» Traffic Shaping
<b>172%</b> speed-ups of our users Speed-Up with cFosSpeed RWIN expansion

How does Traffic Shaping work?

cFosSpeed uses Traffic Shaping to reorder Internet data packets in such a way that urgent traffic is transferred first and the rest of the data later. This results in significant reduction of latency (lag) and typically also results in connection speed up.

image of a stop watch

How Effective is cFosSpeed Traffic Shaping?
Christoph Lüders & Christian Carazo, cFos Software GmbH - October 26, 2018
Download: cfosspeed-traffic-shaping-report.pdf Flag symbol for English language

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. cFosSpeed's RWIN expansion can increase the speed .
    cFosSpeed can also accelerate downloads for certain applications (see test results ).
  • cFosSpeed keeps the overall ping time low, even during heavy uploads and downloads.
Ping times during multiple down­loads & uploads

Prioritization - Your important streams first

  • With the cFosSpeed 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 filesharing 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.


  • 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

cFosSpeed under the hood

Packet flow through the various modules of cFosSpeed - mouse over for further explanations.

cFosSpeed under the hood Makes the most of the available bandwidth while minimizing ping time Improves Traffic Shaping of connections with high latency fluctuations, e.g. mobile connections Improves performance when several PCs share one connection Boosts download speeds for high speed connections with high latency Priority scheme / on-the-fly prioritization / filter rules Allows configuration of max. speeds for protocols & programs Priority scheme / on-the-fly prioritization / filter rules Classifies non-standard protocols, like game-traffic, etc. Detects most common protocols, like HTTP, Mail, VoIP, Filesharing, etc.

Some speed tests

Ping times with different cFosSpeed versions
(down / up - without base delay - = better)

Ping time decrease with newer cFosSpeed versions * LL = Low Latency mode, costs about 5-10% transfer rate

On-the-fly prioritization of connections

Benefits of activating 'Automatic RWIN expansion'

Wi-Fi access point - cFos Traffic Shaping for smartphones, tablets and other mobile devices.

VoIP Software in use with cFosSpeed

Our old Traffic Shaping pages

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