Re: Question on NULL character receiving

[Michael Lau <mlau@xxxxxxxxxxx>]

Paul and Norival,

Thanks for your reply and info.
You even gave me more information which I didn't know before -
NULLs can be anywhere, even including preamble, which means that
PHY can insert NULLs between 1st preamble 32-b word (where SOP locates)
and 2nd preamble 32-b word.

For the transmit direction, there will be some latency from the time
Reconciliation/MAC layer receiving HOLD signal from PHY to the time
MAC sending out NULLs on TXD.
In terms of implementation, I want to know whether this latency time can be
a range (for example, it can be 3 to 5 word-time) or an exact number.
Also, is it possible that Reconciliation/MAC layer will receive HOLD signal during
Tx IPG time?
And if it is possible, could Reconciliation/MAC layer delay sending out SOP/Preamble
by one word-time (if one word-time HOLD signal) and not sending out NULLs later?
This bascially increases the Tx IPG time for rate-control purpose.

Best Regards,
Michael

Paul Bottorff wrote:

Michael:

Yes, NULL characters are inserted in the receive stream whenever
overhead bytes are passing on the wire. These NULLs may be imbedded at
any point within a frame including the preamble and FCS. The NULL
insertion system removes requirements for PHY receive buffers to cover
the OVERHEAD times.

In the transmit direction NULLs are inserted in response to the HOLD
signal. The HOLD signal will be asserted whenever a transmit buffer
threshold is exceeded. This will happen whenever the transmitter is
generating OVERHEADs.

Cheers,

Paul

At 07:15 PM 2/10/00 -0800, Michael Lau wrote:
>>>>

> Norival and Paul,
>
> For your presentation of "10GE WAN PHY : PCS" on
> Jan 2000 IEEE 802.3 HSSG meeting,
> I have a question for your proposal of using NULL character
> for word-based flow control.
> If I am the Reconciliation/MAC layer, RXD<31:0>/RXC<3:0> are
> inputs to me.
> Do I expect to see NULL character in the receive data stream,
> as shown on Page 9 of your presentation?
> I think it makes sense to have it for OC-192 rate going into 10GE
> rate.
>
> Best regards,
> Michael Lau --  Michael V. Lau Allayer Communications Tel:
> 408-570-0888 x157 Fax: 408-570-0880 email: mlau@xxxxxxxxxxx
> <http://www.allayer.com>http://www.allayer.com !This email is
> forwarded by Allayer RoX switch!
>
>
>
>
>
Paul A. Bottorff, Director Switching Architecture
Enterprise Solutions Technology Center
Nortel Networks, Inc.
4401 Great America Parkway
Santa Clara, CA 95052-8185
Tel: 408 495 3365 Fax: 408 495 1299 ESN: 265 3365
email: pbottorf@xxxxxxxxxxxxxxxxxx

-- 
Michael V. Lau
Allayer Communications
Tel: 408-570-0888 x157
Fax: 408-570-0880
email: mlau@xxxxxxxxxxx
http://www.allayer.com

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