RE: Clause 48: unaligned 8b10b stream problem
First lets assume the case you outlined actually happened - that a lane
slipped a bit but did not cause Loss of Sync.
In this case:
- align_status=fail would occur within 8 frames (since the first ||I||
after every other frame would be an ||A||)
- The receiver would then generate local fault
- The RS would then transmit remote fault to the link partner sourcing the
- Upon reception of remote fault, the link partners RS would then inhibit
frame transmission and source ||I||
so in a worse case, if this unlikely scenario was occurring, then after 8
frames + the max round trip propagation delay, the Sync state machine would
lose sync (after receiving 4 bit-slipped /A/,/K/,or /R/ which would cause
Given the unlikely nature of the problem, this "slow" recovery mechanism
seems to be adequate and requires no change to the standard.
UNH InterOperability Lab
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of
Sent: Tuesday, May 01, 2001 3:39 PM
To: stds-802-3-hssg@xxxxxxxx; rtaborek@xxxxxxxxxxxxx
Subject: Clause 48: unaligned 8b10b stream problem
I have a concern about turning off comma detection and not having a timer to
indicate no recent commas.
I believe I am looking at this correctly. Let me know if I am missing
If a valid 8b10b stream becomes out of alignment, I believe there is a
chance that it would never be realigned.
It may be a statistically rare case, but I thought I would mention it.
Here is the case:
- The interface is using maximum bandwidth for packets and is only
transmitting minimum IPG.
- A bit slip or bit insertion in the stream happens so that bit alignment
- Many of the valid codewords if shifted by one are still valid; this may
not cause Loss of Sync. D21.5 can be shifted and be fine. LOSyn takes 4
codeblock violations which consists of 4 codewords. An occasional codeword
violation may not cause Loss of Sync to happen.
- The IPG codewords shifted would not be valid, but they do not occur often
enough (with min IPG) to cause Loss of Sync. This would only definately
cause 6 codeword violations or 2 codeblocks.
- Since Loss of Sync never happened, the commas would never be detected and
the stream would never be realigned.
I have not had a chance to see statistically how many codwords can be
shifted and still be valid. That is an important question. The next
question will be is if that number is ok to not change the state machine.
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