An IP phone is a phone that works on a data network instead of traditional telecommunication networks. It is designed as a network device, running on top of the TCP/IP protocol suite, where speech is digitized and encapsulated in a series of Internet Protocol (IP) packets for transmission over copper or copper transmission lines. fiber. An IP phone is more traditionally known as a VoIP (Voice over Internet Protocol) phone because it uses technology that falls under the general heading of VoIP.
VoIP phone calls can be made over the Internet or private IP networks run by companies and organizations. Like traditional telephony, VoIP needs to use signaling and control protocols for call setup, control, and release. SIP (Session Control Protocol) is the most popular control protocol in use today, and most commercial IP phones support SIP. On the Internet, Skype is the most popular voice over IP system, but it is proprietary and does not support industry standard protocols.
Voice over IP technologies also support multimedia in addition to voice, and there are many video applications that are compatible with VoIP.
In order for the IP phone to work on a digital network, the analog voice input through the microphone must be digitized so that it can be packaged and ready for transmission on the IP network. There are many variations of the digitization process and are generally found under the codec (encoder/decoder) heading. A codec also used in digital telephone networks is the ITU-T G.711 codec, which digitizes analog speech through a sampling and quantization process. The first part of the process is PCM (Pulse Code Modulation), where analog speech is sampled at a constant rate of 8 khz to produce 8-bit binary words that represent the original analog speech. It should be noted that when the binary data is converted back to an analog form at the receiver, there is a drop in quality due to what we call quantization error. Other popular codecs include G.729, G.726, and G.723, and many IP phones support multiple codecs.
Traditional telephones can be used in VoIP systems as long as an intermediate device is used to provide conversion and connection to the data network. These devices come under the heading of Analog Telephone Adapters or ATA.
VoIP phones can communicate directly with each other over a data network, but they are often used with an IP PBX, which is a hardware or software device that emulates the operation of a traditional PABX used in the Internet industry. telecommunications. The IP PBX will provide functionalities such as registration services for phones, proxy services, and add-on services such as call forwarding, call forwarding, ring groups, and voice mail. In fact, an IP PBX should be able to provide all the services that traditional PABXs currently provide.
Like any other IP network device, such as a PC or server, an IP phone needs some basic configuration settings, such as a valid IP address, netmask, and MAC address. Phones can be manually configured with IP addresses or given IP addresses from a DHCP (Dynamic Host Configuration Protocol) server like most network devices on our IP networks today.
VoIP phones need a power source, just like any other network device, and in recent years technology has been developed to supply these phones with DC power directly from the network connection to the local switch. Power is transmitted through Ethernet patch cables using the previously unused copper pairs within the cable. A standard known as IEEE 802.3af was released in 2003 and can provide up to 15.4 watts of DC power to each device directly from the switch port. The standard was updated in 2009 as IEEE 802.3at to provide up to 25.5 watts of power per device.
IP phones have to compete with other network protocols in our packet-based data networks, but because they transmit real-time information in the form of voice, they must be given some kind of special handling or prioritization in the network. Methods of giving priority to some network protocols over others are known as QoS (Quality of Service). In other words, we must minimize the amount of network delay for IP packets containing digitized speech. Too much delay through the network will result in a two-way conversation that is difficult to handle, such as talking on a satellite phone where the delay to and from the satellite makes conversation difficult unless users are disciplined and understand the issues. Variable delay, often referred to as packet switching delay, is where the delay between individual packets varies based on network conditions. This type of delay usually comes under the heading of jitter, and there are a number of techniques that can be employed to alleviate the effects of jitter.
There are many manufacturers of IP phones, and if you’re buying a VoIP phone, you need to make sure it’s compatible with the standards supported elsewhere in your network, such as the correct codecs, inline feed standard, and of course, features. what do you need.