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The two most popular open-source VoIP communication technology platforms in the VoIP domain are Asterisk and FreeSWITCH. Not only are they open-source technologies, but both are also powerful enough for developers to develop any complex communication and team collaboration VoIP solutions. Both hold a king’s share of the VoIP application market share, but each technology holds an advantage over the others, even though both platforms share many commonalities. By choosing one over the other technology, businesses enjoy certain benefits. In this article, we will have a quick brief on each of these VoIP solution development platforms to understand what makes them different.

Introduction to Asterisk and FreeSWITCH

What is Asterisk?

Mark Spencer developed Asterisk in 1999 as a software program that distributes calls just like an expensive PBX. His small team developed the Asterisk software for call handling and distribution for their company, Linux Support Systems, which was later rebranded as Digium. Being an open-source technology, the Asterisk program was adapted to be the base for many open-source, proprietary, and hybrid PBX systems, such as FreePBX, Elastix, and PBX in a Flash. Over the course of time, Asterisk has evolved to be an open-source PBX in its own right and can be used as a standalone system.

What is FreeSWITCH?

Limitations and shortcomings of the Asterisk platform resulted in the conception of FreeSWITCH in 2006. A reputable Asterisk developer, Anthony Minessale, decided to fix some of the perceived issues of the Asterisk platform and built a program from the ground up. It eventually became known as FreeSWITCH by 2007. FusionPBX is predominantly using FreeSWITCH solution as its switching core.

If you are wondering why to switch from traditional to VoIP calling, here is an article on “PSTN v/s VoIP

Internal Workings of Each Technology

Dialplan is the core of any Asterisk system. It is a scripting language with the modules placed in the configuration directory instructing the Asterisk system on what to do. Developers can achieve different functionalities, such as receiving calls on a specific SIP channel, connecting calls to IVR, or routing calls using dial plans in Asterisk development. The configuration files for Asterisk are saved as normal text files.

FreeSWITCH uses a different approach; the system is developed in C, and the fundamental program basis is more structured. In contrast to the Asterisk design, where each channel has its thread and memory space, FreeSWITCH processes threads that execute consistently throughout memory. This is also one of the reasons why FreeSWITCH requires more RAM than Asterisk. In addition, the configuration files for FreeSWITCH are saved as XML files which may be difficult to alter but highly beneficial for automating certain processes.

FreeSWITCH features a well-defined API, where the different functionalities are turned into modules. Developers, offering FreeSWITCH development services, can cherry-pick the needed modules and integrate them into the FreeSWITCH system based on the needed modules. Asterisk’s open and fragmented design means dependencies on parent modules for certain functionalities. So while the developers can experiment with unique features, they are also more prone to encounter errors, functionality breaks, and bugs.

Basic Functionality

Both technologies provide most of the same features on the most basic level. Any FreeSWITCH or Asterisk-based switch on the market should provide voicemail, call recording, and IVR menus. The process of creating extensions and gateways is very similar for either architecture. However, the number of users supported would vary based on RAM and the core performance of the server.

In addition to connecting between different endpoints, including mobile networks, VoIP systems, and the Public Switched Telephone Network (PSTN), both architectures have specialized interfaces for connecting to other servers of the same platform (i.e., Asterisk connecting to other Asterisk servers or FreeSWITCH to other FreeSWITCH servers) Asterisk uses a dedicated interface for connecting to other Asterisk systems using the IAX protocol (Inter-Asterisk eXchange). Thankfully, FreeSWITCH doesn’t require specialized protocols to communicate with other servers.

Advanced Functions


FreeSWITCH characteristics include the ability to provide multi-tenancy capabilities. This means multiple user branches can use a single FreeSWITCH system under individual domains or subdomains as exclusive entities. Unfortunately, to support multi-tenancy in an Asterisk system would require a proprietary system developed on top of the Asterisk platform. This is an expensive affair, and a major reason companies avoid multi-tenant Asterisk VoIP solutions.


