VoIP Gateway Overview

Your VoIP gateway can be simple

Or it can be a complex nightmare…

You're a smart person. You want to avoid the tossing, turning and sleepless nights that a VoIP gateway can cause.

But how do you avoid a complex nightmare?

Simple. You start by educating yourself about VoIP gateways. Exactly what the information below well help you do.

So read on and avoid turning your VoIP gateway into a nightmare.

What is a VoIP gateway?

A VoIP gateway is a piece of hardware with the standard purpose of converting TDM telephony traffic from the PSTN into digital packets IP packets for transport over an IP network (such as your LAN). A VoIP gateway can also convert digital IP packets into TDM telephony traffic for transport across the PSTN (Publicly Switched Telephone Network).

How does a VoIP gateway work?

VoIP gateways are rather simple. A VoIP gateway works as a bridge between an IP network and the PSTN. Depending on where the voice traffic originates from a VoIP gateway will convert the voice traffic into the proper form for receipt by the destination network (IP or PSTN).

If the voice traffic is originating from the PSTN the VoIP gateway will convert the analog voice signal into a digital signal. This digital signal is then compressed using a codec and broken into a series of packets that are transferred across the IP network using a signaling protocol.

If the voice traffic is originating from an IP network the VoIP gateway will decompress the digital packets into a digital signal that is then converted into an analog signal to be sent across the PSTN.

VoIP gateway protocols and codecs

Hopefully your head's not spinning from the explanation of how a VoIP gateway works. Because it's now time to talk about VoIP protocols and voice codecs.

Even if you're not technical you still need a basic understanding of VoIP protocols and codecs. In order for your gateway to work properly it must use a protocol and codec that is compatible with your VoIP phone system and or VoIP service. The protocol and codec you use can also drastically increase or decrease the quality of your calls.

VoIP protocols

A VoIP protocol determines how your voice packet is transported across a network. A VoIP gateway will typically support a single protocol.

The most common VoIP protocols are:

  • SIP (Session Initiation Protocol) – SIP is a standards-based protocol that is used and supported by the vast majority of VoIP phone systems and services.
  • SCCP (Cisco Skinny Client Control Protocol) – SCCP is a proprietary protocol used by Cisco's Call Manager and IP phones.
  • MGCP – MGCP is an older VoIP protocol you might come across. It is no longer widely used and or supported.
  • H.323 – Similar to MGCP, H.323 is an older VoIP protocol that you might come across, but is no longer widely used and or supported.


Voice codecs

A voice codec is responsible for the compression of your voice stream within a digital packet. It also determines sound quality and bandwidth required to send the packet. A VoIP gateway typically supports multiple voice codecs.

The most common voice codecs are:

  • GSM – 13 Kbps
  • iLBC – 15 Kbps
  • G.711 - 64 Kbps
  • G.722 - 48/56/64 Kbps
  • G.726 - 16/24/32/40 Kbps
  • G.728 - 16 Kbps
  • G.729 - 8 Kbps


If you're the person responsible for the set-up, installation and maintenance of a VoIP gateway you will want to further your knowledge in the area of protocols and codecs. If not, simply make sure your VoIP gateway supports the same protocols and codecs that your VoIP service and or VoIP phone system support.

The types of VoIP gateways

With the techno babble out of the way it is time for you to dig into the different types of VoIP gateways.

There are two main types of gateways that you need to concern yourself with – analog and digital.

  • Analog – An analog VoIP gateway is used to connect your traditional analog telephones to a VoIP phone system or to connect your VoIP phone system to the PSTN. Due to this dual purpose an analog VoIP gateway comes in two different forms – FXS and FXO.
    • FXS gateway – An FXS gateway is used to connect your traditional telephones and fax machines to a VoIP phone system.
    • FXO gateway – An FXO gateway is used to connect your VoIP phone system to your PSTN lines.
  • Digital – A digital VoIP gateway is used to connect your VoIP Phone system to your digital voice lines such as T1/E1/BRI. A digital VoIP gateway can also be used to connect your traditional PBX system to an IP network.

You might be thinking that analog and digital gateways both do the same thing. This is correct.

The real difference between an analog VoIP gateway and a digital VoIP gateway are the interfaces each one uses to connect to various solution components together.

Before we take a closer look at the applications mentioned above let's take a few minutes to take a look at the features and configurations of a VoIP gateway.

Features of a VoIP gateway

VoIP gateways are very robust devices. The vast majority of VoIP gateways come with the following features:

  • Compliant with multiple protocols including SIP, H.323 and MGCP
  • Support for G.711, G.723.1, G.726, and G.729A voice codecs
  • T.38 compliant (for faxing)
  • Echo cancellation, Jitter Buffer, VAD and CNG
  • Web based administration/management
  • Automatic provisioning via TFTP/HTTP
  • Call routing and least cost call routing capability

These are merely the standard features found in the majority of VoIP gateways. Each VoIP gateway has subtle differences. For more information on a specific VoIP gateway please refer to its full product description on VoIPSupply.com.

Standard VoIP gateway Configurations

VoIP gateways can be found in the following configurations:

  • FXS gateways
    • 4 Port
    • 8 Ports
    • 16 Ports
    • 24 Ports
    • 48 Ports
  • FXO gateways
    • 4 Port
    • 8 Ports
    • 16 Ports
    • 24 Ports
    • 48 Ports
  • Digital gateways
    • 1T1, 2T1, 4T1
    • 1E1, 2E1, 4E1
    • 1BRI, 2BRI, 4BRI

The number of ports you will need on your VoIP gateway is dependant on the number of lines and or devices you are looking to connect to the VoIP gateway. For instance if you want connect your VoIP phone system to your two PSTN lines, you will need a two FXO analog VoIP gateway.

Well, that's it for now. Hopefully this educational information has given you more insight into a VoIP gateway.

For more VoIP gateway information, check out our VoIP Gateways Frequently Asked Questions page.

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