Presentation slides used at the Workshop on Factory Communication Systems (WFCS) 2018

1. Scheduling in Time-Sensitive Networks (TSN) for
Mixed-Criticality Industrial Applications
Voica Gavrilut¸ Paul Pop
Technical University of Denmark (DTU)
DTU Compute
Kongens Lyngby, Denmark
(voga—paupo)@dtu.dk

2. Motivation
The Automation Pyramid:
Soon to be Ancient History?
22
Rigid infrastructure with
separation between levels
of functionality
Levels connected by dedicated,
specialist networks
Data exchange only via gateways
or proprietary systems
Difficulties to transparantly
access data at the cyber
pyramid (machine) level
(a) Automation Pyramid
Creating a Flexible IoT Infrastructure
with Deterministic Ethernet
24
OPC UA over TSN: one unified
architecture for all communication
infrastructure elements
Logical machine/control
boundaries are dissolved
Direct access to machine
data from ERP/MES
Real-time and non-real-time
domains integrated
OPC UA provides leading
technology of proven security
concepts
Learning from the Internet
Experience: Digital Platforms
and Open Innovation win.
Source: TTTech
(b) Distributed CPSs
Figure
Specialized protocols as ProfiNet or EtherCAT replaced by TSN
Single infrastructure supporting mixed-criticality applications
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3. Time-Sensitive Networking (TSN)
TSN: a set of substandards extending IEEE 802.1Q
Shapers and schedulers:
IEEE 802.1Q-2005: prioritized best-effort
IEEE 802.1BA: Audio-Video-Bridging (AVB)
IEEE 802.1Qbv: enhancements for Time-Triggered (TT) traffic
our focus: mixed AVB and TT traffic
IEEE 802.1Qat, IEEE 802.1Qcc: stream reservation
IEEE 802.1CB: stream reservation for redundant streams
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4. Architecture Model
ES1
ES2
BR1 ES3
r1
r2
(a) Example architecture
0
for TT traffic in ES1 is open, therefore the TT frame of tTT1
is initiated to be transmitted from [ES1,SW1].
Researchers have proposed methods to synthesize the G-
CLs [14], [24], and have outlined the constraints that have
to be satisfied for schedule feasibility. For example, when
associated gate for TT traffic is open, the remaining gates
for other traffic are closed, and vice versa. In Fig. 3, the red
and blue queues are respectively dedicated for Class A and
Fig. 2. A TAS for an output port in an ES/SW
B o
TT
Clas
from
is c
The
tran
A. T
H
sion
TT
3
(b) TSN switch
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5. Application Model
flow type vs vt r T D P
f1 · · · f4 TT ES1 ES3 r1 150 µs 150 µs 750 B
f5 · · · f8 AVB ES2 ES3 r2 150 µs 150 µs 1500 B
1.1 3.12.1 4.1 8.1 6.17.1 5.1
2.1 4.18.1 6.1
1.1 3.17.1 5.1
50 100 150
50 100 150
50 100 150
ES1,
SW1
ES2,
SW1
SW1,
ES3
6, 8
7 58 6
151.76 us
5
Figure: GCL for an outgoing port: WCD(f5) = 151.76µs
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6. Problem Formulation
Given:
The network G and
The set of flows F = FTT
∪ FAVB
with their routes and timing
properties
Determine:
The number of TT queues,
Mapping of TT flows to egress port queues and
GCLs S of TT queues
Such that:
All TT flows are schedulable
Objective function:
Cost = fi ∈FAVB max(0, WCD(fi ) − fi .D)
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7. Optimization Strategy
NP-hard problem
TT+AVB: metaheuristic strategy
Metaheuristic: Greedy Randomized Adaptive Search
Procedure (GRASP)
Has 2 phases:
1. Construction phase;
generate a list of candidates
using variations of List Scheduling heuristic
2. Search phase;
improvement of each candidate by
applying destroy/repair operators.
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8. Preliminary Experimental Results
TT latency TT Queues TT+AVB
Test case
Exec. Sched. Exec. Sched. Exec. Sched.
Motiv. 1.1 No 0.8 No 32 Yes
TC1 2.2 No 2.6 No 403.9 Yes
TC2 8.7 No 9.6 No 612.8 Yes
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9. Closing Remarks
Summary
Addressed the scheduling of mixed-criticality applications on
TSN-based networks
Problem: decide the GCLs of TT queues
Solution: a GRASP-based metaheuristic
Message
Is not obvious what schedule tables are more convenient also for
AVB traffic
We need scheduling tools to
(1) Synthesize GCLs in TSN and (2) Modify the GCLs such that
also AVB traffic requirements are met
Future work
Determine the GCLs for multicast flows
Modify also the routes
Modify also the idle/sending slopes of AVB classes
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