Re: Question about Open-loop in XGMII MAC ...
I have a couple of questions pertaining to Shimon Muller's proposed
MAC/PHY rate control solution:
1. Are the IDLES added by the MAC to perform rate compensation in
addition to those added by the RS to perform start-of-packet
octet-0 alignment?
2. Does this imply that the MAC will always in effect be adding IDLE's
in multiples of four to the data stream, which in turn will be filtered
out by the PHY?
3. Will the 12 IDLE IPG minimum be required once the MAC data
is mapped into the SONET frame, or is this only a MAC/PHY
interface requirement?
Fundamentally if the method of rate control is going to be through
additional null-data being added to the stream, then it is of my
opinion that the standards committee has an obligation to detail the
precise mechanism in which this data is to be added in order to
insure reliable, predictable, and interoperable performance of the
link. To date this detail has not yet been provided. The proposed
method requires the PHY to process the input stream by filtering the
IPG at both the MAC/PHY and PCS/WIS interfaces. To assure that
we don't encounter packet loss due to buffer overflow/underflow,
the IPG needs specific definition at all interfaces to allow PHY
designers to precisely determine buffer size, and other design
details. Otherwise, link performance will be highly vendor
specific, undeterministic, and unreliable.
John Irwin