These days, setting up a software based IP Telephony system (IP PBX) that can be downloaded from the Internet on any standard PC/Server hardware has become very easy. What is required though, is the hardware interface to connect the PRI/E1/T1 lines to the IP Telephony server. That’s exactly what the Digium cards are for, and in this article we will look at the factors you need to consider before selecting the appropriate Digium card.
Digium is the company behind the creation of Asterisk, the most common open source based IP Telephony software PBX system. Today, if even an engineering college student can set up a full fledged VOIP system in a few hours, its because of the popularity, ease of use and functionalities offered by freely down-loadable softwares like Asterisk. In fact, Asterisk can be downloaded in a GUI (Graphical User Interface) version through projects like Asterisk NOW, Trixbox etc which makes the installation of Asterisk on any normal computer hardware, a breeze.
The other two components that are required for completing the VOIP set up would be IP Phones (Hard IP Phones are easily available in local market – Just make sure that the phone supports SIP protocol (or) even a soft phone like X-Lite can be downloaded free of cost and can be used along with a headset-mic in a PC) and Hardware Interface Modules for connecting the PSTN lines to the computer server (to make local/STD calls over the PSTN network). For companies and organizations, it is more economical to purchase a PRI line as the volume of calls are generally higher, and hence we would concentrate on the PRI Cards offered by Digium in this article (There are other Digium cards that help connect analog PSTN trunks and analog extensions (analog phones) to the computer server as well – for details on the same, you could refer to the Digium official website).
By the way, a PRI/E1 line supports up to 30 channels to be transmitted on a single line and hence can terminate on a single hardware interface and a T1 line supports up to 24 channels to be transmitted on a single line as well. Channels refer to voice channels provided by a telecom service provider and each channel corresponds to an individual line in which you can dial out or receive a local/STD/ISD call.
If you have decided to terminate a PRI/E1/T1 connection to your IP Telephony server using a Digium Card, you need to make a note of the following:
- The Digium PRI/E1/T1 card supports all the three standards – PRI, E1 and T1.
- The Digium Cards come in 1 port, 2 port or 4 port configurations on a single card.
- The Digium Cards can be terminated on the PCI or PCI-Express interface in a Computer/ Server. Please note that the PCI interface has two variants – PCI 3.3 Volts (which is more commonly found in Servers) and PCI 5.0 Volts (which is more commonly found in computers). All the three interfaces – PCI 3.3 V, PCI 5.0 V, PCI-Express are different from each other and hence Digium offers separate cards for all of them. A card that supports PCI 3.3V interface cannot work in PCI 5.0V or PCI-Express interfaces. So, double check with your PC/ Server specifications on the type of interface your PC/ Server supports and how many such interfaces are present and if any additional modules can be added in the future for expansion.
- The echo cancellation module is optional – But it is recommended to buy the Digium cards with the echo cancellation hardware module as some echo is generated when the Digital Lines are converted in to IP and vice versa. In case you do not want to buy the echo cancellation hardware module, be sure to do the echo cancellation in software which would utilize additional computer CPU resources.
- Make sure that the Digium card would fit fully into the PC/ Server as some servers / PC’s have a very small form factor, these days – Probably you could check with the physical dimensions of the card you want to buy. For further details, you could check the Digium product page for the same.
- If your installation is totally based on the IP platform (without any PSTN termination), then there is no need to buy the above mentioned cards.
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