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Data Communication DivisionCYPRESS
November 14, 2001, page 1dvj_transit_01
802.17 presentation
m Prepared for 802.17, November 2001m Dr. David V. James
Chief ArchitectNetwork Processing SolutionsData Communications Division110 Nortech ParkwaySan Jose, CA 95134-2307Tel: +1.408.942.2010Fax: +1.408.942.2099Base: [email protected]: [email protected]
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Data Communication DivisionCYPRESS
November 14, 2001, page 2dvj_transit_01
Flow control
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Data Communication DivisionCYPRESS
November 14, 2001, page 3dvj_transit_01
data[n]unprovisioned or
unused provisioned
overprovisioned,unbounded latency
Arbitration classes
Class-B1
Class-C
provisioned bandwidth,bounded latency Class-B0
provisioned bandwidth,low latency Class-A
guar
ante
ed
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Data Communication DivisionCYPRESS
November 14, 2001, page 4dvj_transit_01
nodeA
Opposing arbitration
• Data packets flow in one direction• Arbitration control flows in the other*
nodeB nodeC packetcontrol
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Data Communication DivisionCYPRESS
November 14, 2001, page 5dvj_transit_01
Supported topologies
n A physical ring
n Dual ringlets
n Duplex ringlet
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Data Communication DivisionCYPRESS
November 14, 2001, page 6dvj_transit_01
Internal MAC arbitration signals
• Arbitration affects opposing run • My congestion affects upstream node• Downstream congestion affects me
dataPaths
arbitration
arbitration
dataPaths
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Data Communication DivisionCYPRESS
November 14, 2001, page 7dvj_transit_01
External MAC arbitration signals
arbs
arbs
application
MAC receives informationMAC FIFOs are $$, latency++, inflexible
Application receives informationAllows reordering and run selection
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Data Communication DivisionCYPRESS
November 14, 2001, page 8dvj_transit_01
B
Arbitration related components
• Distinct class-A & class-B/C paths • Load dependent policing
passBC
passA
policeApoliceBA
Precedence: Fa, A, B, C, Fbc
C BpoliceC
C BpoliceC
C BpoliceC
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Data Communication DivisionCYPRESS
November 14, 2001, page 9dvj_transit_01
Class-A flow control(proactive and reactive)
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Data Communication DivisionCYPRESS
November 14, 2001, page 10dvj_transit_01
Class-A flow control
m ProactiveMinimal (nonexistent?) passBC transit bufferLess available bandwidthEach station maintains constant classAp traffic
m ReactiveSignificant passBC transit bufferFull bandwidth utilizationEach station responds/regenerates throttle messages
m Interoperable?This is a bandwidth vs memory $$ tradeoff
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Data Communication DivisionCYPRESS
November 14, 2001, page 11dvj_transit_01
nodeA
Proactive class-A partitions
• Data packets go source-to-destination• Residue returns destination-to-source
to provide subsistence for transmissions
nodeB nodeC
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Data Communication DivisionCYPRESS
November 14, 2001, page 12dvj_transit_01
nodeA
Proactive class-Acompatibility options
• Reactive node trickles class-A bandwidth• Reactive node recycles class-A bandwidth
class-A => class-A’, thus preserving BW
nodeB Reactive
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Data Communication DivisionCYPRESS
November 14, 2001, page 13dvj_transit_01
nodeA
Reactive class-A control
• Transmission of packets causes• Backup of passBC FIFO that• Returns flow-control information that• Provides consumable idle packets
nodeB
(1)
(2)(3)
(4)
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Data Communication DivisionCYPRESS
November 14, 2001, page 14dvj_transit_01
nodeA
Reactive class-A compatibility
• Flow control passes upstream• Proactive stations pass these indications
nodeB
(1)
(2)(3)
(4)
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Data Communication DivisionCYPRESS
November 14, 2001, page 15dvj_transit_01
Frame formats
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Data Communication DivisionCYPRESS
November 14, 2001, page 16dvj_transit_01
headerCRC
payload
Frame formats
type
headerCRC
header
32 bits
compact headerCRC
payloadtype
headerCRC
complete
sourceMacLodstLo srcHi
destinationMacHiheader
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Data Communication DivisionCYPRESS
November 14, 2001, page 17dvj_transit_01
Header formatw
rap
destStationID
71
ring
destStationID
71
flood
1 8
mac
s
1
clas
s
2
depthBC
4
timeToLive
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Data Communication DivisionCYPRESS
November 14, 2001, page 18dvj_transit_01
headerCRC
payload
RPR control frames
802.17 discover
headerCRC
header
headerCRC
payload
802.17 congest
headerCRC
header
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Data Communication DivisionCYPRESS
November 14, 2001, page 19dvj_transit_01
Topology discovery
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Data Communication DivisionCYPRESS
November 14, 2001, page 20dvj_transit_01
Frame interchanges
m Triggered on state changem Triggered on state changem Also sent periodically
– Automatic fault recovery– Piggyback on heartbeat
m Also distributes stationID addresses– Previous: derived from topology and EUI-48 info– Bit map supportive “reclaiming” precedence
m Robust!– Context-less behavior (update rate only)– No addressing or timeouts required
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Data Communication DivisionCYPRESS
November 14, 2001, page 21dvj_transit_01
Topology collection
• Prepend your macAddress(no duplicate copies present…)
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Data Communication DivisionCYPRESS
November 14, 2001, page 22dvj_transit_01
Topology maintenance
• Prepend your macAddress• Strip duplicate macAddress & beyond
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Data Communication DivisionCYPRESS
November 14, 2001, page 23dvj_transit_01
headerCRC
payload
Discovery formats
type17
complete
dstLo ??
