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✈ | JAL wins APEX "WORLD CLASS" First among Japanese airlines

Photo APEX CEO (left) and JAL Americas Manager Morioka (right)

JAL wins APEX "WORLD CLASS" First among Japanese airlines

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It is comprehensively evaluated as the world's highest level in terms of service quality, safety and security, and sustainability initiatives.

Japan Airlines (JAL) is "2021 APEX EXPO" sponsored by APEX, an American airline industry group ... → Continue reading


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Quality of Service

QoSWhat is (Quality of Service)?Computer networkThis is a technology for appropriately managing network availability by marking important communication packets and processing them with priority.[1]..Also called service quality[2][3].. It is realized by LAN switch (layer 2 switch) etc.


QoS is a performance characteristic that provides, maintains, and manages networks to meet the specific needs of customers.Companies that provide servicesIt can be guaranteed in advance by a service level agreement with.For this reason, QoS without a measure of customer joy or discomfort with the service is not sufficient to provide the appropriate service to the user.[4].

By enabling the QoS function, it is possible to make a difference in handling depending on the content of the data to be carried.For exampleIP phoneThen, it makes the user feel uncomfortable when the call is cut off in the video distribution, so if it is carried with priority over other data flowing on the network at the same time, the convenience on the network line will be improved. improves. QoS is mainlyPriority controlBandwidth controlIt is divided into[2][3]

Priority control

Priority determination

Both the priority control and bandwidth control functions executed in routers and layer 3 switches are the same in that they differ in the order of packet processing.There are two main methods for routers to determine packet priority, one is the source and destination IP addresses, the protocol used, and the port number.The other is to explicitly specify the packet priority in a field in the packet.In the latter case, in the IP headerCOUGH,DSCPIt has a dedicated field for specifying QoS such as.

  • COUGH(Type of service) is the 9th to 16th bit field of the IP header.The first 3 bits are called "IP Precedence" and specify 8 levels of transfer priority.
  • DSCP(Differentiated services code point) uses the first 6 bits of the TOS field to specify 64 levels of transfer priority.[3][5].

Priority control operation

No matter how many low-priority packets are queued, the high-priority packets are sent out earlier according to the priority determination.Such a function is called PQ (Priority queuing).

If the line is congested and only high-priority packets continue to flow, low-priority packets may not flow at all, and the application that sent the low-priority packets may give up communication. ..In many applications, communication is continued if even a small amount of packets flow, so low-priority packets are also flowed at a constant rate.High-performance routers can set transmission weights for these low priorities.CQ(Custom queuing, weighted queue) and, in order to equalize the transmission of packets with the same priority while weighting, the packet matrix is ​​subdivided for each connectionWFQIt has a function called (Weighted fair queuing)[2].

Bandwidth control

Internet service providers, such as some SoftBank, are improving their services through network optimization.That is, someInternet service provider(ISP) Is uniqueContent distribution network(CDNCache nodeTo improve the delivery of video and other high-bandwidth services to customers[6].

Bandwidth control is often used at the entrance to a WAN line, etc., when the bandwidth used is limited or to specify the minimum guaranteed value.

Packet discard occurs when low-priority packets overflow the queue. When a TCP packet is discarded, retransmission occurs, which leads to the discarding of other packets.When the amount of waste increases, the amount of packets swells due to retransmission and congestion occurs.To avoid this, the router discards the received TCP packet when the packet is queued to some extent.This is a TCP featureFlow controlWorks, and the amount of packets sent from the sending terminal is suppressed.By such pre-disposalCongestion controlFunctionRED(Random Early Detection) function (Random initial detection).These functions performed by routers do not identify all communications, so bandwidth controllers are used when finer control is required.[2][3].

Limitations of priority control and bandwidth control

Priority control and bandwidth control are router functions, so they do not work inside the Internet separated by routers.Even if you specify the packet priorityL2 switch,L3 switchJust ignore.

