Machine
CN
A 10 | B 25 | C 25 | |
Type I: 30 | 50 | 45 | 30 |
Type II: 20 | 40 | 42 | 28 |
Type III: 10 | - | 38 | 25 |
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Car body electrical practice - 8
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If the voltage is out of specification, replace the wire or connector.
If the voltage is within specification, install the front fog light relay and follow step 5.
Step 5 Check the front fog light switch
- Remove the D4 connector of the fog light switch
- Use a multimeter to measure the resistance of the front fog light switch.
Measurement location
Condition
Standard
D4-3 (BFG) -D4-4 (LFG)
Light switchFront Fog OFF
>10kΩ
D4-3 (BFG) -D4-4 (LFG)
Front fog light switchON
<1 Ω
- Standard resistor
D4 connector is located on the combination switch assembly.
If the resistance is out of specification, replace the combination switch (the fog light switch is located in the combination switch).
If the resistance is within specification, follow step 6.
Step 6 Check wiring and connectors (front fog light relay-light selector switch)
- Disconnect connector D4 of the combination switch assembly
- Use a voltmeter to measure the voltage value of jack D4 on the wire side.
Measurement location
Control modecontrol
Standard
D4-3 (BFG) - (-) AQ
TAIL
11 to 14 V
D4 connector for the wiring of the combination switch assembly
If the voltage does not meet the standard, replace the wire or connector.
If the voltage is within standard, there may have been an error in the previous measurements.
Step 7 Check the front fog lights
- Remove the front fog light electrical connector.
- Supply battery voltage to the fog lamp terminals
Jack 8, B9 of front fog lamp on the electrical side
blind first.
Power supply location
Terms and Conditions
Battery positive terminal - Terminal 2Battery negative terminal - Terminal 1
Fog lightsbefore morning
- If the light does not come on, replace the bulb.
If the light is on, re-plug the jack and continue to step 8.
Step 8 Check wiring and connectors (relay and front fog lights)
- Disconnect the B8 and B9 connectors of the front fog lights.
- Use a voltmeter to measure voltage at the following locations:
Measurement location
Switch location
Terms and Conditions
B8-2 - (-) AQ
Electric lock ON TAIL size switchFog switch ON
11 to 14 V
B9-2 - (-) AQ
Electric lock ONTAIL size switch Fog switch ON
11 to 14 V
B8 and B9 connectors on the front fog lamp wiring side
Voltage is not up to standard, repair or replace the jack. If up to standard, there may have been an error in the measurement process.
2.2.4. Procedure for removing, installing and adjusting fog lights 1. Procedure for removing
- Remove the front inner ear pads
Use a screwdriver to remove the 3 screws and remove the front part of the front inner ear liner
-Remove the fog light assembly
+ Disconnect the connector.
+ Use a screwdriver to remove 3 screws to remove the fog light cover
2. Installation sequence
-Rotate the fog lamp bulb in the direction indicated by the arrow as shown in the figure and remove the fog lamp from the fog lamp assembly.
-Rotate the fog light bulb in the direction indicated by the arrow as shown in the figure and install the light into the fog light assembly.
- Use a screwdriver to install the fog light cover
-Install the electrical connector
Attention: Be careful not to damage the plastic thread on the lamp assembly.
- Install the front inner ear pads
Use a screwdriver to install the front inner bumper with 3 screws.
3. Prepare the vehicle to adjust the fog light convergence. Prepare the vehicle:
- Make sure there is no damage or deformation to the vehicle body around the fog lights.
- Add fuel to the fuel tank
- Add oil to standard level.
- Add engine coolant to standard level.
- Inflate the tire to standard pressure.
- Place spare tire, tools and jack in original design position
- Do not leave any load in the luggage compartment.
- Let a person weighing about 75 kg sit in the driver's seat.
4. Prepare to check the fog light convergence
a/ Prepare the vehicle status as follows:
- Place the car in a dark enough place to see the lines. The lines are the dividing line, below which the light from the fog lights can be seen but above which it cannot.
- Place the car perpendicular to the wall.
- Keep a distance of 7.62 m between the center of the fog lamp and the wall.
- Park the car on level ground.
- Press the car down a few times to stabilize the suspension.
Note: A distance of approximately 7.62 m is required between the vehicle (fog lamp center) and the wall to adjust the convergence correctly. If the distance of 7.62 m cannot be achieved, set the correct distance of 3 m to check and adjust the fog lamp convergence. (Since the target area varies with the distance, please follow the instructions as shown in the figure.)
b/ Prepare a piece of thick white paper about 2 m high and 4 m wide to use as a screen.
c/ Draw a vertical line through the center of the screen (line V).
d/ Set the screen as shown in the picture. Note:
- Keep the screen perpendicular to the ground.
- Align the V line on the screen with the center of the vehicle.
e/Draw the reference lines (H, V LH and V RH lines) on the screen as shown in the figure.HINT:
Mark the center of the fog lamp on the screen. If the center mark cannot be seen on the fog lamp, use the center of the fog lamp or the manufacturer's name mark on the fog lamp as the center mark.
H line (fog light height):
Draw a line across the screen so that it passes through the center mark. Line H should be at the same height as the center mark of the fog light bulb.
Line V LH, V RH (center mark position of left fog lamp LH and right fog lamp RH):
Draw two lines so that they intersect line H at the center marks.
5. Check the fog light convergence
a/ Cover the fog lamp or remove the connector of the other side fog lamp to prevent light from the unchecked fog lamp from affecting the fog lamp convergence test.
b/ Start the engine.
c/ Turn on the fog lights and make sure that the dividing line is outside the standard area as shown in the drawing.
6. Adjust the fog light convergence
Use a screwdriver to adjust the fog light to the standard area by turning the toe adjustment screw.
Note: If the screw is adjusted too far, loosen it and then tighten it again, so that the last rotation of the light adjustment screw is clockwise.
