Session initiation protocol (SIP) trunking effectively allows enterprises and small businesses to continue leveraging their voice-over-IP (VoIP) infrastructure and related IP-based productivity suites (desktop sharing, web conferencing) while connecting to the larger circuit-switched and mobile telecommunication systems operated by national, regional, or local telephony operators. The connection between the enterprise (or small business) and the larger telecommunications system is achieved through an SIP trunk, which is essentially an IP link that carries SIP traffic. This short position/opinion paper explores the trade-offs involved in moving to SIP trunking.

The paper outlines the issues to be reckoned with when implementing an SIP trunking solution. The primary issue the paper posits is one of security. This issue touches end-user privacy and confidentiality, as well as the ability of the SIP trunking provider to live up to the expectations in a service level agreement (SLA) document. The answer to end-user privacy and channel confidentiality is ameliorated through the presence of a session border controller (SBC), which is a special device in SIP networks that handles incoming and outgoing traffic. SBCs have access to SIP signaling as well as the media session set up by the signaling protocol, and can thus provide several value-added services. Of course, the problem with SBCs is that they act as a man-in-the-middle, thus there is no true end-to-end confidentiality. However, the author does not consider this issue in the paper, and the SBC is used to provide an illusion of security. Regarding the SLA, the author advises the enterprise to review trunking providers using a number of standard metrics such as reliability, feature richness, troubleshooting capabilities, and so on, to arrive at an equitable match.