(a residential ethernet sg presentation) david v james jgg
TRANSCRIPT
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IEEE 802.3 RE Study GroupAtlanta
1March 2005
Clock synchronizationClock synchronization(a Residential Ethernet SG presentation)(a Residential Ethernet SG presentation)
David V JamesDavid V James JGGJGGAlexei Alexei BeliaevBeliaev GibsonGibsonGeorge George ClasemanClaseman MicrelMicrelGeoff GarnerGeoff Garner SamsungSamsung
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IEEE 802.3 RE Study GroupAtlanta
2March 2005
Categories of workCategories of work
– Service discovery (out of scope)• Identify/control “talkers” and their available “plugs”
– Subscription (802.1 centric)• Establish conversation between talker and listener(s)• Reject unless: linkBandwidth < linkCapacity
– Clock synchronization• Synchronous reception, forwarding, and presentation
– Prioritized queues• Talkers and 100Mb bridge ports must be gated
– Formats• Frame formats and content (stream IDs, time stamps)• Time aware service interfaces
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IEEE 802.3 RE Study GroupAtlanta
3March 2005
OverviewOverview
• What?– The clock slaves time-of-day tracks the grand master– No requirement for slaves to be clock-synchronous
• How?– Periodic exchanges of small messages
• Why?– Bridges: synchronized 125us cycles– Applications: accurate presentation times
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IEEE 802.3 RE Study GroupAtlanta
4March 2005
Leveraged protocolsLeveraged protocols
• Spanning tree protocol (STP)– Defines the grand-master precedence format– But, we use a distinct value and distribution protocol
(The STP root and grand master could be distinct!)
• NTP (RFC-1305) and SNTP (RFC-2030)– Definition of the 64-bit time-of-day value
• IEEE 1588-2002– Techniques for delayed-sampling synchronization
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IEEE 802.3 RE Study GroupAtlanta
5March 2005
Clock synchronizationClock synchronization
What?What?
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IEEE 802.3 RE Study GroupAtlanta
6March 2005
House reference clockHouse reference clock
802.11e
Ethernet
802.11e
1394 1394
Room #1 Room #2
Ethernet
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IEEE 802.3 RE Study GroupAtlanta
7March 2005
Legend:clock masterclock slave
Cascaded TOD synchronizationCascaded TOD synchronization
bridge[0]
bridge[1]
bridge[2]
Physical topology constraints
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IEEE 802.3 RE Study GroupAtlanta
8March 2005
Cascaded TOD synchronizationCascaded TOD synchronization
bridge[0]
bridge[1]
bridge[2]
Wall-clock distribution model
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IEEE 802.3 RE Study GroupAtlanta
9March 2005
Cascaded TOD synchronizationCascaded TOD synchronization
bridge[0]
bridge[1]
bridge[2]
Cascaded adjacent-synchronization hierarchy
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IEEE 802.3 RE Study GroupAtlanta
10March 2005
TimeTime--ofof--day format optionsday format options
fractionsseconds
nanosecondsseconds
>150 years <250 ps
(IEEE 1588)
OR(…)
ticks
(EPON)
16 ns
(NTP RFC-1305, SNTP RFC-2030)
(+epoc)
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IEEE 802.3 RE Study GroupAtlanta
11March 2005
Format selection criteriaFormat selection criteria
– Highest possible precision• Binary number (not BCD)
– Complete solution• 64-bit number
– Consistent with 1588, etc.• 32-bit seconds component
– Simple computations• 64-bit: seconds and fractions-of-second
– Client interface? • A logical interface (doesn’t really matter)
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IEEE 802.3 RE Study GroupAtlanta
12March 2005
TimeTime--ofof--day rate adjustmentsday rate adjustments
fractionsseconds
delayed carry
add6 add26
rate
carry56
rate
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IEEE 802.3 RE Study GroupAtlanta
13March 2005
systemID portNumbsp
TimeTime--ofof--day precedenceday precedence
stationID (byte swapped EUI-64)
1394 precedence
preferred
stationID (MAC-48)
802.1 STP precedence(IEEE Std 802.1D-2004)
pp
larger
smaller
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IEEE 802.3 RE Study GroupAtlanta
14March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
How?How?