3. Self-study questions
1. Describe the operating principle of the lighting system with automatic headlight function
2. Describe the operating principle of the lighting system with the function of rotating headlights when turning
3. Draw diagram and connect lighting system on Hyundai Porter car
4. Draw diagram and connect lighting system on Honda Accord 1992
5. Draw the lighting circuit on a 1993 Toyota Lexus
LESSON 3 MAINTENANCE AND REPAIR OF SIGNAL SYSTEM
I. IMPLEMENTATION GOAL
After completing this lesson, students will be able to:
- Distinguish between types of signals on cars
- Correctly describe common symptoms and suspected areas causing damage.
- Connecting signal circuits ensures technical requirements
- Disassemble, install, check, maintain and repair the signal system to ensure technical requirements.
- Ensure safety in work and industrial hygiene
II. LESSON CONTENT
1. General description
The signal system equipped on cars aims to create signals to notify other vehicles participating in traffic about the vehicle's operating status such as: stopping, parking, braking, reversing, turning...
Signals are used either by light such as headlamps, brake lights, turn signals….. or by sound such as horns, reverse music….
Just like the lighting system. A signal system circuit usually consists of: battery, fuse, wire, relay, electrical load and control switch. Only some switches of the signal system are on the combination switch. The switches of other signals are usually located in different locations such as in the gearbox or brake pedal……
2. Maintenance and repair
2.1. Turn signals and hazard lights
The installation location of the turn signal is shown in Figure 3.1. The turn signal control switch is located in the combination switch under the steering wheel. Turning this switch to the right or left will make the turn signal turn right or left.
The hazard light switch is used when the vehicle has a problem while participating in traffic. When the hazard light switch is turned on, all the turn signals on the vehicle will light up at a certain frequency. The hazard light switch is usually placed separately from the turn signal switch (some old cars integrate the hazard and turn signal switches on the same combination switch cluster).
Figure 3.1 Turn signal switch Figure 3.2 Hazard switch
The part that generates the flashing frequency for the lights is called a turn signal relay. The turn signal relay usually has 3 terminals: B (positive power supply); E (negative power supply); L (providing the turn signal switch to distribute to the
lamp)
2.1.1. Circuit diagram
To generate the frequency for the turn signal, a turn signal relay is used in the turn signal circuit. The current from the turn signal relay will be sent to the turn signal switch assembly to distribute the current to the turn signal lights for the driver's purpose.
Figure 3.3. Schematic diagram of a turn signal circuit without a hazard switch
1. Battery; 2. Electric lock; 3. Turn signal relay; 4. Turn signal switch; 5. Turn signal lamp; 6. Turn signal lamp; 7. Hazard switch
Figure 3.4 Schematic diagram of turn signal circuit with hazard switch
1. Battery; 2. Combination switch cluster; 3. Turn signal;
4. Turn signal light; 5. Turn signal relay
Today's cars no longer use three-pin turn signal relays (B, L, E) but use eight-pin turn signal relays (figure 3.5) (pin number 8 is used for hazard lights).
For this type, the current supplying the turn signal lights is supplied directly from the turn signal relay to the lights.
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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 ports bandwidth is sufficiently large, combined with small buffer sizes and other network resources dedicated to EF packets, to allow the routers service rate for EF packets on an output port to exceed the arrival rate λ of packets at that port.
This means that packets with PHB EF are considered with a pre-allocated amount of output bandwidth and a priority that ensures minimum loss, minimum delay and minimum jitter before being put into operation.
PHB EF is suitable for channel simulation, leased line simulation, and real-time services such as voice, video without compromising on high loss, delay and jitter values.
Figure 2.10 Example of EF installation
Figure 2.10 shows an example of an EF PHB implementation. This is a simple priority queue scheduling technique. At the edges of the DS domain, EF packet traffic is prioritized according to the values agreed upon by the SLA. The EF queue in the figure needs to output packets at a rate higher than the packet arrival rate λ. To provide an EF PHB over an end-to-end DS domain, bandwidth at the output ports of the core routers needs to be allocated in advance to ensure the requirement μ > λ. This can be done by a pre-configured provisioning process. In the figure, EF packets are placed in the priority queue (the upper queue). With such a length, the queue can operate with μ > λ.
Since EF was primarily used for real-time services such as voice and video, and since real-time services use UDP instead of TCP, RED is generally
not suitable for EF queues because applications using UDP will not respond to random packet drop and RED will strip unnecessary packets.
2.2.4.2 Assured Forwarding (AF) PHB
PHB AF is defined by RFC 2597. The purpose of PHB AF is to deliver packets reliably and therefore delay and jitter are considered less important than packet loss. PHB AF is suitable for non-real-time services such as applications using TCP. PHB AF first defines four classes: AF1, AF2, AF3, AF4. For each of these AF classes, packets are then classified into three subclasses with three distinct priority levels.
Table 2.8 shows the four AF classes and 12 AF subclasses and the DSCP values for the 12 AF subclasses defined by RFC 2597. RFC 2597 also allows for more than three separate priority levels to be added for internal use. However, these separate priority levels will only have internal significance.
PHB Class
PHB Subclass
Package type
DSCP
AF4
AF41
Short
100010
AF42
Medium
100100
AF43
High
100110
AF3
AF31
Short
011010
AF32
Medium
011100
AF33
High
011110
AF2
AF21
Short
010010
AF22
Medium
010100
AF23
High
010110
AF1
AF11
Short
001010
AF12
Medium
001100
AF13
High
001110
Table 2.8 AF DSCPs
The AF PHB ensures that packets are forwarded with a high probability of delivery to the destination within the bounds of the rate agreed upon in an SLA. If AF traffic at an ingress port exceeds the pre-priority rate, which is considered non-compliant or “out of profile”, the excess packets will not be delivered to the destination with the same probability as the packets belonging to the defined traffic or “in profile” packets. When there is network congestion, the out of profile packets are dropped before the in profile packets are dropped.
When service levels are defined using AF classes, different quantity and quality between AF classes can be realized by allocating different amounts of bandwidth and buffer space to the four AF classes. Unlike
EF, most AF traffic is non-real-time traffic using TCP, and the RED queue management strategy is an AQM (Adaptive Queue Management) strategy suitable for use in AF PHBs. The four AF PHB layers can be implemented as four separate queues. The output port bandwidth is divided into four AF queues. For each AF queue, packets are marked with three “colors” corresponding to three separate priority levels.
