Good discussion!
In most, but not all, cases it's a political/business decision outside of the scope of
the technichal specifications. A commercial SBC delivers a cloud of magic dust that makes
some people feel better and more secure. I have audited several SBC installations that are
totally insecure, where the local techies lack knowledge on how to operate it. Management
people think the SBC is secure by design. I can't blame the vendors here - it's
more correct to blame the decision process.
You can always build an SBC with Kamailio plus a media server like sems, Asterisk or
FreeSwitch in combination with IPtables. It requires experience and knowledge, but it is
propably a better longterm to invest in local knowledge for security instead of relying on
outside companies without building local knowledge...
Another problem is the architecture issue. SIP took off as a PSTN replacement. The design
of the SIP network and a traditional switch/PBX network is radically different, so SIP
networks was built with non-SIP design, with heavy media servers (b2bua) controlling every
call. This put a severe limitation in the service set and forced a big dependency into the
design, that wasn't there in the original SIP design. In order for SIP to get anywhere
beyond G711 calls we need to rip that apart.
Trying to do that is hard, since the endpoints are more and more designed for this design.
Normal phone services like music-on-hold and call parking are hard to deliver without
support from the phones. That forces many design to move back to a PBX design.
It takes time to change people's mindset. We need to prove that we can build better
and interoperable solutions. I can't get SIP presence to work across vendors.
That's bad for the industry, bad for us and hurts the trust in new designs and
solutions. Which moves people back to the old trustworthy and reliant PBX vendor. And the
SBC, because that's what gartner group and similar institutes tell them is the proper
design.
The battle isn't over. We need to prove our vision. Andreas and SIPwise is doing great
work here, as is AG Projects. And, of course, the whole Kamailio community and excellent
developer team.
/O
* The new Edvina SIP Masterclass - Stockholm Oct, Miami, FL Dec 2012
http://edvina.net/training/new-sip-masterclass/