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Ultra Low LatencyTraffic Class @ Industry
2012-01-17 - Munich
IEEE 802.1 AVB TG
Real Time Communication Symposium
Franz-Josef Götz
Siemens AG
franz-josef.goetz@siemens.com
IEEE 802.1 AVB TG Symposium - MunichSeite 2 17.01.2012
Agenda
�Audio / Video Bridging, AVB Gen 1
�Requirements from Industry for AVB Gen 2
�Proposed Mechanism for ULL Streams (1 - 5 )
�Scenario: Routing & Scheduling for ULL Streams (1 - 5)
�Conclusion
IEEE 802.1 AVB TG Symposium - MunichSeite 3 17.01.2012
Audio / Video Bridging, AVB Gen 1
� New mechanism for Ethernet specified from IEEE 802.1 AVB working
group for Version 1.0
� Synchronization protocol and hardware time stamping for time
accuracy << 1µs in bridged Ethernet network
� To guarantee QoS for streams the AVB standard has specified:
� Forwarding and queuing enhancements in network components to
guarantee determinism and max. latency < 2ms for streams
� Multiple Stream Reservation Protocol to guarantee resources in network
components and to avoid packet lost
⇒Synchronization and guaranteed QoS are basic requirements
IEEE 802.1 AVB TG Symposium - MunichSeite 4 17.01.2012
AVB Gen 1 Mechanismen (1)
0 – 712B
0 – 713A
Range
Default regenerated
priority for
SRP domain boundary
ports
Default
priority
SR
class
AV-
Bridge
AV-
Bridge
AV-
Bridge
AV-
Bridge
Class A SRP
DomainLegacy
BridgeLegacy
Bridge
.1AS capable
Class B SRP
Domain
Separate Traffic Class for AV Streams
� Stream Class A with 125 ms transmission period
and max. latency of 2ms over 7 hops
� Stream Class B with 250 ms transmission period
and max. latency of 20ms over 7 hops
Bandwidth reservatiion (MSRP)
� AV End Station & AV-Bridge
� Follows RSTP data tree
� Restricted bandwidth(75% of available bandwidth for AV Streams)
� Domain boundaries
� Avoid flooding for AV streams
� 64-Bit StreamID (Talker SA + ID)
� 32-Bit TSpec (MaxFrameSize, MaxTransmitionPeriod)
IEEE 802.1 AVB TG Symposium - MunichSeite 5 17.01.2012
AVB Gen 1 Mechanismen (2)
AV-Bridge Extensions
� Per SR Class Queue
� Per SR Class separate Resources
� Credit based transmission selection algorithmus
IEEE 802.1 AVB TG Symposium - MunichSeite 6 17.01.2012
Requirements from Industry for AVB Gen 2
Enhancements for gPTP
�Universal time and working clock for synchronized applications
� Industrial parameter set
�High availability of synchronization (guaranteed take over time)
�Security
Ultra low latency for control traffic which is used for industrial applications
…
Media redundancy for high availability industrial applications
…
IEEE 802.1 AVB TG Symposium - MunichSeite 7 17.01.2012
New Ultra Low Latency (ULL) Traffic Class for Streamsfrom Automation Perspective
Contro
ller –
Device -C
ommunication
D
D
D
D
D
D
C
Tx
Rx
Controller
Devices
time
time
Device – Controller -Communication
Application Period / Transmission Period
Transmission Time Application Time
Tx Rx Tx
typical traffic pattern for
industrial closed-loop-
applications
makespan
ULL Stream for automation applications
T L Frame
Transmission Order
Transmission of all ULL Streams within transmission time
Typical traffic pattern for control traffic
IEEE 802.1 AVB TG Symposium - MunichSeite 8 17.01.2012
Objectives to guarantee ultra low latency
�Predictable bandwidth (traffic load) and resources
�Use appropriate (e.g. shortest) communication path
�Minimize delays for ULL Streams caused by
�Traffic shaper
�Bubbling talker
�Traffic congestion
� Interference from
- legacy traffic and other traffic classes (e.g. AV Streams)
- other ULL Streams
IEEE 802.1 AVB TG Symposium - MunichSeite 9 17.01.2012