Even if the specified value of fixed bandwidth control is set, if there is a deviation from the effective bandwidth, the line usage will be adversely affected.Even if the effective bandwidth is widened, if the bandwidth control remains narrow, the line usage will be wasted.If the effective bandwidth becomes narrower and falls below the upper limit of the bandwidth control set value, the bandwidth control does not work and packet discarding tends to occur.To avoid these fixed configuration issues, some new routers are for measurement from the base router.UDPSome have the ability to send some packets to the center router to send back receive interval and loss information, and dynamically change the bandwidth control specifications according to the line conditions.[3].


Need for QoS guarantee

The biggest reason why QoS guarantee is neededconvergence(Congestion).network·trafficThis is because if the amount of QoS is limited, problems related to QoS hardly occur without any special measures.To avoid congestionTelephone networkIn the firstAdmission controlIs done.That is, when QoS cannot be guaranteed, a new service request is rejected.Secondly, in the telephone network, when establishing individual calls, a route that does not cause congestion is searched for and used.on the other hand,インターネットIncluding IP networkIn the past, such control was not performed at the network level.Therefore, it is difficult to use the IP network for communication applications that require high reliability such as emergency communication. As the use of IP networks expands, so does the need for QoS guarantees.

In addition, as a factor peculiar to IP networks, QoS guarantee is gradually required in recent years.ア プ リ ケ ー シ ョ ンIs increasing the need for it.That is, since the beginning of the 1990s, on the InternetVoice callReal-time applications such as video distribution and video distribution are being used, and high-quality services for business are also required.In addition, data communication exceeds voice communication in quantity, and it is becoming necessary to realize quality comparable to that of telephone networks on the Internet.This is an expression from the perspective of the Internet, but from the perspective of the telephone network, the flexibility comparable to (or more than) that of the Internet is added to the new communication network, or NGN (NGN).Next Generation Network) Is the goal.

QoS guarantee in IP networks

Internet standardization IETF(Internet Engineering Task Force) is being promoted, but the following technologies have been standardized in the IETF regarding QoS.

  • IntServ (Intoserve) --A technology or framework for guaranteeing QoS for each individual.
  • DiffServ (Diff serve) --Class of service, which is a collection of multiple communication flows. CoS) Is a technology or framework for guaranteeing QoS.

Use case

QoS is stable by differentiating and prioritizing it from othersthroughputAnd low latency. As for how to use CoS,IP phoneAnd video conferencing /Videophone such asreal timePriority is given to system traffic.SNAPriority is given to mission-critical traffic that is vulnerable to delays such as, and business-related traffic that is of high importance.電子 メ ー ル,WebToDirections and ParkingThe lowest priority is information traffic, which does not pose a problem even if equal delay occurs.

LAN switch (layer 2 switch) priority information. PNG

Priority control on LAN switch

Even with LAN switches (layer 2 switches), IEEE 802.1QVLANThe priority is controlled by using the information contained in the header of the extended MAC frame used in.The first 4 bits of the "Tag Control Information" field in the 3th header of the extended MAC frame is a numerical value indicating the priority.[7].

Reference books

  1. ^ "What is QoS”(Japanese). network.yamaha.com. 2020/9/26Browse.
  2. ^ a b c d Nikkei NETWORK January 2004 "Special Feature 1 QoS" p2-p84
  3. ^ a b c d e Nikkei NETWORK August 2007 Issue "Special Feature 8 Communication Quality" p2-p74
  4. ^ Stallings, William (2016). Foundations of modern networking: SDN, NFV, QoE, IoT, and CloudFlorence Agboma, Sofiene Jelassi. Indianapolis, Indiana. ISBN 978-0-13-417547-8. OCLC 927715441. https://www.worldcat.org/oclc/927715441 
  5. ^ a b Nikkei NETWORK December 2007 issue "Functions for introducing VoIP" p.12
  6. ^ Stallings, William ,. Foundations of modern networking: SDN, NFV, QoE, IoT, and Cloud. Agboma, Florence ,, Jelassi, Sofiene ,. Indianapolis, Indiana. ISBN 978-0-13-417547-8. OCLC 927715441. https://www.worldcat.org/oclc/927715441 
  7. ^ Yoichi Nasuno, Takahiro Okada "Switch Network Stop unnecessary packets and give priority to important packets" Nikkei NETWORK August 2005 issue p.8

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