Transcript 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.

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:
Control Cycle / Transmission Period
 Simple topologies (e.g. line)
 Simple communication relations
Exchange
Control Data
Controller
e.g. PLC
Considering
transmission order
Tx
t
sm
Tran
C
Rx
 Drops Control Data frames received
outside the time window
uts
n Inp
Tran
sm
D
D
typical traffic pattern for
industrial closed-loopapplications
tputs
issio
Frame
Tx Rx
n Ou
 Same link speed on all links of the network
issio
 point-to-point
 Requires an engineered network
compute
D
D
D
D
 Optimized latency for ControlData-Traffic
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devices
e.g. actors
or sensors
t
Tx
IEEE 802.1 AVB TG Meeting – Santa Cruz
Goal:
minimize
makespan
Rx
Tx
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-goetzCtrDataScheduler-0712-v1.pdf)
PLC: Programmable Logic Controller for input/output data
DEV: Device for input / output data (sensor / actuator)
 Meshed networks
 Multiple Transmission Periods within one network
 Complex communication relations
 point-to-point
PLC
 point-to-multipoint
PLC – DEV communication relation
PLC – PLC communication relation
Ethernet
Video
Server
PLC
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
overlapping
functional cells
for PLC <-> DEV
control data traffic
communication
PLC
. . .
PLC
. . .
DEV
DEV
DEV
DEV
DEV
Motion Control Cell
Machinery Cell
 Low latency for Control-Data-Traffic
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IEEE 802.1 AVB TG Meeting – Santa Cruz
September 2012
Pre-emption versus Time Aware Blocking Shaper
Pro Pre-emption:
Pro TABS:
 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
 Provides the best latency performance (less jitter)
for simple topologies
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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
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IEEE 802.1 AVB TG Meeting – Santa Cruz
September 2012
Thank You
Page 6
IEEE 802.1 AVB TG Meeting – Santa Cruz
September 2012