Subject: Re: [Fwd: Re: IPSP proposed text (1st approach)]]

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 31 Oct 2001 23:37:19 -0600

Dennis,

Your example does not highlight any differences
between the single-ended and double-ended approaches.

      +------+                                  +------+
      |      |                                  |      |
      | AS   |                                  | AS   |
      | 100:4|                                  | 201  |
      |      | \                              / |      |
      +------+   \  +-----+   IP   +-----+  /   +------+
                   /       \------/       \
      +------+     | IPSP1 |      | IPSP3 |     +------+
      |      +- - -\       /-+   /\       /- - -+      |
      | AS   |      +-----+   \ /  +-----+      | AS   |
      | 100:3|                 \                | 200  |
      |      |      +-----+   / \  +-----+      |      |
      |      +- - -/       \-+   \/       \- - -+      |
      +------+     | IPSP2 |      | IPSP4 |     +------+
                   \       /------\       /
      +------+   /  +---- +        +-----+  \   +------+
      |      | /                              \ |      |
      | AS   |                                  | AS   |
      | 100:5|                                  | 202  |
      |      |                                  |      |
      +------+                                  +------+

Consider example RC assignment for both the
single-ended and double ended cases at IPSP3
in the following table:

                                     RC Values
				==========    ======
                                  Double      Single
    IPSP/    Remote    Local      Ended        Ended
     Assoc     AS       AS      R->L  L->R     L<->R
    -------  -------   -----    ----  ----     -----
       1      100:4     200      4     1         1  
       1      100:4     201      3     2         2  
       1      100:3     200      2     3         3  
       1      100:3     201      1     4         4  
       2      100:3     200      4     1         1  
       2      100:3     201      3     2         2  
       2      100:5     200      2     3         3  
       2      100:5     201      1     4         4  

As you can see, the same AS pairings occur for both
cases.  With the single-ended approach, IPSP3 has half
the RC values to keep track of.  That's it.

When IPSP1 loses activation of AS100:3 in the double-
ended case it would send ASPIA RC=4 (from the table)
to IPSP3.  If IPSP3 loses activation of AS200 it would
send ASPIA (RC=1,3) to IPSP1.

When IPSP1 loses activation of AS100:3 in the single-
ended case it would send ASPIA RC=1 (from the table)
to IPSP3.  If IPSP3 loses activation of AS200 it would
send ASPIA (RC=1,3) to IPSP1.

The same information is conferred, but in the single-
ended case you need half the RC values and do not have
to worry about half-duplex relationships between AS.

Does this make things perfectly clear to you?

There is absolutely no point in a double-ended
procedure.  Double-ended procedures add overhead and
complexity where not required.

--brian

Dennis Niermann wrote:                                     (Wed, 31 Oct 2001 10:11:03)
>
> Brian,
>
> I don't think that what you suggest is workable.
> If one RC value is used that identifies both 
> ASs in a pair then problems arise.
> 
> If IPSP1 sends an ASPIA to IPSP3 using RC=3 to
> indicate that it is no longer serving AS100:3,
> which of the ASs that IPSP3 is serving need to 
> also use RC3 on that association? 
> Both AS200 and AS201?
> Or, just one of them?
> If both AS200 and AS201 use RC3 then there is no way
> distinguish between them.
> If just one of them use RC3, then it breaks your rule 
> that the same RC value should be used by the ASs on
> each side of the association. 
> 
> /Dennis
> 

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/

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