To Eye for IP Telephony

VoIP also makes possible other services that older telephony systems can’t provide. VoIP telephony services are interoperable, meaning that they work well over all kinds of networks. They are also highly portable, which means they will work with any IP-enabled device such as an IP telephone, a computer,
or even a personal digital assistant (PDA). IP telephony works by taking traditional voice signals and converting them to a form that can be easily transmitted over a local area network. Thus, the heart of IP telephony is the same as traditional data networking with computers. IP-enabled phones handle the voice-to-data conversion well, but don’t be misled — implementing VoIP doesn’t mean that everyone has to use IP-enabled phones. The best VoIP providers implement IP telephony in a manner that protects your investment in existing telephone equipment, even if you have analog telephone stations. (You’ll find more on this topic in Chapter 10.) All IP phones have one important thing in common: a built-in network interface
card (NIC), just like a computer uses. The NIC is critical for any network device because it provides the device with a physical address and a way to communicate over the network. The physical address supplied by a NIC is called a MAC address. MAC stands for media access control. The MAC address uses a standardized address and is usually represented by six hexadecimal numbers separated by dashes. For example, the following is a valid MAC address: 00-0A-E4-02-7B-99. To support IP telephony, a server is typically dedicated to run the software used to manage calls. Servers are just like personal computers, except they have more memory, speed, and capacity. The server stores the database that contains all the MAC addresses corresponding to all the IP telephone extensions assigned to users. Depending on the size of the LAN and the number of users, you may use more than one server. For example, some LANs running IP
telephony dedicate a server just for handling voice mail. Depending on the size of the LAN, one or more devices known as switches are installed. These switches are boxes that have a series of ports into which
all LAN-addressable devices ultimately connect. (Examples of LAN-addressable devices include computers, printers, wireless access devices, gateways, and storage devices.) Usually the switches are set up in the communications closets around the LAN, and they operate 24/7. All the switches are interconnected, often with fiber-optic cable. In a nutshell, all network devices, including your IP telephone, must physically
connect to the LAN through a port on a switch.