Интервал маяка, Short GI, DTIM, сигнальный интервал: точная настройка роутера
Привет, всем! И сегодня у нас будет очень интересная тема. В частности, мы поговорим про более точную настройку Wi-Fi на маршрутизаторе. Обычно ведь как бывает – человек заходит, меняет имя беспроводной сети, устанавливает ключ и уходит. И этого вполне хватает, но некоторых не совсем хватает скорости передачи данных в беспроводном пространстве. И вот тут начинаются танцы с бубном и не только.
А началось с того, что ко мне опять пришло очень интересное письмо: «Short GI в Wi-Fi – что это и для чего нужно?». Если вы читаете эти строки, то скорее всего вы залезли под капот WiFi модуля в настройки маршрутизатора и увидели непонятные параметры. При этом вы можете видеть вот такое окошко.
Чтобы не рассказывать про один пункт я решил написать общую статью, где расскажу про все эти настройки. Поэтому начнем с самого начала. Также я буду рассказывать какой вариант оптимальный и какой лучше выставить.
Пояснения
И так начнем, наверное, с Short GI или Short Guard Interval (короткий защитный интервал). Это специальный интервал между поочередно передаваемыми пакетами данных. То есть маршрутизатор отправляет на компьютер определенный пакет, так вот, прежде чем отправлять следующие данные, выжидается определенное время.
Стандартное значение 800нс. Но если включить Short GI – это значение будет вдвое меньше, то есть информация передаваться будет куда быстрее. Конечно в теории такое быть может, но иногда бывает, что при включении данной функции скорость наоборот падает. Все дело в том, что при значении 800 нс, данные отправляются, а ещё приходит обратный ответ, что все данные дошли в сохранности. А за 400нс компьютер может из-за помех принять данные с ошибкой и отправить сигнал обратно, но ему прилетит следующий пакет. В итоге компьютеру нужно будет ждать, пока маршрутизатор не отправит прошлый пакет.
Помехи возникают от других источников радиочастот – в частности от соседских роутеров, которые работают на той же частоте. Поэтому тут нужно просто экспериментировать. Попробуйте включить данную функцию и протестировать скорость интернета на конечном устройстве. Если скорость упадет — значит вам мешают соседские роутеры, которые глушат сигнал.
Следующий параметр — это «Интервал маяка» (Beacon Interval) или «Сигнальный интервал». По стандарту обычно стоит значение в 100 миллисекунд. Данная функция определяет как часто от роутера идёт сигнальный пакет к конечному клиенту. Тут можно установить значение и в 50, если вы постоянно ходите по квартире с телефоном. Это нужно, чтобы роутер как можно чаще с вами связывался. Для обычного стационарного компьютера или ноутбука – значения 100 будет достаточно.
Порог RTS — это значение максимального размера пакета. То есть какой максимальный пакет должны по размеру отправляться за раз. Если пакет будет больше данного значения, то данные будут отправлены на специальную принимающую станцию. Также отправка пакетов будет постоянно согласоваться с двумя устройствами. Стандартный размер 2346, на самом деле это оптимальный вариант и больше ставить нельзя, так как конечный клиент может не смочь принять такой большой пакет. Если поставить наоборот меньше, то могут возникнуть трудности, так как пакетов будет слишком много, и они все будут отлеживаться при передаче в конце пути.
Порог фрагментации — это максимальный размер, после которого пакет будет фрагментирован или разделен на части. Данное значение устанавливается такое же, как на пороге RTS.
Интервал DTIM — это временный интервал, после которого все пакеты, находящиеся в буфере, будут отправлены клиенту. Самый лучший вариант — это 1. Если установить значение больше, то пакеты будут простаивать и просиживать в буфере. При этом немного экономится электроэнергия. Если установить слишком большое значение некоторые пакеты могут быть потеряны.
Client Isolation (изоляция клиента) – при данной настройке все клиенты будут взаимодействовать и видеть друг друга только через данный маршрутизатор. По идее вещь неплохая, но на деле ничего толкового не меняет. Можете просто выключить эту функцию.
WMM — это режим, при котором каждому пакету определяется уровень приоритетности, и они отправляются в первую очередь. Данную функцию нужно обязательно включать. В некоторых роутерах она включена автоматически.