In addition to the 32 DSCP 1 groups defined in Table 2.8, 21 DSCPs have been standardized as follows: one for PHB EF, 12 for PHB AF, and 8 for CSCP. There are 11 DSCP 1 groups still available for other standards.
2.2.5.Example of Differentiated Services
We will look at an example of the Differentiated Service model and mechanism of operation. The architecture of Differentiated Service consists of two basic sets of functions:
Edge functions: include packet classification and traffic conditioning. At the inbound edge of the network, incoming packets are marked. In particular, the DS field in the packet header is set to a certain value. For example, in Figure 2.12, packets sent from H1 to H3 are marked at R1, while packets from H2 to H4 are marked at R2. The labels on the received packets identify the service class to which they belong. Different traffic classes receive different services in the core network. The RFC definition uses the term behavior aggregate rather than the term traffic class. After being marked, a packet can be forwarded immediately into the network, delayed for a period of time before being forwarded, or dropped. We will see that there are many factors that affect how a packet is marked, and whether it is forwarded immediately, delayed, or dropped.
Figure 2.12 DiffServ Example
Core functionality: When a DS-marked packet arrives at a Diffservcapable router, the packet is forwarded to the next router based on
Per-hop behavior is associated with packet classes. Per-hop behavior affects router buffers and the bandwidth shared between competing classes. An important principle of the Differentiated Service architecture is that a routers per-hop behavior is based only on the packets marking or the class to which it belongs. Therefore, if packets sent from H1 to H3 as shown in the figure receive the same marking as packets from H2 to H4, then the network routers treat the packets exactly the same, regardless of whether the packet originated from H1 or H2. For example, R3 does not distinguish between packets from h1 and H2 when forwarding packets to R4. Therefore, the Differentiated Service architecture avoids the need to maintain router state about separate source-destination pairs, which is important for network scalability.
Chapter Conclusion
Chapter 2 has presented and clarified two main models of deploying and installing quality of service in IP networks. While the traditional best-effort model has many disadvantages, later models such as IntServ and DiffServ have partly solved the problems that best-effort could not solve. IntServ follows the direction of ensuring quality of service for each separate flow, it is built similar to the circuit switching model with the use of the RSVP resource reservation protocol. IntSer is suitable for services that require fixed bandwidth that is not shared such as VoIP services, multicast TV services. However, IntSer has disadvantages such as using a lot of network resources, low scalability and lack of flexibility. DiffServ was born with the idea of solving the disadvantages of the IntServ model.
DiffServ follows the direction of ensuring quality based on the principle of hop-by-hop behavior based on the priority of marked packets. The policy for different types of traffic is decided by the administrator and can be changed according to reality, so it is very flexible. DiffServ makes better use of network resources, avoiding idle bandwidth and processing capacity on routers. In addition, the DifServ model can be deployed on many independent domains, so the ability to expand the network becomes easy.
Chapter 3: METHODS TO ENSURE QoS FOR MULTIMEDIA COMMUNICATIONS
In packet-switched networks, different packet flows often have to share the transmission medium all the way to the destination station. To ensure the fair and efficient allocation of bandwidth to flows, appropriate serving mechanisms are required at network nodes, especially at gateways or routers, where many different data flows often pass through. The scheduler is responsible for serving packets of the selected flow and deciding which packet will be served next. Here, a flow is understood as a set of packets belonging to the same priority class, or originating from the same source, or having the same source and destination addresses, etc.
In normal state when there is no congestion, packets will be sent as soon as they are delivered. In case of congestion, if QoS assurance methods are not applied, prolonged congestion can cause packet drops, affecting service quality. In some cases, congestion is prolonged and widespread in the network, which can easily lead to the network being frozen, or many packets being dropped, seriously affecting service quality.
Therefore, in this chapter, in sections 3.2 and 3.3, we introduce some typical network traffic load monitoring techniques to predict and prevent congestion before it occurs through the measure of dropping (removing) packets early when there are signs of impending congestion.
3.1. DropTail method
DropTail is a simple, traditional queue management method based on FIFO mechanism. All incoming packets are placed in the queue, when the queue is full, the later packets are dropped.
Due to its simplicity and ease of implementation, DropTail has been used for many years on Internet router systems. However, this algorithm has the following disadvantages:
− Cannot avoid the phenomenon of “Lock out”: Occurs when 1 or several traffic streams monopolize the queue, making packets of other connections unable to pass through the router. This phenomenon greatly affects reliable transmission protocols such as TCP. According to the anti-congestion algorithm, when locked out, the TCP connection stream will reduce the window size and reduce the packet transmission speed exponentially.
− Can cause Global Synchronization: This is the result of a severe “Lock out” phenomenon. Some neighboring routers have their queues monopolized by a number of connections, causing a series of other TCP connections to be unable to pass through and simultaneously reducing the transmission speed. After those monopolized connections are temporarily suspended,
Once the queue is cleared, it takes a considerable amount of time for TCP connections to return to their original speed.
− Full Queue phenomenon: Data transmitted on the Internet often has an explosion, packets arriving at the router are often in clusters rather than in turn. Therefore, the operating mechanism of DropTail makes the queue easily full for a long period of time, leading to the average delay time of large packets. To avoid this phenomenon, with DropTail, the only way is to increase the routers buffer, this method is very expensive and ineffective.
− No QoS guarantee: With the DropTail mechanism, there is no way to prioritize important packets to be transmitted through the router earlier when all are in the queue. Meanwhile, with multimedia communication, ensuring connection and stable speed is extremely important and the DropTail algorithm cannot satisfy.
The problem of choosing the buffer size of the routers in the network is to “absorb” short bursts of traffic without causing too much queuing delay. This is necessary in bursty data transmission. The queue size determines the size of the packet bursts (traffic spikes) that we want to be able to transmit without being dropped at the routers.
In IP-based application networks, packet dropping is an important mechanism for indirectly reporting congestion to end stations. A solution that prevents router queues from filling up while reducing the packet drop rate is called dynamic queue management.
3.2. Random elimination method – RED
3.2.1 Overview
RED (Random Early Detection of congestion; Random Early Drop) is one of the first AQM algorithms proposed in 1993 by Sally Floyd and Van Jacobson, two scientists at the Lawrence Berkeley Laboratory of the University of California, USA. Due to its outstanding advantages compared to previous queue management algorithms, RED has been widely installed and deployed on the Internet.