Installing all roles from a single PBX server is like putting all your eggs in a single basket. Therefore, for large-scale or enterprise-level PBX servers, it is suggested to split each system, fulfilling a certain function, into a different server, i.e., distributed architecture.

Asterisk is primarily designed to run on a single system. However, for deployments that require multiple Asterisk servers, distributed device state support allows an Asterisk server to coordinate with multiple Asterisk servers effortlessly. However, Asterisk is still a single system platform at the core level, and certain features may feel set in stone during Asterisk software development.

On the other hand, FreeSWITCH offers strong interconnection capabilities, allowing individual systems in the cluster to perform numerous functions.

IM capabilities

Asterisk and FreeSWITCH systems support advanced communication functions, including chat (instant messaging), video calling, and conferencing. However, most Asterisk solutions rely on an add-on (OpenFire) for IM capabilities, for which companies must shell out additional payments. For IM capabilities in FreeSWITCH, the XMPP service must be activated, and the end devices must be properly configured.

Device Deployment Capabilities

Device deployment on either FreeSWITCH or Asterisk networks varies considerably. Asterisk supports many endpoint management modules for IP phones and softphones, but they cost around $100 for access to the provisioning software. FreeSWITCH systems take a hit here as although it includes various configuration files integrated into the platform for provisioning phones; the choice is severely limited compared to Asterisk. However, FreeSWITCH has an edge as it supports auto-provisioning.


Being a slightly matured environment, most SIP providers have comprehensive documentation for connecting systems to any Asterisk gateways. FreeSWITCH offers sample gateway configuration templates, but it’s better to call your SIP providers for troubleshooting when facing any troubles in connecting a FreeSWITCH gateway.

Minimum Server Hardware Requirements

Asterisk and FreeSWITCH

Asterisk v/s FreeSWITCH – VoIP Platforms Comparison

Performance: While FreeSWITCH requires more RAM and processing capabilities than Asterisk, it can also handle four to ten times the concurrent call volume. Sofia-SIP stack inclusion ensures communications control is now implemented in a trustworthy, well-tested manner for FreeSWITCH.

Stability: Since Asterisk is generally a single system arrangement, it relies on shared resources for performing different tasks. While this works smoothly in a restrictive environment, sporadic deadlocking, race conditions, and possible data corruption are the most common scenarios in large-capacity situations. However, since FreeSWITCH processes threads that execute consistently throughout memory, the system remains stable in large capability situations. Moreover, the overall stability of distributing the functionalities using APIs ensures FreeSWITCH servers have minimal downtime.

Versatility: Asterisk and FreeSWITCH offer flexibility in adding new features and applications. However, FreeSWITCH has the edge over Asterisk. FreeSWITCH supports a wide range of programming languages and platforms, including C/C++, Python, Perl, Lua, JavaScript, and.NET. So, incorporating the FreeSWITCH core library in other programs is relatively simpler.

Applicable Usage: Asterisk is better adapted to suffice the PBX requirements of any organization. FreeSWITCH has a lot better choices to offer in this situation. It is a platform with capabilities to provide better call management and billing features on top of just basic VoIP calling.

Configuration/Design: Setting up and managing administrative tasks on Asterisk is easier as it uses plain text files for configuration and dial plan design. At the same time, FreeSWITCH configuration uses XML, which makes manual configuration file maintenance a slightly difficult affair but makes automation easy. Moreover, dialplan creation at a higher level is possible in FreeSWITCH, all thanks to the improved regular expression support and increased number of matchable call attributes. An expanding FreeSWITCH developer community means FreeSWITCH is a thriving platform where new features are periodically developed.

Wrapping Up

A properly configured system running Asterisk or FreeSWITCH would make no visible difference for the end user. From a development aspect, Asterisk is considerably easier to work with on several levels. On the other hand, ls. FreeSWITCH offers a better range of modularity and wins when choosing a high-end PBX that can handle a large volume of concurrent calls. Vindaloo Softtech is a seasoned VoIP development company with expertise in creating Asterisk and FreeSWITCH-based business communication solutions for 6+ years.