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A new option in Microsoft Edge in Windows 10 is the ability to enable TCP Fast Open. TCP Fast Open (TFO) is a specification to open successive TCP connections faster between clients and servers using a crytographic cookie which stores authentication details to reduce the round-trip delay and lower the latency in the start of data transmission. When enabled, it can improve network performance of the browser. Here is how to enable it.
When a «Fast Open capable» client connects to a server for the first time, it inserts a special encrypted cookie in the initial TCP connection message, prompting the server to send back a valid cookie in response. When this happens, it indicates that both the client and the server support the TCP Fast Open procedure and the server can start sending data to the client before the 3-way handshake completes. Pages you open with the TCP Fast Open option enabled will open faster.
To enable TCP Fast Open in Microsoft Edge, you need to do the following.
- Type about:flags in address bar of Edge.
- The following page will appear:
Scroll it down until you see the Networking section:
- Tick the checkbox «Enable TCP Fast Open».
Now, re-open the browser. You are done. Depending on how many sites you visit supporting the TCP Fast Open feature, you might notice benefits of having this feature enabled.
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One of the benefits of building a browser from the ground up is you get to put in all the best web technology and standards that are available while avoiding older deprecated ones. Microsoft Edge is slowly but surely becoming one of the most modern web browsers available without the bloat of competitors.
TCP Fast Open became available in some of the most recent builds of the Windows 10 Anniversary Update (Slow and Fast Ring) starting in mid-June (build 14352 and higher). Today I’ll explain what it is and why you may want to turn it on in Windows 10 for PC and Mobile.
Get Modern
Microsoft Edge is like Opera, Chrome, and Firefox where users can turn on new features by using the about:flags settings. Users just type ‘about:flags’ in the address bar, and they are taken to a setup page.
By using about:flags developers and advanced users can ‘turn on’ new features that are still in testing. Some of these are ‘beta’ because the World Wide Web Consortium (W3C) is still solidifying the standard for everyone. Other times, it is because Microsoft is still developing the feature. Either way, you get a shot at tinkering today.
We already wrote on the majority of these features in ‘Understanding the ‘about:flags’ settings page in Microsoft Edge for PC’ and you should read that article for a deeper dive into the feature.
What is TCP Fast Open?
TCP Fast Open (TFO) is a new extension meant to replace the old T/TCP system from 1994. It is considered faster and includes some basic encryption (cryptographic cookie). According to Google, it can improve «page load time by 10% to 40%», which is the real benefit. The reason it can do that is by reducing traffic back and forth between the client and the server.
In computer networking, TCP Fast Open (TFO) is an extension to speed up the opening of successive Transmission Control Protocol (TCP) connections between two endpoints. It works by using a TFO cookie (a TCP option), which is a cryptographic cookie stored on the client side and set upon the initial connection with the server. When the client later reconnects, it sends the initial SYN packet along with the TFO cookie data to authenticate itself. If successful, the server may start sending data to the client even before the reception of the final ACK packet of the three-way handshake, skipping that way a round-trip delay and lowering the latency in the start of data transmission. – Wikipedia
In short, the less latency you can have between two far away systems that are trying to connect the faster the load times. By ditching the «three-way handshake» of the old TCP protocol TCP Fast Open can sometimes have dramatic effects on page load times.
All the latest news, reviews, and guides for Windows and Xbox diehards.
Microsoft wrote a detailed blog on Edge, TCP Fast Open, TLS False Start and TLS 1.3 back in June and you should read it more in-depth coverage of these technologies.
Enable TCP Fast Open
Turning on TCP Fast Open in Microsoft Edge is very easy to do.
Note: You can enable this feature for Windows 10 on PC and Mobile
- Open Microsoft Edge
- Type about:flags in the address bar
- Scroll down until you see Networking
- Check Enable TCP Fast Open
- Restart Microsoft Edge (close and re-open)
Of course, like all experimental features, there could be some issues. Microsoft is collecting telemetry usage of the feature to help them improve it in the future, and they will likely enable TCP Fast Open by default by the Anniversary Update.
If you run into any problems, you can just turn it back off again by following the same above directions. In the worst case scenario just select Reset all flags to default in case you start tinkering with other options.
I’m using TCP Fast Open now in Edge full-time, and so far it is a great experience. Give it a shot and let me know what you think!
Daniel Rubino is the Editor-in-chief of Windows Central. He is also the head reviewer, podcast co-host, and analyst. He has been covering Microsoft since 2007 when this site was called WMExperts (and later Windows Phone Central). His interests include Windows, laptops, next-gen computing, and wearable tech. He has reviewed laptops for over 10 years and is particularly fond of 2-in-1 convertibles, Arm64 processors, new form factors, and thin-and-light PCs. Before all this tech stuff, he worked on a Ph.D. in linguistics, performed polysomnographs in NYC, and was a motion-picture operator for 17 years.
Download Windows Speedup Tool to fix errors and make PC run faster
Microsoft Edge browser on Windows 10 v1607 and later offers a feature that can make web pages load faster. To activate this feature, you will have to enable TCP Fast Open, which is an extension of the TCP Protocol that enables data exchange during TCP’s initial handshake. When TCP Fast Open is enabled, data can be sent before the connection completes, so that responses will arrive much faster.
Fast Open protocol is a new mechanism that enables data exchange during TCP’s initial handshake. In doing so, TCP Fast Open decreases application network latency by one full round-trip time, decreasing the delay experienced by such short TCP transfers, says Google.
TCP Fast Open is a new experimental feature of Microsoft Edge (Legacy). It can speed up Edge’s page loading time by over 10% – and which could go up to 40%!
To enable this feature, launch Edge browser, type about:flags in the address bar and hit Enter to open the browser’s Developers settings.