The most fundamental point of their work is that the most effective place to detect congestion and react to it is at the gateway or router.
Source entities (senders) can also do this by estimating end-to-end delay, throughput variability, or the rate of packet retransmissions due to drop. However, the sender and receiver view of a particular connection cannot tell which gateways on the network are congested, and cannot distinguish between propagation delay and queuing delay. Only the gateway has a true view of the state of the queue, the link share of the connections passing through it at any given time, and the quality of service requirements of the
traffic flows. The RED gateway monitors the average queue length, which detects early signs of impending congestion (average queue length exceeding a predetermined threshold) and reacts appropriately in one of two ways:
− Drop incoming packets with a certain probability, to indirectly inform the source of congestion, the source needs to reduce the transmission rate to keep the queue from filling up, maintaining the ability to absorb incoming traffic spikes.
− Mark “congestion” with a certain probability in the ECN field in the header of TCP packets to notify the source (the receiving entity will copy this bit into the acknowledgement packet).
Figure 3. 1 RED algorithm
The main goal of RED is to avoid congestion by keeping the average queue size within a sufficiently small and stable region, which also means keeping the queuing delay sufficiently small and stable. Achieving this goal also helps: avoid global synchronization, not resist bursty traffic flows (i.e. flows with low average throughput but high volatility), and maintain an upper bound on the average queue size even in the absence of cooperation from transport layer protocols.
To achieve the above goals, RED gateways must do the following:
− The first is to detect congestion early and react appropriately to keep the average queue size small enough to keep the network operating in the low latency, high throughput region, while still allowing the queue size to fluctuate within a certain range to absorb short-term fluctuations. As discussed above, the gateway is the most appropriate place to detect congestion and is also the most appropriate place to decide which specific connection to report congestion to.
− The second thing is to notify the source of congestion. This is done by marking and notifying the source to reduce traffic. Normally the RED gateway will randomly drop packets. However, if congestion
If congestion is detected before the queue is full, it should be combined with packet marking to signal congestion. The RED gateway has two options: drop or mark; where marking is done by marking the ECN field of the packet with a certain probability, to signal the source to reduce the traffic entering the network.
− An important goal that RED gateways need to achieve is to avoid global synchronization and not to resist traffic flows that have a sudden characteristic. Global synchronization occurs when all connections simultaneously reduce their transmission window size, leading to a severe drop in throughput at the same time. On the other hand, Drop Tail or Random Drop strategies are very sensitive to sudden flows; that is, the gateway queue will often overflow when packets from these flows arrive. To avoid these two phenomena, gateways can use special algorithms to detect congestion and decide which connections will be notified of congestion at the gateway. The RED gateway randomly selects incoming packets to mark; with this method, the probability of marking a packet from a particular connection is proportional to the connections shared bandwidth at the gateway.
− Another goal is to control the average queue size even without cooperation from the source entities. This can be done by dropping packets when the average size exceeds an upper threshold (instead of marking it). This approach is necessary in cases where most connections have transmission times that are less than the round-trip time, or where the source entities are not able to reduce traffic in response to marking or dropping packets (such as UDP flows).
3.2.2 Algorithm
This section describes the algorithm for RED gateways. RED gateways calculate the average queue size using a low-pass filter. This average queue size is compared with two thresholds: minth and maxth. When the average queue size is less than the lower threshold, no incoming packets are marked or dropped; when the average queue size is greater than the upper threshold, all incoming packets are dropped. When the average queue size is between minth and maxth, each incoming packet is marked or dropped with a probability pa, where pa is a function of the average queue size avg; the probability of marking or dropping a packet for a particular connection is proportional to the bandwidth share of that connection at the gateway. The general algorithm for a RED gateway is described as follows: [5]
For each packet arrival
Caculate the average queue size avg If minth ≤ avg < maxth
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Qos Assurance Methods for Multimedia Communications
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low. The EF PHB requires a sufficiently large number of output ports to provide low delay, low loss, and low jitter.
EF PHBs can be implemented if the output port's bandwidth is sufficiently large, combined with small buffer sizes and other network resources dedicated to EF packets, to allow the router's service rate for EF packets on an output port to exceed the arrival rate λ of packets at that port.
This means that packets with PHB EF are considered with a pre-allocated amount of output bandwidth and a priority that ensures minimum loss, minimum delay and minimum jitter before being put into operation.
PHB EF is suitable for channel simulation, leased line simulation, and real-time services such as voice, video without compromising on high loss, delay and jitter values.
Figure 2.10 Example of EF installation
Figure 2.10 shows an example of an EF PHB implementation. This is a simple priority queue scheduling technique. At the edges of the DS domain, EF packet traffic is prioritized according to the values agreed upon by the SLA. The EF queue in the figure needs to output packets at a rate higher than the packet arrival rate λ. To provide an EF PHB over an end-to-end DS domain, bandwidth at the output ports of the core routers needs to be allocated in advance to ensure the requirement μ > λ. This can be done by a pre-configured provisioning process. In the figure, EF packets are placed in the priority queue (the upper queue). With such a length, the queue can operate with μ > λ.
Since EF was primarily used for real-time services such as voice and video, and since real-time services use UDP instead of TCP, RED is generally
not suitable for EF queues because applications using UDP will not respond to random packet drop and RED will strip unnecessary packets.
2.2.4.2 Assured Forwarding (AF) PHB
PHB AF is defined by RFC 2597. The purpose of PHB AF is to deliver packets reliably and therefore delay and jitter are considered less important than packet loss. PHB AF is suitable for non-real-time services such as applications using TCP. PHB AF first defines four classes: AF1, AF2, AF3, AF4. For each of these AF classes, packets are then classified into three subclasses with three distinct priority levels.
Table 2.8 shows the four AF classes and 12 AF subclasses and the DSCP values for the 12 AF subclasses defined by RFC 2597. RFC 2597 also allows for more than three separate priority levels to be added for internal use. However, these separate priority levels will only have internal significance.
