Understanding VoIP Architecture – A Simple Explanation

Posted on: 2018-02-06 | Categories: Business VoIP

VoIP is a set of standards, devices, protocols and software that allows users to have voice conversations over the Internet instead of the dedicated PSTN. VoIP technology first appeared on the scene as early as 1995 but the systems we have today bear little resemblance to those early prototypes. From consumer grade mobile VoIP apps to enterprise level SIP trunking solutions, VoIP has evolved quite a bit since the last century.

Though the industry has changed, the underlying architecture of VoIP has remained stable. The basic parts that make VoIP possible remain essentially the same. Before your company takes the plunge into uncharted territory with VoIP, you should have a basic understanding of how the technology works.

What Does VoIP Do?

If enterprises are to rely on VoIP for voice communication, it has to perform these basic functions:


This is how various devices on the network communicate with each other. It includes call activation and setting up the various parts needed to complete a call.

Database services

VoIP identifies specific endpoints via IP addresses (similar to phone numbers on the PSTN). Database services dictate how to locate an endpoint and translate addresses that might be different across various networks. It is also used to generate reports for billing and many security functions (deny international calling for a particular user for instance).


Call connect and disconnect


A call within VoIP consists of a multimedia (audio and/or video) stream connecting two or more endpoints. The stream is transported in real time and is sensitive to delays. Specific VoIP protocols take care of connecting, disconnecting and setting the parameters of call sessions.


CODEC operations


The human voice is analog but VoIP requires voice data should be in digital format. Codecs perform this function of converting analog signals to digital packets and vice versa. There are various codecs that are geared towards different goals – efficient transportation, high quality audio, low bandwidth consumption etc. Higher quality audio (with less compression) will require more bandwidth.

The Moving Parts of VoIP

Irrespective of the type of VoIP solution we talk about (hosted or on premise), there are certain components we need for VoIP to function. These are:




This is the main control center for any VoIP implementation. The PBX doesn’t handle the actual VoIP stream (the voice/video part of the call) which flows directly between the endpoints. The IP PBX handles the control or set up of calls and routing network traffic flows. In the case of hosted VoIP, the vendor sets up and maintains the IP PBX which is usually software based. For SIP trunking, you would need to purchase and maintain it yourself.


Endpoint devices


End devices can be dedicated hardware devices or software applications. IP desk phones look and work like traditional phones but they are compatible with VoIP protocols. Meanwhile there are apps that you can download on computers and smartphones to handle VoIP calling functionality. For the purpose of making a VoIP call, the endpoint device doesn’t matter. Calls between IP phones, computers, smartphones or a mix of everything work exactly the same.


IP network


The IP network connects all the various components of VoIP. The voice data packets travel over IP networks between the source and destination. It should be able to differentiate between data and voice packets and be able to prioritize them as well. Voice data is particularly sensitive to time delays and so QoS optimization is necessary to minimize service disruption.


VoIP and Media gateways


Media gateways perform various functions including analog to digital conversions, echo cancellation and silence suppression among others. Some gateways also include the ability to connect to the PSTN for completing calls while others provide analog interfaces to VoIP networks. The function of a gateway depends on the specific VoIP installation.

VoIP Protocols

There are various protocols involved in VoIP to perform different functions. Protocols are a standard set of rules that endpoints use for communicating. TCP/IP, SMTP and FTP are a few of the more common protocols that are used for email, file transfers etc.

H.323 and SIP are the main contenders for VoIP signaling protocols, although it is fair to say that SIP has become the most popular among vendors. It is practically the default standard and most hardware will work with SIP. If your equipment is compatible with SIP, you can switch vendors without worrying about interoperability. The actual VoIP stream of audio and video is transported using the Real-time Transport Protocol. The RTP is specifically geared towards real time streams that are sensitive to delays and packet loss.

Not everyone has the time or inclination to understand VoIP thoroughly before purchasing services. However a basic understanding will allow you to make informed decisions. You should always ask your provider for specific details and clarify any doubts before making a commitment.