Now that we have examined how we can begin to migrate our corporate telephony systems to VoIP, let's bring the conversation home, literally. After all, many homes today have broadband connections, such as digital subscriber line (DSL) or cable modem connections, and many service providers are beginning to offer telephone service over these broadband connections.
You can purchase a small router for your home that has one or more analog telephone jacks and sign up for VoIP service with a carrier, such as Vonage (http://www.vonage.com). Cisco makes a router that can be used with the Vonage service. This router also has an Ethernet connection, allowing you to connect it into your existing home network, or directly into your DSL router or cable modem, as shown in Figure 3-18. When you pick up your phone to place a call, the router supplies your phone with dial tone, and it can interpret the phone's dialed digits.
Figure 3-18. VoIP in the Home
The router in your home forwards the dialed digits over the Internet to the carrier's equipment located in a telephone company's CO. Often times, the carrier leases space for its equipment in the CO. This type of leasing arrangement is called a co-lo (that is, "co-location"). The carrier's equipment in the CO connects into the traditional telephone company's network, using Signaling System 7 (SS7) as a signaling protocol.
Once an end-to-end call is set up, the router in your home converts your voice (that is, analog waveforms) into packets. These packets are transmitted over the Internet to the carrier's equipment in the CO, which sends your voice into the PSTN.
You can, in some cases, keep your current phone number if you convert your existing telephone service to a VoIP-based telephone service. However, because these services are not installed in every local CO, if your home is in a more rural location, the nearest CO you can connect to over the Internet might be in another city, which might mean that you cannot keep your existing phone number. Your friends and family might also need to pay a long-distance charge to reach your new number in the other city. These are just a couple of caveats to watch out for when subscribing to one of these residential VoIP services.
Another critical consideration when signing up for VoIP in your home is 911 emergency service. Please check with your VoIP carrier for the specifics of how its 911 service functions. You might, for example, need to activate 911 service for your line, and you might need to specify the physical location associated with your VoIP phone. Not all residential VoIP services offer Enhanced 911 (E-911), which can automatically send the caller's location to the 911 operator. Therefore, a caller might need to clearly state his location to the 911 operator. Because 911 service can literally mean life or death, and because 911 services with VoIP carriers vary, be sure you understand the specifics of how 911 services are provided by any VoIP carrier that you consider signing up with. Also, if communication between your home phone and the PSTN flows through a VoIP router, consider what would happen if you experienced a power outage. Without some sort of power backup, you would not be able to place any calls, because your VoIP router (and any other broadband router/switch equipment) would be unpowered.