Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: Clock Tolerance and WAN PHY


I strongly agree with your suggestion below, and Brad Booth's note along
the same vein, to leave any conversion between Ethernet and SONET at the
ELTE level. This would allow the LAN PHY, Serial or WWDM, it doesn't
really matter since the ELTE does the required conversion, to natively
serve LAN, MAN and WAN applications at the lowest possible cost. At the
same time, the same LAN PHY can attach to an ELTE and operate in "WAN
PHY mode" to support SONET/SDH. The latter would be applicable to those
legacy SONET/SDH core applications, again, AT THE LOWEST POSSIBLE COST.

Of paramount importance to the customer is our ability to meet the
Economic Feasibility PAR criteria. In a nutshell this criteria states
that the cost of 10GE shall be ~3.5X the cost of Gigabit Ethernet at
product maturity. I don't visualize copying SONET/SDH, requiring +/-20
PPM clock tolerance, supporting overhead bytes, etc. as helping us meet
our economic feasibility objectives. However, I do see straightforward
mappings, the same clock tolerances as Gigabit Ethernet (+/-100 PPM),
protocol simplicity, relaxed jitter specifications, etc. as meeting the
objectives. The latter are characteristics of the LAN PHY, the former
are characteristics of the WAN PHY.

Ethernet has met its economic feasibility objectives for three
generations through selection and leverage of low cost physical layers.
This will happen again through simple extension of Gigabit Ethernet
physical layer technology as is the case for the LAN PHY. It should be
obvious to the most casual observer that the more that SONET/SDH is
leveraged for 10GE, the higher the total 10GE solution cost will be.

Just reading though the notes of this thread, it looks like there's
about as many ways to map Ethernet to SONET as there are to skin a cat.
Here are some of the ones from this thread:

1) Ethernet over LAPS, ITU-T SG7
2) Packet over SONET, ???
3) Ethernet over SONET/SDH, ITU-T SG7 X.86 
4) Ethernet over SONET/SDH, T1X1
5) Digital Wrapper, ITU-T ???
6) G.709, ITU-T (Same as Digital Wrapper???) 
7) IEEE P802.3ae WAN PHY

I'm kind of partial to Ethernet over Ethernet.


Best Regards,

Boaz Shahar wrote:
> MAC - (Serial lan phy) - ELTE - (sonet ring) - ELTE - (serial lan phy) - MAC
> Anyway, the WIS takes 64/66 frames and encapsulates them into the SONET
> frame. So just take the 66/64 bit stream that comes to the ELTE through the
> serial LAN and do the same there with a full SONET compliancy. Is that
> correct? What is the advantage comes from doing the WIS in the PHY? (The
> rate is not a problem Just operate the MAC in SONET rate as you do anyway
> and put the FIFO in the ELETE as you anyway have in the WIS)
> Thanks (Sorry for the long mail)
> Boaz
Richard Taborek Sr.                 Phone: 408-845-6102       
Chief Technology Officer             Cell: 408-832-3957
nSerial Corporation                   Fax: 408-845-6114
2500-5 Augustine Dr.        mailto:rtaborek@xxxxxxxxxxx
Santa Clara, CA 95054