There is still some room to improve. A more compact version of the former code.

my $type = 'unknown/malformed';

if($packet =~ m/sip/i) {
    if ($packet =~ m/sdp/i){$type='sdp'}
    else                   {$type='sip'}
    }
else ($packet !~ m/s[id]p/i)  {$type ='RTP'}

print "packet is of type ", $type, "\n";
[download]