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The Ultimate Guide to Sip Trunking

Last Updated Jul 17, 2023

Written By Top10Ratings

The Ultimate Guide to SIP trunking

SIP trunking has become one of the catchphrases of modern business IT industry today. Short for Session Initiation Protocol, SIP trunking is an internet-based service allowing enterprises with an existing PBX system to employ real-time communications, which includes VoIP. Having emerged as one of the most popular ways of facilitating voice communications over the web, SIP trunking is a great alternative to traditional phone systems and is a single voice connection between one’s business and the Internet.

When a traditional, internal PSTN system is connected to the SIP trunk, businesses can communicate outside the enterprise over IP. SIP trunking allows enterprises to replace the fixed, traditional PSTN lines with IP phone systems connected on the outside through it, enabling the creation of a single channel for multi-media components such as data, video, and voice. SIP trunking, thus, verifiably offers increased reliability and greater savings in costs.

Functionalities of SIP trunking
SIP trunking blends connections for both voice and data into a single line. A SIP-trunking device allows the data network to carry voice traffic by being a converter between a traditional phone system and the internet connection of a company. Some traditional features of SIP trunking include caller ID, directory listing, E911, long-distance, and local calling, all of which can be integrated into the business’ existing phone system.

SIP trunking essentially has 3 primary components:

  • Border element
    The border element facilitates connectivity between an external IP carrier network, the PSTN, and the internal enterprise IP network. Such border elements could be either an SIP-enabling edge device connected to the firewall or an SIP-capable firewall itself, or it can also be a switch used for transferring calls out of and into the PSTN. The service provider usually manages the border elements. Typically, service providers will include SIP trunking a part of the system-phone-IP package, which will be separated into hybrid solutions only when there is a requirement to maintain certain locations on a traditional TDM (time-division multiplexing) system. This TDM system will further connect to the overall IP infrastructure via an SIP trunking service and multiple border elements.
  • Internet telephony service provider (ITSP)
    The ITSP’s role is ensuring connectivity from an IP network to the PSTN for fixed and mobile communication devices. The ITSP also transports IP communications across the public Internet or a private IP network.
  • IP PBX
    IP-based PBX systems communicate with every endpoint over an IP network. IP-based PBX systems are also able to switch calls between VoIP users using local lines, simultaneously enabling all users to share numerous peripheral phone lines. Typically, such systems can moreover also switch calls between two traditional telephone users as well as between a traditional telephone user and a VoIP user in the same way as a conventional PBX system.


There are several benefits of SIP trunking:

  • Access to a whole lot of hosted VoIP service benefits sans discarding the existing investment into the traditional phone systems.
  • Provides points of presence across numerous US cities so that businesses can establish local numbers as against relying on toll-free or vanity 1-800 numbers.
  • Allows businesses to outsource their PSTN connectivity to a 3rd party, and thus reduces charges incurred for long distances.
  • Eliminates the need for BRI (basic rate interface)/PRI (primary rate interface) connections and, thus, lowers telephone costs.
  • Reduces the monthly expenses since SIP trunking needs only one connection for voice and data.
  • Nullifies the need for purchasing equipment like managed-media gateway devices for interfacing between the PSTN and IP voice.
  • Eliminates the need for investing in less capable and costly desktop equipment or TDM-gateway equipment infrastructure.

Challenges involved

  • Problems and issues could arise if businesses attempt to mix equipment from various vendors in a unified IT environment. The same goes for multiple types of equipment based on SIP protocol. This is why businesses need to set the best practices for interfacing an ITSP with a PBX setup to minimize incompatibilities.
  • SIP trunking could, unfortunately, also give rise to security risks. Luckily, SIP server and proxy technologies can manage SIP traffic flow, allowing an IT manager to ensure the application of authentication and verification policies and do correct routing to minimize threats.
  • When it comes to quality, companies need to establish QoS agreements with their SIP trunking providers before signing agreements. Luckily, measures such as prioritizing voice traffic and proper provisioning of links help remove delays and allow for appropriate scaling.

On the whole, SIP trunking will be the new thing in the IT industry in the years to come. While the costs of SIP trunking vary, businesses can realize immediate cost savings from a comparatively modest investment in SIP trunking system.

With over 200 years of combined industry experience, our Editorial Team at Top10Ratings is a diverse group of expert reviewers, product analysts, and content experts. They come from backgrounds in renowned product testing labs, acclaimed review platforms, and leading market research firms. Together, they ensure that every review, ranking, and insight offered on Top10Ratings is comprehensive, expert-driven, and trustworthy. Their dedication to authenticity and clarity guarantees that our readers always receive reliable and actionable advice.