Cell Relay Archive

[cburkhardt2@home.com]

I have a question(s) concerning ATM OAM F4 & F5 Cells. 

Background:  At work, we routinely use the F4 & F5 Cells to test
connectivity on both Segment & End-to-End VPs & VCs.  A typical PVC 
consists of CPE (eg ADSL Modem), DSLAMs, and various ATM VP & VC
switches (eg Lucent, Nortel, Cisco routers, etc).  Other transports are
used (Enet, Fast-Enet, etc) but contain no VP/VC breakouts.

(QUESTION 1):

Concerns how to specifically address "intermediate" VP &or VC breakouts
for Loopback.  

As I understand the workings of F5, the Loopback points are either the
"End" (eg ADSL Modem) or "Segment" (eg next ATM VC switch) of the PVC
under test.  If more than (1) "intermediate" ATM VC switch is used, how
can those be addressed for Loopback test (hence fault isolation)?  I've
read that "Segmnet" F5s can be used for this but have not seen it done.

Same question for VP switching.


(QUESTION 2):

Concerns what activates PVCs (that is, being defined but not active
versus being defined and active).

Again, at work, we have conditions where we need to test PVCs with both
"End-to-End" & "Segment" F5 Loopbacks.  SOMETIMES the "Segment" F5
Loopback passes while the "End-to-End" F5 Loopback fails.  We pretty
much take this to mean that the Customer Premise equipment (ADSL Modem)
COULD be turned off, or the Local Loop is down.  SOMETIMES the "Segment"
& "End-to-End" F5 Loopback both fail, and the ATM VC switch maintainer
swears they have the PVC active.

So with all that, again, who/what controls whether a PVC is actually
"active" once defined/configured in an ATM switch.  

Can some ATM switches leave a PVC "nailed-up" when a Customer Premise
(ADSL modem) equipment is In-Active?  (Hence, good "Segment" F5 Loopback
but failed "End-to-End" F5 Loopbacks).  This condition is seen approx
50% of the time we test.

Can some ATM switches "dynamically" activate a PVC ONLY when the
Customer Premise (ADSL modem) equipment is Active?  (Hence, failed
"Segment" & "End-to-End" F5 Loopbacks).  This condition is seen approx
50% of the time we test.  I know this "dynamic" type of PVC setup sounds
self defeating for F5 Loopback tests, but I have not found a positive
answer yet.

Thanks,

Chris