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Geneva, Switzerland, 13 July 2013 Overview of IEEE 802.1Qbv Time Aware Shaping Don Pannell, Principal Systems Architect Marvell Semiconductor Joint IEEE-SA.

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Presentation on theme: "Geneva, Switzerland, 13 July 2013 Overview of IEEE 802.1Qbv Time Aware Shaping Don Pannell, Principal Systems Architect Marvell Semiconductor Joint IEEE-SA."— Presentation transcript:

1 Geneva, Switzerland, 13 July 2013 Overview of IEEE 802.1Qbv Time Aware Shaping Don Pannell, Principal Systems Architect Marvell Semiconductor Joint IEEE-SA and ITU Workshop on Ethernet

2 Geneva, Switzerland, 2 13 July Need/Desire/Goal of Qbv Get The Lowest Latency Possible – Any Way Possible Want Many Long, ~32 hop, Daisy Chains Small Bursts of frames at known regular intervals (e.g., a 40 uSec long burst of data every 125 uSec) Willing to Engineer Network Segments to meet this goal Non-Engineered (i.e., Consumer) Networks will not be able to depend on this very low latency as it can’t be guaranteed in their Networks The Network Structure and Usage will have to be Engineered, Managed and Controlled

3 Geneva, Switzerland, 2 13 July How Fast Can A Bridge Go? Total time for the Critical frame is: Internal delay of the Bridge Plus the time to transmit the max size interfering frame Plus the time to get the bits down a 100 meter cable Tx of max frame overlaps the Rx of the Critical frame Detailed analysis is shown in pannell-latency-options-0311-v1.pdf pannell-latency-options-0311-v1.pdf The max size interfering frame is the determining factor How does this improve if the interfering frame wasn’t there?

4 Geneva, Switzerland, 2 13 July How Fast If No Interference? Total time for the Critical frame is: Internal delay of the Bridge Plus the time to transmit the largest frame size of the Critical stream Plus the time to get the bits down a 100 meter cable Now the max size of the Critical frame is the determining factor This is due to the Store & Forward nature of most Bridges Since most Critical streams use small frames this is a great improvement And the Critical stream frame size can be part of the ‘Engineering of the Network’

5 Geneva, Switzerland, 2 13 July Interfering Frames are the Problem Some GE speed examples with numbers: The Bridge Latency with Interfering Frame is: Equal to the Size of Interfering frame + Bridge Delay + Cable Delay (max size interfering frame = 1522 bytes) With Max Size interfering frame this is uSec The Bridge Latency without an Interfering Frame is: Equal to the Size of AVB/TSN frame + Bridge Delay + Cable Delay With a 300 byte AVB/TSN frame this is uSec Can we get rid of the Interfering Frames to get the better latency?

6 Geneva, Switzerland, 2 13 July Qbv – Time Aware Shaper Qbv takes advantage of the target low latency data pattern i.e., That they are typically Small Bursts of frames at known regular intervals (for example: a 40 uSec long burst of data every 125 uSec) Then use this information to delay the start of non-Critical frames just before the start of the Burst Window This insures the egress port is idle so the Critical burst is not interfered – All interference is removed! Smart designs can allow non-Critical frames that fit to use the available bandwidth

7 7 Inside an Qbv Bridge (example)  Qbv Time Progression – Fig 1 At Bridge t uSec before the start of the Burst Window the Green AVB Class B frames are being Shaped (gated) by Qav and can’t Transmit So the Red Max size non-AVB High Priority frame ‘n’ can start

8 8  Qbv Time Progression – Fig 2 At Bridge t uSec before the start of the Burst Window the interfering Red Non-AVB frame is done Now the Green AVB Class B frames are available for transmit with enough credits to burst two frames = bytes = Inside an Qbv Bridge (example)

9 9  Qbv Time Progression – Fig 3 At Bridge t uSec before the start of the Burst Window the 1 st Green AVB Class B frame is done Now the next Green AVB Class B frame has credit to go, but it can’t because there is not enough time before t 0 - the start of the Burst Window nor can the Red ‘m’ frame But the 64 byte low priority Yellow non-AVB frame can go and does =64+20 bytes = 672 Inside an Qbv Bridge (example)

10 10  Qbv Time Progression – Fig 4 At Bridge t uSec before the start of the Burst Window the 64 byte Yellow frame is done The next Green AVB Class B frame has credit to go, but it still can’t because there is not enough time before t 0 (its credits are actually increasing) nor can the Red ‘m’ frame The next low priority 64 byte frame can’t go either – not enough time =64+20 bytes = 672 Inside an Qbv Bridge (example)

11 11  Qbv Time Progression – Fig 5 At Bridge t 0 - the start of the Burst Window the port is idle so the newly arrived Blue Critical frames are allowed to egress without any interference! The burst of Blue frames will continue as long as Qbv leaves it queue open for transmission as they are the highest priority queue Inside an Qbv Bridge (example)

12 Geneva, Switzerland, 2 13 July Qbv – With Cut Through Cut-through bridges generally don’t help normal network performance due to the low percentage of improved latency and that this improvement cannot be guaranteed With Qbv the improved latency can be guaranteed Cut-through only works when the target ports are idle and Qbv does exactly that – thus the guarantee With Cut-through the Bridge latency is:

13 Geneva, Switzerland, 2 13 July Latency By The Numbers Non-Qbv Bridge Latency is uSec Due to the Max Size interfering frame Store & Forward Qbv Bridge Latency is uSec Assuming a 300 byte maximum size AVB/TSN frame This number will go up with increasing Critical frame sizes Cut Through Qbv Bridge Latency is uSec! Assuming a 64 byte Cut Through Point This number does NOT change due to frame size! And this performance can be Guaranteed!

14 Geneva, Switzerland, 2 13 July Latency By The Numbers Qbv supports the lowest latency possible But only if the network is ‘Engineered’ It won’t work for all topologies And proper configuration of the timing ‘gates’ is not easy The Qbv Standard will support Control of the timing ‘gates’ – but will not figure the timing out 3 rd Party tools will be required to compute the ‘gate’ timing Multiple timing ‘gate’ windows will be supported per port with each window having nSec configuration resolution TSN Bridges already have network timing information by their support of IEEE 802.1AS

15 Geneva, Switzerland, 2 13 July Questions?


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