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IEEE 1722a

An Axon application note

IEEE 12722a transport protocol for AVB networks

Introduction IEEE 1722a is the transport protocol used for AVB networks. This draft proposes additions to support broadcast use. First addition - The encapsulation of SDI in Ethernet packets. This transport format is introduced to easily convert from coaxial SDI to Ethernet and back. Second addition - The encapsulation of raw video data. Audio, video and data are transported as separate Ethernet packetized streams.


IEEE 1722A FOR AVB NETWORKS

SDI Video Format (SVF) The focus of the SDI transport format is to cover most common SDI standards used in broadcast and leave flexibility to add remaining, or new, standards. Some benefits of SVF over other standards: JJ

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the End of Active Video (EAV) flag. This enables recovery of the next line following an error, although an error is very unlikely. JJ

SVF packet length depends on the video format transmitted. A standard definition (SD) 625 packet has a packet length of 1080 bytes. All packets are of equal size for the given video format. A 1080P60 packet has a length of 1375 bytes and, again, is an equal length for all packets. In figure 1, the conversion from a SDI video frame to Ethernet packets is shown.

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Each packet contains the line number and sequence number within the line to locate the packet in a frame. Each packet at a start of a line contains a timestamp. This makes timing recovery very easy since the difference in the timestamp between two lines is the line timing. This can easily be used to recover the line frequency. Markers inside the header define the safe switching periods.

Each new line starts with a new packet. Therefore, the first bytes in the first packet of a line, always contains

Line 1

Packet 1

Packet 2

Packet 3

Packet 4

Line 2

Packet 5

Packet 6

Packet 7

Packet 8

Line 3

Packet 9

Packet 10

Packet 11

Packet 12

Line 4

Packet 13

Packet 14

Packet 15

Packet 16

Ancillary Data

Packet n-3

Last line Horizontal Sync Point (EAV)

Active Video (Image Data)

Packet n-2

Packet n-1

Packet n

Figure 1: 1080p60 video frame with Ethernet packet distribution overlay

The last Ethernet packet of a video frame contains a Start of Frame (SOF) indicator in the header to signal that the next packet received belongs to a new video. The table to the right displays SVF Ethernet packet payload size for common video formats.

Format

Packets per line

Packet payload size (bytes)

525i/59.94

2

1073

625i/50

2

1080

1080i/59.94

4

1375

1080i/50

5

1320

720p/59.94

3

1375

720p/50

4

1238

1080p/23.98

5

1375

1080p/59.94

4

1375

1080p/50

5

1320

This application note is based on the IEEE 1722a Draft 7 and is subject to changes


IEEE 1722A FOR AVB NETWORKS

RAW Video Format (RVF) The SVF format, as described in the first chapter, has its limitations with respect to Ethernet flexibility, and scalability. Therefore is recommended to use separate audio, video and data streams on a single link. For this reason RVF is to be added to the IEEE1722 standard. Audio and Data is transmitted by using other ieee1722 formats. However, this is out of scope of this whitepaper. The RVF formats transports only the active area of a video raster. Although there is some flexibility to add several vertical blanking lines, the primary objective is the active picture area only. Horizontal blanking cannot be packetized using RVF. Some benefits of the RVF standard are listed below: JJ

900 bytes. All packets are equal in size for the given video raster. A 1920 x 1080 raster has a packet length of 1200 bytes and, again, is equal for all packets. In figure 2, the conversion from a raster to Ethernet packets is visualized. JJ

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Bandwidth saving, depend on the video format, is between 15% and 25%. The first packet of each raster line starts with the first active pixel of that line. Start of Active Video (SAV) indicator from SDI is not included.

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Line clock recovery is identical to SVF.

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Support for broadcast and computer graphic formats.

RVF packet length depends on the video raster transmitted A 720 x 480 raster has a packet length of

Active line 42

Packet 1

Packet 2

Packet 3

Active line 43

Packet 4

Packet 5

Packet 6

Active line 44

Packet 7

Packet 8

Packet 9

Active Video (Image Data)

Ancillary Data

Packet n-2

Last active line

Packet n-1

Packet n

Figure 1: 1080p60 video frame with Ethernet packet distribution overlay

The last Ethernet packet of a video frame contains a Start of Frame (SOF) indicator in the header to signal that the next packet received belongs to a new video. The table below displays RVF Ethernet packet payload size for common video formats.

Format

Sample words per pixel

bits per sample word

Packet per line Packet payload size (bytes)

720

2

10

2

900

1280

2

10

3

1067

1920

2

10

4

1200

3840

2

10

7

1372

This application note is based on the IEEE 1722a Draft 7 and is subject to changes


AN2014-16 IEEE 1722a for AVB networks.pdf