Subject: Question on outgoing calls in L2TP

From: Christian Huitema <[email-masked]>
Date: Mon, 29 Jun 1998 16:11:04 -0400 (EDT)

Looking at the L2TP draft (draft-ietf-pppext-l2tp-11.txt) I could
not find the answer to what I would call the "dial-out redirection"
problem.

Suppose that a tunnel has been established an LNS and a LAC, and that
the LNS requires to set up an outgoing call towards some telephone
number. Suppose now that the LAC is unwilling or unable to set-up
that call, but that it could "redirect" that call towards another
NAS, that would either have more available ports or be nearer, from
a phone tariff point of view, from the dialed number.  I did not
find a way to encode this redirection.  Should it be added to the
spec, or did I simply not look close enough?

-- 
Christian Huitema
----------
See you at INET'98, Geneva 21-24,July 98 http://www.isoc.org/inet98/

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From: "W. Mark Townsley" <[email-masked]>
Date: Mon, 29 Jun 1998 17:32:29 -0400 (EDT)

> spec, or did I simply not look close enough?

There is a Result Code and optional Error Code included in the CDN that is
sent from the LAC when an unacceptable Outgoing Call-Request is received.

As a basic indication of lack of resources, one of the following Result
Codes could be utilized within the CDN, depending on which is more
appropriate: 

      4 - Call failed due to no appropriate facilities being
          available (temporary condition)
      5 - Call failed due to no appropriate facilities being
          available (permanent condition)

Alternatively, there is a set of General Error Codes that are shared
between the CDN and StopCCN messages which also could convey a similar
messsage:

      4 - Insufficient resources to handle this operation now

      7 - Try another.  If LAC is aware of other possible LNS
          destinations, it should try one of them.  This can be used to
          guide an LAC based on LNS policy, for instance, the existence
          of multilink PPP bundles.

There are no mechanisms to "suggest" another LAC to the initiating LNS
beyond these. Thus, currently it is fully up to the LNS to be aware of
alternatives if they exist.