Теперь пару слов про мощность передатчика. По умолчанию почти на всех интернет-центрах мощность стоит на 100%, но как показала практика не всегда это хорошо. Если у вас небольшая квартирка, то мощный передатчик может навредить беспроводной сети и сделать связь хуже и уменьшить скорость передачи. Более подробно я писал об это в этой статье.
Network Adapter Optimization
The information in this article is intended to improve understanding of all common and advanced network adapter settings under current Windows versions. We will also offer some general suggestions on setting up your LAN for the best possible network performance. Keep in mind that many of these settings can significantly affect performance and reliability in a good or bad way. Consider testing performance using some type of network analyzer or even a simple throughput test before and after making changes. Many settings depend upon your particular network and usage.
General Recommendations
Changing Network Adapter Settings
Network Adapter General Settings
Speed and Duplex: Just as the name suggests, this allows for selecting the desired speed and duplex of the network adapter, the default setting is usually auto negotiation. It is recommended to set the highest speed your adapter supports (Gigabit, if supported), full duplex (two-way simultaneous communication), and auto-negotiation (enabling the adapter to negotiate the highest possible reliable speed). It may sometimes be necessary/helpful to manually set the adapter speed instead of using auto-negotiation.
Gigabit Master Slave Mode: Determines whether the adapter or the link partner is designated as the master; the other end of the link would be the slave. When this is set at the default (usually «Auto Detect», or «Hardware Default»), the devices automatically negotiate this based on the IEEE 802.3ab standard: multi-port devices such as switches become the master when connected to a single port device. If both ends are multi-port devices, the one with higher seed bits becomes the master.
MAC Address / Locally Administered Address: Enables overriding the default MAC address of the adapter by the user. This is an example of how easy it is to bypass MAC address filtering techniques; do a simple packet capture to find an authorized MAC address and apply it here in the advanced settings. However, a more legitimate use of this could be changing the MAC to match the address authorized by your ISP when you’re connecting a PC directly to the modem.
Log Link State Event: This allows you to enable or disable logging of the adapter’s link state changes (such as up/down, duplex mismatch, and STP detection) in the system logs.
QoS Packet Tagging: Enables the adapter to send and receive 802.1p QoS and 802.1Q VLAN indications.
Advanced Settings
Jumbo Frames: This allows for increasing the standard 1500-byte MTU Ethernet frames to carry up to 9000 bytes of data. Using jumbo frames can help increase throughput and decrease CPU utilization on Gigabit LANs, however, the functionality and the same frame size needs to be supported by all devices on the network.
Receive Side Scaling (RSS): This enables the distribution of incoming network processing across multiple processor cores in multi-core computers, to help increase performance. It is the same setting that can be enabled/disabled at the OS level using our tweaking articles and the TCP Optimizer for newer Windows versions.
Adaptive Inter-Frame Spacing: This setting enables a time gap between packets to help compensate for excessive Ethernet packet collisions on the network.
Flow Control: Helps increase the efficiency of traffic regulation for connections that both support flow control frames. These frames are sent by an adapter when their receive queues reach a predefined limit, to signal the sending station to pause transmission so the adapter does not drop the packets. The implementation of Flow Control (Rx & Tx) in some Network Adapters is known to be buggy, likely at the driver level (Realtek Gigabit adapters confirmed). Flow control does not work well with QoS, and is generally not recommended. Disabling this feature can help reduce timeouts and improve throughput.
Interrupt Moderation Rate (coalescing): Sets the rate at which an adapter interrupts the system to handle incoming or outgoing packets. A lower rate causes the system to be more responsive to packet handling, but can decrease performance of other applications and services on the machine. A higher rate means less responsiveness of packet handling but can help increase machine performance, especially useful for when the adapter is sending and receiving larger packets. Interrupt Moderation should be disabled to get the lowest possible latency (at the expense of a bit more CPU utilization). It should be disabled for gaming, and set at a very conservative setting for pure throughput unless you are aiming for low CPU utilization at the expense of some possible delay.
Receive/Transmit Descriptors: Both settings are used to sets the number of descriptors that are allocated in the host memory for storing either received packets, or packets to be transmitted. These buffers can be increased to improve network performance if there is plenty of memory available.