Proposed Mechanism for ULL Streams (1)
A new Traffic Class for Ultra low Latency (ULL) Streams
(e.g. combinable with AV Stream class A)
� Range of transmission periods in steps of 2N x 31,25µs
(31,25µs - 1ms)
� Worst case latency (max. E2E Latency) over all received ULL Streams within
transmission period,
required latency < 2 µs / Gb hop (length < 64 Bytes by empty tx queue)
Transmission
period
1
Transmission
period
Transmission
period
Transmission
period
1 1 1 12a2a 2a2b 2b4a 4b 4c 4d 4a
1 1 1 1 12a2a 2a4a 4a2b 4b 4c 4d 4b 4c 4d2b 2b
Transmission
period
control systems
e.g. PLC
control systems
e.g. motion
control
Transmission
period
Transmission
period
Transmission
period
Transmission
period
Transmission
period
Multiple transmission periods in parallel
IEEE 802.1 AVB TG Symposium - MunichSeite 10 17.01.2012
Proposed Mechanism for ULL Streams (2)
Forwarding and queuing enhancements
for bridges and end stations
� ULL SR Class Queue
� ULL SR Class separate Resources
� Enhanced traffic shaper in bridges and
end station for ULL Streams
� isochronous transmission for ULL
Streams by end station
� bursty or time aware scheduler for
ULL Streams in bridges (e.g. get always highest priority when ULL Stream
is in transmit queue)
� Cut Through
� Pre-emption for ULL Streams
� Peer-to-Peer fragmentation of legacy
traffic and AV Streams on demand
Prio 4..7
0...1
ULL Class(6)
AV Class A(3)
802.1Q + Extentions
AVC-Bridges
B
C
P
B: Burst
C: Credit-
Based
150 Byte
150 Byte
FragLength
128 Bytes
(8Byte granular)
Min. 64 Bytes
IEEE 802.1 AVB TG Symposium - MunichSeite 11 17.01.2012
Proposed Mechanism for ULL Streams (3)
Specify mechanism and strategy to avoid and resolve traffic congestion
of ULL Streams
� Identify overload situations (e.g. bubbling idiot) and aged ULL Streams
� Discard these conflicting ULL Streams
Minimize interference of ULL Streams in bridges
� Support for optimized sequence of ULL Steams on egress port
IEEE 802.1 AVB TG Symposium - MunichSeite 12 17.01.2012
Proposed Mechanism for ULL Streams (4)
Calculable and guaranteed bandwidth and resources
� Routing
� Transmission path for ULL Streams is independent from RSTP
� Guaranteed bandwidth
� Shortest path
� Multiple path for high availability- Duplicated ULL Stream in parallel over 2nd independent shortest communication path
Configuration of shortest communication path with topology network information+ offline – engineered+ at runtime – centralized or decentralized with routing protocol
DD
D D
root
X
X
XRSTP
data tree
A
B
A <-> B communication path with RSTP
DD
D D
root A
B
Shortest Path Communication
for ULL Streams
RR
D
IEEE 802.1 AVB TG Symposium - MunichSeite 13 17.01.2012
Proposed Mechanism for ULL Streams (5)
The following slides show a scenario for scheduling:
Assumption:
� All end station are synchronized
� ULL Streams are transmitted over shortest path
� Same packet length for all ULL Streams (packet slot)
� No interference legacy traffic or additional delays
� No pre-emption
� No bridge delay
� E2E hop count is always 4
� Store & Forward for ULL Streams
� Scheduling
� transmission time to minimize make span
� minimize and guaranteed resources in bridges for ULL Streams
Configuration of schedule with topology network information
+ offline – engineered
+ at runtime – centralized or decentralized with routing protocol
Scheduling
11/14
S
14Tx 1
12/14
13/14
S
15
S
16
S
17
24/14
11/15
12/15
13/15
34/15
11/16
12/16
13/16
44/16
11/17
12/17
13/17
51/17
B 1
11/14
11/15
11/16
11/17
12/14
12/15
12/16
12/17
Tx 2 Tx 3
13/14
13/15
13/16
13/17
Tx 8Tx 4 Tx 5 Tx 6 Tx 7
24/14
34/15
44/16
51/17
B 4
Tx 8
17/47
27/46
37/45
54/44
...