DISCOV
headerCRC
header
32 bits
ring bridge
destinationMacHi
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Data Communication DivisionCYPRESS
November 14, 2001, page 24dvj_transit_01
CRC processing
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Data Communication DivisionCYPRESS
November 14, 2001, page 25dvj_transit_01
CRC processing
m Store&forward/Cut-through agnosticm Invalid data is effectively discarded
– store-and-forward discards– cut-through stomps the CRC
m Maximize error-logging accuracy– Separate header&data CRCs– “most” corruptions hit the data
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Data Communication DivisionCYPRESS
November 14, 2001, page 26dvj_transit_01
payloadCRC
payload
Separate header and data CRCs
headerCRC
header
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Data Communication DivisionCYPRESS
November 14, 2001, page 27dvj_transit_01
crcA data[n]core
Cut-through CRCs
• Corrupted packet remains corrupted• Error logged when first detected • if (crcA!=crc) {
errorCount+= (crcA!=crc^STOMP);crcB= crc^STOMP;
}
node crcB data[n]core
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Data Communication DivisionCYPRESS
November 14, 2001, page 28dvj_transit_01
Distinct CRCs reduces discards
• Discard the corrupted packet
data head node
X
data head node
X(nothing)
• Discard the corrupted data
head
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Data Communication DivisionCYPRESS
November 14, 2001, page 29dvj_transit_01
??
End-to-end CRC protected TTL
CRC checkCRC generate
zero dt zero
EXOREXOR
crcB ttl' header
t+= 1
crcA ttl header
CRC checkCRC check/stomp
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Data Communication DivisionCYPRESS
November 14, 2001, page 30dvj_transit_01
Pre-emption(a physical layer decision)
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Data Communication DivisionCYPRESS
November 14, 2001, page 31dvj_transit_01
Pre-emption
m Suspend class-B/C for class-A packetm Only one level is sufficient
– class-A is the latency critical traffic– more levels complicate hardware
m Physical layer dependent– marginal for high BW & small packets– distinctive “suspend” symbol required
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Data Communication DivisionCYPRESS
November 14, 2001, page 32dvj_transit_01
Pre-emption fragments
• Packets can be suspended• The class-A packet can be stripped
• egress queues are store&forward• distinctive idle markers needed
data[n]partB data[n]partA node data[n]partB classAdata[n]partA node data[n]partB Idle' data[n]partA
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Data Communication DivisionCYPRESS
November 14, 2001, page 33dvj_transit_01
Pre-emption compatibility
• Pre-emption mandates egress S&F
• Simplistic node has no such S&F
• Interoperability burden on elegant• boundary node has S&F bypass • cut-through in preemptive domain
preemptive domain
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Data Communication DivisionCYPRESS
November 14, 2001, page 34dvj_transit_01
Limits of scalability
n The metro area
n Terrestrial
n Geosynchronous
n To the curb
n To the home
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Data Communication DivisionCYPRESS
November 14, 2001, page 35dvj_transit_01
Lessons of the past…m Flow control mandates 2-out-of-3
– Low latency transmissions– Fair bandwidth allocation– High bandwidth utilization
m Feedback control systems– Low latency signaling– Control can pass class-B/C packets– Separate class-A queue is utilized
m Other observations– Local control => global perversions – Fairness is inherently “approximate”– Strange beating sequences DO OCCUR
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Data Communication DivisionCYPRESS
November 14, 2001, page 36dvj_transit_01
Allowed transmissions
A,B,Cb,Cc,F----≥≥0
A,BA,B,Cb,F--pass≥≥1/4
AA,FA,Fpasssend≥≥1/2
A,FA,FA,Fsendsend≥≥3/4
HILOnoneHILO
transmissionswarnings
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Data Communication DivisionCYPRESS
November 14, 2001, page 37dvj_transit_01
Arbitration summarym Dual levels
– Class-A, pre-emptive low latency – Class-B, less latency sensitive
m Jumbo frames– Affect asynchronous latencies– NO IMPACT on synchronous latency
m Cut-through vs store-and-forward– Either should be allowed– Light-load latency DOES matter
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Data Communication DivisionCYPRESS
November 14, 2001, page 38dvj_transit_01
MAC interface links
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Data Communication DivisionCYPRESS
November 14, 2001, page 39dvj_transit_01
LiteLink features
mByte-wide 10Gb/s link (Gb/pin/s)– 11 pins total for clock, control, and data
mSLVS-400 transmitter, matched impedance– Technology independent 0.8V driver supply– .2V and .6V low and high signal levels
mDifferential receiver, matched impedance– Near DC encoding (5/11 or 6/11 ones)– Termination derived reference voltage
mSource synchronous, DDR clock
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Data Communication DivisionCYPRESS
November 14, 2001, page 40dvj_transit_01
Byte-wide coding properties
enco
der
data{0..7}
strobed
ecod
er
data{0..7}
strobe
error
2) About 1/2 asserted on each link1) Uncoded strobe
3) About 1/2 asserted on each group
4) Benefits of error detectionvia legal code checking
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Data Communication DivisionCYPRESS
November 14, 2001, page 41dvj_transit_01
LiteLink signaling
(…)(common reference)
(…)
enco
ded
Dat
a5a
strobe
enco
ded
Dat
a5b