There are multiple supported ways in FreePBX to connect your PBX to the PSTN (Public Switch Telephone Network): VoIP Trunks, Analog Cards, Digital Cards, and Gateways.
VoIP Trunks
SIP Trunks provide the most flexibility in call routing and redundancy. The FreePBX Project is funded in part by SIPStation.com service, so please consider that for your phone service needs.
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But if you must keep your voice services with your local provider, you will need to find out how those services are being delivered. The FreePBX Marketplace has Analog Cards, Digital Cards and Gateways available for purchase. If ordered with a FreePBX Appliance, your card will be shipped preinstalled.
Analog Cards or Digital Cards?
Analog Cards
Many smaller businesses receive their existing service through analog trunks. In most markets, these analog lines can be ported to SIP Trunk providers for a cost savings. If this isn’t available, or you want to keep some analog lines on site for other services (alarms, emergency 911 call routing, external fax machines, modems etc.), then you will need an analog card. Analog lines are the traditional copper pairs coming from the local phone company. If using Analog lines, you will need to install an analog card in your server. Before you can build your system, you will need to find out how many incoming lines you have (FXO ports). If you are going to be using analog devices on your PBX, you will want to know how many devices you will need to connect (FXS Ports).
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Echo.Echo...ho...ho...oo! Echo is not traditionally a problem on traditional analog systems. However, once you bring VoIP into the mix, it can be a nightmare if not handled properly. VoIP systems often introduce latency, which analog systems do not have. VoIP systems will also be converting audio between different codecs and different types of systems. The result of this can be an echo in your conversation, which can be extremely frustrating to your end users. There are two primary ways you can combat this problem: software and hardware. If using only software echo cancellation, all of the echo cancellation is processed by your PBX server's CPU. You can purchase cards with or without hardware-based echo cancellation. Hardware echo cancellation can be more successful, because it removes the burden of echo cancellation from the PC. Hardware echo cancellation is also advantageous when handling large call volumes or a high number of channels that would otherwise stress the CPU and result in the potential for poor audio quality.
Gateways
Gateways are dedicated devices that have any combination of PRI, FXS, FXO ports and convert them to SIP to be used by your PBX.
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