By
Jyoti Tejpal
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SIP Trunking Software is a network service that allows businesses to connect VoIP phone systems to the traditional phone network. While this service is generally included with “per-user” licenses for cloud-based phone systems, if you have an on-premise system you’ll most likely need a SIP provider to connect calls with it.
But like real roadways, the Internet has many layers below the surface. These lower layers support—and determine the quality of—the layers above them. Each layer has its own specific set of languages used to communicate within that layer. These languages are called “protocols.”
VoIP—phone conversations over the Internet—are one very particular type of traffic. They require audio to be delivered consistently with minimal delay. SIP is an application layer protocol designed to provide a very certain type of road surface for this special traffic. SIP initiates the sessions (or connections) that prepare the network to best meet the specific needs of a real-time audio connection over the Internet.
SIP trunking is a network service. It’s necessary because VoIP calls travel over the internet rather than the traditional phone network. This means that you need some way to connect calls between the internet and the traditional phone network, as otherwise you’d only be able to call other users with VoIP. SIP trunking is the solution to this problem.
Get SIP trunking from the same company that provides your internet service, but in other cases you may need to use separate providers for SIP trunking service and internet service.
Lower trunking costs. Combined voice and data connections have traditionally been provided by telecoms in the form of Integrated Services Digital Network (ISDN) lines, also known as trunks. ISDN trunks come with fixed quantities of lines per trunk. Businesses often pay for unused capacity. SIP trunks are comprised of bandwidth, a flexible commodity, and their capacity can be increased on the fly.
Lower equipment expenses. Offices without SIP trunks use media gateways to translate between the analog PSTN and the office’s internal digital traffic. A SIP trunk also makes it more practical for an office to use a cloud-based phone system rather than purchasing and maintaining an in-office hardware version.
Lower calling charges. Traditionally, and under many existing calling plans, charges are calculated based on the physical length of the PSTN line required to complete a call. Calls made via SIP trunks bypass most of the PSTN and so avoid many long-distance charges.
More communications options. A SIP trunk extends, in a virtual sense, an office’s internal network to the outside world. Click-to-call website options for customers, application sharing and simple call transferring for work-at-home or abroad employees, for example, can all be done more easily with SIP trunks.
SIP client apps can facilitate communication via a mobile device over an Internet connection, with capabilities like voicemail, SMS messaging and more.
Bursting : If you needed more calling capacity on your phone lines, your provider took a month or longer to deliver it. SIP providers, on the other hand, can scale capacity up and down in as little as 24 hours, a vital cost-saving feature for businesses with fluctuating call volume.
Port sharing : If you have multiple sites, and one site maxes out its number of simultaneous calls, you can connect calls via open ports at one of your other sites. Again, this is a vital cost-saver for call centers.
Disaster recovery : In case of a service outage at one of your sites, your SIP provider can forward calls made to critical phone numbers.
911 and E.911 support : Your SIP provider can support 911 calls by providing location information with the call. Without E.911 support, VoIP isn’t compatible with emergency services.
MPLS support : Multi-protocol label switching is a networking technology that allows information to be routed within a network using path labels rather than the network protocols we discussed above. This offers performance, reliability and security benefits, and some businesses prefer to have SIP trunks delivered over MPLS. You’ll need to make sure your provider offers both MPLS and SIP trunking services.
Phone system deployment type. Whether you have an on-premise or cloud-based system is the most important factor affecting your approach to SIP trunking. Businesses with cloud systems may not even need a separate SIP provider.
Phone system brand. Different phone system vendors have implemented the SIP protocol in their systems in different ways. This means that not all SIP providers will be compatible with your specific brand of phone system. Check with your phone system vendor, as many list the SIP providers that their systems support.
Connection type. A SIP trunk can be provided over most any high-speed Internet connection. The cheapest option uses an existing broadband Internet connection from a standard Internet service provider (ISP), and simply has the ITSP service share it. Call quality and capacity may be reduced because both data and voice are sharing the connection.
Quality of service and service level agreements. Quality of Service (QoS) and Service Level Agreements (SLAs) are common components of the contracts businesses sign with their ITSP. The QoS agreement defines (in technical terms regarding IP traffic’s delay, jitter and packet loss) the acceptable average quality of a voice call.
Trial period. Many SIPTS offer full or limited trial periods. The trials can be adopted on a small scale to make sure everything is functioning as expected before making the switch. Make sure to test any devices such as FAX machines that are connected to the phone network as well as the actual features of your phones.
911 dialing. The FCC has mandated that all “interconnected” VoIP services provide functionality to connect 911 calls to the appropriate local emergency services authority.
Firewall and security. If not properly managed, SIP trunks can expose an office network to external privacy and security threats. Traditionally, offices have used standard firewalls to keep out unwanted IP traffic, but SIP traffic does not always travel smoothly through firewalls. Other security options, like Virtual Private Networks (VPNs) and session border controllers, are increasingly common.