Gigabit Lite: This is a legacy setting developed by Alcatel in 1998, generally supported by Realtek adapters. It allows for 500Mbps transfers over longer cable lengths, it is rarely used and should be turned off in residential settings. We recommend disabling this setting.
Offloading Settings
Note that some of the «TCP offload» settings should be applied both globally at the OS level, and in the Network adapter properties. They have to be supported by the OS and the adapter to work. Offloading works better with fast/quality network adapters, and has been plagued by buggy implementations in the past. It can help reduce CPU utilization and power consumption, and it can improve throughput in some scenarios. However, some offloads (TCP Offloads, LSO Offloads) can can also add some latency to the connection, and introduce issues. We generally recommend enabling only Checksum offloads, and disabling other types of TCP offloads, because of many buggy driver implementations causing timeouts, incomplete file transfers, known SQL server issues, etc. See our broadband tweaks articles for more information.
IPv4/TCP/UDP Checksum Offload: Enables the adapter to compute the IPv4/TCP/UDP checksum of packets instead of the OS, which reduces CPU utilization, and may theoretically increase adapter performance. This should be set to «enabled» in most common scenarios.
Offload TCP Segmentation: Allows the adapter to perform any necessary TCP segmentation of outgoing packets instead of the host OS, which can help increase transmission performance while also reducing CPU utilization. We recommend turning this off because of buggy implementations.
Large Send Offload / Large Receive Offload: This is enabled by default on many Intel/Broadcom adapters, however, there are known issues with its implementation. We recommend disabling this setting to avoid incomplete FTP file transfers and other sporadic internet issues.
ARP Offload: Enables the adapter to respond to ARP requests, which prevents the computer from having to wake for them when asleep.
NS Offload: Enables the adapter to respond to Neighbor Discovery Neighbor Solicitation requests, which prevents the computer from having to wake for them when asleep.
Power Saving and Wake-On-LAN
In general, «Energy Efficient Ethernet (EEE)», «Green Ethernet» and «Power Saving Mode» settings allow for lower power consumption during periods of low network activity, with the goal to reduce power consumption by 50% or more while retaining full compatibility with existing equipment. Consumer Ethernet switches that support EEE automatically adjust their respective power-saving settings to match the adapters, but some switches are known not to perform this properly, resulting in poor throughput and increase in dropped packets. This is why we recommend turning off the EEE and Green Ethernet settings with residential setups in general to eliminate possible dropped packets, reduced throughput and occasional disconnects.
Energy Efficient Ethernet (EEE): Allows the network adapter to toggle power saving mode on or off when not in use, while still keeping the connection active. Recommended: Disabled unless laptop on battery.
Green Ethernet (Short Reach Mode): Reduces the adapter’s power consumption if the connected cable is detected under a certain length. Recommended: Disabled unless on battery.
Power Saving Mode: We recommend disabling this setting unless on battery.
Auto Disable Gigabit: When enabled, any Ethernet connections will be limited to 100Mbps, which requires less power. May be useful for laptops when using battery, to reduce power drain. We recommend disabling this to get gigabit speeds.
Wake on Magic Packet: Enables you to remotely power on the computer from sleep, hibernation, or when fully powered off by using the magic packet of the Wake-On-LAN feature.
Wake on pattern match: Enables you to remotely power on the computer from sleep, hibernation, or when fully powered off by using the pattern of the Wake-On-LAN feature.
Shutdown Wake-On-LAN: Enables Wake-On-LAN functionality if the computer is fully shutdown.
Wake-On-LAN and Shutdown Link speed: Specifies the link speed of the adapter when the computer is in sleep or hibernation.
Wireless Adapter Advanced Settings
Below is a number of additional wireless options that generally exist in some more advanced network adapter drivers (802.11ac Broadcom, Intel, ASUS, etc.).
20/40 Coexistence: When enabled, allows the 802.11n radio to drop from 40MHz mode to 20MHz mode when it detects interference. This allows it to coexist with older 802.11g radios that do not support 40MHz wide wireless channels.
40 Mhz Intolerant/Fat channel Intolerant: Setting forces the use of 20MHz channels only when enabled. Wider channels may be needed for higher throughput.
