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cFosSpeed 12.51 Build 2532 Beta/ 12.50 Build 2525

cFosSpeed 12.51 Build 2532 Beta/ 12.50 Build 2525
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cFosSpeed optimizes your Internet connections with Traffic Shaping and Prioritization. It increases your throughput and reduces your Ping. Whenever you access the Internet with more than one data stream cFosSpeed can optimize the traffic.

cFosSpeed now has a context menu option to start and configure the Wi-Fi access point easily. If your PC is connected to the router via Wi-Fi, you can share the same adapter for the ad hoc Wi-Fi access point. In this case the Wi-Fi bandwidth is fully available for your mobile devices, like smartphone or tablet.

When you have this app installed on this PC, the Wi-Fi data is routed through cFosSpeed. And, via its Layer-7 protocol detection, it can prioritize the traffic.

If you frequently use smartphones and tablets for VoIP or streaming traffic, like music or movies, we recommend to add a Wi-Fi adapter to your PC and route the traffic of your mobile devices through this PC and cFosSpeed.

cFosSpeed also reduces network congestion for downloads by lowering the TCP window size to keep the sender from sending too much data at once.

  • Keep your internet fast during heavy upload/download
  • Improve your Ping for online games
  • Reduce audio/video streaming problems
  • Wi-Fi access point
  • cFos Traffic Shaping for smartphones, tablets and other mobile devices.

For all access types: DSL, Cable, Mobile Broadband (2G/3G), Wi-Fi, etc.


  • Broadband: Cable and DSL
  • Narrow band: Modem and ISDN
  • Mobile (LTA, UMTS, WiMAX, HSDPA, W-CDMA, WCDMA, CDMA, CDMA2000, 3G Mobile, HSCSD)
  • Media:
    • VDSL
    • DSL, PPPoE
    • ISDN
    • DSL, PPPoA (Vcmux and LLC)
    • DSL, PPTP
    • Cable
  • IP over AAL
  • RFC1483/2684 bridged

In addition, cFosSpeed contains a packet filter firewall, time and volume online budgets, a skinnable transfer monitor and several other special purpose features. It has a filter language that allows experts to write their own traffic classifications.

Internet Tuning / Traffic Shaping:

  • If ACKs are not sent fast enough, downloads may be slow during uploads (the classic Traffic Shaping).
  • Windows TCP Auto-Tuning may result in too slow downloads. RWIN expansion can increase the speed. It can also accelerate downloads for certain applications.
  • Keeps the overall ping time low, even during heavy uploads and downloads.

Prioritization – Your important streams first:

  • With the prioritization scheme you can always give all your programs full bandwidth, because cFosSpeed decides which streams must be prioritized.
  • For example Game-Traffic, VoIP, or Audio/Video content will be prioritized higher than uploads / downloads.
  • Your file sharing may use unlimited speed of your Internet connection, but it will be slowed down when you have important traffic.
  • The whole prioritization scheme is configurable and you can change the prioritization on-the-fly.

Benefits of cFosSpeed:

  • Full download rate during upload
  • Consistently quick response time of your Internet even under heavy load
  • Substantially less lag in online games
  • Improved VoIP speech quality
  • Nice status window (with skins), so you always see what’s going on

Changes in cFosSpeed 12.51 build 2532 Beta:

Changes in cFosSpeed 12.50 Build 2525:

  • New! The cFosSpeed Game Analyzer: When you are gaming there are often situations where both your Internet connection and your computer performance is very important. So if you are in a big fight and experience problems, the Game Analyzer can help you diagnose bottlenecks in speed, latency, CPU, GPU, and memory performance. Click on “Game Analayzer” in the cFosSpeed context menu to open it.
  • The built-in UI HTTP server now prefers its own mime types. This prevents UI loading problems if Windows mime types have the wrong values.
  • Added pcnt statistics for RSC and LSO packets. Use “spd pcnt” to display.
  • The “Adapter Info” UI now displays WiFi frequency usage graphs for the 2.4 GHz, 5 GHz, and 6+ GHz bands. This can help you optimize the used WiFi channels for optimal performance.
  • Fixed a bug where the Game Analyzer would sometimes flicker with Chrome.
  • Fixed a bug where “Expires” HTTP header was sometimes garbled.
  • Trying to use Webview when starting the Game Analyzer from the context menu.
  • Old .HTA functionality that was removed in cFosSpeed 10.20 is available again.
  • Update for Windows 11.
  • Updated Visual Studio.
  • Updated multi-language files.
  • Improved name tags for the frequency usage graph.

Changes in cFosSpeed 11.10 Build 2483:

  • Fixed a handle leak. Many thanks to Tin Yeuk for the report.
  • Fixed a bluescreen if cFosSpeed was used in bridged mode.
  • Added more games to settings.ini.
  • Added CPU speed measurement in “spd ver”.
  • Changes for new C++ compiler.

Changes in cFosSpeed 11.08 Build 2473:

  • Fixed erroneous ping ballon on WAN connections. Thanks to Avatar for report and testing.
  • Fixed a long-standing bug (since 10.59) caused by copying all NDIS information types. Now gset copy_oob = 0 is default. Thanks to Michael B and Andreas B for testing.
  • Added gset oob_bits = 0xffffffff, meaning it’s enabled for all supported NDIS information types (currently 1, 8, 9, 11, 12, and 14).

Changes in cFosSpeed 11.06 Build 2462:

  • Speed-up for high-speed connections. Now you should get full thruput, even on slower machines. Please report how that works for you.
  • Added new passthru mode 3; old modes 3 and 4 are now 4 and 5. Added a passthru mode 6, which causes the whole NET_BUFFER_LIST chain to be ignored.
  • Status window position is now stored with respect to monitor resolution. Thanks to Frank H. for the idea!
  • Fixed problems with WAN Dial-Up if you had only one of IPv4 and IPv6 connectivity.
  • Fixed a crash in status window. Thanks to Michael S. for dumps.
  • Fixed a spurious bluescreen when RX shaping was active. Thanks to Avatar for testing.
  • Fixed a bluescreen in the 32-bit version.
  • cFosSpeed accessed RSC structures on NDIS < 6.30, where such structures are not yet supported. This led to all kinds of statistical miscalculations. Fixed.
  • Fixed wrong average transfer units (spd cons -atu). This is used in rx shaping as well.
  • Some users experienced mouse hangs while downloading heavily. Now the number of worker threads has been limited to half the number of CPU cores to fix this.
  • Fixed installation problem on Windows 8.1.
  • Improved cFosSpeed thruput on Gigabit connections. Thanks to Thomas Q. and all the others for testing.
  • Default program icon image was always small — fixed.
  • Finally fixed spd.exe crash! That bug was ancient, but now it’s gone.
  • Finally fixed hanging downloads with NordVPN when RWIN expansion was used. This turned out to be poor programming of NordVPN’s driver. Thanks to Contor for traces and tests.
  • Fixed dumping of LSO/RSC packets.
  • Fixed motionless HTML skin window. Thanks to Luis R. for the report.
  • cFosSpeed will no longer lower the MSS when RWIN expansion is used. This could have resulted in slower downloads on high bandwidth connections.
  • Fixed a bluescreen when data was transferred in multiple MDLs. Thanks to Pedro S. for dump file.
  • Fixed a bluescreen when RWIN expansion was used. Thanks to Johann S. for dump file.
  • Support for Windows 20H2 (version 2009).
  • Added gset copy_oob. It can be disabled for debug purposes.

Homepage –

Supported Operating Systems: Windows 7, 8, 8.1, 10 (32-bit, 64-bit).