Do You Need A Special Phone For VoIP?

I’ve been getting inquiries from people who are wondering if you need to buy a special phone to use VoIP as a replacement for regular telephone service. So, do you?

Answer: It depends.

Here’s why. You have probably figured out that you can’t just take a regular telephone and plug it into your router or broadband modem. The connectors aren’t the same size. That’s good, because you might just cause some equipment damage by plugging these incompatible devices together. What you need is a special phone designed to work on a data network or an adaptor for the phone you have now.

Most VoIP services designed for residential and home business (SOHO) take the adaptor approach. A good example is PhonePower’s VoIP service. You can get residential and small business plans with unlimited calling to the U.S. and Canada for $14.95 a month. Your order the service online and they send you a free adaptor for your phone. In this case it’s the Grandstream HandyTone 502 ATA or Analog Telephone Adaptor. You plug your phone in the phone jack that’s exactly the same size as the phone jack on your wall. You connect the ATA to your broadband modem or router using a standard Ethernet cable. Voila! You now have a regular telephone that works on VoIP.

But what’s going on in that ATA box to work the magic? There is circuitry that makes the phone connection look like it is coming right from your telephone company. That means generating the standard line voltage and ringing voltage that your phone is designed for. Those are analog signals because the phone is analog. The ATA also has to take care of converting between analog voice signals for the phone handset and digital packets for the Internet data network. This is done with CODECS or Coder/Decoders. In summary, the telephone needs to see its standardized analog signals and the Internet needs to see something that looks like a piece of computer equipment.

There’s a little more to it. Signaling for VOIP uses a standard called SIP or Session Initiation Protocol. SIP handles things like dialing and knowing when the phone is off-hook. SIP data is sent through the network just like other packets so it works just fine on the Internet or a private data network.

Because VoIP has become so popular for business, there are phones you can buy called SIP phones. These phones have the analog to digital circuitry of the ATA built-in. You can tell you have a SIP phone because it has a standard RJ-45 Ethernet jack on the back instead of the RJ-11 telephone jack. A SIP phone will connect directly to a LAN, a router or a broadband modem. It will need to be programmed for the VoIP service you are using. Some providers will give you instructions for how to do this. Others insist that you use their adaptor and an analog phone.

If you take your home phone into the corporate office, you may be shocked to find that there’s no place to plug it in. The company has installed an Enterprise VoIP system so that all desk phones plug into the corporate computer network. There is no separate phone network. All the phones are SIP phones. If for some reason you absolutely have to use your phone in that office, you’ll need to get an ATA and have it programmed to look like a SIP phone.

The bottom line is that regular telephones are analog. VoIP is digital. The way to make everything work is to use a phone that is matched to the network it is running on or use an adaptor to connect them.

The Analog Telephone Adaptor Enables VoIP

The role of the ATA or Analog Telephone Adaptor is to turn regular telephones into VoIP telephones. To perform this magic, the ATA has to fool the telephone set into thinking it is plugged into a standard telephone line. It also has to fool the broadband Internet connection into thinking it is plugged into a SIP (Session Initiation Protocol) telephone compatible with the VoIP provider's service.

The electrical interface is perhaps the easiest to achieve. On the analog side, the phone plugs into a standard RJ-11 jack like you would find on a wall socket. This delivers the standard -48 V DC to power the handset along with the dial tone, AC ringing, and Caller ID signals when needed. It has to detect standard DTMF (Dual Tone Multi-Frequency) touch-tone waveforms from the keypad and convert them to digital format for IP signaling using Session Initiation Protocol, the standard for VoIP.

How does the analog voice become digital and back to analog again? That's the function of the Codec or Coder/Decoder. The standard in use since digital telephony was invented is G.711. But there are other codecs that must also supported. These may include G.723, G.729, G.728 and G.726.

On the network side, The ATA has to terminate a standard Ethernet connection, usually 10/100 Mbps through a RJ-45 connector labeled as WAN. Many newer ATAs take this a step further by including a second Ethernet port labeled LAN. This is for connection to a PC in lieu of connecting the PC directly to DSL, Cable Modem or T1 WAN. The ATA performs the function of an Ethernet switch or router. This is not just to save the cost of a separate device so that PC and telephone can share the same broadband connection. When a router is included in the ATA, it then has the ability to ensure quality of service by giving voice packets priority over computer data packets so that using the PC doesn't interrupt telephone calls.

Maintaining voice quality while minimizing bandwidth is also the function of signal processing within the ATA. Some common processes include line echo cancellation and dynamic jitter buffer that compensates for variations in Internet line speed. PLC or Packet Loss Concealment deals with missing or out of sequence packets. Either the packet is replaced with a zero packet, a copy of an already received packet, or an interpolation between the preceding and following packets. VAD or Voice Activity Detection senses when you are talking and stops generating packets while you are listening to reduce bandwidth needs. Because digital lines have no traditional analog "hiss", people sometimes equate silence with a lost connection. CNG or Comfort Noise Generation recreates that low level background noise to indicate that the connection between phones is still in place.

All of these functions have been integrated into a package you can hold in your hand, in the HandyTone 502 ATA that is provided at no cost when you order PhonePower VoIP telephone service for residential and small business use. You can use the analog phone you have now, including cordless phones with multiple handsets.

Other VoIP service providers have also gone the route of providing their customers with complimentary ATAs to make the transition from traditional analog to digital VoIP as easy as possible.