Subject: Re: [Adslmib] Re: About configuring line mode in draft-ietf -adslmib-vdsl-09

From: Bob Ray <[email-masked]>
Date: 28 May 2003 13:30:24 -0500

On Wed, 2003-05-28 at 10:30, Ettore Guadagnino wrote:

> thank you Bob.  I'm just wondering why in the ADSL-EXT-MIB the object
> adslConfProfileLineType has been defined so that the manager can select
> among the line mode to use (noChannel, fast, interleaved, fastOrInterleave,
> fastAndinterleave).
> Why this is not needed for VDSL?
> What do I miss ?
> 
> Bye, Ettore.

I agree that SOME mechanism for changing the line type is needed
for establishing which channel(s) are being used. 

The reason such an object is NOT in the VDSL Line MIB is that
it introduces a great flood of complications, not to mention
violating a bunch of rules.  You need to remember that a VDSL
Line has THREE entries in the ifTable: 

    the physical line, ifType = vdsl(97),
    a fast channel, ifType = fast(124), and
    an interleave channel, ifType = interleave(125)

If we were to make vdslLineType read-write, for example, then an
administrator/user might change vdslLineType from both(5) to 
noChannel(1).  One might expect such a change to influence the 
ifTable in various ways.  Perhaps even to expect the agent to 
delete the entries (horror!) of type fast and interleave.  Given 
that there are rules about the persistence of interfaces, this
would introduce a dilemma (not to mention the additional text
I would have to write for the VDSL Line MIB!!!).

An alternative to deleting the entries in the ifTable (or adding 
them somehow when the converse change is made), would be to change 
the status of the entries.  That is, change ifOperStatus to 
notPresent(6) (or up(1) in the converse).  But if this interaction 
between an ifEntry and a VDSL Line must be maintained by an agent, 
then why not simply use the facilities in ifTable to control the 
channels in the first place?  

For example, when a VDSL Line Card is first inserted, create three 
new entries in the ifTable - the line, fast, and interleaved.  Then
enable and/or disable these elements via ifOperStatus or ifAdminStatus
per the mechanics discussed in RFC 2863.  vdslLineType would reflect
these settings.

Does this help?

Regards,
Bob Ray
PESA Switching Systems
http://www.pesa.com

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