IEEE 1722.1-2013 pdf download IEEE Standard for Device Discovery, Connection Management, and Control Protocol for IEEE 1 722™ Based Devices
5.4.2 Multiple Controllers
There may be multiple AVDECC Controllers on a single LAN at the same time. These Controllers maydiscover and interact with any AVDECC entities on the network.
When an AVDECC Controller needs exclusive control of an AVDECC Entity for changing or limitingchanging the state of the AVDECC Entity, the AVDECC Controller uses the ACOUIRE ENTITY orLOCK ENTITY AVDECC Entity Model (AEM) AECP commands. While an AVDECC Entity has beenacquired with the ACOUIRE ENTITY command or locked with the LOCK ENTITY command, anotherAVDECC Controller is not allowed to perform any modifications to the AVDECC Entity, however it mayread values or descriptors from the AVDECC Entity Model. Typically, an AVDECC Controller would onlyuse the LOCK ENTITY command on another AVDECC Entity for the time needed to complete a singleatomic operation, whereas it would use the ACOUIRE ENTITY command on the AVDECC Entity forlong-term exclusive control of the AVDECC Entity.
5.4.3 Controller behavior
5.4.3.1 How to handle gPTP Domain and SRP Domain changes
When the AVDECC Controller itself is participating in an AVB domain and is actively filtering entitiesthat are in that AVB domain, and the generalized precision time protocol (gPTP, IEEE Std 802.1AS-2011)grandmaster of that AVB domain changes, then the AVDECC Controller needs to make a decision on whatEntities are still in the same AVB domain as the AVDECC Controller since the grandmaster change mayhave been triggered by a network topology change that resulted in one or more Entities being removedfrom the AVB domain
This decision seems trivial on the surface, since it applies the same check used to initially determine if theAVDECC Entity was in the same AVB domain, which is to look at the grandmaster ID in the discoveryprocess. However, it is not as simple as that, since it takes tie for the discovery process to propagate the grandmaster change. The AVDECC Controller shall therefore wait a period of time after it has finished running its gPTP Best Master Clock Algorithm before deciding that an AVDECC Entity is no longer in its gPTP domain. It is recommended that the delay be a minimum of 2 seconds, although this can still cause an AVDECC Entity to be falsely removed if it has a large time between announces and the first announce frame after the grandmaster changeover is lost.