Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Gates vs. Windows and
Scheduled Traffic
Christian Boiger
christian.boiger@hdu-deggendorf.de
IEEE 802.1 Interim
January 2013
Vancouver, Canada
D E G G E N D O R F
U N I V E R S I T Y
O F
A P P L I E D
S C I E N C E S
Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Terminology “Scheduled Traffic”
26 July 2016
IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Terminology
 What is Scheduled Traffic?
 To call everything scheduled is on the one hand correct, but
people might think they have to engineer / schedule their
best effort traffic
 In reality the “schedule for best effort” is a consequence of
the schedule for the Scheduled Traffic
 802.1 Qbv PAR:
“Virtual Local Area Network (VLAN) tag encoded priority
values are allocated allowing simultaneous support of
scheduled traffic, credit-based shaper traffic and other
bridged traffic over Local Area Networks (LANs).”
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Terminology
 I think we should stick to Best Effort, Reserved and
Scheduled Traffic
 What does Scheduled Traffic distinguish from other traffic?
 It is scheduled in the end station on a per stream basis
 It has the highest priority/priorities
 It is registered in bridges (domain concept, priority
regeneration, no flooding, …)
 How do we call the TSN traffic in general?
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Possible Solution
Best Effort Traffic
Time Sensitive Traffic
Reserved Traffic
26 July 2016
IEEE 802.1 TSN TG – January 2013 Vancouver, BC
Scheduled Traffic
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Gates and Transmission Windows
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Background
In Santa Cruz we had a discussion about alternative ways
to configure the Time Aware Shaper
 Configuration of the Scheduled Traffic windows instead of
the configuration of the gates in order to allow a floating
guard band
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Impacts on the Time Aware Shaper
 The general question is:
What should be configured? Gates or transmission
windows?
t0
Transmitted
Data:
t1 t2 t3
scheduled traffic frame
t4
scheduled
traffic frame
scheduled
Scheduled
Traffic Gate:
Other Gates:
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Configuring Gates
 Configuring gates is complicated in combination with an
intelligent guard band usage (i.e. transmitting lower priority
frames during the guard band if they end before the start of
the Scheduled Traffic transmission)
 If the gate events are defined as the points in time when
the queues are getting (dis)connected from/to the
transmission selection it is not possible to transfer frames
during the guard band
t0
Transmitted
Data:
t1 t2 t3
scheduled traffic frame
t4
scheduled
traffic frame
Scheduled
Traffic Gate:
Other Gates:
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
How it is specified in IEEE 802.1Qbv-D0.2
 “… frames are selected from the corresponding queue for
transmission if and only if
…

b) The transmission gate (8.6.8.4) associated with that queue is
in the open state; and

c) If there are gate events associated with that queue, then there
is sufficient time available to transmit the entirety of that frame
before the next gate-close event associated with that queue;”
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Implications of the Current Definition
 The gate-closing event is not really defining the time when
the queue is disconnected from the transmission selection
 It is not possible to start the transmission of a scheduled
traffic frame when the corresponding gate is in the open
state, if it is not possible to transmit the frame until the
closing event
 The idea to open the gate only a very short time in order to
reschedule the traffic is not possible anymore
 But now it is possible to reschedule the frames with the
gate-closing events
 The usage of the term gates in D0.2 is not really
compatible with the definition of gates, it seems to be the
definition of transmission windows
 Should we change the name?
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
IEEE 802.1Qbv D0.1
 The example (slide 8) with the D0.2 shaper would look like
this:
t0
Transmitted
Data:
t1
t2
scheduled traffic frame
t3
scheduled
traffic frame
schedu
Scheduled
Traffic Gate:
Other Gates:
 The queues get disconnected before the gate-closing event,
the exact time depends on the frame size of the frames in
the other queues.
 The gates define now the transmission windows rather than
the connection or disconnection from the transmission
selection
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Pros and Cons of the IEEE 802.1Qbv D0.2 Shaper
Pros:
 Not necessary to define a guard band
 Flexible configuration
 Gate-closing event allows to reschedule the traffic
Cons:
 If the scheduled traffic windows are smaller than a max
frame (this might be the usual case) and a frame bigger
than the transmission window enters the queue (a talker
sends a too big frame (fault)) the queue is blocked (“for
ever”)
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Time Aware Shaper – Gate Model
Scheduled
Traffic Queue
Reserved Traffic
Queue
Best Effort
Traffic Queue
Best Effort
Traffic Queue
Time Aware Shaper
Gate Driver
T0:01111111
T1:10000000
T2:01111111
T3:10000000
T4:01111111
T5:10000000
T6:01111111
.
.
.
T125:10000000
T126:repeat
Credit Based
Shaper
Time Aware
Gate
Time Aware
Gate
Time Aware
Gate
Time Aware
Gate
Transmission Selection
scheduled traffic
frame
gate closed
other traffic
gate open
tR = reference time
126
t x  t R  ( n   Ti ) 
i0
t0
t1
T1
Transmitted
Data:
t2
T2
scheduled traffic frame
t3
T3
T4
t4
t5
T5
scheduled
traffic frame
T6
x

