the member must notify the association within 30 days before 12 noon (GMT) on 20 February, and coverage will end at the end of the current financial year.
If, after the notice of termination of the insurance contract has been issued, the Association and the member agree on new conditions before 12 noon on 20 February, the notice of termination of insurance will be revoked and the vessel will continue to be insured for the new financial year under the new terms. Unless approved by the Association or the contract is terminated by law, the member may not withdraw the insurance contract at any time.
3.2 . P & I insurance premium calculation techniques
3.2.1. Fee calculation principles
The P&I Club's insurance premiums are contributed by members according to the club's operating principle of balancing income and expenditure. Therefore, the insurance premiums contributed by each member are based on the balance of income and expenditure of the club in each period. Before signing an insurance contract, the member and the club must agree on the insurance premium rate. The decision on the insurance premium rate must be based on the estimated level of risk for the insured vessel.
3.2.2. Basis of charging
As we know, insurance premiums are calculated based on the balance of income and expenditure in each period. The association's income includes:
- Insurance premiums paid annually by members;
- Income from idle investment interest has not compensated for losses to members.
The branches of the association include:
- Compensation for losses to other members of the international P&I insurance group;
- Reinsurance expenses;
- Management fee;
- Compensation for losses due to inflation.
Due to the characteristics of P&I insurance, losses occur within the insurance year, but dispute resolution often takes several years. Therefore, each Association often collects an amount of prepaid premium from members to meet the spending needs arising in that year. Thus, in essence, calculating P&I insurance premiums is calculating prepaid and postpaid premiums from members.
3.2.3. Fee calculation method
There are two methods of calculating fees: prepayment method and postpayment method;
a. Prepayment calculation method
There are two methods of calculating prepayment: by compensation rate and by tonnage.
1) Method of calculating fees based on compensation ratio:
Under this method, the average compensation rate of the association for 5 years for each member is calculated as the basis for calculating the rate or net premium. Then, consider the compensation rate in the 5th year, reinsurance costs, group insurance costs, management costs and inflation, etc.
The procedure is as follows:
◊ Calculate the average compensation rate of the association in 5 years
T tb = (Total amount of money the association has paid and will pay in 5 years)/(Total amount of membership fees paid and will pay in 5 years)
◊ Calculate the fee payable in the 5th year
P= Amount of fees paid in advance + Estimated amount of fees to be paid
◊ Calculate reinsurance premiums of association members:
P tb = gQ
In which: P tb is the member's reinsurance premium, g is the insurance premium price on the international market for 1 GRT, Q is the total tonnage of the member's fleet.
◊ Calculate the amount of membership fees paid to the association to compensate other Associations in the International group
P qt =(P 5 - P tb ).y 1
P qt is the compensation fee for the International group, y 1 is the compensation fee rate of the member for the International group
Management cost calculation:
P ql =(P 5 -P tb ).y 2
P ql is the management cost, y 2 is the management cost standard ratio
± Calculate the allowable compensation rate of the business year (next year)
T 6 =(P 5 -P tb -P qt -P ql ).100/P 5
Calculate the difference between the compensation rate of the business year (T 6 ) and the average compensation rate (T tb )
y 3 = T 6 – T tb ≥ Inflation compensation costs. The Association stipulates that dues are paid in US dollars. The inflation rate (y 4 ) is based on the currency market and international payments.
Calculate the insurance premium payable per ton of GRT in year 5
p = (Total premium paid in year 5)/Total tonnage of member's ship
Calculate the prepaid insurance premium of the member for the professional year (next year)
P t =(p – p.(y 3 -y 4 )).Q
P t is the prepayment fee
The method of calculating fees based on compensation rates has the advantage of being quick and neat. But it also has certain limitations. That is, it does not reflect changes in the fleet (buying more or selling). It cannot be applied to members with large losses, loss rates exceeding 100%... To overcome the above disadvantages, prepayment fees can be calculated based on ship tonnage.
