SIP vs VoIP vs PBX – What’s the Difference? (Pros and Cons)

SIP vs VOIP vs PBX – What’s the Difference?.  Some terms in the network and communication domain such as PBX, SIP and VoIP make people confused. They doubt what they are, how to use and when to use these technologies, or in other words, protocols. Hence in this article, we will discuss what these three words mean and how they are going to be used with other protocols. 

What is SIP?

SIP stands for Session Initiation Protocol. It is used for initiating, maintaining and terminating interactive, communication sessions within VoIP systems. These sessions can be used for multimedia communication, instant messaging, virtual reality as well as online streaming games.SIP is not only being used in VoIP but also in presence, 3G telephony and other networking applications. SIP trunking services are offered by hosted Unified Communications vendors. They are responsible for providing Unified Communications as a Service (UCaaS).

Pros of SIP

  • Higher flexibility since it works independently of the session type/media.
  • Support for multi-vendor integration
  • The ability to accommodate multiple users with customized capabilities.
  • Convenience for troubleshooting as SIP messages are clear

Cons of SIP

  • High load on gateways due to processing text messages
  • Messages need to be translated into a format that the router identifies, and then fed to the router
  • Since it is a new protocol majority of users are not familiar with it
  • Not yet matured as it is still being inspected
  • Conversion between in and out-band DTMF tones should be done if using both SIP and SCCP within the same network.

What is VoIP?

What is VoIP ? Voice over Internet Protocol is also known as VoIP. VoIP technology provides the service to make calls through the internet. Voice is first broken into small chunks of data (data packets) and then will be transferred to anywhere in the world within a few seconds. Therefore it is known as IP telephony or Internet calling which is an alternative for landline systems. VoIP uses the IP address of your device for communicating. VoIP is a cost-effective method of communication to handle a large number of call events.

VoIP architecture
VoIP Architecture

Pros of VoIP

  • Low in cost since there is no need to have dedicated resources and infrastructure changes such as wiring and cable installation when VoIP planning.
  • Audio is not fuzzy, less distorted and not muffled.
  • Availability of advanced features such as automatic call attending, call recording, call ques handling, voice mails, voice to text, call analytics, and spam call rejection
  • Remotely available since no technical setup is required.
  • Worldwide communication can be  obtained at a very less cost – you only have to pay for the internet charges as per your consumption

Cons of VoIP

  • Needs a high-speed and stable internet connection as  VoIP is strictly based on it. All the available features can only be obtained with a strong internet connection. Hence you need at least 100 kbps per phone line.
  • Unable to support in an emergency as most of the service providers do not provide emergency call services. Hence it will be a complex process to integrate it.
  • VoIP does not rely on analog signal based technologies and components.

What is PBX?

A PBX is an acronym for Private Branch Exchange, which is a private telephone network that allows users to talk to each other. Different hardware components work in tandem to provide connectivity to the telephone network.

PBX is capable of providing features such as call forwarding, call ques, auto attending, voice mail and call transfer etc. These systems are working with either VoIP or phone lines (analog or digital). The unique feature of PBX is that you can split your phone line into multiple lines allowing you to support many telephony devices.

There are two types of PBX; self hosted PBX systems and cloud PBX systems

PBX Architecture
PBX Architecture

Pros of PBX

  • Calls within the same networks are free of charge
  • Convenient call management: can pre-programme calls and can set its own rules in the PBX network tree. For example, some divisions can be restricted from having international calls or calls in external numbers etc.
  • Transferring calls within the divisions are easier. You can use warm transfer or cold transfer to transfer calls reliably
  • Can play customized recorded messages, greetings, music or audio trailers to indicate facts about the company. This is a handy way to alert the customers about sales, offers and other marketing matters.
  • Ability to use cloud-based PBX to handle a large number of calls and distribute them among various teams.
  • Can be used along with PBX management tools such as FreePBX to increase the experience and customize the features
  •  The easy and convenient call routing mechanism

Cons of PBX

  • On-premise PBX can suffer from Single Points of Failure. If one point of the network fails, it will cause the whole network to stop.
  • Premise based PBX is much costly and provide fewer features when compared to hosted PBX 
  • There can be more technical jargon which makes implementation and management hectic
  • Premise based PBX is less scalable since there are only a limited number of lines you can split the original into. This issue can be eliminated with the hosted PBX as it allows users to have any number of phones and offer hassle-free growth to the business.

SIP vs VOIP vs PBX - What are the Differences?

As now we know what these terms individually mean, let’s see how they can be used together. 

VoIP with SIP

SIP can be used to enhance VoIP systems. The combination of these twotechnologies offers some special benefits. 

  • Provides user-friendly admin tools for lines and feature management.
  • Can be easily integrated with cloud applications as SIP supports Unified Communication implementations.
  • Enhanced productivity using built-in integration with common business apps and software.
  • The ability to create hybrid phone systems by integrating with PRI (Primary Rate Interface) lines. (PRIs are end to end dedicated circuits for networking)

As with any other protocol, SIP with VoIP also has some drawbacks.

  • SIP integration requires sufficient internet bandwidth to provide quality service.
  • Features provided by SIP vendors may not include all the UCaaS features.
  • The quality of service of each SIP provider may not be the same.


While you do not need PBX to have VoIP, VoIP can be integrated with PBX for better performance. Most of the VoIP providers offer some PBX features too.

  • Unlike VoIP, Installing on premise PBX is a large project which requires dedicated hardware resources such as static power supply, expensive routers and other hardware along with software and VoIP gateways. Even the installation is costly.
  • VoIP and Cloud-based PBX are highly scalable when compared to on-premise PBX as it comes with physical limitations.
  • On-premise PBX relies on the internal network and cannot access it from outside. VoIP is a better choice over PBX if your company has a work from home practice.
  • Security of VoIP depends on the service provider. There is a potential risk to the security as it is exposed to external networks. On the other hand, on-premise PBX routes external calls directly to the Public Switched Telephone Network (PSTN). Hence there is no risk of cyber theft even if the system is not connected to the internet.
  • PBX are subjected to the regular phone company states, hence will be charged high for the international calls. VoIP has only the data cost which is very affordable and reasonable.

SIP vs VOIP vs PBX Conclusion

You do not have to choose only one of these technologies and exclude the rest to make a better choice for your company. Instead, you can use a PBX system connected with a VoIP system with the help of SIP trunking to make a great and smart solution.

Avatar for Shanika Wickramasinghe
Shanika Wickramasinghe

Senior Software Engineer at WSO2 which is the 6th largest Open Source Software Company in the World. My main skills are machine learning and software development. I have 5+ years of experience as a Software engineer.

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