B 0
17/47
Tx 1 Tx 2 Tx 3 Tx 4 Tx 5
15/24
16/37 24/14
26/36
27/46
34/15
35/25
37/45
44/16
45/26
46/35
51/17
52/27
53/34
54/44
S
54Rx 1
54/44
15/24
16/37
17/47
Tx 1 Tx 2 Tx 3 Tx 4
B 5
51/17
52/27
53/34
54/44
Tx 1Tx 1Tx 1Tx 1
IEEE 802.1 AVB TG Symposium - MunichSeite 14 17.01.2012
Scenario: Routing & Scheduling for ULL Streams (1)
IEEE 802.1 AVB TG Symposium - MunichSeite 15 17.01.2012
Scenario: Routing & Scheduling for ULL Streams (2)
IEEE 802.1 AVB TG Symposium - MunichSeite 16 17.01.2012
Scenario: Routing & Scheduling for ULL Streams (3)
Worst Case Latency without optimized Scheduling
11/14
S
14Tx 1
12/14
13/14
S
15
S
16
S
17
24/14
11/15
12/15
13/15
34/15
11/16
12/16
13/16
44/16
11/17
12/17
13/17
51/17
B 1
11/14
11/15
11/16
11/17
12/14
12/15
12/16
12/17
Tx 2 Tx 3
13/14
13/15
13/16
13/17
Tx 8Tx 4 Tx 5 Tx 6 Tx 7
24/14
34/15
44/16
51/17
B
111Tx 2
11/14
11/15
11/16
11/17
B
112Tx 2
11/14
11/15
11/16
11/17
S
11
11/14
11/15
11/16
11/17
Rx 1
B 2
Tx 8
15/24
35/25
45/26
52/27
... ...
S
12-13
B 3
Tx 8
16/37
26/36
46/35
53/34
...
S
24 …47
B 4
Tx 8
17/47
27/46
37/45
54/44
...
B 0
17/47
Tx 1 Tx 2 Tx 3 Tx 4 Tx 5
15/24
16/37 24/14
26/36
27/46
34/15
35/25
37/45
44/16
45/26
46/35
51/17
52/27
53/34
54/44
S
54Rx 1
S
51- 53...
54/44
makespan
15/24
16/37
17/47
Tx 1 Tx 2 Tx 3 Tx 4
B 5
51/17
52/27
53/34
54/44
Tx 1Tx 1Tx 1Tx 1...
S
17Rx 1
17/47
makespan = 15 packetslots
IEEE 802.1 AVB TG Symposium - MunichSeite 17 17.01.2012
Scenario: Routing & Scheduling for ULL Streams (4)
IEEE 802.1 AVB TG Symposium - MunichSeite 18 17.01.2012
Scenario: Routing & Scheduling for ULL Streams (5)
makespan
makespan
[ - ]
IEEE 802.1 AVB TG Symposium - MunichSeite 19 17.01.2012
Overview of proposed Mechanism
--AAAPre-emption (Fragmentation on Demand) + LLDP
--AAGuaranteed transmission order in
end stations
AAAABBandwidth observation
AAAAA-high availability
AAALimited and guaranteed bandwidth
--AGuaranteed transmission order in
bridges
-BAhigh accuracy < 1µsSynchronization
AAAAAScheduling protocol
AAA--multiple Path
--AAAShortest PathRouting protocol
--AACut Through with Pre-emption
--AAABursty or time aware shaperForwarding and
queuing
enhancements
(inside bridge or end
station)
AAAA-Separate ULL queue with guaranteed
resources
-AASeparate traffic class for control (ULL Streams)
AvailabilityRobustnessUltra Low LatencyMechanism
Rating
IEEE 802.1 AVB TG Symposium - MunichSeite 20 17.01.2012
Conclusion
The pre-emption is an important mechanism but Routing and Scheduling has
the same relevance for ultra low latency.
An additional ultra low latency stream class for high performance and robust
closed loop controls which can handle temporary overload situations
in bridged Ethernet networks is a not-easy-to-establish but a
feasible technology.