Aspects for Pre-emption resp. Time Aware Blocking Shaper (TABS) September 2012 IEEE 802.1 AVB TG Meeting Santa Cruz Franz-Josef Götz, Siemens AG Albert Tretter, Siemens AG

TABS a Solution for Simple Networks TABS is a solution for networks with the following characteristic: Simple topologies (e.g. line) Simple communication relations point-to-point Same link speed on all links of the network Requires an engineered network Drops Control Data frames received outside the time window  Optimized latency for Control-Data-Traffic Line or Comb structures

Pre-emption a Solution for Meshed Networks Pre-emption in combination with BLSA (Burst Limiting Shaper Algorithm) is a solution for more complex networks with the following characteristics: (for BLSA see Franz Götz's presentation: http://www.ieee802.org/1/files/public/docs2012/new-goetz-CtrDataScheduler-0712-v1.pdf) Meshed networks Multiple Transmission Periods within one network Complex communication relations point-to-point point-to-multipoint multipoint-to-multipoint Different link speeds within one network (e.g. 100MBit/s, 1GBit/s, … ) Robust behavior in case of failure suitable for safety critical applications Supports periodic and event-based CDT  Low latency for Control-Data-Traffic Robust behavior in case of failure - suitable for safety critical applications - ======= Fail operational behavior Emergency operation features Robust for safety critical applications =============== 􀂃 Emergency operation features – (fail operational behavior)

Pre-emption versus Time Aware Blocking Shaper Pro Pre-emption: Easy to add to existing networks Adding devices or bridges that support pre-emption to a network containing devices or bridges that do not support pre-emption is possible and vica versa Works well in networks with different link speeds No need to configure the bridges for pre-emption Flexibility, it is easy to change the network (e.g. add new stations, change the topology, …) No synchronization of the bridges (scheduler) required Robust against miss-configuration Usage of 100% of the available bandwidth is possible (see Norman Finn's presentation http://www.ieee802.org/1/files/public/docs2012/new-avb-nfinn-preempt-advantage-0112-v02.pdf) Transmission periods in the range from 31.25µs to 250µs (@100MBit/s) are not possible without pre-emption Pro TABS: Provides the best latency performance (less jitter) for simple topologies Compatible Erweiterung möglich

Some relevant Issues for the Bandwidth and Window Size Calculation for TABS Synchronization inaccuracy (1µs?) Sync tree is not identical with the data path Cable length (e.g. assumption 100m  real 5m) Bridge forwarding delay for Control Data Frames must be known Forwarding mechanism (CT / S&F) Scheduling has to avoid overtake situation e.g. huge number of fan in and low number of fan out Bridges with different link speeds on ingress and egress ports e.g. 100MBit/s  1GBit/s and one window  more switching resources are required e.g. 100MBit/s  1GBit/s and multiple window

Thank You