It all starts with a phone service provider. Examples of a phone service providers include Verizon, AT&T and TimeWarner/Spectrum. Once a contract is signed the chosen phone service provider will delivery the service to a demarcation point. The demarcation point is the location on a property to where a phone service provider is responsible delivery of service. Examples: telephone box on the side of a building, telephone rooms and server rooms. There are three types of phone service; Analog, Digital and IP.
Analog Phone Lines – These are the oldest form of telephone line and are still in use. Now day these lines are not pure analog line because they transmitted/delivery not as analog but are only analog at the customers location (DEMARC). The reason for using analog today is simple…most phones and older phone systems are made to work with analog lines.
Digital Phone Lines – Surprise…digital lines are digitized. This means that voice calls are converted to 1’s and 0’s which shrinks the amount of “space” needed to transport a conversation. This allows phone service provides to use existing telephone infrastructure while increasing the number of lines it can handle. These type of lines do require interface devices to connect the provider with the phone system. Examples include: Prime Rate Interface (PRI) and T1s.
IP Phone Lines – Internet Protocol phone line are lines that are transmitted through the internet. Voice calls are broken down into IP packets and then sent back and forth across the world wide web. Then these packet reach their location (caller or receiver) they are reassemble back into voice calls. Some packets can be lost or delayed, this is what causes poor call quality at some sites. Phone systems that are capaible in using IP phone lines have a network interface card (NIC). Example Include: SIP Trunks and IP Gateways.