Sometimes there is a need for simple and quick analysis of a SIP server and its call functions. Of course, we should use the well-known
tcpdump, mentioned in the article Using tcpdump for SIP diagnostics. However, for some occasional Linux users this may be too difficult and unclear. But actually there exist some simpler utilities, that could work fine, as ngrep, and for me newer, sipgrep and sngrep (love at first sight).
All utils are directly available and can be installed online from Debian repo using
apt-get install ngrep sipgrep sngrep.