Gate Operations and Automatic Guard Band Feature

Transcription

1 automotive mobile automation embedded systems Gate Operations and Automatic Guard Band Feature Christian Boiger IEEE 802 Plenary July 2015 Waikoloa Village, HI

2 Current Problem Traffic Queue Reserved Traffic Queue Best Effort Traffic Queue Best Effort Traffic Queue IEEE 802.1Qbv Gate Control List Transmission Gate Credit Based Shaper Transmission Gate Transmission Gate Transmission Gate T0: Cooooooo T1: occccccc T2: Cooooooo T3: occccccc T4: Cooooooo T5: occccccc T6: Cooooooo... T125: occccccc Cycle Start Transmission Selection Traffic other traffic gate closed gate open t0 t1 t2 t3 t4 t5 t6 T0 T1 T2 T3 T4 T5 Traffic Gate: Other Gates: Transmitted Data: Traffic 1 Traffic 3 Traffic 2 4 Transmitted Data: 1 2 Traffic July 2015 IEEE TSN TG 2 Traffic 2 Traffic 3

3 Current Traffic Description Qbv currently describes two different types of traffic schedules Window approach t 0 t 1 t 2 t 3 Transmitted Data: scheduled traffic frame scheduled traffic frame scheduled traffic frame Traffic Gate: Other Gates: Transmission Gate approach t 0 t 1 t 2 t 3 t 4 Transmitted Data: scheduled traffic frame scheduled traffic frame scheduled traffic frame Traffic Gate: Other Gates: 16 July 2015 IEEE TSN TG 3

4 Current Traffic Description The window approach is the default description for scheduled traffic In addition to the other checks carried out by the transmission selection algorithm, a frame on a traffic class queue is not available for transmission (as required for tests (a) and (b) in 8.6.8) if the transmission gate is in the closed state or if the frame size is known and there is insufficient time available to transmit the entirety of that frame before the next gate-close event (3.1) associated with that queue. The gate approach is used when the frame size is unknown 16 July 2015 IEEE TSN TG 4

5 What is the problem with this description? The god box that calculates the schedule does not know which of the two versions is used by a bridge Two different bridges with the same configuration might show two entire different behaviors It is very vague What does if the frame size is known mean? My assumption is that a 802.1Q bridge knows the size of a frame (implementations might not), therefore this part seems to be irrelevant from an standards point of view From an implementation point of view (I don t think that we should define implementations) especially when proprietary features like cut-through are supported the frame size might be unknown But even if one would interpret this condition as a condition for an implementation and not the behavior of the standards model, this is in reality very complicated What if for some queues the frame size is known and for others not? What if the frame size is known for small frames e.g. 64 byte frames but not for bigger frames? 16 July 2015 IEEE TSN TG 5

6 Proposal We should get rid of the if the frame size is known The gate approach shall be mandatory (every bridge that supports scheduled traffic should be capable to support this) This requires almost no changes, in most parts of the document this is already the case, e.g. definition of open and close: a) Open: Queued frames are selected for transmission, in accordance with the definition of the transmission selection algorithm associated with the queue. b) Closed: Queued frames are not selected for transmission. Define an optional configurable automaticguardband feature that covers the window approach In addition to the other checks carried out by the transmission selection algorithm, a frame on a traffic class queue is not available for transmission (as required for tests (a) and (b) in 8.6.8) if the transmission gate is in the closed state or if the frame size is known automaticguardband is active and there is insufficient time available to transmit the entirety of that frame before the next gate-close event (3.1) associated with that queue. 16 July 2015 IEEE TSN TG 6

7 automaticguardband automaticguardband should be configured with the schedule automaticguardband is optional and might not be supported by every device / port / queue or in every configuration mode automaticguardband should be configured on a per queue basis, this would for example allow the following configuration: automaticguardband is not activated on the high priority scheduled traffic queues automaticguardband is active for the other queues 16 July 2015 IEEE TSN TG 7

8 automotive mobile automation embedded systems Thank You 16 July 2015 IEEE TSN TG 8