Michael Johas Teener

Heterogeneous Networks for Audio and Video: Using IEEE 802.1 Audio Video Bridging

The IEEE 802.1 Audio/Video Bridging Task Group has created a series of IEEE standards that specify methods used to provide the appropriate quality of service (QoS) for audio/video (A/V) streams in a heterogeneous network. This paper describes the requirements for such a network and summarizes the methods described in these standards and how they are used in some example higher layer protocols.

New simulation and test results for IEEE 802.1AS timing performance

IEEE 802.1AS is a standard being developed in the 802.1 Working Group to provide precise timing and synchronization for bridged networks. It is one of the 802.1 Audio/Video Bridging (AVB) standards, and a major use of it will be to ensure that jitter, wander, and time synchronization requirements for time-sensitive applications in a residential AVB network are met. However, 802.1AS (and the other AVB standards) can be used in other applications as well. Each application will be specified by an ‘AVB profile’, and each profile will provide for very few options to simplify the configuration and operation by the user and result in low cost. IEEE 802.1AS includes an IEEE 802-specific layer-2 profile of IEEE Std. 1588TM - 2008; plus additional specifications to allow transport over 802.11 (WiFi), Ethernet PONs, and coordinated shared networks such as MoCA; plus additional requirements needed to ensure timing performance. IEEE 802.1AS is nearing completion, and is expected to be balloted by 4Q2009. This paper gives a brief overview of IEEE 802.1AS, focusing on recent developments. It then describes new simulation modeling and results for jitter, wander, and synchronization performance. Finally, it describes performance test results using 802.1AS bridges and end-stations.

Using an IEEE 802.1AS network as a distributed IEEE 1588 boundary, ordinary, or transparent clock

IEEE 802.1AS includes a very specific profile of IEEE 1588 that only runs at layer 2 over networks that follow the IEEE 802 architecture. It has some significant performance and scalability advantages, but at the cost of not allowing non-PTP-aware devices. This paper describes how a network having a common source of time can act as a distributed IEEE 1588 boundary, ordinary, or transparent clock, allowing the network to transport synchronization between portions of an IEEE 1588 network domain, and do this for any number of domains simultaneously. The network that acts as a distributed clock can be a PTP network supporting a profile that is different from that of the domains whose timing it is transporting. As one example, an IEEE 802.1AS network can act as a distributed IEEE 1588 boundary, ordinary, or transparent clock. As part of the discussion, the paper also shows that an IEEE 1588 boundary clock and peer-to-peer transparent clock are functionally equivalent in the manner in which they transport synchronization, and that the principal difference between the two is that the former invokes a best master clock algorithm (either default or alternate) and implements the full PTP state machine, while the latter does not. The concepts of distributed BC, TC, and OC, and the equivalence of the BC and peer-to-peer TC may be considered a new way of looking at the transport of synchronization in a network based on IEEE 1588.