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

RE: (Another) Question Regarding Open-Loop Control Mechanism

I do not see any problem with removing the first /R/ column of the XAUI,
even if the MAC generated a 12 bytes gap. It just that if the DTE-XGXS chip
is doing it, the minimum gap of the transmitter can be as low as 9-4=5

However, this happens only if the PHY clock frequency is much lower tnan the
MAC clock. There is no "danger" that in the other side (In the receive side)
there will be a need for further compresion of the IPG because the 200ppm
difference is End-To=End requirement.

In the WAN-PHY case, this can be done by the PHY-XGXS.

I do not think it is good idea to limit the /R/ removal operation for IPG
which are grater than 2 columns, because if you do that, you have to provide
additional IPG criteria like "Avarage size of IPG" or to say that you must
provide an IPG which is at least 3 columns periodically, and it is complex.

I think we can agree that while packets are generated, the min IPG is 2
columns as in the current proposals, but may decrease to one column before
going to the MDI.
-----Original Message-----
From: pat_thaler@xxxxxxxxxxx [mailto:pat_thaler@xxxxxxxxxxx]
Sent: Thursday, August 31, 2000 7:27 PM
To: boazs@xxxxxxxxxxxx; stds-802-3-hssg@xxxxxxxx
Subject: RE: (Another) Question Regarding Open-Loop Control Mechanism


Part of the purpose of the non-extended IPG (that is, the traditional 96
bits) is to allow physical
layer devices to drop some of the idle in order to move between clock
domains that have the 
ppm clock difference. The difference in maximum size packet duration between
slowest and
fastest clocks is less than 3 bits. The MAC does not need to lengthen the
gap to compensate
for this.

Because our physical layer devices will only be able to drop or add idles in
increments of 4
bytes, dropping an idle from a 12 byte IPG will reduce it to 8 bytes. We
will need to consider
the limits on shortening idle in order to specify the limit of IPG
shrinkage. For instance, if
a device gets a 9 byte IPG, can it shorten that IPG or should it wait for a
longer idle? For
some alignments, the 10GBASE-R PCS encoding requires 8 bytes of idle
(counting the /T/
as part of the idle) to produce valid codes so at least for that case, it
will need to look for
a long enough IPG before shortening. Since short gaps can not happen
constantly, within
a packet or two a long enough one will arrive.

By the way, if you do the calculation for the open-loop control mechanism,
you will see that
when extending the IPG to adapt to the WIS data rate, it adds less than a
byte per a minimum
size packet. Therefore, a 10GBASE-R PCS doing the adaptation for WIS also
receives IPGs
as short as 9 bytes and will need to wait for a long enough IPG to do the
idle deletion.


-----Original Message-----
From: Boaz Shahar [mailto:boazs@xxxxxxxxxxxx]
Sent: Tuesday, August 29, 2000 11:53 PM
To: HSSG (E-mail)
Subject: (Another) Question Regarding Open-Loop Control Mechanism

When the MAC device and the PHY device are driven by a different clock
source, How does  Clock Tolerance Compensation between the two done? 
(That is, since the max difference between the two is 200ppm, then the MAC
may always adjust the rate to the nominal rate - 200ppm? And if so: Is it
acceptable ?)

Sorry if this was asked before.