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IEEE 802.3 RE Study GroupAtlanta
15March 2005
local offset
add
global
AdjacentAdjacent--station synchronizationstation synchronization
aTx
local offset
add
global aRx
bRx
bTx
Station A Station B
Timing snapshots
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IEEE 802.3 RE Study GroupAtlanta
16March 2005
local offset
add
global
AdjacentAdjacent--station synchronizationstation synchronization
aTx
local offset
add
global aRx
bRx
bTx
(aTx,aRx,bTx)
StationA StationB
Snapshot value distribution(information for stationB)
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IEEE 802.3 RE Study GroupAtlanta
17March 2005
local offset
add
global
AdjacentAdjacent--station synchronizationstation synchronization
aTx
local offset
add
global aRx
bRx
bTx(bTx,bRx,aTx)
Station A Station B
Snapshot value distribution(information for stationA)
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IEEE 802.3 RE Study GroupAtlanta
18March 2005
local offset
add
global
AdjacentAdjacent--station synchronizationstation synchronization
• rxDelta = (bRx – aTx); • txDelta = (bTx – aRx);• clockDelta = (rxDelta – txDelta) / 2; • cableDelay = (rxDelta + txDelta) / 2;• offsetB = offsetA – clockDelta;
aTx
local offset
add
global aRx
bRx
bTx
Station A Station BStationB offset adjustments
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IEEE 802.3 RE Study GroupAtlanta
19March 2005
local offset
add
global
Adjacent station synchronizationAdjacent station synchronization
local offset
add
global
Station A Station B
8 kHz
…
125µs
…
clockSync
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IEEE 802.3 RE Study GroupAtlanta
20March 2005
clockSyncclockSync frame format…frame format…
cycle[n-1]header
syncInfoselectInfo
trailer
cycleStartisoch0isoch1isoch2
isoch
async1async2
asyncN
asynch
async0cycle
increasingtime
(cycleCount)thisOffset
thisTxTimethatRxTimethatTxTime
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IEEE 802.3 RE Study GroupAtlanta
21March 2005
Why synchronous clockWhy synchronous clock--syncs?syncs?
– Simple• Uses existing isochronous transmission state machine
• Like IEEE 1588, requires only frame-sent snapshots
– Timely• Quasi-periodic transmissions
– Responsive• Sampling-to-adjustment delays are minimized
– Efficient• sequenceNumber is the cycleCount
– Consistent• Just another isochronous frame…
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IEEE 802.3 RE Study GroupAtlanta
22March 2005
rxInfo
Clock slave details (1)Clock slave details (1)
Rx
Tx
StationB
rxInfo
txInfo txInfo
cycle[n-1] cycle[n-0]
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IEEE 802.3 RE Study GroupAtlanta
23March 2005
ClockClock--slave details (2)slave details (2)
cycle[n-1] cycle[n-0]
TX
RX
headeroffsetTime
myRxTimer
thisTxTimethatRxTimethatTxTime
trailer
headeroffsetB
myTxTimer
thisTxTimethatTxTimethatRxTime
trailer
headeroffsetB
myTxTimer
thisTxTimethatRxTimethatTxTime
trailer
headeroffsetTime
myRxTimer
thisTxTimethatRxTimethatTxTime
trailer
rxDeltasubtracttxDeltasubtract
+−
globalTimer.offset+−
addition1/2
myOffset
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IEEE 802.3 RE Study GroupAtlanta
24March 2005
Timing specifics…Timing specifics…
(from IEEE 1588-2002, subclause D.1.1, page 127)
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IEEE 802.3 RE Study GroupAtlanta
25March 2005
A viable design modelA viable design model
PHY
globallocaloffset
MACclientglobalTime
rxStrobe txStrobe
txrxFIFOFIFO
convert
Notes:Rate matching FIFOsare not within our scope.
