Subject: [mpls-tp] question about FPath in draft-ietf-mpls-tp-linear-protection-01

From: Francesco Fondelli <[email-masked]>
Date: Tue, 11 May 2010 14:15:31 +0200

Hi all,

FPath field must be used only in case of SF or SD according to:

---- http://tools.ietf.org/html/draft-ietf-mpls-tp-linear-protection-01

4.2.3. Path fault identifier (FPath)

   The Fpath field of the PSC control SHALL be used only in a Signal
                                      ^^^^^^^^^^^^^^^^^^
   fault (0110) or Signal degrade (0101) control packet.

---

but later on it's used for LO

---

4.3.3. Lockout of Protection

   If one of the LSRs (for example, LSR-A) receives a management command
   indicating that the protection is disabled, then it SHOULD indicate
   this to the far-end LSR (LSR-Z in this example) that it is not
   possible to use the recovery path.  The following actions MUST be
   taken:

   o  Transmit a PCS control packet, using GACH, with the Request code
      set to Lockout of protection (1110), the Fpath may be set to 0,
                                               ^^^^^^^^^^^^^^^^^^^^^^
      and the Path set to 0.
[cut]

   o  Begin transmission of a PCS control packet, using GACH, with the
      appropriate Request code (Lockout of protection), the Fpath set to
                                                        ^^^^^^^^^^^^^^^^
      0, and the Path set to 0, indicating that traffic is now being
      ^
---

and for MS or FS

---

4.3.5. Operator Controlled Switching

   If the management system indicated to one of the LSRs (for example
   LSR-A) that a switch is necessary, e.g. either a Forced Switch or a
   Manual Switch, then the LSR SHOULD switch the traffic to the recovery
   path and perform the following actions:

   o  Switch all data traffic to the recovery path only.

   o  Transmit a PCS control packet, using GACH, with the appropriate
      Request code (either Manual switch or Forced switch), the Fpath
                                                                ^^^^^
      may be set to 1, to indicate that there is an event that affects
      ^^^^^^^^^^^^^^^
      the working path, and the Path set to 1, indicating that traffic
      is now being forwarded on the recovery path.

[cut]

  o  Begin transmission of a PCS control packet, using GACH, with the
     appropriate Request code (either Manual switch of Forced switch),
     the Fpath may be set to 1, to indicate that there is an event that
         ^^^^^^^^^^^^^^^^^^^^^
     affects the working path, and the Path set to 1, indicating that
     traffic is now being forwarded on the recovery path.

---

Is this on purpose?  I mean, "SHALL be used only in a SF or SD pkt"
seems crystal clear to me.  Thus FPath field should be set to 0 on TX
and MUST be ignored on RX... or if you think it might be useful even in case
of LO, MS or FS then remove the "SHALL be used only in a SF or SD pkt"
text from Section 4.2.3 (I'd go for this option).

thanks a lot
Ciao
FF

PS
just a word about hold off timer (introduced at Section 3.1).

For WTR we have:

---
4.3.6.1. Wait-to-restore timer

   In revertive mode, in order to prevent frequent activation of
   protection switching due to an intermittent defect, the working
   transport path must become stable and fault-free before reverting to
   the normal condition.  In order to verify that this is the case a
   fixed period of time must elapse before the normal traffic uses the
   working transport path.  This period, called the Wait-to-restore
   (WTR) period, should be configurable by the operator in 1-minute
   intervals within the range 1-12 minutes.  The default value is 5
   minutes.
---

shouldn't we say something about HOFF too. Like "should be configurable
by the operator in 100ms intervals within the range 0-10 seconds.  The
default value is 0ms."?

---

From: "Weingarten, Yaacov (NSN - IL/Hod HaSharon)" <[email-masked]>
Date: Thu, 13 May 2010 09:01:54 +0200

Francesco. Hi

Thank you for your comments.

1. Regarding the FPath - yes you are correct that we should change the
"SHALL only be used" and maybe qualify it better as to when it will be
used.  However, most of the other quotes that you cite are of the nature
"may be set to..." and therefore are not technically in contradiction.
However, if only for the sake of clarity we need to clean up the
original statement.

2. Regarding the Holdoff timer - yes we can add something of this
nature.

Best Regards,
Yaacov Weingarten

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of ext Francesco Fondelli
Sent: Tuesday, May 11, 2010 15:16
To: [email-masked]
Subject: [mpls-tp] question about FPath
indraft-ietf-mpls-tp-linear-protection-01

Hi all,

---

---

and for MS or FS

---

[cut]

---

and MUST be ignored on RX... or if you think it might be useful even in
case

thanks a lot
Ciao
FF

PS

For WTR we have:

---

shouldn't we say something about HOFF too. Like "should be configurable
by the operator in 100ms intervals within the range 0-10 seconds.  The
default value is 0ms."?
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