Differences Between IEEE 802.1AS-2011 and IEEE 1588-2008

IEEE 802.1AS-2011, also known as the generalized precision time protocol (gPTP), is a profile of IEEE 1588. A sbRIO-96xx controller can be configured to use either the IEEE 802.1AS-2011 profile or the IEEE 1588-2008 profile by configuring the port’s time reference. If a user does not explicitly specify which time reference to use a sbRIO-96xx controller will default to use the IEEE 802.1AS-2011 profile. There are some differences between the IEEE 802.1AS-2011 profile and the IEEE 1588-2008 profile which are called out below:

  • IEEE 802.1AS-2011 assumes all communication between devices is done on the OSI layer 2, while IEEE 1588-2008 can support various layer 2 and layer 3-4 communication methods. The IEEE 1588-2008 profile National Instruments implements on the sbRIO-96xx only supports layer 3-4 communication methods. Operating on the layer 2 yields better performance for the IEEE 802.1AS-2011.

  • IEEE 802.1AS-2011 only communicates gPTP information directly with other IEEE 802.1AS devices within a system. Therefore, there must be IEEE 802.1AS-2011 support along the entire path from one IEEE 802.1AS-2011 device to another. With IEEE 1588-2008, it is possible to use non-IEEE 1588-2008 switches between two IEEE 1588-2008 devices. The benefit of having IEEE 802.1AS-2011 support along the entire path is a faster performance and lower jitter compared to IEEE 1588-2008.

  • With IEEE 802.1AS-2011 there are only two types of time-aware systems: time-aware end stations and time-aware bridges. Whereas with IEEE 1588-2008, there are the following: ordinary clock, boundary clock, end-to-end transparent clock and a time-aware bridges. Based on these factors, IEEE 802.1AS-2011 can reduce complexity and configuration challenges compared to IEEE 1588-2008. A sbRIO-96xx controller acts as a time-aware end station for both protocols.