802.11n Preamble: Preamble type is an error checking function that helps with data transmission when signals are weak. Long Preamble is needed for older 802.11b/g adapters, for weaker signals (lower RSSI), while strong signals and 802.11n/ac devices generally work well with short preamble. The short preamble will yield slightly better performance if the signal is strong and there is no packet loss, however, it needs to be set the same on all devices (routers/access points/repeaters). In noisy wireless environments, for better compatibility, and in low-signal distant connections it is best to use long preamble.
Afterburner: Proprietary Broadcom throughput boosting technique used with 802.11g only, must also be supported by the access point. Only use with 802.11g adapter and compatible AP, disable otherwise.
Antenna Diversity: wireless technique that uses multiple antennas to receive or transmit signals along different propagation paths to compensate for multi-path interference. Useful, if available.
Assoc Listen Interval: A number of beacons that a «dozing» adapter is not listening for beacon frames. It is a power-saving technique where the adapter signals an interval to the access point. The access point then should not drop any queued frames until the adapter’s Listen Interval elapses. Usually defaults to 1.
Association Roam Preference: When a specific band is preferred (2.4GHz or 5GHz), and the client encounters a dual AP with the same SSID for both bands, this setting chooses which band to use. Generally 2.4GHz has better wall penetration and coverage area, while 5GHz is less congested and has higher throughput at smaller distances.
Bandwidth Capability: (20MHz, or 20/40MHz) Specifies whether the adapter should use 20MHz wide channels only, or allow for 40MHz channels if there is no interference. Generally, this should be set to 20/40MHz to allow for higher throughput.
Beamforming: an important MIMO companion, enabling considerable improvement in 802.11n/ac performance, reliability, range and throughput. It should be enabled, if available.
Bluetooth Collaboration: minimizes interference with Bluetooth devices by enabling I/O transmit suppression protocol.
Channel Width: Controls the width of the channel (20 or 40MHz) used by the AP to communicate with client devices. Recommended «Auto (AP determines width)» if available for pure throughput. Setting this to 40MHz-only mode may prevent older clients from connecting.
D2 Listen Interval: similar technique to «Assoc Listen Interval», use values between 3-7. In general, higher beacon periods and DTIM intervals in wireless networks allow for better battery life, however, data has to be buffered at the AP between DTIM beacons, which may be undesirable for VoIP/gaming.
Fat Channel Intolerant: 802.11n setting, recommended «Disabled» for pure throughput.
Fragmentation Threshold: Specifies the maximum number of bytes a packet can contain before it is fragmented. Typically, the default value is 2347 bytes and should be left alone, unless there is a high number of collisions and/or interference.
GTK rekeying for WoWLAN: Group Temporal Key (GTK) rekey is used to encrypt/decrypt network traffic Enabled by default.
HT Mode: Allows for choosing which specific wireless modes are supported. High Throughput (802.11n), and/or Very High THroughput (802.11ac).
Intel Throughput Enhancement: Enables Intel packet bursting technology for transmissions. It utilizes either a WMM capable access point, or client enhancements (even without AP support).
LTR Enable/Disable, LTR Active Value: (default = 60 microseconds) Latency Tolerance Reporting (LTR) is a PCI Express power-saving technique allowing the the adapter to specify when it is idle, and maximum latency. LTR is optional.
MIMO Power Save mode: a.k.a. «Spatial Multiplexing Power Save» (SMPS). Allows the client to save power by keeping one antenna in a receive idle state.
— Auto SMPS: the client decides SMPS mode automatically depending on network conditions
— Dynamic SMPS: client keeps only one antenna active. AP must send RTS packet to trigger the client to wake sleeping radios/antenna before sending MIMO packets.
— Static SMPS: client keeps only one antenna active; AP cannot send MIMO packets to the client
— No SMPS: client always keeps all antennas active; AP can send MIMO packets to the client
Minimum Power Consumption: when enabled, the client can turn off the radio or stop scanning for networks when the adapter is not associated with an access point, or when the computer is in idle state. It is useful to enable in many cases.
Mixed mode protection: Avoid data collisions in a mixed 802.11b and 802.11g environments. Not valid when 802.11n only mode is enabled.
— RTS/CTS Enabled (default): allows mixed clients to hear each other.
— CTS-to-self Enabled: allows to gain more throughput where clients are closer.
NS Offload: responds to network discovery when computer is asleep. It should be left enabled in most cases.
