... | ... | @@ -219,7 +219,7 @@ The enhancements to current IEEE 802.1AS include |
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### P802.1Qbv : Enhancements for Scheduled Traffic - Time Aware Shaper
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- to provide lower network delays
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- to provide lower network delays for time-sensitive data
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- defines ways for bridges and end stations to schedule the
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transmission of frames based on timing derived from IEEE Std 802.1AS
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- Time Aware (Blocking/De-blocking) Shaper in bridges and end
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... | ... | @@ -229,7 +229,7 @@ The enhancements to current IEEE 802.1AS include |
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sent - enables to ensure that time-sensitive traffic does not
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interfere with best-effort traffic (the former does not need to wait
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for the latter to be finished sending)
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- best used with preemption
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- it seems that its usage is more efficient with preemption
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([page 15](http://www.ieee802.org/1/files/public/docs2011/new-avb-boiger-meeting-gen2-latency-req-1111.pdf))
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- preemption enables to decrease the bandwidth overhead
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([page 11](http://www.ieee802.org/1/files/public/docs2012/new-avb-nfinn-preempt-advantage-0112-v02.pdf))
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... | ... | @@ -245,8 +245,8 @@ The enhancements to current IEEE 802.1AS include |
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- most efficient when used with Time Aware Shaper (would be defined in
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P802.Qbv),
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[page 15](http://www.ieee802.org/1/files/public/docs2011/new-avb-boiger-meeting-gen2-latency-req-1111.pdf)
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and page
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11":http://www.ieee802.org/1/files/public/docs2012/new-avb-nfinn-preempt-advantage-0112-v02.pdf
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and
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[page 11](http://www.ieee802.org/1/files/public/docs2012/new-avb-nfinn-preempt-advantage-0112-v02.pdf)
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### Possible effort on new topology resolution (probably enhancement of IEEE 802.1Qat-2010)
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... | ... | @@ -265,8 +265,7 @@ The enhancements to current IEEE 802.1AS include |
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receiver exist but only one is used at a time - no duplication
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at the receiver
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- Toyota: quick version of RSTP+802.1AS+802.1Qat (\< 100ms),
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[page 6](http://www.ieee802.org/1/files/public/docs2011/new-avb-KimNakamura-automotive-network-requirements-0311.pdf),
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this includes:
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[page 6](http://www.ieee802.org/1/files/public/docs2011/new-avb-KimNakamura-automotive-network-requirements-0311.pdf)
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- Broadcom: abandon RSTP, improved MSRP (802.1AS defines SRP,
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802.1Q-2011 defines multi-SRP) to provide multi-path support
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(all the potential paths from the talker to the listener are
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... | ... | @@ -275,7 +274,7 @@ The enhancements to current IEEE 802.1AS include |
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[here](http://www.ieee802.org/1/files/public/docs2012/avb-phkl-ext-msrp-0312-v1.pdf)
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- Cisco: simultaneous delivery of data through multiple paths
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([here](http://www.ieee802.org/1/files/public/docs2012/new-avb-nfinn-spb-tsn-0112-v01.pdf)),
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creating of disjoint paths using:
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creating disjoint paths using:
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- VLANs: Shortest Path Bridging or Spanning Tree Protocol
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inside a VLAN, one VLAN per path
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- SPB+SRP: use Shortest Path Bridging to identify
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... | ... | @@ -287,7 +286,7 @@ The enhancements to current IEEE 802.1AS include |
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- Ultra-low latency for critical traffic
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- CERN
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- maximum latency: 1000us over ~5 bridge hops @ 1Gbps
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- maximum latency: below 1000us over ~5 bridge hops @ 1Gbps
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([page 10](https://www.ohwr.org/project/white-rabbit/uploads/1244844e3c3cf850fad84e575f3b3f61/wrCernControlAndTiming.v1.1.pdf))
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- guaranteed latency over tree-like topology
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([page 19](https://www.ohwr.org/project/white-rabbit/uploads/1244844e3c3cf850fad84e575f3b3f61/wrCernControlAndTiming.v1.1.pdf))
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... | ... | @@ -321,16 +320,34 @@ The enhancements to current IEEE 802.1AS include |
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### Timing and Synchronization
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- profile/extension of PTP: WRPTP
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- interoperable with "standard" PTP (default profile)
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- requires physical syntonization using Synchronous Ethernet
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- uses phase detection (DDMTD) to enhance HW-timestamping precision to
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picosecond level
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- auto-calibration of link asymmetry (single fiber and DDMTD phase
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detection)
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- support of network redundancy and seamless (no time) reconfiguration
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- fault tolerance /isolation:
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- isolation of different acceleration networks
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synchronization-wise (but not within accelerator network)
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[page 9](https://www.ohwr.org/project/white-rabbit/uploads/1244844e3c3cf850fad84e575f3b3f61/wrCernControlAndTiming.v1.1.pdf),
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- tracking of time provided from different (redundant) sources
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(many ports can work in slave mode). This gives possibility of
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some comparison or voting logic which has not been investigated
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yet.
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- as soon as we detect that no connection to a grandmaster is not
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valid (link down), we kill all the master ports (in a boundary
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clock) not to propagate wrong time downstream - this is because
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in the static state we synchronize simultaneously through
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multiple paths, in a fault condition we do switching to backup
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source rather then holdoff -- this is to meet very stringent
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stability requirements, in less stringent applications holdoff
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can be considered.
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### Reliability
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- optional network redundancy
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- optional support of network/data redundancy
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- the bases of seamless redundancy is Forward Error Correction (FEC) -
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critical data sent over WR network is encoded into several frames
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(i.e. 4), only subset of the frames (i.e. 2) is needed by the
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... | ... | @@ -348,27 +365,22 @@ The enhancements to current IEEE 802.1AS include |
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### Latency and scheduling:
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- it need to be taken into account FEC and the fact that "single
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- FEC overhead needs to be taken into account -- the fact that "single
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critical data" translates into many Ethernet Frames
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- preemption was considered but is currently considered obsolete idea
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- strict priority scheduling of output queues (Class of Service),
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resource reservation for critical data and strict control of
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critical data transmission are considered sufficient for CERN
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- preemption was considered but is currently stated an obsolete idea
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- strict priority scheduling of output queues (Class of Service) for
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critical data, resource reservation for critical data and strict
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control of critical data transmission are considered sufficient for
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CERN
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- cut-through forwarding in the switches
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- fault tolerance / isolation
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- VLANs will be used to isolate different network and limit a
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propagation of destruction by mis-behaving node/switch
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- VLANs will be used to isolate different logical (accelerator)
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network and limit a propagation of fault due to a mis-behaving
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node/switch
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- FEC header has ID and sequence number - can prevent some
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duplication issues
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- control of throughput from nodes which are not supposed to send
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too much data (if any)
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- isolation of different acceleration networks
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synchronization-wise (but not within accelerator network), as
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soon as we detect that connection with grandmaster is not valid
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(link down) we kill all the master ports not to propagate wrong
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time downstream (since we synchronize simultaneously to more
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then one source of time, it is possible to make
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voting/comparision)
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