PHB Class
PHB Subclass
Package type
DSCP
AF4
AF41
Short
100010
AF42
Medium
100100
AF43
High
100110
AF3
AF31
Short
011010
AF32
Medium
011100
AF33
High
011110
AF2
AF21
Short
010010
AF22
Medium
010100
AF23
High
010110
AF1
AF11
Short
001010
AF12
Medium
001100
AF13
High
001110
Table 2.8 AF DSCPs
The AF PHB ensures that packets are forwarded with a high probability of delivery to the destination within the bounds of the rate agreed upon in an SLA. If AF traffic at an ingress port exceeds the pre-priority rate, which is considered non-compliant or “out of profile”, the excess packets will not be delivered to the destination with the same probability as the packets belonging to the defined traffic or “in profile” packets. When there is network congestion, the out of profile packets are dropped before the in profile packets are dropped.
When service levels are defined using AF classes, different quantity and quality between AF classes can be realized by allocating different amounts of bandwidth and buffer space to the four AF classes. Unlike
EF, most AF traffic is non-real-time traffic using TCP, and the RED queue management strategy is an AQM (Adaptive Queue Management) strategy suitable for use in AF PHBs. The four AF PHB layers can be implemented as four separate queues. The output port bandwidth is divided into four AF queues. For each AF queue, packets are marked with three “colors” corresponding to three separate priority levels.
In addition to the 32 DSCP 1 groups defined in Table 2.8, 21 DSCPs have been standardized as follows: one for PHB EF, 12 for PHB AF, and 8 for CSCP. There are 11 DSCP 1 groups still available for other standards.
2.2.5.Example of Differentiated Services
We will look at an example of the Differentiated Service model and mechanism of operation. The architecture of Differentiated Service consists of two basic sets of functions:
Edge functions: include packet classification and traffic conditioning. At the inbound edge of the network, incoming packets are marked. In particular, the DS field in the packet header is set to a certain value. For example, in Figure 2.12, packets sent from H1 to H3 are marked at R1, while packets from H2 to H4 are marked at R2. The labels on the received packets identify the service class to which they belong. Different traffic classes receive different services in the core network. The RFC definition uses the term behavior aggregate rather than the term traffic class. After being marked, a packet can be forwarded immediately into the network, delayed for a period of time before being forwarded, or dropped. We will see that there are many factors that affect how a packet is marked, and whether it is forwarded immediately, delayed, or dropped.
Figure 2.12 DiffServ Example
Core functionality: When a DS-marked packet arrives at a Diffservcapable router, the packet is forwarded to the next router based on
Per-hop behavior is associated with packet classes. Per-hop behavior affects router buffers and the bandwidth shared between competing classes. An important principle of the Differentiated Service architecture is that a router's per-hop behavior is based only on the packet's marking or the class to which it belongs. Therefore, if packets sent from H1 to H3 as shown in the figure receive the same marking as packets from H2 to H4, then the network routers treat the packets exactly the same, regardless of whether the packet originated from H1 or H2. For example, R3 does not distinguish between packets from h1 and H2 when forwarding packets to R4. Therefore, the Differentiated Service architecture avoids the need to maintain router state about separate source-destination pairs, which is important for network scalability.
Chapter Conclusion
Chapter 2 has presented and clarified two main models of deploying and installing quality of service in IP networks. While the traditional best-effort model has many disadvantages, later models such as IntServ and DiffServ have partly solved the problems that best-effort could not solve. IntServ follows the direction of ensuring quality of service for each separate flow, it is built similar to the circuit switching model with the use of the RSVP resource reservation protocol. IntSer is suitable for services that require fixed bandwidth that is not shared such as VoIP services, multicast TV services. However, IntSer has disadvantages such as using a lot of network resources, low scalability and lack of flexibility. DiffServ was born with the idea of solving the disadvantages of the IntServ model.
DiffServ follows the direction of ensuring quality based on the principle of hop-by-hop behavior based on the priority of marked packets. The policy for different types of traffic is decided by the administrator and can be changed according to reality, so it is very flexible. DiffServ makes better use of network resources, avoiding idle bandwidth and processing capacity on routers. In addition, the DifServ model can be deployed on many independent domains, so the ability to expand the network becomes easy.
Chapter 3: METHODS TO ENSURE QoS FOR MULTIMEDIA COMMUNICATIONS
In packet-switched networks, different packet flows often have to share the transmission medium all the way to the destination station. To ensure the fair and efficient allocation of bandwidth to flows, appropriate serving mechanisms are required at network nodes, especially at gateways or routers, where many different data flows often pass through. The scheduler is responsible for serving packets of the selected flow and deciding which packet will be served next. Here, a flow is understood as a set of packets belonging to the same priority class, or originating from the same source, or having the same source and destination addresses, etc.
In normal state when there is no congestion, packets will be sent as soon as they are delivered. In case of congestion, if QoS assurance methods are not applied, prolonged congestion can cause packet drops, affecting service quality. In some cases, congestion is prolonged and widespread in the network, which can easily lead to the network being "frozen", or many packets being dropped, seriously affecting service quality.
Therefore, in this chapter, in sections 3.2 and 3.3, we introduce some typical network traffic load monitoring techniques to predict and prevent congestion before it occurs through the measure of dropping (removing) packets early when there are signs of impending congestion.
3.1. DropTail method
DropTail is a simple, traditional queue management method based on FIFO mechanism. All incoming packets are placed in the queue, when the queue is full, the later packets are dropped.
Due to its simplicity and ease of implementation, DropTail has been used for many years on Internet router systems. However, this algorithm has the following disadvantages:
− Cannot avoid the phenomenon of “Lock out”: Occurs when 1 or several traffic streams monopolize the queue, making packets of other connections unable to pass through the router. This phenomenon greatly affects reliable transmission protocols such as TCP. According to the anti-congestion algorithm, when locked out, the TCP connection stream will reduce the window size and reduce the packet transmission speed exponentially.
− Can cause Global Synchronization: This is the result of a severe “Lock out” phenomenon. Some neighboring routers have their queues monopolized by a number of connections, causing a series of other TCP connections to be unable to pass through and simultaneously reducing the transmission speed. After those monopolized connections are temporarily suspended,
Once the queue is cleared, it takes a considerable amount of time for TCP connections to return to their original speed.
