Существует 4 способа коммутации. Каждый из которых это комбинация параметра времени ожидания и надежности передачи.
С промежуточным хранением (Store –And-Forward) Коммутатор читает всю информацию во фрейме, проверяет его на отсутствие ошибок, выбирает порт коммутации и после этого посылает в него фрейм.
Сквозной (cut-through). Коммутатор считывает во фрейме только адрес назначения и после выполняет коммутацию. Этот режим уменьшает задержки при передаче, но в нем нет метода обнаружения ошибок.
Бесфрагментный (fragment-free). Этот режим является модификацией сквозного режима. Передача осуществляется после фильтрации фрагментов коллизий. (фреймы размеров 64 байта обрабатываются по технологии store-and-forward, остальные по технологии cut-throigh)
Адаптивная коммутация(intelligent, adaptive) Коммутатор сам выбирает для каждого порта оптимальный режим работы. Вначале все порты устанавливаются в режим сквозной коммутации, затем те из них , на которых возникает много ошибок , переводятся в режим бесфрагментной коммутации .Если и в этом случае количество ошибок остается большим, промежуточным хранением, что гарантирует полную фильтрацию от ошибочных кадров.
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NAT acceleration is a feature that is available on Asus branded routers. It is also known as hardware acceleration in some cases by other branded routers. It can also be named as CTF (Cut-Through Forwarding) and FA (Flow Accelerator) This is a general guide that can potentially help you troubleshoot the issues that you may have with your wired or wireless network.
Please note that the language and information written here is intended for the average basic user. We will not go into detail on how and why NAT acceleration work, but rather some observations and guidelines on how you can make the best out of this feature.
What is NAT Acceleration
NAT Acceleration is a set of special designed software rules with hardware features created to speed up internet connections. They are usually required for peak speed when you have incoming internet speed above certain level. You typically do not need it for internet speed below 100 mb/sec.
The NAT acceleration or hardware acceleration option are usually found under the LAN settings for your router. At the time of writing, there are two levels of the NAT acceleration, some models of routers allow you to set the the level. Below is what NAT acceleration actually does and how it accelerates your speed.
Level 1: CTF (Cut Through Forwarding): Software optimization technique to accelerate NAT traffic.
You may need this option if your internet provider is offer you speed above 100 mb /sec. You generally need this option if you want to achieve peak speeds especially for speed above 200 mb/sec.
CTF or Cut-Through Forwarding is achieved by the router starting to send out transmission frames as soon as it receives its destination. However, the router relies on the end device to tell it whether the data is corrupted for resend. This restriction can cause problems with a few common home uses.
When you have CTF or level 1 NAT Acceleration disabled, the router will “store” the entire frame before sending it out to its destination. This holding period may require more router’s CPU use.
Level 2: Level 1 (CTF) + FA (Flow Accelerator): Hardware NAT acceleration mechanism design for accelerating wired DHCP and Static IP connections.
You will need Flow Accelerator option to fully take advantage of internet provider’s Gigabit service is offered.
Flow Accelerator is achieved through special hardware related designs.
When You Should Use or Enable NAT Acceleration
You should typically enable NAT acceleration or Cut-Through Forwarding when you have internet speed above 100 mb/sec. You will typically only see a difference for speed above 200 mb/s.
You should generally set the option as Auto or ON, unless you need to use features that directly conflict with NAT acceleration.
Potential NAT Acceleration Issues and Conflicts
NAT Acceleration, specifically the CTF Cut Through Forwarding portion can conflict with a few other common features. You should consider disable NAT acceleration or turn it to off if you experience any of the problems below.
QoS or Quality of Service features come in direct conflict with the implementation of NAT Acceleration or Cut-Through Forwarding. Quality of Service options let your router “prioritize” the type of traffic that will be transmitted first. However, it requires to router to actually hold some data and make that choice.
NAT acceleration removes that possibility by starting the transmission as soon as it receives the destination. Below is a quick list of NAT acceleration and QoS level allowed.
