» cFosSpeed Documentation, Great Voice-over-IP (VoIP) speech quality

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Great Voice-over-IP (VoIP) speech quality

Not only is minimal latency absolutely essential for Voice-over-IP, it is the single most important factor in improving speech quality.

Traffic Shaping technology does keep ping times low and transfer rates consistently high at the same time.

RTP detection integrated in cFos and cFosSpeed permits prioritizing VoIP and other live streams (like conference channels).

Deactivation of strict RTP verification

Its prioritization can be adjusted under Protocol or Program Settings. Should a particular live stream not be recognized, you can prioritize the respective program by name.

Please note that some programs (like VoIPBuster, IxChariot) only use RTP but not the corresponding RTCP connection. For these, you should deactivate strict RTP verification in the settings.

Dropouts During Download:

VoIP connections usually suffer from dropouts when downloads are simultaneously run at full speed. Thanks to their integrated RX shaping, cFos and cFosSpeed help avoid this problem by keeping ping times consistently low.

Program prioritization of Skype


Skype employs a proprietary encrypted protocol that cannot be detected by a Layer-7 analysis without considerable effort. To allow users to prioritize Skype nevertheless, we have entered it in our program list.

VoIP via Router Prioritization:

Some routers (like the Fritz!Box) are equipped with phone jacks. If a jack is used, all VoIP data will be transmitted directly to the Internet bypassing cFosSpeed entirely. Such routers may restrict the available bandwidth when a VoIP call is made causing a negative impact on Traffic Shaping performance. Therefore we recommend making VoIP calls from your computer, not the router, to allow cFosSpeed to detect and prioritize them.

Optimizing Connection Settings:

DSL connection settings

You can specify exactly what transfer medium you use under Connection Settings. The more information about a connection is available to cFos or cFosSpeed, the better ping times will be. Default is "Adaptive". But if you were for instance using a DSL connection, you should select the appropriate DSL standard or protocol as your medium.

Favor Ping:

Display favor ping

In addition, you can also use the settings in the context menu or status window to activate "Favor Ping". A green arrow will then show up on the status window. This setting will have cFos or cFosSpeed do everything to keep ping times to a minimum but at the expense of transfer speed, which may slow down considerably.

VoIP Software in use with cFosSpeed


Measurements with IxChariot

We tested our software using IxChariot (a network performance testing tool provided by Ixia) to evaluate the benefits of cFosSpeed Traffic Shaping. For this purpose we monitored the VoIP parameters with IxChariot while performing multiple uploads.

You can easily notice that without cFosSpeed normal VoIP communication is not possible during an upload, but it proceeds almost unaffected when using cFosSpeed.

MOS value

In particular, you can see the MOS value ( http://en.wikipedia.org/wiki/Mean_opinion_score ) decreasing rapidly towards 1 after starting the upload. This means that the connection has become unusable for voice transfer. When using cFosSpeed the value doesn't decrease - the speech transmission retains its high quality.


The delay is a crucial part of the MOS value. Using cFosSpeed keeps the increase of this delay within bounds, whereas it raises up to 700 milliseconds when not using cFosSpeed (red graph).

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