Section one of this series provided the background on VoIP islands and why they serve the interests of vendors and service providers better than those of the enterprises investing in IP. With SIP now being the standard for IP telephony, the opportunities really open up to bridge those islands and allow enterprises to get the full value from their IT investment.
This section focuses on how these islands can be connected and how -- with that -- enterprises can think beyond the voice-centric nature of their IP PBXs and embrace the broader multimedia communications environment enabled by SIP. For enterprises that see their IP PBXs only as silos to provide telephony, VoIP islands are not really problematic; but for those who want the benefit of a more integrated communications solution, SIP trunking is the best path to follow.
SIP trunking has emerged in 2009 to help enterprises adopt convergence technologies and services. Enterprises are recognizing not only how these capabilities can make their business more efficient and their employees more productive but also how they can drive down the cost of communications.
Briefly, SIP trunking serves as a substitute for PRIs to provide connectivity, but over IP instead of the PSTN. SIP trunks are less expensive than T1s, and enterprises need fewer of them. In addition to saving money on trunking, telephony costs are reduced in many areas, most notably long-distance and toll charges. Another important benefit of SIP trunking is that it creates a direct IP connection between the IP PBX and the service provider, eliminating the need for a costly media gateway. Voice traffic enters and leaves the enterprise network as IP, and no TDM-IP conversion is required inside the network.
When service providers have this direct IP connection with the IP PBX, voice quality and reliability is on a par with TDM, and the benefits shift in favor of the enterprise. The onus of converting traffic now falls on the service provider because the conversion occurs in its network, and the enterprise gets the all-IP foundation upon which it can really start to take advantage of convergence-based communications.
This sounds almost too easy, but there are challenges involved with SIP trunking, not just within an enterprise network but in linking to other IP networks. The first is that IP networks and IP PBXs still need an intermediary device to be connected. Media gateways are not built for IP-to-IP, which is why they can be dispensed with here. The primary issue with IP-to-IP is network address translation (NAT) traversal, and the best solution is to deploy a SIP-aware firewall.
Conventional firewalls are very effective at managing data traffic -- but not voice, which is a real-time mode of communication. This is what a SIP-aware firewall does, effectively playing the role of a media gateway and allowing a clear IP connection between the carrier network and the IP PBX. The good news is that these firewalls are far less costly than media gateways, so economics should not be an impediment to adoption of SIP trunking. The best-known vendor of SIP-aware firewalls is Ingate, which -- along with others in this space -- is doing good work to educate the market about the value of SIP trunking.
On a broader scale, the SIP forum plays a vital industry-based role, not just to make SIP trunking work but ultimately to make it possible for VoIP islands to be connected. Even though SIP is a standards-based protocol, interoperability issues exist, although not to the extent found with legacy protocols. To address this, the forum leads various initiatives, most notably SIPconnect and SIPit.
The SIPconnect initiative is the forum's most important work, as it serves to develop interoperability guidelines between service providers and IP PBX vendors. The SIP Forum has recently added a certification program, SIPconnect Compliant, which serves as a seal of approval for those who successfully demonstrate interoperability. On a more granular level, the SIPit events are closed interoperability sessions where members can test with one another in a controlled environment.
Taken together, these activities make the SIP Forum central for linking islands of VoIP. They establish best practices for interoperability and strive to make SIP as plug-and-play as possible. This makes it easier, faster and less expensive not only to deploy SIP trunking with almost any IP PBX vendor but also to link the islands, which requires vendor-to-vendor interoperability. With all the major IP PBX vendors participating in the SIP Forum, the groundwork is now in place to make VoIP islands a thing of the past.
Read the rest of this tutorial on VoIP islands and how they can be connected and leveraged using SIP trunking.