From: "Ed Tremblay (254-5515)" <[email-masked]>
Date: Thu, 1 Jul 93 08:06:03 EDT

Some questions on DLUR from Choon Lee:

(1) If a PU is directly attached to multiple DLURs, and/or co-located
;with a DLUR, how does it choose which one to use? Does it
;necessarily select the co-located one over the others?

>>>> I'm not sure what "co-located" means; if it means it is in the same
>>>> box or is an internal PU, it would use the DLUR in its own box.
>>>> As far as an external PU, if we're talking about a PU 2.0, I would
>>>> think it was usually attached to one subarea BF and would similarly
>>>> be attached to one DLUR BF.  If we're talking about a more
>>>> intelligent device supporting dependent LUs, maybe it could have
>>>> some smarts about selecting its DLUR.  One thing to consider is
>>>> predefining the same LU in more than one place; multiple DLURs may
>>>> or may not be served by the same DLUS, and different DLUSs
>>>> should not have the same LU defined, except for backup purposes.

(2) Page 8-3, section 8.2 DLUR EN tail vector registration
;If there is no DLUR/S involved, the EN waits until it gets a Find
;from its NNS before relaying its tail vector info. Why doesn't it
;do the same (i.e. wait until DLUS asks for it?) in the DLUR/S
;scenerio?

>>>> DLUR EN tail vector registration gets the tail vectors to the NNS
>>>> (in this case the DLUS) before the server needs to ask for them,
>>>> saving a Find.  It's a function first being introduced in DLUR/S,
>>>> but could be also some day be used by non-DLUR ENs and their NNSs.

(3) Page 8-4, section 8.2.1 DLUR/S capabilities exchange
;Since a DLUR which is also NN does not do tail vector registration,
;does it also not do the capabilities exchange?

>>>> All DLURs, whether they are NN or EN, will perform a DLUR/S
>>>> capabilities exchange.  That exchange is not solely done for FRSE
>>>> initialization, but to learn, for example, whether the DLUR is in
>>>> fact an EN or a NN to know whether tail vector registration will
>>>> be done or not.

(4) Page 11-2, section 11.2.2 DLUS and PLU in different subnets
;to calculate the route between PLU and DLUR, what is the
;significance of the NNS? Can a route not be determined by the
;NN topology map and the tail vectors?

>>>> Topology maps are only kept for a given subnet; for the section to
>>>> which you refer, where the DLUS and PLU are in different subnets:
>>>>   - if the DLUS and DLUR are in the same subnet, then the PLU is
>>>>     is a different subnet, and the NNS(PLU) does not have all of
>>>>     the topology to calculate a PLU-SLUR route (neither does the
>>>>     NNS(SLU))
>>>>   - if the PLU and DLUR are in the same subnet, or if all three
>>>>     (PLU, DLUS, DLUR) are in different subnets, the DLUS doesn't
>>>>     have valid tail vectors for an EN DLUR and must request them.
>>>> The NNS is where Locates are sent as part of a directory search of
>>>> an LU (PLU or SLU).  The NNS of the LU replies with tail vectors
>>>> if any so that whichever NN is calculating a route from its
>>>> topology, it can add the tail vectors to create a complete route.
>>>> This gets more complicated with multiple subnets, where no NN has
>>>> all of the topology to calculate a complete multi-subnet route by
>>>> itself.

Ed Tremblay