VoIP providers strive to insulate clients from problems with their new service, however, SIP trunking deployments are still prone to a number of difficulties. According to a 2018 report from SIP School, there has been little recent progress. 80% of enterprises adopting SIP trunking still experience some issues.

Although we talk about Session Initiation Protocol as if it were now a single commodity, in practice implementing a SIP trunk involves numerous protocols, technology providers, and carriers. This diversity of technologies and practices underlies the majority of issues. The most common underlying causes include PBX configuration errors, misconfigured codecs, and conflicts between NAT, SIP, SBC, and RTP.

Common problems for clients

Echo, stuttering, time lag and one way audio are often bandwidth issues. However bandwidth bottlenecks are not always local and can be aggravated by protocol incompatibilities, but typically quality of service is not a contractual responsibility of the SIP provider.

Many fax machines, credit-card terminals, telephones and exchanges will not work with SIP.

Too many voice codecs are in use (PCMU, PCMA, G729A/B) and they cause conflicts.

Tinkering with SIP configurations can inadvertently turn off important security features.

ADSL quality, port numbers, Network Address Translation, router and firewall configurations, antivirus software and IP conflicts all complicate the unravelling of a VoIP problem.

Buck passing

The situation isn’t helped when the engineers, carriers, and VoIP providers pass the blame instead of working closer together. For example, the SIP School survey reveals that customers blamed providers for 33% of the issues while providers admit responsibility only 9% of the time, instead blaming PBX vendors for over 50% and SBC device vendors for another 36%.

Wholesale VoIP termination rates

Automated call connections and bill settlement between the different companies involved in a connection facilitate swift connections anywhere. But it also insulates all the players involved from each other. Ironically, most will never speak.

Typically 3 or 4 companies are involved in just setting up a company’s VoIP; the PBX/UC vendor, SBC vendor, SIP trunk provider and a value-added reseller. Each call depends on services provided by other carriers, network operators, and device manufacturers. Finally, the receiver of a call has their own PBX, SBC and SIP vendor.

It isn’t enough for vendors and service providers to have knowledge of their own product. They also need detailed knowledge of the products provided by every other vendor and service provider with whom they will interoperate. If a customer raises a support ticket and the service provider just blames the device vendor, where does the customer turn?

Enterprises are emerging that offer specialised integration services, interoperability pre-testing and bespoke solutions development. Pre-modelling deployments makes sense for large corporations, but small businesses are lucky if they even get a manual.

Once SIP trunking and VoIP are the norm as everyone takes advantage of wholesale VoIP termination rates, we can expect to see more compatibility and fewer problems. In the meantime, the best advice for customers is to choose a mature provider such as IDT on the basis of their customer service reviews.