FranzJosef 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
Controller e.g. PLC
C
D
D
D
Frame
Tx Rx
Tx
Rx
Control Cycle / Transmission Period
Exchange
Control Data
Considering transmission order compute
T ra s n m is io s n
I n p ts u
T ra s n m is s io n
O tp u ts u typical traffic pattern for industrial closed-loopapplications
D
D
 Optimized latency for Control-
Data-Traffic
D devices e.g. actors or sensors
Tx Goal: minimize makespan
Rx
Tx t t
Page 2 IEEE 802.1 AVB TG Meeting
– Santa Cruz
September 2012

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
PLC
 point-to-multipoint
PLC
 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
PLC
. . .
PLC
PLC
PLC: Programmable Logic Controller for input/output data
DEV: Device for input / output data (sensor / actuator)
PLC – DEV communication relation
PLC – PLC communication relation
Ethernet
Video
Server overlapping functional cells for PLC <-> DEV control data traffic communication
. . .
DEV DEV
DEV DEV
DEV
Machinery Cell
 Low latency for Control-Data-Traffic
Motion Control Cell
Page 3 IEEE 802.1 AVB TG Meeting
– Santa Cruz
September 2012

Pre-emption versus Time Aware Blocking Shaper
Pro Pre-emption:
 Easy to add to existing networks
 Adding devices or bridges that support preemption 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 preemption
Pro TABS :
 Provides the best latency performance (less jitter) for simple topologies
Page 4 IEEE 802.1 AVB TG Meeting
– Santa Cruz
September 2012

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
Page 5 IEEE 802.1 AVB TG Meeting
– Santa Cruz
September 2012

Page 6 IEEE 802.1 AVB TG Meeting
– Santa Cruz
September 2012