fundamentals series standards -...

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Fundamentals SeriesStandards

© Polycom, Inc. All rights reserved. 2

Fundamentals Series

Signals

Analog vs. Digital

Defining Quality

Standards

H.323

SIP

Network

Communication I

Network

Communication II

Welcome to Standards, the fourth module in the Polycom Fundamentals series. This module is approximately 8 minutes long.


Introduction

In order to understand how videoconferencing works it’s important to understand the underlying technologies at work behind the scenes. In this short module we will talk about standards, what they are and how we use them.


Standards

When we talk about videoconferencing, we often discuss the standards that systems support and describe endpoints and infrastructure as being standards-based. So what are standards and what are they good for? Standards are agreed upon processes and configurations that allow different manufacturers’ systems to talk to each other. And how does it become a standard?

If we talk about a company developing their own software which is not compatible with anyone else’s, we call it proprietary. This is the most common way of a feature appearing in software, and logically so, as if I want to see a 22kHz audio codec and if no-one else has done it, I will need to do it. But then what? I don’t want to be the only person who can use it, after all. What happens next is that once I have written my feature and am ready and willing to share it, I submit it to the body which holds all the standards for that technology (we’ll come to this next). They will review it, and if they confirm that it will do what I say it will and work in the way I say it can, it can be ratified (approved) and given a name which follows their convention. Once that happens, it becomes a standard, and the code becomes available for use.

That is, of course, a very simplified version, but you get the idea.


Standards Bodies

There are two primary organizations that we’re concerned with when discussing standards.

The International Telecommunications Union (ITU) develops standards for the telecommunications industry. They created the first standards for use in videoconferencing when it was only really available over ISDN.

More recently, the Internet Engineering Task Force (IETF) has become important because it is responsible for standards relating to the internet and networks.


Umbrella Standards

Umbrella standards are standards which have other standards under them.

The ITU is responsible for the H.320 umbrella standard that governs ISDN videoconferencing and the H.323 umbrella standard that is used for IP-based networks.

The IETF has created the SIP protocol for multimedia, that is video, audio and data devices for only IP-based networks. SIP is not an umbrella standard, and we’ll talk about that further a little later on.

You can think of these three standards as the languages that a videoconferencing device can speak.


H.320

ISDN

Let’s start off with the H.320 standard. This is the ITU standard developed for multimedia transmission across ISDN networks.

It includes within it several other standards that have to do with how the call connection works, how the video and audio are handled as well as how the data is bundled up and sent across the network. Each of these areas is included under the umbrella standard H.320.

We will not look specifically at the mechanics of ISDN videoconferencing further in this training series.


H.323

IP Network

Let’s look now at the standards for IP networks. H.323 is the ITU standard developed for multimedia transmission across IP networks.

It also includes within it several other standards that have to do with how the call connection works, how the video and audio are handled as well as how the data is bundled up and sent across the network. Each of these areas is included under the umbrella standard H.323.

We will take a look now at some of the most commonly used video and audio codecs. These are all supported under both H.320 and H.323 standards.


Video codecs

Under the H.320 umbrella come three video codecs we commonly see which were mentioned briefly in the last module – H.261, H.263 and H.264. We will look at these again in a little more detail here.


H.261

H.261 recommends picture refresh rates at 7.5, 10, 15, or 30 frames per second. The minimum recommended for full motion video is 24 fps, which is what motion pictures use. Below that and the motion starts to look choppy.

Supported resolutions are CIF and QCIF (which has a quarter of the resolution of CIF).


H.263

H.263 and H.264 keep the recommendations from H.261 of 7.5, 10, 15 and 30 frames per second. But it also adds recommendations to allow lower frame rates for certain uses, like graphics when showing content. So we can also do 1, 2, 3, 4 or 5 frames per second for those images. This gives a wider flexibility to have the most efficient bandwidth usage for each call, especially when combined with the added resolutions in these codecs.

H.263 can support all the resolutions H.261 supports, with the addition of 4CIF.


H.264

H.264 is a newer codec which supports many resolutions up to and including 1920 x 1080 (HD 1080) at 30fps.


Audio Codecs

When comparing audio codecs, important factors are the frequency in Hertz which gives us the range of frequencies captured from the analog waveform, and the bandwidth in bits per second which tells us how many bits per sample are needed to transmit the signal.

So in the audio corner we have G.711, the first digital audio codec. G.711 captures 4kHz of the frequency range with no compression, using 64kbps. It is the base standard an endpoint must have to be compliant with the ITU.

Following this, more advanced codecs have been added over time. For example, G.722 captures 7kHz using 64kbps, G.728 compresses a 4kHz frequency at a much smaller 16kbps, G.729 takes that down even further to only 8kbps, and there are many more. Improvements have also been made to existing codecs. For example, G.722.1 gives a 7kHz bandwidth but uses 24 or 32 kbps. Later on, this was developed further; G.722.1C gives us 14kHz audio with 24, 32 or 48kbps.

Just like video codecs, these come under the H.320 umbrella but are commonly used in IP-based conferencing also.


SIP

IP Network

Now let’s move onto SIP. SIP stands for Session Initiation Protocol, and is the more recent IETF signaling protocol for making voice and video transmissions across IP networks.

SIP was designed to work with other protocols already in existence, like many of the IETF protocols. Because of this it can interact with other IP standards to perform tasks, which is part of why it doesn’t have to be an umbrella standard to control the process of video and audio sessions on the network.

The two modules following this one will take a more in-depth look at both H.323 and SIP to explain these two commonly used standards further.

fundamentals series standards -...

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