− Full Queue phenomenon: Data transmitted on the Internet often has an explosion, packets arriving at the router are often in clusters rather than in turn. Therefore, the operating mechanism of DropTail makes the queue easily full for a long period of time, leading to the average delay time of large packets. To avoid this phenomenon, with DropTail, the only way is to increase the router's buffer, this method is very expensive and ineffective.
− No QoS guarantee: With the DropTail mechanism, there is no way to prioritize important packets to be transmitted through the router earlier when all are in the queue. Meanwhile, with multimedia communication, ensuring connection and stable speed is extremely important and the DropTail algorithm cannot satisfy.
The problem of choosing the buffer size of the routers in the network is to “absorb” short bursts of traffic without causing too much queuing delay. This is necessary in bursty data transmission. The queue size determines the size of the packet bursts (traffic spikes) that we want to be able to transmit without being dropped at the routers.
In IP-based application networks, packet dropping is an important mechanism for indirectly reporting congestion to end stations. A solution that prevents router queues from filling up while reducing the packet drop rate is called dynamic queue management.
3.2. Random elimination method – RED
3.2.1 Overview
RED (Random Early Detection of congestion; Random Early Drop) is one of the first AQM algorithms proposed in 1993 by Sally Floyd and Van Jacobson, two scientists at the Lawrence Berkeley Laboratory of the University of California, USA. Due to its outstanding advantages compared to previous queue management algorithms, RED has been widely installed and deployed on the Internet.
The most fundamental point of their work is that the most effective place to detect congestion and react to it is at the gateway or router.
Source entities (senders) can also do this by estimating end-to-end delay, throughput variability, or the rate of packet retransmissions due to drop. However, the sender and receiver view of a particular connection cannot tell which gateways on the network are congested, and cannot distinguish between propagation delay and queuing delay. Only the gateway has a true view of the state of the queue, the link share of the connections passing through it at any given time, and the quality of service requirements of the
traffic flows. The RED gateway monitors the average queue length, which detects early signs of impending congestion (average queue length exceeding a predetermined threshold) and reacts appropriately in one of two ways:
− Drop incoming packets with a certain probability, to indirectly inform the source of congestion, the source needs to reduce the transmission rate to keep the queue from filling up, maintaining the ability to absorb incoming traffic spikes.
− Mark “congestion” with a certain probability in the ECN field in the header of TCP packets to notify the source (the receiving entity will copy this bit into the acknowledgement packet).
Figure 3. 1 RED algorithm
The main goal of RED is to avoid congestion by keeping the average queue size within a sufficiently small and stable region, which also means keeping the queuing delay sufficiently small and stable. Achieving this goal also helps: avoid global synchronization, not resist bursty traffic flows (i.e. flows with low average throughput but high volatility), and maintain an upper bound on the average queue size even in the absence of cooperation from transport layer protocols.
To achieve the above goals, RED gateways must do the following:
− The first is to detect congestion early and react appropriately to keep the average queue size small enough to keep the network operating in the low latency, high throughput region, while still allowing the queue size to fluctuate within a certain range to absorb short-term fluctuations. As discussed above, the gateway is the most appropriate place to detect congestion and is also the most appropriate place to decide which specific connection to report congestion to.
− The second thing is to notify the source of congestion. This is done by marking and notifying the source to reduce traffic. Normally the RED gateway will randomly drop packets. However, if congestion
If congestion is detected before the queue is full, it should be combined with packet marking to signal congestion. The RED gateway has two options: drop or mark; where marking is done by marking the ECN field of the packet with a certain probability, to signal the source to reduce the traffic entering the network.
− An important goal that RED gateways need to achieve is to avoid global synchronization and not to resist traffic flows that have a sudden characteristic. Global synchronization occurs when all connections simultaneously reduce their transmission window size, leading to a severe drop in throughput at the same time. On the other hand, Drop Tail or Random Drop strategies are very sensitive to sudden flows; that is, the gateway queue will often overflow when packets from these flows arrive. To avoid these two phenomena, gateways can use special algorithms to detect congestion and decide which connections will be notified of congestion at the gateway. The RED gateway randomly selects incoming packets to mark; with this method, the probability of marking a packet from a particular connection is proportional to the connection's shared bandwidth at the gateway.
− Another goal is to control the average queue size even without cooperation from the source entities. This can be done by dropping packets when the average size exceeds an upper threshold (instead of marking it). This approach is necessary in cases where most connections have transmission times that are less than the round-trip time, or where the source entities are not able to reduce traffic in response to marking or dropping packets (such as UDP flows).
3.2.2 Algorithm
This section describes the algorithm for RED gateways. RED gateways calculate the average queue size using a low-pass filter. This average queue size is compared with two thresholds: minth and maxth. When the average queue size is less than the lower threshold, no incoming packets are marked or dropped; when the average queue size is greater than the upper threshold, all incoming packets are dropped. When the average queue size is between minth and maxth, each incoming packet is marked or dropped with a probability pa, where pa is a function of the average queue size avg; the probability of marking or dropping a packet for a particular connection is proportional to the bandwidth share of that connection at the gateway. The general algorithm for a RED gateway is described as follows: [5]
For each packet arrival
Caculate the average queue size avg If minth ≤ avg < maxth
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Economic group model - operations of Vietnam Oil and Gas Group in the period 2006 - 2008 and development trends - 1 -
Content of Implementation of Legal Policy on Management of Education Sector Officials -
Research Model of Factors Impacting Work Motivation of Tour Guide Team in Binh Dinh Province
How to assign workers to operate machines so that the total number of products made in an hour is the largest, knowing that type III workers cannot operate machine A.
a) Model the problem. b) Solve the problem.
Answer : b) X
10
= 0
20 0
5 15 , f
= 2280
opt
0
0 10
max
Lesson 3.8A farm needs to grow 30 hectares of rice X 1 ; 20 hectares of rice X 2and 40 hectares of rice X 3on three plots of land I, II, III with areas of 25 ha, 25 ha, 40 ha respectively. The yield of each type of rice on each plot of land (tons/ha) is given in the following table:
Land
Rice varieties
I 25 | II 25 | III 40 | |
X 1 : 30 | - | 8 | 6 |
X 2 : 20 | 6 | 9 | 7 |
X 3 : 40 | 5 | 4 | 6 |
Plan the land allocation so that the total yield is the highest knowing the rice variety X 1Cannot be grown on grade I soil.
a) Model the problem. b) Solve the problem.