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IEEE 802.3 RE Study GroupAtlanta
26March 2005
fractions
offset
Conversion example: 1394Conversion example: 1394
fractionsseconds
cycle
(NTP RFC-1305, SNTP RFC-2030)
sec
b = (a*125)>>7
a
b
cycles
d = (c*3)>>6
c
d
Notes:Two 32-bit additions for b:
b= ((a<<7) - (a<<2) + a) >> 7;One 16-bit addition for d:
d = ((c<<2) + c) >> 6;
(IEEE 1394 CYCLE_TIME)
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IEEE 802.3 RE Study GroupAtlanta
27March 2005
Conversion example: EPONConversion example: EPON
fractionsseconds
(NTP RFC-1305, SNTP RFC-2030)
b = (a*193125)>>24
a
b
Notes:Thus, eight 36-bit additions compute a very precise b value:b= ((a<<17)+(a<<16)-(a<<12)+(a<<9)+(a<<6)+(a<<5)+(a<<2)+a) >>24;
(nanoTick = 16ns)
nanoTicks
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IEEE 802.3 RE Study GroupAtlanta
28March 2005
PassbyPassby PLLs PLLs (proposal 1)(proposal 1)
slave
PLL
clock
master
clock
master
clock
master
clock
gate gate gate gate
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IEEE 802.3 RE Study GroupAtlanta
29March 2005
Passthrough PLLs Passthrough PLLs (option 2)(option 2)
slave
PLL
clock
master
clock
master
clock
master
clock
gate gate gate gate
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IEEE 802.3 RE Study GroupAtlanta
30March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
Why?Why?
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IEEE 802.3 RE Study GroupAtlanta
31March 2005
Consider possible congestion…Consider possible congestion…
rx0 rx1 rx2 rx3 tx4
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IEEE 802.3 RE Study GroupAtlanta
32March 2005
delay
Bursting causes jitterBursting causes jitter
rx38 kHz
time
tx4
rx21 kHz
rx11 kHz
rx01 kHz
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IEEE 802.3 RE Study GroupAtlanta
33March 2005
delay
Bunching causes jitterBunching causes jitter
time
rx0
time
rx1
time
rx2
time
rx3
time
tx4
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IEEE 802.3 RE Study GroupAtlanta
34March 2005
Bridge reBridge re--clocking contains jitterclocking contains jitter
bridge
… gate
cycleCount
high
low
isochronous
…asynchronous
transmit
receivecycle-stamp(etc.)
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IEEE 802.3 RE Study GroupAtlanta
35March 2005
100Mb
Frame transmission timingsFrame transmission timings
time
Concept
1Gb
isochronouscycleStart asynchronous
10Mb
120µs
1200µs = 9.6 cycles
…
…
…
…
n-1 n-0 n+1 n+2 … n+9 n+10cycle:
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IEEE 802.3 RE Study GroupAtlanta
36March 2005
Synchronized reception/presentationSynchronized reception/presentation
clockA clockB clockC
No long-term drift: clockA, clockB, clockCClock jitter: sub nanosecond (after PLL)
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IEEE 802.3 RE Study GroupAtlanta
37March 2005
In summaryIn summary
– Time-of-day synchronization (house clock)• Global synchronization is required• Implemented as cascaded adjacent synchronizations
– Time synchronization formats• Binary time is accurate with simple add/subtract• Clock-master voting: 48+ or 64+ selection priorities
– Time-of-day applications• Synchronous reception and presentation, within applications• Synchronous re-clocking within bridges
– Time-of-day distribution• Pipelined sampling for highest accuracies• Cable delays can be derived, based on the same information
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IEEE 802.3 RE Study GroupAtlanta
38March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
Questions?Questions?
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IEEE 802.3 RE Study GroupAtlanta
39March 2005
SubscriptionSubscription(some possibilities)(some possibilities)
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IEEE 802.3 RE Study GroupAtlanta
40March 2005
Vocabulary terms (1)Vocabulary terms (1)
talker
audience
listener listener
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IEEE 802.3 RE Study GroupAtlanta
41March 2005
Vocabulary terms (2)Vocabulary terms (2)
– audience• The set of listeners associated with a talker
– clock master• A bridge or end station that provides a link clock reference
– clock slave• A bridge or end station that tracks the clock reference
– grand clock master (grand master)• The clock master that provides the network time reference
– listener• A sink of a stream, such as a television or acoustic speaker
– path• A logical concatenation of links and bridges for a stream
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IEEE 802.3 RE Study GroupAtlanta
42March 2005
Vocabulary terms (3)Vocabulary terms (3)
– service discovery*• The process used to identify/control/configure talkers
– stream• An RE frame sequence with a distinct streamID
– subscription**• Establishing committed paths between talker and listener(s)
– talker• A source of a stream, such as a cable box or microphone
* A complete solution/vocabulary includes out-of-802 scope activities** A complete solution/vocabulary includes out-of-802.3 scope activities
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IEEE 802.3 RE Study GroupAtlanta
43March 2005
FIFO
DelayDelay--matching matching listenerlistener FIFOsFIFOs
talker FIFO
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IEEE 802.3 RE Study GroupAtlanta
44March 2005
Multicast addresses!Multicast addresses!
