There's a lot of discussion about the merits of different Voice over IP services, but choosing a service provider isn't the only decision you'll need to make once your company takes the plunge to deploy VoIP; it helps to have a working knowledge of the hardware devices involved in transmitting voice calls over an IP network, and an idea of what different components do and which ones you need.
Some VoIP services are software based. That means, at the user's end, the only hardware device needed is a computer with an Internet connection. The computer requires the appropriate audio equipment: a sound card with speakers or earphones to hear the other party's transmissions, and a microphone to input your own side of the conversation.
A soft phone is the industry name for a software program that users can install on a PC to make IP phone calls; most free soft phone services handle only PC-to-PC calls. Users typically pay a monthly or per-call fee for public switched telephone network (PSTN) gateway services to allow them to place calls from their soft phones to regular landlines and cell phones. Perhaps the best known soft phone software is Skype.
Some examples of business-oriented soft phone software are:
Hardware for soft phones
One big drawback of soft phones is the physical interface. Although some users prefer the headset or microphone/computer speaker setup, others are uncomfortable with it and want to be able to talk on a "real" phone. USB handsets can give soft phone users the familiar telephony experience along with the improved voice quality of PC-based VoIP communications. Soft phones plug into the computer's USB port.
USB phones come in many styles, including handsets, desksets with speaker phones, and base station/cordless models. Some USB phone sets require driver software, so it's important to be sure there are drivers available for the operating system(s) on which a user runs the soft phone software. USB phone sets are available from Yuxin, World Phone, and Eutectics. (Note that USB phones are different from IP phones, which do not have to connect to a PC.)
Hard phones (IP phones)
A hard phone is a dedicated, self-contained computer that looks like a conventional phone and plugs into an Ethernet port on a router. It can communicate directly with the VoIP server or gateway and doesn't need to go through a PC, so a user doesn't have to install any software to use it. Hard phones cost a lot more than USB phones (typically starting at around $100, as opposed to less than $20 for a USB phone).
A special category of hard phones has a built-in modem in place of an Ethernet port. These phones use a dial-up Internet service to connect to a remote VoIP server and thus do not require a broadband connection. They are popular in countries outside the United States.
Another variation on the hard phone is the Wi-Fi phone. This is an IP phone with a built-in 802.11 wireless transceiver in place of or in addition to an Ethernet port. It connects wirelessly to a wi-fi base station (called an access point), which is then connected to the Internet. Like other hard phones, it doesn't have to connect to a PC. Wi-fi phones are made by many of the same companies that make Ethernet-based IP phones.
Analog telephone adapters (ATAs)
An ATA allows users to use a regular analog telephone to make VoIP calls. It has an RJ-11 port (for a regular phone line) into which users can plug an ordinary telephone handset. It also has an Ethernet port by which users can connect it to the local network. The ATA communicates with the VoIP server, using a standard VoIP protocol such as SIP, H.323, or IAX. The ATA converts the analog signals of the phone to digital data so it can go over the Internet.
The VoIP "box" provided by consumer-level VoIP services such as Vonage and Lingo is an ATA. Another name for an ATA is VoIP router.
Digital telephone adapters (DTAs)
DTAs, also called handset gateways, allow businesses with digital Private Branch Exchange (PBX) handsets to use their existing infrastructure for VoIP calls. An IP PBX—which replaces the PBX itself—integrates with all the legacy handsets already in place throughout the enterprise, saving companies from having to replace all those handsets. Handset gateways are available from Citel and Intel.
VoIP interface cards
VoIP interface cards are expansion cards that go into a computer's PCI slot to add VoIP capabilities. Users can plug several phone lines into a single card, install the software that works with the card, and create a system that can automatically answer and redirect calls and record voice mail messages. Vendors include VoiceTronix and Digium.
These devices connect VoIP networks to the PSTN system, allowing calls between VoIP phones and PSTN or mobile phones. Gateways perform compression and decompression of voice transmissions, as well as call routing. VoIP gateways may interface with gatekeepers, softswitches, or other external controllers, and can incorporate features such as network management and accounting.
PBX systems perform the same functions as a traditional PBX, including call switching/routing within an organization. Technically, a PBX system uses a live operator to route calls, whereas PABXs (Private Automatic Branch Exchanges) are modern systems that do so automatically. In next week's column, we'll discuss IP PBX systems in more detail.
Debra Littlejohn Shinder, MCSE, MVP is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. Deb is a tech editor, developmental editor, and contributor to over 20 additional books on subjects such as the Windows 2000 and Windows 2003 MCSE exams, CompTIA Security+ exam, and TruSecure's ICSA certification.