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RE: [EFM] EPON TDMA - Small timeslots/DBA

Hi Xu,
	I'll take the liberty of answering this for Glenn. EPON uses a much
larger 'guard-band' than APON. This greatly simplifies the system timing,
however the trade off is a loss of efficiency. A typical EPON guard band -
this includes laser turn-off, turn-on, reciever AGC settling time, and PLL
locking - can be 5 to 10 micro-sec. At 8 ns per byte a 10 micro-sec gaurd
band is 1250 bytes. So using 64-byte timeslots would lead to an efficiency
of 64/(1250 + 64) ~ 4.8% .

	I hope this answers your question on why we dont use a small
timeslot. We will have to take another approach to DBA.

-----Original Message-----
From: xu zhang [mailto:zhangxu72@xxxxxxxxx]
Sent: Thursday, July 12, 2001 7:01 PM
To: glen.kramer@xxxxxxxxxxxx
Subject: [EFM] EPON TDMA

hi, glen:
 I had seen your presentation file about EPON TDMA in
PHY, it help me a lot to understand your EPON system. 
We had developed the first APON system in china, when
I think of the TDMA of EPON, I think though the uplink
data rate is 1Gbits/s when shared by 16 or 32 users is
still not enough, so the dynamic bandwidth
allocate(DBA) protocal must be a requiremant
especially when take care of the QoS performance. In
DBA protocal, in order to achieve high performance the
time slot need be to small, I think why not we divide
the ethernet packet to 64 byte per solt, it is often
used in ethernet switch when store packet in SRAM.

best regards
xu zhang

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