1. Check you internet connection quality - instructions below.

2. Check if the call is intermittend when you are calling to Czech Republic too

Run batch file to test your internet quality or follow the instructions below:

CLick to button Start → Run …, write cmd in opened window cmd and press OK. Write the command below:

ping www.odorik.cz -t

and press ENTER. Let the command work for a while. You stop the command by pressing Ctrl+C. The result should look like below:

C:\WINDOWS\system32>ping www.odorik.cz -t 
Command PING to www.odorik.cz [89.185.255.62] s délkou 32 bajtů
Odpověď od 89.185.255.62: bajty=32 čas=30ms TTL=57
Odpověď od 89.185.255.62: bajty=32 čas=36ms TTL=57
Odpověď od 89.185.255.62: bajty=32 čas=35ms TTL=57
Odpověď od 89.185.255.62: bajty=32 čas=33ms TTL=57
Odpověď od 89.185.255.62: bajty=32 čas=32ms TTL=57
Statistika ping pro 89.185.255.62:
Pakety: Odeslané = 6, Přijaté = 6, Ztracené = 0 (ztráta 0%),
Přibližná doba do přijetí odezvy v milisekundách:
    Minimum = 30ms, Maximum = 36ms, Průměr = 33ms

The most important for you is the information “čas=XXms” in every line, or lines, where is writen “Request timed out” (Vypršel časový limit žádosti) - it indicates the packet loss. It is important to have less than 5% packet loss. Time (čas) should not exceed 100ms and should be with the minimum dispersion (there should be no big difference between values).

Usual values are 0% packet loss and time between 10 and 40ms with low dispersion - Internet with excellent characteristics suitable for calling.
Unacceptable connection is with a large packet loss (over 5%), or if the packets delay is larger than 300 ms.

** It's not depending on your internet speed, but your internet quality! **
The internet quality may change frequently during the day. Check your internet connection just when you encounter intermittent call or another problems with call quality.