Though it has bounced around for over a decade, Voice over Internet Protocol (VoIP) has only recently seen a surge in activity, with clear movement toward widespread adoption. Slowly but surely, companies and individuals are replacing their standard plain-old telephone service (POTS) on the public switched telephone network (PSTN) with VoIP on the Internet.
Why on earth would we give up one of the best, most highly developed, and ultrareliable electronic systems ever built? Simply because we can. A more practical answer, though, is the array of benefits it offers— lower monthly telephone bills, the long-term reduced cost of maintaining both voice and data networks, and the ability to adopt a variety of converged services including video.
Gradually, companies are replacing their legacy phone systems and private branch exchanges (PBXs) with VoIP systems. Many consumers are buying phone service from cable TV companies and independents, such as AT&T and Vonage. Phone companies like Verizon (and SBC via its acquisition of AT&T) additionally are beginning to offer VoIP to their DSL customers. They won't be tearing down the PSTN any time soon, if ever. But as they lose revenue from their PSTN business, they're replacing it with VoIP services and eventually television.
Ann Powell, a consumer from San Antonio, Texas, switched her SBC standard phone service for Time Warner Cable's Internet phone service. She said the initial experience was rocky until the bugs were worked out, but now it works great. However, she didn't expect to lose phone service during a power outage.
The PSTN is totally self-powered, so customers have phone service even during the longest of power outages. But when the cable box and the analog terminal adapter (ATA) lose power, consumers can't use their VoIP phones. Also, there's no 911 service yet.
"I guess that is what cell phones are for," says Powell. Otherwise, she is happy with the service because it really has cut down her overall phone bill, including long distance.
The 911 issue is still being resolved. The FCC has required all VoIP carriers to provide a link to the local 911 service or cut off service to the subscribers. While most providers have complied, a few have yet to meet the requirement. Some companies have applied for an extension, which the FCC recently granted.
Jeanne Gibson, a telecom guru with Apache Oil Corp. in Houston, said her company just went through a major switch from standard phone service to a full IP-based system from Cisco. The switch at corporate headquarters went well, and the conversion at the various field offices is proceeding nicely. Long-distance service alone will save Apache costs in the mid-six figures annually, which is more than enough to pay for the switch.
Yet Gibson's main concern as a telecom person and not an IT person is to ensure that the IT people eventually get a voice service mindset, which currently isn't offered. The Holy Grail in any company is dial tone, not e-mail. While individuals will occasionally endure a short network outage, rarely will they sit still for a phone service failure. Quality of service (QoS) seems to be the first priority for IT departments that switch over.
HOW IT WORKS
All sorts of complicated operations take place during an Internet phone call, making POTS look as complex as a flashlight. Lots of different protocols are used. During the "dialing," the caller enters the phone number. This initiates a "connection," but it won't be a continuous connection like a POTS call. Instead, a packet protocol is used to establish an initial link.
Protocol H.323 from the International Telecommunications Union (ITU) is used to set up the call and maintain transmission. It doesn't guarantee QoS. However, H.323 is now giving way to a newer protocol called the Session Initiation Protocol (SIP). This Internet Engineering Task Force (IETF) protocol includes the individual protocols called Request for Comments (RFC), specifically RFC 3261, RFC 3262, and RFC 2543. The Media Gateway Control Protocol (MGCP) is another IETF standard, dubbed RFC 2805. The Media Gateway Control (Megaco) ITEF RFC 3015 also is defined by the ITU as H.248.
Next, an analog-to-digital converter samples the voice signal and converts it to serial digital format. The usual sample rate is 8 kHz, creating 8-bit voice words. This process creates a 64-kbit/s serial data rate signal, just as in other digital telephony. This is too fast for some connections, so a voice encoder is used to compress the digital data and reduce the serial data rate.
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