40
xI.
about sIP
NOTE: This section is taken directly from our VoIP Primer. You can view and download the primer at www.comrex.com.
Introduction
At Comrex, it’s our job to keep ahead of new and intriguing technologies that we can leverage for our customer, the
broadcaster. But it’s important that as we ride the wave of new tech, we don’t forget about the people in our industry who
have “stuff to get done”, and can’t afford to spend hours reading about all the newest developments.
We’ve found this to be the case in recent years with the introduction of ISDN, POTS codecs, and IP audio codecs. In each
case, we decided to put together a “primer” for those who wished to gain the knowledge needed to use these tools effectively,
but were short on time. The goal was to put together all the vital information in a booklet that could be consumed in under
an hour. The feedback we’ve received has proven these efforts to be worthwhile.
A new disruptive technology is taking hold, and it’s now time to cut another primer. Due to cost and necessity, broadcasters
are finding they need to learn about Voice over IP (VoIP), and they need to learn fast.
This booklet provides some basics about VoIP in an easily digestible form.
VoIP provides a way for computer networks and other devices to emulate traditional phones and phone lines. Most modern
business PBX systems have migrated to VoIP already. In some circumstances, legacy phone lines (PSTN or POTS) are no
longer available and VoIP is the only choice.
Like a traditional line, a VoIP link consists of a service provider and an end user who owns a telephone instrument. But in this
case, the provider is based in the “cloud”. Alternately, the VoIP lines can be delivered from an upstream PBX. The end-user
gear is a specialized VoIP telephone, or software running on a PC or mobile device that performs the same functions.
The Comrex STAC VIP is a sample of a device designed to interface with VoIP service. It can handle six or twelve calls
simultaneously and provide the typical screening, audio processing, and control functions expected of broadcast call-in
systems. For users with less call volume, the VH2 Hybrid is a dual-channel VoIP-to-studio interface. In addition, all Comrex IP
codecs like ACCESS and BRIC-Link can communicate over standard VoIP protocols.
IP Concepts you need to know
If you’re already an expert on IP networking concepts in general, feel free to skip to the next section about RTP. But here are
a few basic concepts you’ll need to master to continue learning. This is much less than a complete overview of IP networking-
-only concepts directly relevant to VoIP are covered.
IP basics
IP is short for Internet Protocol, but it doesn’t always pertain to the Internet (as in, the public version). In a nutshell, IP
networking involves creating packets of data, attaching certain headers to specify contents and assign addresses, and
applying them in sequence to some kind of network capable of transmitting them. Physically, the network is usually Ethernet,
although it may be Wi-Fi, 3G, satellite, or lots of other mediums.
Addressing
Devices connected to an IP network are dealt an “IP Address”. Under the IPv4 protocol (the most widely implemented),
this address consists of a 32-bit numeric value. Putting on your “binary thinking cap”, this can also be thought of as four
8-bit bytes. A byte can have a value from 0-255, so IP addresses are usually written as a sequence of four decimal numbers
(separated by dots) like 192.168.0.23 with each integer having an upper limit of 255.
Summary of Contents for VH2
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