No HW or NAT Acceleration = Traditional QoS
Level 1 (CTF) = Adaptive QoS Only
Level 2 (CTF + FA) = No QoS Allowed
Port Forwarding Not Compatible
NAT Acceleration is reported to not be compatible with port forwarding feature. This means that when you have the NAT Acceleration, you will typically unable to host gaming sessions from your home. So you will not be able to host any game servers such as Minecraft, MMO, or First person shooters since players will not be able to connect to it.
IP Traffic Monitoring and Parental Control
Traffic Monitoring and Parental Control require the router to examine the type of traffic. This means that it is not compatible with the CTF feature as CTF transmits the data almost as soon as it receives the proper destination.
Issues with Mirroring of Streaming Devices
In some cases, CTF can cause choppiness in the mirroring of stream devices such as Apple TV, Chromecast, and VoIP. This is because the data transmitted may be corrupted and routers “resend” those data. However, your end point devices show those corrupted data since they are designed to be latency sensitive.
NAT Acceleration ON or OFF Conclusion and Recommendation
You should generally leave the option as Auto for the NAT Acceleration in Asus Router. Since it does improve the peak connection speed of your home network’s internet service.
However, you should consider turning it off if you require any of the following features: Port Forwarding, QoS, IP Traffic Monitor, and Parental Control.
If your mirroring of video streaming devices have errors often and appear to be choppy, consider testing the effect of having an “disabled” NAT Acceleration or CTF.
To get the peak speed offered by your internet provider while having the features you need, consider combining two different routers with different settings to create your suitable network.
NAT Acceleration is a set of software rules and hardware features used to speed up fast internet connections through a NAT router, typically used with internet bandwidth over 100 Mbits/s. It improves throughput and reduces CPU/hardware utilization on the router by bypassing some of the features of the TCP/IP stack. NAT acceleration (a.k.a. hardware acceleration) is usually a NAT router admin panel setting, with some router models allowing you to also set the level, as follows:
No NAT Acceleration
When NAT Acceleration is disabled, routers use the full TCP/IP stack with flow/congestion control, QoS, etc. causing a bit higher CPU/resource utilization. In this mode, NAT routers store the entire frame before sending it out to its destination. It is better with faster routers, multiple simultaneous local clients, when you need to use QoS, and with speeds that do not overwhelm the router’s CPU/RAM (typically under 150Mbits/s).
Level 1: CTF (Cut Through Forwarding)
Software optimization technique to accelerate NAT traffic, usually used with speeds over 100Mbits/s, may be required for peak speeds over 200Mbits/s depending on your router hardware.
When CTF/Level 1 acceleration is enabled, the router sends out frames as soon as it knows their destination, without waiting for any acknowledgements, or flow control. This method relies on the destination device to provide information whether the data is corrupt and needs to be resent, however, it only supports adaptive QoS and may cause issues with some applications. It is recommended for fast connections (over 150Mbps) and few local clients, as it improves throughput while reducing latency and router CPU/memory utilization.
Level 2: CTF+FA (CTF/Level 1 + Flow Acceleration)
Hardware NAT acceleration mechanism designed for accelerating wired internet connections. This is typically only needed with very fast broadband connections at speeds over
500 Mbps, as the traditional full TCP/IP stack and congestion/flow control becomes very taxing on the router’s CPU and limited hardware resources.
CTF+FA (Level 2 NAT Acceleration) does not support QoS, and you may have to disable PPPoE and STP (Spanning Tree Protocol).
Pros: NAT Acceleration improves throughput while reducing latency and router CPU utilization. It may be needed to achieve higher WAN throghput.
Cons: NAT Acceleration supports only adaptive QoS (Level 1 CTF), no QoS (Level 2 CTF+FA), may not support port forwarding (hosting game servers, etc.), parental controls, PPPoE, STP. The increased retransmissions caused by NAT Acceleration may also cause shuttering on some streaming devices (Apple TV, Chromecast, VoIP).
Notes: "Auto" NAT Acceleration may be an option on some routers.
If the router admin interface provides CPU utilization statistics, that information can be used as an indicator of whether you need to turn on NAT Acceleration to reduce resource utilization under load for your particular internet speed.