Scroll down till you see Enable TCP Fast Open and select the checkbox.
Having done this, restart Edge and see if loading of web pages is faster for you. We would love to hear if this made a difference for you.
Anand Khanse is the Admin of TheWindowsClub.com, a 10-year Microsoft MVP (2006-16) & a Windows Insider MVP (2016-2022). Please read the entire post & the comments first, create a System Restore Point before making any changes to your system & be careful about any 3rd-party offers while installing freeware.
Anniversary Update adds support for newer TCP protocol options to improve speed and reduce latency
2018-11-02 (updated: 2018-11-23) by
Tags: TFO, ICW, TCP, ACK
Windows 10 Anniversary update adds support for a few newer TCP protocol options aimed to improve web browsing speed and reduce latency. Even though many of them are not user-editable in the client variants of the OS, I will outline the important changes below.
TCP Fast Open (TFO) — RFC 7413
TFO allows for sending and receiving data in the initial SYN packets during the TCP handshake. If supported by both the client and the server, it allows for reduced latency in establishing successive TCP connections to the same server. This is accomplished by storing a TFO cookie on the client after the initial TCP handshake. This TFO cookie is sent to the server if the client later reconnects, allowing successive TCP handshakes to skip one roundtrip delay, reducing latency.
TCP Fast Open is enabled by default in the Windows 10 Anniversary update and newer Linux 3.7+ kernels. It is not available in Chrome for PCs (Only under Android/Chrome OS, see: chrome://flags/ and look for «TCP Fast Open» flag). It can be enabled in MS Edge (look at the About:Flags setting «TCP Fast Open»).
You can see the current value in command prompt using: netsh int tcp show global
It can be set using: netsh int tcp set global fastopen=enabled
(default: enabled, possible values: enabled, disabled, default)
Recommendation: Leave as is, enabled in the OS is ok as applications need to support/enable it separately. It still needs wider adoption.
Note: It may cause issues with dropped packets by some older middleware/routers/firewalls that do not like SYN packets with larger headers.
Initial Congestion Window (IW, or ICW) — RFC 6928
The Initial Congestion Window determines how much data TCP can send out before waiting for acknowledgements and adjusting the transfer speed depending on line conditions. Traditionally (RFC 3390), this was between 2 and 4 segments, however, with faster broadband connections it has been proposed to increase the permitted TCP Initial Window (IW) to 10 segments.
The default value in Windows 10 and Server 2012 R2 was 4 MSS, it was increased to 10 MSS for the Internet template with the anniversary update, which is a good thing. It can’t be changed directly on Windows 10 Home/Pro, you’d have to change the template to «compat» to limit it, which is counterproductive.
Our take: IW of 10 is better than 4.
Tail Loss Probe (TLP) — experimental IETF draft
Aims to improve packet loss recovery. It is enabled by default for connections with over 10ms rtt. Again, for client variants of Windows 10 (Home/Pro), it is only adjustable if you change the template from «Internet» to «compat», which disables it.
Our take: It is better to leave enabled, which is the default.
Recent ACKnowledgement (RACK) — experimental IETF draft
Detects packet loss based on time rather than checking packet sequence. It is enabled by default for connections over 10ms rtt that use SACK. Client Windows 10 OSes have it enabled in the «Internet» template, disabled in the «compat» template, and the setting is read-only.
Our take: undecided, may be useful in some fringe situations and the benefit may be offset by overhead. Needs further testing.
Windows Low Extra Delay BAckground Transport (LEDBAT) — RFC 6817
It is a Congestion Control module designed for background transfers, so that they consume only unused background bandwidth, without interfering with other TCP connections. It is undocumented, experimental, and not easily configurable.
Our take: irrelevant, as we can’t test, change, or use it.
TL;DR;
The Anniversary update improves and builds up on some new experimental TCP options which is a good thing. Increasing the Initial Congestion Window to 10 segments and support for TCP Fast open are both great. At the same time, Microsoft has locked down a lot of those settings and they are not user-editable in Windows 10 Home/Pro.
References
Building a faster and more secure web with TCP Fast Open, TLS False Start, and TLS 1.3
New Transport Advancements in the Anniversary Update for Windows 10 and Windows Server 2016
Shaving your RTT with TCP Fast Open
See Also
Windows 8, 10, 2012 Server TCP/IP Tweaks
Новая опция Microsoft Edge в Windows 10 — это возможность включить TCP Fast Open. TCP Fast Open (TFO) — это спецификация для более быстрого открытия последовательных TCP-соединений между клиентами и серверами с использованием криптографических cookie, в котором хранятся данные аутентификации, чтобы уменьшить задержку приема-передачи и уменьшить задержку в начале передачи данных. Когда он включен, он может улучшить сетевую производительность браузера. Вот как это включить.
Когда клиент с поддержкой Fast Open впервые подключается к серверу, он вставляет специальный зашифрованный cookie в исходном сообщении TCP-соединения, предлагая серверу отправить обратно действительный файл cookie в отклик. Когда это происходит, это означает, что и клиент, и сервер поддерживают процедуру TCP Fast Open, и сервер может начать отправку данных клиенту до завершения трехстороннего рукопожатия. Страницы, которые вы открываете с включенной опцией TCP Fast Open, будут открываться быстрее.
Чтобы включить TCP Fast Open в Microsoft Edge, вам необходимо сделать следующее.
- Введите about: flags в адресной строке Edge.
- Появится следующая страница:
Прокрутите его вниз, пока не увидите раздел «Сеть»: - Установите флажок «Включить TCP Fast Open».
Теперь снова откройте браузер. Вы сделали. В зависимости от того, сколько сайтов вы посещаете, поддерживающих функцию TCP Fast Open, вы можете заметить преимущества включения этой функции.