RE: [802.3ae] Regarding Sequence ordered sets (Clause 48)
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
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
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.
From: Grow, Bob [mailto:bob.grow@xxxxxxxxx]
Sent: Monday, November 26, 2001 4:49 PM
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.
From: Naresh Raman [mailto:naresh@xxxxxxxx]
Sent: Sunday, November 25, 2001 8:36 PM
Subject: [802.3ae] Regarding Sequence ordered sets (Clause 48)
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.