Burst Mode Timing Ad-Hoc
Initial Discussion Document
Frank Effenberger
Huawei Technologies Co. Ltd
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Topics
• Burst mode capabilities
• Historical perspective
• Suggested path forward
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Burst mode capabilities
• OLT and ONT burst mode quality is highly
dependent on technology used
• Reuse of continuous mode parts yields rather
poor timing (microseconds)
• Use of specially customized circuits can yield
quite fantastic timing (10’s ns)
– However, such circuits are hard to get at first
• Thoughtful design can obtain anything in
between
– The choice is generally a matter of cost and other
pragmatic issues
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Historical Perspective
• IEEE side: Loose specification of both
– ONT got much better
– OLT got somewhat better
– But recovering the lost time is an issue
• ITU side: Tight specification on both
– ONT was never a problem
– OLT was very hard, and eventually needed to
be loosened
– This caused a market delay
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What we’ve already agreed
• Draft already captures the agreement:
– To specify a “loose” maximum value of Ton
and Toff (512ns)
– ONU to report actual values via MPCP
– OLT can thereby recover efficiency
• Why not extend this concept to the OLT
timing?
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Suggested path forward
• Loose maximum values of Tagc and Tcdr are
specified (400ns each)
– Optionally, informative ‘suggestions’ on better values
could be added: 200ns each for “AC coupled” designs,
50ns each for “dynamic coupled” designs
• OLT is free to do better, of course
• OLT broadcasts its burst-mode overhead
requirements in the downstream
– How long a series of 0x55 is needed
– What amount of rise-time control is needed
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Complexity consideration
• A downstream broadcast is not complicated
– There is no negotiation
– There is not much of a state machine impact
• ONU must simply wait until it hears a verified
“Downstream overhead” message
• Once received, the ONU:
– Sets the required parameters
– Proceeds with the remainder of the activation state
machine
• It is expected that upstream overhead will be
constant, therefore, other transitions are not
needed
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Thank you !
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