Answer : b) X
0
= 0
25 5
0 20
or X
0
= 0
5 25
20 0 f
= 585
opt
25
0 15
opt
25
0 15
max
Lesson 3.9People need to grow 4 types of flowers: Chrysanthemum, Rose, Orchid, Gladiolus on 3 different gardens I, II, III. Knowing that the existing land area corresponding to each garden is 40, 60, 80 (a). The planned planting area for each type is Chrysanthemum - 50 (a); Rose - 70 (a); Orchid - 30 (a); Gladiolus - 30 (a). In addition, due to the nature of different types of soil, roses cannot be grown on land I, and Gladiolus cannot be grown on land III. Knowing the estimated harvest of each type of flower on each type of soil is as follows: (unit: hundred thousand VND/a). Plan to grow flowers to get the most profit.
10
6
C =
8
9 12
9
12
15 10 10
Solve the problem of finding the optimal plan.
Answer : X
10
= 0
0 0
30 30
30
0
or X
0
= 0
0 10
40 20
30
0 f
= 200,000,000 dong
opt
0
40 40 0
opt
50 30 0
max
0
Lesson 3.10Solve the transportation problem given by the following table: ( f min )
Collect
Play
B 1 60 | B 2 70 | B 3 40 | B 4 30 | |
A 1 : 100 | 2 | 1 | 4 | 3 |
A2 : 80 | 5 | 3 | 2 | 6 |
A 3 : 20 | 6 | 2 | 1 | 5 |
Lesson 3.11The transportation problem is given by the table ( f min )
Collect
Play
10 | 30 | 50 | |
25 | 7 | 6 | 5 |
10 | 2 | 1 | 4 |
45 | 3 | 5 | 2 |
a) Model the problem.
b) What would the model look like if the second receiving station had to receive the full load?
c) Solve the problem in two cases.
Lesson 3.12The Olympic Games are held simultaneously on the same day in 4 locations. Material requirements (tons) are sent from 3 locations. Data on transmission and reception requirements and distance (km) are given in the table below. Due to the characteristics of material means, time and means of transport, it is not possible to transfer more than 150 km. Find a transportation plan so that the total number of T.km is the smallest.
Collect
Play
15 | 10 | 17 | 18 | |
20 | 160 | 50 | 100 | 70 |
30 | 100 | 200 | 30 | 60 |
10 | 50 | 40 | 30 | 50 |
Lesson 3.13A mechanical factory has 3 workers A, B, C who have to operate 3 lathes I, II, III to produce a type of machine part. The productivity of each worker for each type of machine (parts/day) is given in the following table.
Machine
Human resource
I 1 | II 1 | III 1 | |
A : 1 | 19 | 21 | 25 |
B : 1 | 20 | 18 | 24 |
C : 1 | 17 | 26 | 18 |
Make a plan to assign workers to operate the machine so that the total number of parts produced per day is the largest.
a) Model the problem.
b) How would the model change if worker B could not operate machine I?
c) Solve the problem in two cases.
Lesson 3.14
To prepare goods for sale during the Lunar New Year, the transport team must transport goods from 4 factories: A, B, C, D to 5 stores: C 1 , C 2 , C 3 , C 4 , C 5. The number of tons of goods needed at the stores, the distance between the factories and the stores (km) are given in the table:
CH
XN
C 110 | C 210 | C 310 | C 420 | C 520 | |
A : 5 | 5 | 1 | 4 | 6 | 7 |
B : 15 | 3 | 4 | 2 | 7 | 8 |
C : 20 | 4 | 3 | 1 | 7 | 9 |
D : 30 | 6 | 5 | 4 | 9 | 11 |
Want to plan transportation so that the total T.km is the smallest.
a) Solve the problem
b) Solve the problem in the case where bridge A has just collapsed and the route from A to C 2 and from C to C 3must cross this bridge
Lesson 3.15A mechanical company signed a contract to deliver to a customer 7 products of type A1 , 8 products of type A2 , 5 products of type A3 .within 1 month .The company has 3 factories I, II, III and factory II cannot produce product A2 . The production capacity of each factory I, II, III in 1 month is 9 products, 5 products, 6 products respectively. The profit earned on each product produced by the factories is given in the following table (unit: 15,000,000 VND/product).
X.Product Industry
I 9 | II 5 | III 6 | |
A 1 : 7 | 9 | 5 | 10 |
A2 : 8 | 5 | -- | 6 |
A 3 : 5 | 7 | 4 | 4 |
Ask how to assign production to the factories to carry out the contract with the greatest profit and tell the amount of profit earned?
Lesson 3.16
Solve the transportation problem (f min) below with the condition that station B 1must collect enough goods
Collect
Play
B 1 70 | B 2 80 | B 3 65 | B 4 85 | |
A 1 : 90 | 6 | 7 | 4 | 5 |
A 2 :100 | 5 | 4 | 6 | 7 |
A 3 : 50 | 8 | 5 | 6 | 6.5 |
Lesson 3.17 Solve the transportation problem ( f max ) below with the condition that station B 2must collect enough goods
Collect
Play
B 1 80 | B 2 120 | B 3 100 | |
A 1 :140 | 7 | 5.5 | 8 |
A 2 :110 | 5 | 6 | 5.5 |
Lesson 3.18A company has 3 factories located at 3 different locations to produce the same product. The capacity (products/month) and production cost (thousand VND/product) at each factory are given in the following table:
Factory
Capacity | Production cost | |
A 1A 2 A 3 | 100,000 150 000 200 000 | 24 22 23 |
The company's products are distributed to 4 general agents with consumption levels and selling prices (thousand VND/product) as follows:
General agent
Consumption capacity | Selling price | |
B 1 B 2 B 3 B 4 | 70 000 95 000 145 000 100,000 | 32 31 30 33 |
The shipping cost of a product from factories to general agents is given in the following table:
Factory General Agent
B 1 | B 2 | B 3 | B 4 | |
A 1 | 5 | 4 | 1 | 5 |
A 2 | 6 | 4 | 4 | 6 |
A 3 | 3 | 3 | 2 | 3 |
a) Make a mathematical model of the problem of determining the production and distribution plan from factories to general agents in a month so that the company's total profit is maximized.
b) Determine the company's optimal production plan and product distribution plan.
