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RE: [802.3ae] Clause 49: S Type Definition and PCS Receive State machine ( Figure 49-13)




Tuan,

A frame of 
  10 0x33 Invalid_control Idle Idle Idle Data Data Data
Is an E rather than an S. Therefore, the example you give of
  10 0xff Data Data Data Data Data Data Data
  10 0x33 Invalid_control Idle Idle Idle Data Data Data
is a T frame followed by an S frame. When the state machine is in 
RX_D and receives the T it will RX_TYPE_NEXT will be E and the state 
machine will go directly to RX_E. It will not go to RX_T.

The state machine and type definitions are just fine.

The principles on which Clause 49 is built are:

  Bit error rate is very very low.
  Undetectable corruption of data is very very very bad.
  Because bit error rate is very very low, discarding a frame because
an error occurred just before it or just after it causes a negligable 
change in the number of dropped frames.
  Therefore, if there is an error on the boundary of a frame it is better
to discard the frame rather than risk processing a bad frame which might
get through the CRC check.

Pat

-----Original Message-----
From: Tuan Hoang [mailto:tuanh@xxxxxxxxxxxx]
Sent: Friday, December 07, 2001 11:41 AM
To: stds-802-3-hssg@xxxxxxxx
Cc: Sheila Qiu (E-mail); Sumit Das (E-mail); Chung-Jue Chen (E-mail);
Nong Fan (E-mail)
Subject: [802.3ae] Clause 49: S Type Definition and PCS Receive State
machine ( Figure 49-13)





In clause 49, the S type definition is :

The vector contains Syn header of 10 and one of the following :
a) A block type filed of 0x33 and four valid control chearacters.
b).....



In a minimum IPG case, there might be two consecutive 64b/66b frames
transmitted by the PCS TX as followed:

  10 0xff Data Data Data Data Data Data Data
  10 0x33 Idle Idle Idle Idle Data Data Data

Due to a bit error, the above frames might be seen at the PCS receiver as:

  10 0xff Data Data Data Data Data Data Data
  10 0x33 Invalid_control Idle Idle Idle Data Data Data

According the the S type definitition, the second frame can not be decoded
as valid frame of "C C C C SOP Data Data Data".  However, the PCS Receive
State machine (Figure 49-13) does not allow a direct trasition of RX_T to
RX_E state.  Then how should the PCS Receiver decode this frame?  Should it
decode the invalid_control byte to ERROR byte and leave the rest of frame
intact? Or should it make the whole frame to be ERROR frame?  It looks like
that the requirment of S type and the state machine are in conflict for this
minimum IPG case.

Tuan