Subject: [Dime] Comment about draft-moncaster-pcn-3-state-encoding-00

From: Fortune HUANG <[email-masked]>
Date: Thu, 24 Jul 2008 17:35:51 +0800

Hi all,

The table in section 6 seems to show that if a packet contains the DSCP
value DSCP1 or DSCP2 and Not-ECT(00) at the same time, it is a Not-PCN
packet.
      +--------+--------------+-------------+-------------+---------+
      |  DSCP  | Not-ECT (00) | ECT(0) (10) | ECT(1) (01) | CE (11) |
      +--------+--------------+-------------+-------------+---------+
      | DSCP 1 |    Not-PCN   | NM(Not-ECT) |    NM(CE)   |   ThM   |
      | DSCP 2 |    Not-PCN   |  NM(ECT(0)) |  NM(ECT(1)) |   ETM   |
      +--------+--------------+-------------+-------------+---------+
In this case, for each incoming packets, the interior node needs to identify
whether it is a PCN packet or not by two factors: the DSCP, and the ECN
bits. Because as is shown in the table, even if a packet contains the DSCP
value DSCP1 or DSCP2, it can also be a Not-PCN packet.
However, as is known to us all, one factor (i.e. the DSCP) is enough to
identify a PCN packet. And it will improve the performance before putting a
packet into the PCN queue by using only one factor to identify a PCN packet.
IMO, Not-ECT(00) doesn't need to be used. I wonder if we could put the table
in this way:
+--------+--------------+-------------+-------------+---------+
|  DSCP  | Not-ECT (00) | ECT(0) (10) | ECT(1) (01) | CE (11) |
+--------+--------------+-------------+-------------+---------+
| DSCP 1 |      -       | NM(Not-ECT) |    NM(CE)   |   ThM   |
| DSCP 2 |      -       |  NM(ECT(0)) |  NM(ECT(1)) |   ETM   |
| DSCP x |    Not-PCN   |  Not-PCN    |  Not-PCN    | Not-PCN |
+--------+--------------+-------------+-------------+---------+
NOTE: DSCPx is a DSCP codepoint other than DSCP1 and DSCP2.

Best regards,
Fortune
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