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al
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Review and Update ofCarrier Extension Propos
Howard M. Frazier, Jr.Sun Microsystems Computer Company
Internet and Networking Products Group11-November-1996
IEEE 802.3z TF
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IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Outline
■ Introduction
■ Topologies
■ Bit Budget
■ Issues
■ Solution
■ Impact on MAC
■ MAC Parameters
■ Impact on Reconciliation Sublayer
■ Performance
■ Conclusions
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/s switched
mplicated than
/s
ulously
sential
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Introduction
■ Scaling CSMA/CD to 1000 Mb/s is a good idea
■ Widely implemented, well understood protocol
■ Demonstrated low cost at 10 and 100 Mb/s
■ Cost benefit of 1000 Mb/s shared versus 1000 Mb
■ Scaling CSMA/CD to 1000 Mb/s is slightly more coscaling it to 100 Mb/s
■ Wire delays are 10x larger (in BT) than at 100 Mb
■ “shift the decimal point” approach results in a ridicsmall collision domain diameter
■ Backwards compatibility with 10 and 100 Mb/s is es
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repeater
domain
d desktops
desktops
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Topologies
■ Most useful CSMA/CD topologies have at least one
CSMA/CD used in a single repeater collisionwithin a server room
1000 Mb/s repeater
100/1000 switches
10/1000 switches
high en
low end
servers
1000
1000
1000
1000
1000
100
10
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omains
esktops
sktops
d desktops
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Topologies (cont)
CSMA/CD used in single repeater collision dwith 1000 Mb/s horizontal runs
1000 Mb/s switch
1000 Mb/s repeaters
100/1000 switches
higher end d
high end de
servers &ultra high en
1000
1000
1000
1000
1000
1000
100
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sktops must
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Topologies (cont)
■ Horizontal runs are 100 meters maximum
■ A CSMA/CD topology with horizontal runs out to desupport a diameter of at least 200 meters
100 m100 m
200 m
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d bit budget
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Bit Budgets
■ Bit budget calculations are highly dependent on:
■ Physical layer signalling method and architecture
■ MAC <=> PHY data path width
■ MAC state machine frequency
■ Repeater data path width
■ Repeater state machine frequency
■ Fairness issues
■ See Stephen Haddock’s presentation for an updateanalysis
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,
tic
12 bits
es
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Bit Budgets (cont)
■ Conclusions from bit budget analysis
■ Cable delay dominates, but even with short cablesthe bit budget exceeds 512 BT
■ DTE and repeater delay estimates may be optimis
■ The minimum frame size must be increased from 5to achieve useful topologies at 1000 Mb/s
■ Recommend a new minimum frame size of 512 Byt
■ Simply change bits to bytes!
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ameSize
x linksm size
10 Mb/s networks,
e 802.3 MAC when format
only onher Ethernet or
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Issues
■ It’s not that simple
■ Trying to solve the problem by increasing the minFrto 512 Bytes has harmful side effects
■ Degrades maximum small packet rate on full duplewhere it is not necessary to use the larger minimu
■ Can’t propagate the inflated packets to 100 Mb/s orthe performance loss would be hideous
■ Can’t rely on the padding/stripping mechanism in thusing protocol stacks which use the Ethernet frame
■ Must find a way to extend the minimum frame size 1000 Mb/s, CSMA/CD networks, regardless of whet802.3 frame format is used
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nt without
ls
ation
d passing the
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Solution
■ Conceptually, extend the duration of the carrier eveextending the data field, or altering the FCS field
■ Introduce a new mechanism which appendsnon-data symbols to the end of short frames
■ Extend the collision window to include these symbo
■ Include the extension in the fragment discard calcul
■ Remove the extension before checking the FCS anframe to LLC
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are recognized
n integer
FCS Extension
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Solution (cont)
■ Frame extension
■ The extension symbols are non-data symbols, and as such by the MAC and the PHY
■ The extension starts on an octet boundary, and is anumber of octets in length
Preamble SFD DA SAType/Length
Data
64 bytes min
512 bytes min
FCS Coverage
Duration of Carrier Event
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e 4.4}
end of frame}
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC
■ New const (4.2.7.1)const
extendSize = ...; {in bits, implementation-dependent, seextensionBit = ...; {a new type of non-data bit}
■ New Transmit State Variable (4.2.7.2)var
extension:0..extendSize; {length of extension}
■ New Receive State Variable (4.2.7.3)var
extendCount: 0..extendSize; {count of extension bits at
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IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC
■ Mod to StartTransmit (4.2.8)procedure StartTransmit;begin
extension := 0;currentTransmitBit := 1;lastTransmitBit := frameSize;transmitSucceeding := true;transmitting := true;lastHeaderBit := headerSize
end; {StartTransmit}
■ Mod to StartReceive (4.2.9)procedure StartReceive;
begincurrentReceiveBit :=1;extendCount := 0;receiving := true
end; {StartReceive}
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+ extendSize);
itBit]);
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC (Transmitter)
■ Mod to BitTransmitter (4.2.8)process BitTransmitter;begin
cycle {outer loop}if transmitting thenbegin {inner loop}
if halfDuplex then (extension : = minFrameSizePhysicalSignalEncap; {send preamble and sfd}while transmitting dobegin
if currentTransmitBit > lastTransmitBit thenTransmitBit(extensionBit)
elseTransmitBit(outgoingFrame[currentTransm
if newCollision then StartJam else NextBitend;
end; {inner loop}end; {outer loop}
end; {BitTransmitter}
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it)
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC (Transmitter)
■ Mod to NextBit (4.2.8)procedure NextBit;
begincurrentTransmitBit := currentTransmitBit + 1;transmitting := ((currentTransmitBit ≤ lastTransmitB
or (currentTransmitBit ≤ extension))end; {NextBit}
■ Mod to StartJam (4.2.8)procedure StartJam;
begincurrentTransmitBit := 1;lastTransmitBit := jamSize;extension := 0;newCollision := false
end; {StartJam}
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extendSize) then
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC (Transmitter)
■ Mod to WatchForCollision (4.2.8)procedure WatchForCollision;begin
if transmitSucceeding and collisionDetect thenbegin
if currentTransmitBit > (minFrameSize - headerSize +lateCollisionError := true;
newCollision:= true;transmitSucceeding := false
endend {WatchForCollision}
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sfd}a Access}
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC (Receiver)
■ Mod to BitReceiver (4.2.9)process BitReceiver;
var b: Bit;begin
cycle {outer loop}while receiving dobegin {inner loop}if currentReceiveBit = 1 then
PhysicalSignalDecap; {strip off the preamble andb := ReceiveBit; {get next bit from physical Mediif receiveDataValid then
if b = extensionBit thenextendCount := extendCount + 1elsebegin {append bit to frame}
incomingFrame[currentReceiveBit] := b;currentReceiveBit := currentReceiveBit + 1
endreceiving := receiveDataValidend {inner loop}frameSize := currentReceiveBit - 1 + extendCount
end {outerloop}end; {BitReceiver}
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rriving}
t boundary}
ize + extendSize));
);
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on MAC (Receiver)
■ Mod to ReceiveLinkMgmt (4.2.9)procedure ReceiveLinkMgmt;begin
repeatStartReceive;while receiving do nothing; {wait for frame to finish aexcessBits := frameSize mod 8;frameSize := frameSize - excessBits; {truncate to octeif halfDuplex thenbegin
receiveSucceeding :=((frameSize ≥ ³(minFrameSframeSize := frameSize - extendCount
endelse
receiveSucceeding := (frameSize ≥ minFrameSizeuntil receiveSucceeding
end;
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IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
MAC Parameters
■ New Parameter Table 4.4.2.4
Parameters Values
slotTime 4096 bit timesinterFrameGap 96 nsattemptLimit 16backoffLimit 10jamSize 32 bitsmaxFrameSize 1518 octetsminFrameSize 512 bits (64 octets)addressSize 48 bitsextendSize 448 octets
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ATA.request
d by the
ATA.indicate
d by the
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Impact on Reconciliation Sublayer
■ 22.2.1.1.2 Semantics of the service primitive PLS_D
■ Add EXTEND to the range of values communicateOUTPUT_UNIT parameter
■ 22.2.1.2.2 Semantics of the service primitive PLS_D
■ Add EXTEND to the range of values communicateINPUT_UNIT parameter
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P
tribution
sults using
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
erformance
■ Simulations used “workgroup average” packet size disderived from some “real world” sampling
■ See Mohan Kalkunte’s presentations for simulation re“workgroup average” packet size distribution
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/s
ate
IEEE P802.3zGigabit Task Force
Howard M. Frazier, Jr.
Conclusions
■ Useful CSMA/CD networks can be built at 1000 Mb
■ The performance of the baseline proposal is adequ