Packet Coalescing: Enables power saving by reducing the number of receive interrupts. The setting combines some broadcast or multicast packets. Default is «enabled», setting to «Disabled» may help in some gaming environments.
PLCP Header (BSS PLCP Header): Used to set the header type for CCK (Complimentary Code Keying) rates (long, or auto short/long), only relevant for 802.11b. By default it automatically switches between long and short depending on the situation the card is in. In some environments with older clients it may be necessary to set this to long for backward compatibility.
Power Output: Usually in percentage increments, allows for reducing the transmit power below 100%. Wireless Power outputs that are unnecessarily high may actually degrade performance by introducing additional noise to the area.
Preferred band: In an environment where one band is very noisy (congested by cordless phones, other APs, client devices, microwaves, etc.), one can reduce interference by preferring the 5GHz band over the 2.4GHz band, or the reverse.
Priority & VLAN: By default, packets are send using FiFo (First-in, First-out) regardless of any priority information in the packet. When this is enabled, you can give certain classes of traffic a priority in the queue. This setting is related to WMM/QoS and only useful if one needs to improve throughput of one of the four WMM classes at the expense of other traffic.
Rate: This setting can limit the wireless transmit/receive rate of the network adapter, it should be left at auto in most cases.
Roaming Aggressiveness: Recommended «Medium»
Roaming Decision: Specifies the signal strength when other access points in the area should be considered for connections. This can be lowered to make the client switch access points faster. «Optimize bandwidth», or «Optimize distance» are automatic settings in some Broadcom adapter drivers as well.
Roam Tendency: Specifies how fast the client should switch to a new distant access point, lower values can make the adapter switch faster.
RTS Threshold: Numeric value, typically 2347, range from 0 to 2347. Lowering the RTS Threshold causes the device to use «Request-to-send/Clear-to-send» (RTS/CTS) whenever it sends data, essentially clearing the channel before data is sent. RTS clears the area around the transmitter, and CTS clears the area around the receiver. Lowering the value can sometimes help reduce collisions in very congested Wi-Fi areas (many adapters/APs on the same channel). However lowering RTS/CTS also adds overhead to the channel by increasing the number of packets without data. Only lower in areas with significant interference.
Short GI: Shortening the Guard Interval is a 802.11n standard that specifies shorter delay between transmitted packets and can reduce wireless latency. It should be set to «auto», or «enabled» for 802.11n and newer WLANs.
Transmit Power: Recommended setting to «Highest» unless in a noisy wireless environment.
Throughput Booster/Enhancement: Enhance the transmit throughput by allowing the client Wi-Fi adapter to hold longer possession of the connection than normally to send data to the AP. This only improves upload throughput (from client to the AP) and only useful for uploading large files. It may negatively impact other Wi-Fi clients since only one client can transmit at a time. Recommended setting is «Disabled»
WMM Power Save / U-APSD: WMM-PS allows for power saving with latency-sensitive applications like VoIP. It may also improve their receive (RX) throughput.
WFD Channel Number: Wireless Flash Drive channel number.
WiFi Rekeying Offload (GTK rekeying): Speci fies if the network adapter can offload GTK rekeying tor WoWLAN (Wake on WLAN) when the computer goes to sleep state.
WMM / WME: Wi-Fi Multimedia (WMM), previously known as Wireless Multimedia Extensions (WME) is a wireless quality of service (QoS) standard subset of 802.11e. It prioritizes data packets according to four categories (voice, video, best effort, background) and also features a power save mode. It should only be enabled if needed for power saving or VoIP. It may reduce throughput in some cases.
Xpress Technology: Broadcom adapter specific based on 802.11e and WMM. Aims to improve Wi-Fi network efficiency and boost throughput by repackaging data to reduce overhead. It is only useful for mixed 802.11b/g/n networks, disable for n/ac networks. Also see: What is Xpress Technology
Notes:
Use only the protocols and options that you need with network adapters. For example, you can turn off «QoS Packet Scheduler», «IPv6», etc. if you do not use them.
Some of the advanced network adapter settings above can vary between different models and drivers, and typically not all of them will be available.
If you’re experiencing problems with your network after editing the above settings, you can reset TCP/IP and Winsock, delete and reinstall your Network adapter driver from the Device manager to restore its factory defaults.
