SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
AVBTP or 1722 sits above the IEEE 802.1 AVB plumbing and below the application layer. It acts as the conduit between an Ethernet MAC and a streaming application. AVBTP abstracts the underlying network transmission channel to enable the virtual connection of distributed audio and video CODECs over reliable Ethernet networks. A complete AVBTP Ethernet packet is shown in Figure 24-195 and illustrates how IEC 61883-6 AM824 uncompressed audio samples are encapsulated in an Ethernet frame.
1722 or AVBTP Presentation Time and Synchronization:
Synchronization in an AVB network starts with the Precision Time Protocol but ends with synchronized media clocks. PTP is responsible for synchronizing all nodes in an AVB network to identical wall clock time; not for synchronizing media clocks. In other words, PTP does not actually transport synchronized media clocks but instead provides a low-level building block crucial for managing a distributed media synchronization system.
A crucial benefit of this approach is coexistence of multiple, independent media clock domains on an AVB network. Unrelated audio and video streams can simultaneously exist in the same LAN.
AVBTP assumes that AVB node media clocks are clocked by free-running oscillators. It is also assumed that the node's internal concept of wall clock time has been synchronized to the PTP Grandmaster. AVBTP media clock sources embed "AVBTP Presentation Timestamps" in AVBTP streaming packets. Figure 24-196 illustrates the relationship between PTP network time and AVBTP Presentation Timestamps.