Answer : b)
Factory A 2produce 110,000 products and distribute to general agent B 2,000 products, B 315,000 products. | 95 |
Factory A 3produce 200,000 products and distribute to general agent B 1,000 products, B 330,000 products, B4100,000 products. | 70 |
Maximum total profit: 2,305,000,000 VND |
Multiple choice questions
(choose 1 of 4 sentences: A, B, C, D)
Sentence 1Which of the following statements is false?
A) The balanced transmission and reception transport problem always has PATU.
B) The dual problem of the balanced transmission and reception transport problem always has PATU.
C) The objective function of the transportation problem is always bounded.
D) The optimal solution of the transportation problem is always unique.
Sentence 2Which of the following statements is false?
A) The unbalanced transport problem always has PATU.
B) The dual problem of the unbalanced transmission and reception problem always has PATU.
C) The objective function of the unbalanced transmission and reception problem is always bounded.
D) The optimal solution of the unbalanced transmission and reception problem is always unique.
Sentence 3Which of the following statements is false?
A) The transport problem with the objective function maximizing the balance of transmission and reception always has PATU.
B) The dual problem of the transport problem with the objective function maximizing the balance of transmission and reception always has PATU.
C) The objective function of the transportation problem is always bounded.
D) The optimal solution of the transportation problem has a maximum objective function that is always unique.
Sentence 4Which of the following statements is false?
A) The transport problem with the objective function maximizing the balance of transmission and reception always has PATU.
B) The dual problem of the transport problem with the objective function maximizing the balance of transmission and reception always has PATU.
C) The transportation problem with restricted cells always has a unique optimal solution.
D) The dual problem of the synchronous production problem always has PATU.
Chapter 4
SYNCHRONIZED PRODUCTION PROBLEM
§ 1 CONTENT AND NATURE OF SYNCHRONIZED PRODUCTION ESSAY
1.1. Content and mathematical model of the problem.
Suppose a product is assembled by n different parts C 1 , C 2 , ..., C nand each product needs exactly 1 part of each type. Participating in the production process of these parts are m types of machines M 1 , M 2 , ...., M mand each type has exactly 1. Call c ijis the capacity of machine M iwhen used to produce C j parts(calculated by time unit)
can be hours, days, shifts, weeks, months,...). For convenience of presentation, we use the convention of productivity.
m n
calculated by shift. Matrix C = c ijcalled the productivity matrix (c i j 0). Arrange your time.
Working time for machines so that the total output obtained in one shift is the largest.
Problem analysis: Let x ijis the time period (in units of shifts) for machine M i
C j detail production(i = 1, m
; j = 1, n
) and z is the total number of assembled products.
The total number of products produced is at most: f(z,x) = z max
n
Machines used up the entire shift: x ij
j 1
= 1 , i = 1, m
The number of assembled products does not exceed the number of parts of each type that can be produced.
m
in song:
z c ij x ij0 , j = 1, n
i 1
We have a mathematical model to find (z,x) = (z,x i j ) so that: (we call this problem (P) )
(1) f(z,x) = z max
(2)
n
j 1
x ij
1,
i 1, m
z
m
c
i 1
ij x ij
0,
j 1, n
(3) z 0 ; x ij 0 (i = 1, m , j = 1, n )
Each set (z,x ij) satisfying (2) and (3) is called a solution. The solution satisfying (1) is called PATU.
1.2. Put the problem in table form.
The synchronous production problem is a QHTT problem. But because it has a special form, people do not solve it by the simplex method but by another method. To facilitate the presentation of this algorithm, we represent the problem in a table form.
m n
with the yield matrix C = c ij
. All the concepts of cells, rings,... are similar.
transportation problem
Machine Details
C 1 1 | C 2 1 | … | C j 1 | … | C n 1 | |
M 1 : 1 | c 11 x 11 | c 12 x 12 | … | c 1j x 1j | … | c 1n x 1n |
M 2 : 1 | c 21 x 21 | c 22 x 22 | … | c 2j x 2j | … | c2n x 2n |
|
|
| … |
| … |
|
M i : 1 | c i1 x i1 | c i2 x i2 | … | c ij x ij | … | print Ask for |
|
|
| … |
| … |
|
M : 1 | c m1 x m1 | c m2 x m2 | … | c m j x mj | … | c mn x mn |
1.3. Properties of synchronous production problem.
Property 1 : Synchronous production problems always have PATU.
Prove
0,
The SXDB problem has the following solution: z = 0 , x ij= 1 ,
j 1
j 1
The SXDB problem has a bounded objective function on: f(z,x) m.maxc ij
So the SXDB problem has PATU .
Consider the synchronous production problem (P):
(1) f(z,x) = z max
(2)
n
j 1
x ij
1,
i 1, m
z
m
c
i 1
ij x ij
0,
j 1, n
(3) z 0 ; x ij0 (i = 1, m , j = 1, n ) The dual problem of this problem is (D)ø:
m
(1) g(u, v) = u i min
i 1
(2)
n
v j
j 1
1,
i 1, m
u i c ij v j 0 i 1, m; j 1, n
(3) and0 (j = 1, n ), u iarbitrary (i = 1, m ). The dual constraint pairs are:
n
z 0 v j 1
j 1
u i c ij v j 0 x ij 0 (i = 1, m
; j = 1, n )
z c i j x ij0 v j0
(j = 1, n )
Based on the weak complement theorem we have the following properties.
Property 2: The necessary and sufficient conditions for solution (z,x i j ) of problem (P) and solution (u i ,v j ) of problem (D) to be optimal are:
n
z v j 1 0
(1)
(*)
j 1
0
(2)
x ij u i c ij v j
m
v j z c ij x ij 0
(3)
i 1
This property follows easily from the weak complement theorem.