Abstract - When placing a call from one SIP Service Provider to
another, the call is traditionally routed over PSTN, instead of
IP. This can lead to higher costs, reduced quality, and lack of
functionality. These issues can be addressed by setting up a SIP peer
between providers. A SIP peer is a layer 5 interconnection between two
SIP Service Providers for the purpose of routing real-time and
quasi-real-time call signalling between their customers. We survey the
SIP peering architecture and show security implications.