– Multicasts are 1-to-N, not N-to-N• However, listener stations can listen to more than
one talker – Unicast
• Unicast is just a special case of 1-to-N (N is 1)• 1-to-N is an architectural/temporal extension
– Allocation of multicast addresses?• Multicasts addresses come from a server• Multicast address assignments are “distributed”• Multicast addresses == streamId == {source, plug}
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IEEE 802.3 RE Study GroupAtlanta
45March 2005
First access requestFirst access request
talker
listener
subscription request
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IEEE 802.3 RE Study GroupAtlanta
46March 2005
First access responseFirst access response
talker
listener
subscription response
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IEEE 802.3 RE Study GroupAtlanta
47March 2005
Second access requestSecond access request
talker
listener
subscriptionrequest
listener
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IEEE 802.3 RE Study GroupAtlanta
48March 2005
Second access responseSecond access response
talker
subscriptionresponse
listenerlistener
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IEEE 802.3 RE Study GroupAtlanta
49March 2005
Established pathsEstablished paths
talker
paths
audience
listenerlistener
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IEEE 802.3 RE Study GroupAtlanta
50March 2005
Teardown: talkerTeardown: talker audienceaudience
talker
teardown
audience
listenerlistener
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IEEE 802.3 RE Study GroupAtlanta
51March 2005
Teardown completedTeardown completed
talker
listenerlistener
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IEEE 802.3 RE Study GroupAtlanta
52March 2005
ThirdThird--party activationsparty activations
talker
Legend:Third-party activates the listener, provides talker’s streamIDListener subscribes to the talker’s streamID
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IEEE 802.3 RE Study GroupAtlanta
53March 2005
ListenerListener--initiated heartbeats (RSVP)initiated heartbeats (RSVP)
– RSVP based timeout strategy• Periodic local listener confirmations • Confirmations are really just subscription requests• Tolerate single-frame losses• Tolerates configuration changes
– Talker “leaves” if no requests observed– Listener “leaves” if no responses returns– Talker “responses”
• Is the flow of isochronous traffic sufficient?
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IEEE 802.3 RE Study GroupAtlanta
54March 2005
otherInfo
type/length
Subscription requestsSubscription requests
destinationAddress
sourceAddress
Frame format
FCS
Endpoint talker
Local listener
Endpoint listenerTalker’s plugRequired bandwidth
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IEEE 802.3 RE Study GroupAtlanta
55March 2005
Stream addressing?Stream addressing?
• A New Resource ReSerVation Protocol (RSVP)
(Again, in the Internet context a data source can be specified by the source host address plus source port number. We only refer to the source host address here.)
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IEEE 802.3 RE Study GroupAtlanta
56March 2005
What is a What is a streamIDstreamID??pl
ug[0
]
plug
[1]
plug
[2]
plug
[3]
plug
[4]
plug
[5]
plug
[6]
plug
[7]
plug
[8]
plug
[9]
plug
[10]
…pl
ug[6
5525
]
plug
[655
26]
plug
[655
27]
plug
[655
28]
plug
[655
29]
plug
[655
30]
plug
[655
31]
plug
[655
32]
plug
[655
33]
plug
[655
34]
plug
[655
35]
EUI-48
![Page 57: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/57.jpg)
IEEE 802.3 RE Study GroupAtlanta
57March 2005
What is the talker’s What is the talker’s streamIDstreamID??
plugIDOUIDA: 1 tag
payload
RE_STREAM
!STREAM_ID!
dependentOUISA: 0
EUI-48
![Page 58: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/58.jpg)
IEEE 802.3 RE Study GroupAtlanta
58March 2005
Are bridge changes necessary?Are bridge changes necessary?
