Post on 13-Jun-2020
22 October 2008 IEEE 1722
Dave Olsen (dolsen@harman.com)
22 October 2008
Media Clock Distribution in a 1722
Network
22 October 2008 IEEE 1722
Capabilities
• Synchronize Media clock on multiple 1772 endpoints
• Allow multiple talkers to produce multiple 1722 streams that are all synchronized
• Listener can receive 1722 streams from multiple sources without making use of sample rate conversion
22 October 2008 IEEE 1722
Media clock sources
• Any active stream can be designated as the media clock source stream
• This stream could be a standard stream or a null stream that contains only clock information
• Since any stream can supply media clock, there is no need for a special stream type
22 October 2008 IEEE 1722
Talkers
• Talkers receive the designated stream and synchronize their media clock to the incoming stream
• Streams produced by the talker are then automatically syntonized with the designated stream
22 October 2008 IEEE 1722
Listeners
• Listeners receive the designated stream and synchronize their media clock
• Listeners utilize the presentation time of individual stream to time align the streams
22 October 2008 IEEE 1722
Outgoing Stream
A/D 1722 Data
AVBTP
Timestamp
Generator
7166667
00
00
0
0
0
0
9000000
0
0
0
0
0
0
00
8833333
0
0
0
0
0
0
0
0
8666667
0
0
0
0
0
0
0
0
...
00
00
0
0
0
0
7333333
00
00
0
0
0
0
1722 Stream
Timestamps Data
Media clock
(local oscillator)
Incoming Analog
Data
802.1AS
Wall Time
22 October 2008 IEEE 1722
Incoming Stream
D/A
AVBTP Timestamp
Comparator
7166667
00
00
0
0
0
0
9000000
0
0
0
0
0
0
0
0
8833333
0
0
0
0
00
0
0
8666667
0
0
0
0
00
00
...
0
0
0
00
0
00
7333333
0
0
0
00
0
0
0
1722 Stream
Timestamps Data
AVBTP timestamps
Generated media
clock
Outgoing Analog
Data
802.1AS
Wall Time
Clock Generator
22 October 2008 IEEE 1722
Outgoing Stream
A/D 1722 Data
AVBTP
Timestamp
Generator
6500000
0
0
0
00
0
0
0
4333333
0
0
0
0
00
00
4666667
0
0
0
0
00
00
4833333
0
0
0
0
00
00
...
0
0
0
00
0
00
6333333
0
0
0
00
0
0
0
Media clock stream
Timestamps Data
7166667
0
0
0
00
0
0
0
9000000
0
0
0
0
00
00
8833333
0
0
0
0
00
00
8666667
0
0
0
0
00
00
...
0
0
0
00
0
00
7333333
0
0
0
00
0
0
0
1722 Stream
Timestamps Data
AVBTP timestamps
Generated media
clock
Incoming Analog
Data
802.1AS
Wall Time
22 October 2008 IEEE 1722
Incoming Stream
D/A
AVBTP Timestamp
Comparator
6500000
0
0
0
0
0
0
0
0
4333333
0
0
0
0
0
0
0
0
4666667
0
0
0
0
0
0
0
0
4833333
0
0
0
0
0
0
0
0
...
0
0
0
0
0
0
0
0
6333333
0
0
0
0
0
0
0
0
Media Clock Stream
Timestamps Data
7166667
0
0
0
0
0
0
0
0
9000000
0
0
0
0
0
0
0
0
8833333
0
0
0
0
0
0
0
0
8666667
0
0
0
0
0
0
0
0
...
0
0
0
0
0
0
0
0
7333333
0
0
0
0
0
0
0
0
1722 Stream
Timestamps Data
AVBTP timestamps
Generated media
clock
Outgoing Analog
Data
802.1AS
Wall Time
22 October 2008 IEEE 1722
Sync Streams
• Locally administered Sync Streams– Allow completely user defined environment
– No wasted bandwidth on unused sync streams
– All equipment must be manageable– Interoperability between brands could be
problematic
22 October 2008 IEEE 1722
Sync Streams
• Globally defined Sync Streams– Reduce system setup
– Interoperability between brands improved – No need to assign sync streams for each
piece of equipment– Possible wasted bandwidth on unused
streams
– Who supplies the sync streams must be managed
22 October 2008 IEEE 1722
Sync Streams
• Global sync streams must be easily identifiable– Defined multicast address
– Defined Stream ID
22 October 2008 IEEE 1722
Sync Streams
• Sync streams need to be stable– A recurring election process may introduce
too much instability– Can we use MAAP to allocate designated
multicast addresses?
– First one to acquire the address supplies the designated sync stream forever
– Management interface need to reliably set the provider of sync streams
22 October 2008 IEEE 1722
Sync Streams
• Number of sync streams to be defined– Default Audio sync
• Set at the default rate for the network
– Standard set of audio syncs• 44.1, 48, 88.2, 96, ….
– Default Video sync• Set at the default rate for the network
– Standard set of video syncs• ????
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream
48khz AVB Stream
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream44.1khz Sync Stream
48khz AVB Stream
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream44.1khz Sync Stream
44.1khz AVB Stream48khz AVB Stream
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream44.1khz Sync Stream
44.1khz AVB Stream48khz AVB Stream
Video Sync Stream
22 October 2008 IEEE 1722
Sync Streams
48khz Sync Stream44.1khz Sync Stream
44.1khz AVB Stream48khz AVB Stream
Video AVB StreamVideo Sync Stream
22 October 2008 IEEE 1722
Proposal
• Reserved addresses/Stream IDs for a set of Sync Streams
• Network default audio/video sync streams– Allows a device to learn the defaults for the network
and sync to it if possible
• A set of designated rate audio/video sync streams– Allows for interoperability of multiple clock domains– A device that cannot sync to the default can still find a
compatible sync domain
22 October 2008 IEEE 1722
Proposal
• 64 reserved Multicast addresses from the MAAP range– xx:..:01 Default Audio Sync
– xx:..:02 Default Video Sync– xx:..:03 48khz Audio Sync
– xx:..:04 44.1khz Audio Sync– xx:..:05 ??? Video Sync
– etc.
22 October 2008 IEEE 1722