Video Basics

IP packet video can be categorized into two main categories:

• Interactive video—Includes H.323-compliant video conferencing systems, such as Cisco's IP/VC 3500 series of products, and Microsoft's NetMeeting desktop videoconferencing product. H.323-compliant video-conferencing tools use the familiar RTP protocol for transmission of the voice and audio payload, typically sending the audio in a separate RTP stream than the video.

• Noninteractive video—Includes typical e-learning video services and streaming media, and includes products such as Cisco's IP/TV, Microsoft Windows Media Technologies products, and RealNetworks products. Some noninteractive video uses H.323 standards for video call setup and teardown, and some do not—for instance, RealNetworks most recent servers use Real-Time Streaming Protocol (RTSP) for call setup/teardown, and either the proprietary RealNetworks Data Transport (RDT) or RTP for video payload, depending on the video player used.

Like voice, video codecs convert the analog audio and video to packetized form. Codec delay, packetization delay, and de-jitter initial playout delay are all included in video delay, just like with voice. Familiar voice codecs, including G.711 and G.729, convert the audio stream, which is typically sent as a separate flow from the video signal. The video signals use a large variety of codecs, including ITU H.261, and the popular Moving Pictures Experts Group (MPEG) codecs. Figure 1-28 depicts a typical video conference between two H.323-compliant videoconference systems.

Figure 1-28 H.323 Video Conference

Server 1

Figure 1-28 H.323 Video Conference

Server 1

Before the video conference can be begin, several things must happen:

• A user must point/click the correct application settings to ask for a conference, typically something as simple as telling the H.323 application that you want a conference with a particular host name.

• The VC units must perform the H.323/H.225 call setup messages.

• Two RTP streams must be established—one for audio, and one for video.

So far, the similarities between voice and video outstrip the differences. The biggest difference is the bandwidth required for video. (Bandwidth requirements are covered in the upcoming section "Video Bandwidth Considerations.") Table 1-20 summarizes the type of QoS characteristics that video requires, as well as voice.

Table 1-20 Comparing Voice and Video QoS Requirements

Bandwidth

Delay

Jitter

Loss

Voice Payload

Low

Low

Low

Low

Video Payload

High

Low

Low

Low

Voice Signaling

Low

Low

Medium

Medium

Video Signaling

Low

Low

Medium

Medium

Just like with voice, most QoS effort goes toward giving the video payload flows the QoS characteristics it needs. However, you might still want to treat video signaling traffic differently than other data traffic, and treat the video payload traffic differently. To classify, the QoS tool needs to be able to refer to a field in the packet that signifies that the packet is video payload, video signaling, or some other type of packet. Table 1-21 lists the various protocols used for signaling and for voice payload, defining documents, and identifying information.

Table 1-21 Video Signaling and Payload Protocols

Protocol

Documented By

Useful Classification Fields

H.323/H.225

ITU

Uses TCP port 1720

H.323/H.245

ITU

TCP ports 11 xxx

H.323/H.225 RAS

ITU

TCP port 1719

RTSP

IETF RFC 2326

TCP or UDP port 554

Real-Time Transport Protocol (RTP)

RFC 1889

UDP ports 16384-32767, even ports only

The next few sections of this book examine video more closely in relation to the four QoS characteristics:

Advance SEO Techniques

Advance SEO Techniques

Turbocharge Your Traffic And Profits On Auto-Pilot. Would you like to watch visitors flood into your websites by the 1,000s, without expensive advertising or promotions? The fact is, there ARE people with websites doing exactly that right now. How is that possible, you ask? The answer is Advanced SEO Techniques.

Get My Free Ebook


Post a comment