– End-station throttling (assuming highest priority)• With 1Gb/s switches, this may be sufficient
– Source device spreads transmissions evenly• Bunching may be tolerable within the home (needs study)• Must ensure that nothing else uses the highest priority
– But, some access control changes needed anyway• Bridges are naturally encountered along the path• Central topology database is thus unnecessary
![Page 59: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/59.jpg)
IEEE 802.3 RE Study GroupAtlanta
59March 2005
SummarySummary
• We need an RSVP-like lower level protocol– Restricted to 1-to-N traffic– Restricted to “no-filter” streams
• The IP admission control alternative– Out of scope– Layering violations (non-IP synchronous traffic?)– Not generally supported by residential bridges– Multiple components (and synchronized use) required:
• A multicast address server?• IGMP/snooping for multicast setup?
• RSVP/snooping for bandwidth negotiation?
![Page 60: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/60.jpg)
IEEE 802.3 RE Study GroupAtlanta
60March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
Questions?Questions?
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IEEE 802.3 RE Study GroupAtlanta
61March 2005
Service discoveryService discovery(some possibilities)(some possibilities)
![Page 62: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/62.jpg)
IEEE 802.3 RE Study GroupAtlanta
62March 2005
DisclaimerDisclaimer
– “Service discovery” email has been “vocal”.• But, what is service discovery at Layer 2?
– This presentation clarifies a possible meaning• To stimulate and/or resolved internal discussions
– This is _not_ an advocated position!• Service discovery is not normally an L2 protocol• Higher level protocols have better flexibility&consensus
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IEEE 802.3 RE Study GroupAtlanta
63March 2005
What is service data?What is service data?
directoryleaf
directoryleaf
leaf
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IEEE 802.3 RE Study GroupAtlanta
64March 2005
What is service data?What is service data?
directoryleaf
directoryleaf
leaf
leafID
leafID-dependent
base length
DIRECTORY_ID
base length
base length
leafId
base length
…
base length
![Page 65: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/65.jpg)
IEEE 802.3 RE Study GroupAtlanta
65March 2005
SummarySummary
– Service discovery could be simple• Single frame of information keeps protocol simple
– Service discovery could be elegant• Directory structure supports organized data
– Service discovery could be flexible• 64-bit identifiers are easily self administered!• proprietary information well supported.• stealth protocols are easily defined.
![Page 66: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/66.jpg)
IEEE 802.3 RE Study GroupAtlanta
66March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
Questions?Questions?
![Page 67: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/67.jpg)
IEEE 802.3 RE Study GroupAtlanta
67March 2005
Synchronized timeSynchronized time--ofof--day clocksday clocks
Backup slides…Backup slides…
![Page 68: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/68.jpg)
IEEE 802.3 RE Study GroupAtlanta
68March 2005
Residential EthernetResidential Ethernet(an unofficial cumulative slide set; 2005Mar11)(an unofficial cumulative slide set; 2005Mar11)
Maintained by David V James
For most recent copy:
http://groups.yahoo.com/group/REInterestGroup
![Page 69: (a Residential Ethernet SG presentation) David V James JGG](https://reader034.vdocuments.site/reader034/viewer/2022042623/6264d09b2a2b9a700f6efbaa/html5/thumbnails/69.jpg)
IEEE 802.3 RE Study GroupAtlanta
69March 2005
Categories of workCategories of work
– Service discovery (out of scope)• Identify/control “talkers” and their available “plugs”
– Subscription (802.1 centric)• Establish conversation between talker and listener(s)• Reject unless: linkBandwidth < linkCapacity
– Clock synchronization• Synchronous reception, forwarding, and presentation
– Prioritized queues• Talkers and 100Mb bridge ports must be gated
– Formats• Frame formats and content (stream IDs, time stamps)• Time aware service interfaces
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IEEE 802.3 RE Study GroupAtlanta
70March 2005
Ethernet compatibility (yes!)Ethernet compatibility (yes!)
legacy bridge
Legend:legacy bridgelegacy endpoint
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IEEE 802.3 RE Study GroupAtlanta
71March 2005
otherInfo
type/length
Isochronous addressing?Isochronous addressing?
destinationAddress
sourceAddress
Frame
FCS
sourceAddress plugID stream
static assignments dynamicvs