[Serusers] How necessary is DNS in SIP ?

The question is just about that in the subject ... Do I need, as Dan Austin's howto says, a DNS SVR Resrouce Record, or can I just use IP numbers, instead of names ? The thing is I have some doubts: - the variable SIP_DOMAIN needs to be a name or can it be just an IP number ? - if so, I believe that at the ser.cfg file, I can put uri="a.b.c.d" instead of uri="mydomain.com" - if so, I can write down if (!www_authorize("a.b.c.d", .... ) instead of if (!www_authorize("mydomain.com", .... ) - how is related the sip domain to the host name and domain, set both respectively by hostname and domainname commands in linux ?? In other words, does the domain name of my host needs to be the sip domain ? - what is a realm ? Thanx a lot Lucas --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.762 / Virus Database: 510 - Release Date: 9/13/2004