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Over the next week on Network Performance Daily, we’ll excerpt sections of the new NetQoS VoIP ebook entitled VoIP: Do You See What I’m Saying. Today, we take a look at the hardware needed to equip your VoIP infrastructure. Obviously, VoIP systems don’t just require some server configuration and special software. Quite frankly, you can’t plug an RJ-10 phone line into an RJ-45 ethernet port and say you’ve got VoIP.
(We all know someone who might actually do that. If you’re lucky, he or she is not in your IT department…)
So, what is some of the VoIP hardware you need?
First, in terms of sheer numbers, IP phones will make up the largest group of new devices on your network. These IP phones connect to the network via Ethernet and many of them get power-over-Ethernet (POE) from LAN switches that support it. Each of these phones runs an embedded operating system with a TCP/IP stack for communications, which means each phone needs its own IP, and software called a codec to convert a voice conversation to IP packets.
Depending on how fancy your phone is, many of these phones can also run applications. Additionally, there are also “soft” phones – basically headsets that connect to the computer and an application which runs on it.
Both hard and soft IP phones register with a call server that provides the call setup functionality needed to make a phone call.
A call server is the “core” of the VoIP system. Its primary function is to provide call processing, communicating with IP phones, voice gateways, application servers, (and silently plotting the overthrow of Man to usher in a new age of perfect, robotic utopia. Or maybe that’s just ours here in-house.)
Anyway, dreams of robo-geddon aside, sometimes called an IP PBX, the call server provides the telephony features similar to a traditional PBX – features like hold and resume, or transfer. IP phones register with the call server and communicate it during the call setup phase of the phone call.
These phone servers also run their own operating system – sometimes an embedded one, though Windows and Unix variants are also common. It is through this OS that it manages the configuration for the dial-plan of the enterprise.
Often, these call servers are clustered together for fault tolerance and load balancing.
All the major VoIP vendors have different classes of call servers for different sizes of work environments – Cisco CallManager, for example, is designed for the needs of large enterprises.
Of course, there comes a point where you have to go off-network and connect your VoIP line with one a more traditional telephone. That’s where Voice Gateways come in.
The primary function of the Voice Gateway is to connect the IP network and the PSTN. They must be able to communicate using many different protocols to route phone calls.
Gateways provide many different connection types to the PSTN, including analog and digital Primary Rate Interfaces (PRI). A single voice gateway can support multiple T1 PRI connections, and each T1 PRI connection can provide 23 voice channels.
They can also provide translation between the PSTN and the IP network if translation between the PSTN, which outputs in the Pulse Code Modulation (or G.711 codec.) G.711 is also used on VoIP networks as well – but not exclusively, and when the codec needs to be change, it is the Voice Gateway that performs the transcoding.
Next post, we’ll start looking at some of the protocols used in the call setup portion of a VoIP call.
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More Information:
- Get a sneak preview of the Free VoIP eBook
Webinar
- VoIP Monitoring Webinar
NetQoS VoIP Solutions
- Converged VoIP and Data Networks
- NetQoS VoIP Monitor
