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.

Soft phones

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.

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Some examples of business-oriented soft phone software are:

  • 3CX
    VoIP Phone for Windows
    . This is a Session Initiation Protocol (SIP)-based product available in both free
    and enterprise editions. It works with providers such as Asterisk and Sipgate.
  • ArrowPhone. Another
    Windows software-based phone, this one for H.323 networks. Customers can use
    the ArrowPhone over VPN networks behind a firewall. A free demo version is
    available for download.
  • AGEphone.
    Uses a “microSIP” stack and runs not only on Windows but also on CE/Pocket PC
    and Windows Mobile, with Linux and Symbian versions planned for the future. Has
    web-based interface that allows users to make and receive calls through a web
  • E-Phone. Free IAX2 soft
    phone for Windows.
  • Gizmo.
    Free soft phone for Windows, Macintosh OS X, and Linux.
  • SIP
    . Java-based open source VoIP client that supports both audio
    and video sessions over both IPv4 and IPv6.
  • 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).

    Hard IP phones are made by a large number of companies,
    including Texas
    , 3Com,
    D-Link, and Cisco.

    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.

    VoIP gateways

    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.

    VoIP gateways are also known as media gateways. They are made
    by many of the same companies listed in the IP phone section, as well as Nortel,
    SysMaster, and
    Oki Network Technologies.

    VoIP PBX

    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