2) Method of calculating charges based on ship tonnage
According to this method, the average compensation amount is calculated according to the tonnage of the ship that the member bears in that loss and is considered as the compensation amount of the association. The calculation sequence is as follows:
◊ Calculate the average compensation level for the past 5 years per ton of ship's tonnage:
M tb = (Total amount of compensation paid and to be paid in 5 years / Total tonnage of member's ships in 5 years)
M tb is the average compensation level per ton of load.
According to the convention, when a major loss occurs, the compensation for that loss is only calculated for the part that the ship owner (member) bears, not the part that the association bears.
◊ Calculate reinsurance premium per ton of ship's tonnage according to the reinsurance premium price of the international market (M 1 )
◊ Calculate compensation for international P and I insurance group M 2 = M tb .xy 1
◊ Charge to cover the management costs of the Association M 3 = M tb .xy 2
* Calculate the cost support fee due to inflation M 4 = M tb .xy 4
± Insurance fee calculated for 1 ton of load
f = M tb + M 1 + M 2 + M 3 + M 4
or f = M tb (1 + y 1 + y 2 + y 4 ) + M 1
The insurance premium that members pay to the association will be:
P = fQ
Q = (Total tonnage of member's fleet in 5 years)
It should be noted that in P and I insurance, deductibles are usually applied for each type of risk. Therefore, when calculating insurance premiums, each specific case must be compared.
b. Post-payment calculation method
Each member participating in insurance must pay a certain amount of fees in advance, usually 75% of the annual premium. The fees are used to pay compensation to members, international groups, reinsurance, and association management expenses. During the year, if the fees are not fully paid, they will be put into the association's reserve fund. If there is a shortage, members can request additional payments. Members pay additional payments based on compensation expenses arising during the year that have been resolved or on the exact amount that the association must pay.
Additional fees (post-payment) of each member must be based on the expenses in the business year and the association's revenues for allocation.
- Expenses (a): + compensation for members;
+ compensation for international groups;
+reinsurance costs;
+management fee
- Collecting advance fees from members (b); collecting investment interest (c)
Based on the revenue and expenditure, calculate the following fee rate for each member according to the formula:
t =(abc).100% / b So the fee paid later by each member will be:
P s = P t . t In which:
P s : Post-payment fee; P t : Pre-payment fee;
t: Post-payment fee rate.
3.3 . Risks covered by the Association
3.3.1. General principles
The association only covers the liabilities, losses and expenses incurred by the shipowner arising from incidents occurring during the period of the insurance contract, relating to the shipowner's interests and connected with the operation of the vessel. P&I insurance is in principle liability insurance, but in addition this type of insurance also accepts insurance for many other types of losses.
3.3.2. Liability and loss insured by the Association
a. Responsibility for casualties
The Association insures the insured against liability arising from bodily injury, death and salvage, provided that all such losses occur in direct connection with the operation of the insured vessel. In this case, the liability of the shipowner is insured regardless of where and how the loss occurs or the origin of the loss or accident.
1) Casualties and illnesses of the crew
This section sets out the coverage for seafarers in the event of illness, injury or death, including:
- Responsibility to pay for losses, compensation for damages (except hospital, medicine, funeral) for injuries, illnesses and deaths of crew members whether occurring on board or not.
- Responsibility for paying for hospital fees, medicine, funeral expenses related to injuries, illnesses or deaths of crew members (not including salaries and repatriation or replacement costs).
- Medical examination costs of crew members.
In the event of any liability, costs or expenses arising, the seafarer's charter or any contract of service or employment must have been concluded in advance and the liability shall be deemed not to have arisen in the absence of such contract. In the event of injury to a seafarer on leave, such liability, costs or expenses shall only be covered by the Association if, to the extent that they have been previously approved in writing by the Manager and only if the insured vessel is the last vessel on which he was employed before the injury or loss occurred.
The liability of the shipowner for crew injuries varies according to the laws of each country and varies greatly between countries. The liability of the shipowner for crew injuries is usually governed by the laws of the flag state. However, some countries apply their laws to those working on ships not registered in their country.