i0
Ti
t6
scheduled traffic frame
Scheduled
Traffic Gate:
Other Gates:
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Time Aware Shaper – Window Model
Scheduled
Traffic Queue
T0:0
T1:1
T2:0
T3:1
T4:0
T5:1
T6:0
.
.
.
T125:1
T126:repeat
Reserved Traffic
Queue
Best Effort
Traffic Queue
Best Effort
Traffic Queue
T0:1
T1:0
T2:1
T3:0
T4:1
T5:0
T6:1
.
.
.
T125:0
T126:repeat
Credit Based
Shaper
Time Aware
Shaper
Time Aware
Shaper
T0:1
T1:0
T2:1
T3:0
T4:1
T5:0
T6:1
.
.
.
T125:0
T126:repeat
T0:0
T1:1
T2:0
T3:1
T4:0
T5:1
T6:0
.
.
.
T125:1
T126:repeat
Time Aware
Shaper
Time Aware
Shaper
T0:1
T1:0
T2:1
T3:0
T4:1
T5:0
T6:1
.
.
.
T125:0
T126:repeat
T0:1
T1:0
T2:1
T3:0
T4:1
T5:0
T6:1
.
.
.
T125:0
T126:repeat
Transmission Selection
scheduled traffic
frame
window
closed
other traffic
window
open
tR = reference time
126
t x  t R  ( n   Ti ) 
i0
t0
t1
T1
Transmitted
Data:
t2
T2
t3
T3
scheduled traffic frame
T4
t4
t5
T5
scheduled
traffic frame
T6
x

i0
Ti
t6
scheduled traffic frame
Scheduled
Traffic windows:
Windows other
queues:
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Event List
 One list per queue
 Events:
Gate events:
 Window close event = 0
 Window open event = 1
Other events:
T0:0
T1:1
T2:0
T3:1
T4:0
T5:1
T6:0
.
.
.
T125:1
T126:repeat
 Repeat
 Gate event time interval (T0, T1, …, Tx)
 Relative to last gate event
 Granularity: 1ns
 32 bit unsigned integer in units of 1 ns (max ≈ 4.2s)
 In order to have a defined start condition at tR, T0 must be 0
 tR = PTP epoch
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
Important Device Specific Parameters

Device specific latency t_Device
 Necessary to calculate the schedule

Device specific Time Aware Shaper granularity
 Necessary to define the minimum window size

Maximum event list length
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
End Station – Talker
Shaping in the end stations
 Per stream shaping in the end stations
 Less complicated than CBS
 Ensures that a frame from the scheduled stream is
transmitted
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Hochschule Deggendorf – Hochschule für angewandte Wissenschaften
End Station – Talker
Scheduled
Traffic Stream
Queue 1
Scheduled
Traffic Stream
Queue 2
Scheduled
Traffic Stream
Queue n
Reserved Traffic
Stream Queue 1
Reserved Traffic
Stream Queue 2
Reserved Traffic
Stream Queue 3
Reserved Traffic
Stream Queue n
Time Aware
Shaper
Time Aware
Shaper
Time Aware
Shaper
Credit Based
Shaper
Credit Based
Shaper
Credit Based
Shaper
Credit Based
Shaper
Reserved Traffic
Queue
Best Effort
Traffic Queue
Best Effort
Traffic Queue
Time Aware
Shaper
Time Aware
Shaper
Credit Based
Shaper
Time Aware
Shaper
Transmission Selection
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Traffic Class and PCP
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Time Aware Domain and Class

Time Aware (TA) domain

Time Aware (TA) class
time aware (TA) class:
A traffic class whose frames are scheduled in order to achieve
minimum latency. A priority value is associated with each TA class.
TA classes are denoted by consecutive letters of the alphabet,
starting with A and continuing for up to seven classes.

New PCP for Scheduled Traffic: 4 (default for TA class A)

Scheduled Traffic has the highest priority (above AVB Gen1 SR
class A)
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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Thank You
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IEEE 802.1 TSN TG – January 2013 Vancouver, BC
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