Hardphones, Softphones, and ATAs

There are three types of endpoints you would typically provide your users with that could serve as a telephone set. They are popularly referred to as hardphones, softphones, and Analog Terminal Adaptors (ATAs).

A hardphone is a physical device. It looks just like an office telephone: it has a handset, numbered buttons, etc. It connects directly to the network, and it’s what people are referring to when they talk about a VoIP telephone (or a SIP telephone).

A softphone is a software application that runs on a laptop or desktop. The audio must pass through the PC’s sound system, so you normally need a headset that will work well with telephony applications. More recently, softphone applications have been written for smart phones that allow you to connect to other networks other than just the cellular network. The interface of the softphone is often styled to look like a physical telephone, but this is not necessary.

An ATA is designed to allow traditional analog telephones (and other analog devices, such as fax machines, cordless phones, paging amplifiers, and such) to connect to a SIP network,[44] and will typically be a sandwich-sized box that contains an RJ-11 connector for the phone (commonly referred to as an FXS port), an RJ-45 connector for the network, and a power connector. Some ATAs may support more than one phone.

Hardphones have the advantage that the handsets have good acoustic properties for voice communications. Any decent-quality telephone is engineered to pick up the frequencies of the human voice, filter out unwanted background noise, and normalize the resulting waveform. People have been using telephones for as long as the telephone network has existed, and we tend to like what is familiar, so having a device that communicates with Asterisk using a familiar interface will be attractive to many users. Also, a hardphone does not require your computer to be running all the time.

Disadvantages to hardphones include that they are nonportable and expensive, relative to the many quality softphones on the market today that are available for free. Also, the extra clutter on your desk may not be desirable if you have limited work space, and if you move around a lot and are not generally at the same location, a hardphone is not likely to suit your needs (although, one at each location you frequent might be a valid solution).

Softphones solve the portability issue by being installed on a device that is likely already moving with you, such as your laptop or smart phone. Also, their minimal cost (typically free, or around the $30 price range for a fully featured one) is attractive. Because many softphones are free, it is likely that the first telephone set you connect to Asterisk will be a softphone. Also, because softphones are just software, they are easy to install and upgrade, and they commonly have other features that utilize other peripherals, like a webcam for video calling, or perhaps an ability to load files from your desktop for faxing.

Some of the disadvantages of softphones are the not-always-on nature of the devices, the necessity to put on a headset each time you take a call, and the fact that many PCs will at random times during the day choose to do something other than what the user wants them to do, which might cause the softphone to stop working while some background task hogs the CPU.

ATAs have the advantage of allowing you to connect to your SIP network analog devices,[45] such as cordless phones (which are still superior in many cases to more advanced types of wireless phones[46]), paging amplifiers, and ringers. ATAs can also sometimes be used to connect to old wiring, where a network connection might not function correctly.

The main disadvantage of an ATA is that you will not get the same features through an analog line as you would from a SIP telephone. This is technology that is over a century old.

With Asterisk, we don’t necessarily need to make the choice between having a softphone, a hardphone, or an ATA; it’s entirely possible and quite common to have a single extension number that rings multiple devices at the same time, such as a desk phone, the softphone on a laptop, a cell phone, and perhaps a strobe light in the back of the factory (where there is too much noise for a ringer to be heard).

Asterisk will happily allow you to interact with the outside world in ways that were scarcely dreamed of only a few years ago. As we see more unification of communications applications with the popularity of social networks, communities such as Skype, and more focus on network-based services such as those provided by Google, the flexibility and popularity of software-based endpoints will continue to grow. The blurring of the lines between voice and applications is constantly evolving, and softphones are well positioned to rapidly respond to these changes.

We still like a desk phone, though.

[44] Or any other network, for that matter. ATAs could more formally be said to be analog-to-digital gateways, where the nature of the digital protocol may vary (e.g., proprietary ATAs on traditional PBXs).

[45] An ATA is not the only way to connect analog phones. Hardware vendors such as Digium sell cards that go in the Asterisk server and provide analog telephony ports.

[46] For a really awesome cordless analog phone, you want to check out the EnGenius DuraFon devices, which are expensive, but impressive.