2) Casualties of other persons working on board
Includes cases of illness, injury and death of persons other than crew or passengers:
- Liability for payment of damages and compensation for injury, illness and death of any person other than crew or passenger.
- Responsibility to pay for hospital, medical and funeral expenses related to injuries, illnesses and death.
For this group of insurances, some countries have social insurance which reduces the shipowner's liability to some extent, while others have the shipowner assume most or almost all of the liability. Such extensions of the shipowner's liability are only covered when they are considered normal in the trade.
3) Passenger casualties
Liability for injury to insured passengers includes:
- Responsibility to pay for losses and compensation for cases of injury, illness or death of passengers on board and related hospital, medical and funeral expenses;
- Liability for payment of losses and compensation for the cost of transporting passengers to the port of destination, or returning to the port of departure and the cost of caring for passengers on shore arising as a result of an accident occurring to the insured vessel;
- Responsibility to pay or compensate passengers on board affected or impacted.
4) Repatriation and replacement costs
Includes costs of repatriating seafarers and providing replacement crew: Costs of repatriating seafarers who are sick or injured; or whose spouse, children, or parents (in the case of an only child) are dangerously ill and whose presence at home is absolutely necessary; or whose repatriation is required by law.
b. Responsibility for wages and unemployment compensation due to shipwreck
This section provides coverage for payment of wages to seafarers injured or sick while on board and during repatriation in the event of abandonment or loss of ship:
- Responsibility for paying wages to the ship's sailors during treatment in a hospital abroad, or during repatriation due to injury or illness, or for replacements during the waiting period for replacement and repatriation.
- Liability for compensation for loss of employment of seafarers in case these seafarers are working on board the ship, in the process of arriving at the ship or leaving the ship due to actual total loss or estimated total loss of the ship.
c. Property liability
1) Loss of property of sailors or others
Includes liability to pay or compensate for damage or loss to property of:
- Any crew member on board the insured vessel;
- Any other person on board
The Society shall not indemnify against claims relating to money, negotiable instruments, precious metals or stones, valuables or objects of natural value. In the event of loss or damage to property, articles which the manager considers unfit for the use of seamen shall not be indemnified.
2) Loss of property on board
The Association is responsible for indemnifying third party claims for loss or damage to property on board the insured vessel. Property here includes any containers, equipment, fuel or other property on board the insured vessel (other than cargo and personal property).
The liability under this section does not include loss or damage to property which is part of the vessel or which is owned or leased to the member or to a partnership or jointly managed by the member.
3) Loss of machine or other property damage
When a ship is traveling in a channel, entering or leaving a bridge or anchoring, it can cause damage to locks, wharves, structures as well as other fixed and floating objects.
The Association shall be liable to pay for losses or compensation for loss or damage to property, whether on land or in water, movable or immovable.
If the insured vessel causes loss or damage to property or interests belonging wholly or partly to the member, the member shall have the same right of recourse against the association as if such property or interests belonged wholly to other owners.
d. Liability for collision accidents
The Company insures against liability arising out of collision between the insured vessel and any other vessel, but provided and to the extent that such liability is not subject to the collision liability provisions of the hull insurance policy. This liability includes:
- 1/4 collision liability or such other proportion as may be agreed in writing by the manager (other than the liabilities listed below);
- 4/4 collision liability arising from collision accident or related to:
+ The removal or clearance of wrecks, cargo or any other obstructions;
+ Any personal property, real estate or anything else (except another vessel or property on another vessel);
+ Goods and assets on board the ship are insured, contributing to general average, special expenses or salvage fees that the cargo owner or property owner must bear;
+ Loss of life, injury or illness;
+ Pollution or damage to personal property, real estate or any other objects (except pollution or damage to another vessel or property on another vessel).
- The member's liability arising from collision accidents (not including the liabilities mentioned above) exceeds the amount of compensation just paid under the hull insurance policy of the insured vessel.



![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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