RE: [802.3ae] Regarding Sequence ordered sets (Clause 48)
Hi Pat,
RS may choose to truncate the ongoing frame with inserting /E/ in frame and delineating it with /T/.
I would think this should be legal to do too rather than just transitioning from Data to Idle or
sequence_ordered sets. In anycase it could be fragment and neither case packet will be accepted.
Do you see any harm in it?
Thanks,
Sanjeev
At 02:56 PM 11/28/2001 -0700, pat_thaler@xxxxxxxxxxx wrote:
>
>Bob,
>
>Good explanation. I want to clarify something. Naresh asked: "Is it
>possible for sequence ordered sets to appear in the middle of a data frame?"
>
>The answer is sequence ordered sets cannot appear "in the middle of a data
>frame" One will not see Start of a frame/sequence ordered sets/remainder of
>that frame.
>
>When the RS is sending a frame and needs to switch to sending a sequence
>ordered sets, that ends the frame in an errored state. One wouldn't want the
>RS to put a T character out to terminate the frame because that might create
>a fragment that looks like a valid frame (if by chance the last 4 bytes had
>a correct CRC for the prior content). The rules in clause 46 cover receiving
>a transition from data to control without a T.
>
>An intermediate device such as a PCS may detect a fault condition and
>similarly transition from sending data to sending the Local Fault sequence
>ordered set.
>
>Also, note that at the receiver, the transition from data to sequence
>ordered sets may appear as a transition from data to idle (without a T) if
>there is an XGXS or a 10GBASE-X PCS between the transmitter and the
>receiver. These sublayers convert a series of sequence ordered sets into an
>idle with sequence ordered sets interspersed every 16 to 32 columns to
>prevent the EMI effects of sending a repeating data pattern.
>
>Pat
>
>-----Original Message-----
>From: Grow, Bob [mailto:bob.grow@xxxxxxxxx]
>Sent: Monday, November 26, 2001 4:49 PM
>To: 'stds-802-3-hssg@xxxxxxxx'
>Subject: RE: [802.3ae] Regarding Sequence ordered sets (Clause 48)
>
>
>I don't what your clause 48 concern is. I think the possible cases are all
>described in clause 46.
>
>A Remote Fault sequence ordered set is only generated by the RS, and only in
>response to detecting a Local Fault condition on the receive path.
>Conceptually, the link fault state machine on the receive path switches a
>transmit path mux from MAC frames to RS generated Remote Fault ordered sets.
>This is done without sending a Terminate (sending a Terminate would increase
>the undetected error rate). Action is similar for detection of a Remote
>Fault condition, with the exception that a frame in transmission would be
>truncated with Idle instead of sequence ordered sets.
>
>Transmission of the Remote Fault sequence ordered sets (or Idle) continues
>until the link fault condition is cleared. It is theoretically possible
>when the condition is cleared to be in the middle of a transmitted frame
>(either the same frame or a different one. At the remote receive RS, the
>reception of either Idle or Remote Fault ordered sets will terminate the
>initial starting frame fragment as an error frame. The trailing frame
>fragment (no Start) will be ignored by the remote receiving RS.
>
>So, only looking at the data stream, at the receiving RS, a beginning frame
>fragment and an trailing fragment can be separated by a string of columns
>starting with a non-data column. The standard only describes generation of
>that string as Local Fault sequence ordered sets, Remote Fault sequence
>ordered sets, or Idle. The receiving RS though will behave the same if
>something else is received within the string (e.g., a corrupted sequence
>ordered set, inserted Idle, ect.)
>
>Therefore, a PCS encoder or decoder can will be hit with changes from data
>to ordered sets, data to Idle, Idle to ordered sets, ordered set to
>different ordered set, etc.
>
>--Bob Grow
>
>-----Original Message-----
>From: Naresh Raman [mailto:naresh@xxxxxxxx]
>Sent: Sunday, November 25, 2001 8:36 PM
>To: stds-802-3-hssg@xxxxxxxx
>Subject: [802.3ae] Regarding Sequence ordered sets (Clause 48)
>
>
>All,
>
> I have a question regarding Sequence ordered sets. Is it possible for
>sequence ordered sets to appear in the middle of a data frame?
>
> Clause 46.3.4 (lines 27-29) says that the RS can possibly truncate a MAC
>frame being transmitted to generate Remote Fault Status over the transmit
>path. I would like to know if this means that there will be a sequence
>ordered set inserted in the middle of the MAC frame or will the MAC frame be
>terminated (by sending a Terminate control character) before the Sequence
>ordered set is inserted in the transmit path.
>
>Thanks,
>Naresh Raman.
>LSI Logic.
>