1. Check your internet connection quality - instructions below.

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

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

CLick to button Start → Run …, write cmd in open 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 each 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 does not depend on your internet speed but on 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.