When comes to peering, the hot word about is 'security'. How trust able the other party is, how can you ensure safety and security for your subscribers. Many VoIP services are isolated islands, walled gardens. This is not something most of VoIP fans look for, they want freedom and ability to talk with people around the world, no matter of VoIP provider.
One solutions is federation, alliance between VoIP providers sharing the trust relationships. Klaus Darilion from enum.at introduced such solution in OpenSER, based on domain policies and secure communication via TLS.
The management of trustable federations and domains become more flexible and dynamic. The slides are going to low level of technical aspects to exemplify such configuration with OpenSER.
Download slides of Practical Peering With OpenSER