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SIP Trunk Providers: What works (and what doesn’t)

Yes or No

In the huge world of SIP Trunk providers it can be hard to figure out who provides the best service that works well with Fax over IP (FoIP) and RightFax. In this article, I’ll go over what I’ve seen work and what are some gotchas that hinder successful FoIP integrations with SIP trunk providers.


The first and most important feature that a SIP trunk provider should support is (drum roll please) T.38. I can’t emphasize this enough, T.38 is the most important part of any FoIP implementation. Yes, G.711 can work just fine for FoIP… In a pinch, but in all of my experience, the only really successful FoIP setups have used T.38. The first question I would ask any potential SIP trunk provider would be: “Do you fully support T.38 fax?” If the potential SIP trunk provider does not say “Yes we do!”, I would recommend walking away.


The second area where we see issues, is in the providers telecom equipment. Your SIP trunk provider should use a high quality, Session Border Controller (SBC). The SBC is the physical interface between your network and the providers network. In small implementations, the SBC does not have to be a huge feature rich piece of equipment. We have seen small implementations (less than 24 channels of fax, and less than 1000 faxes per day) worked just fine on something as small as a Cisco ASA being double tasked as both a firewall and SBC. Enterprise class implementations should be using (let’s stay with Cisco stuff in our example) at least a 2800 series Cisco router as the SBC. The SIP trunk provider will be able to recommend the appropriately sized SBC for your environment.


The last but not least important feature in any successful FoIP integration with a SIP trunk provider is a highly knowledgeable technical staff. The engineers on the provider side need to understand how to make FoIP work across their network, and on your side, you need engineers to understand how fax is used in your organization, and how to best utilize the FoIP features of RightFax.