[cisco-voip] CCM4.1, Gatekeeper and tech prefix routing

[Andre Beck]

Hi,

I've got a network of several H.323 gateways (IOS, currently running
CCME) and a central gatekeeper to which they all nicely register their
phone numbers, allowing me to do dynamic call routing even with a random
(non-hierarchical) dial plan the organization uses and needs to stay
with. The gatekeeper is also a gateway (registering to itself) and besides
running CCME it has the E1 egress point to the PSTN as a dialpeer.

Now this architecture is beeing merged to a central CCM 4.1 cluster
with all the former CCME gateways beeing turned into SRST gateways.
I plan to stay with the gatekeeper so if CCM fails altogether, the
phones will register to their respective SRST gateways, the gateways
will register the phone numbers to the gatekeeper and given that they
are still reachable, call routing will continue to work.

Sadly enough, CCM has a major flaw IMO: It doesn't register the numbers
it knows about to the gatekeeper. I've got the gatekeeper and trunk set
up perfectly, the CCM registers, but the GK doesn't know what numbers
are there. I've read docs up and down and assume that is the way it is -
no option to activate number registration anywhere (probably a scalability
issue).

Now the basic question is: How does the gatekeeper decide which unknown
(not registered) number is routed to which gateway? The tech support
proposes to use tech prefixes and the IOS GK feature "default-technology"
which essentially defines a default route for all unknown numbers towards
the gateway with a certain tech prefix. In the trivial setups shown in
these tech papers, this is sufficient.

My problem: It is not sufficient here, as I have *two* kinds of unknown
numbers, and they have to be routed to *different* gateways: The numbers
that should be routed to the PSTN (must be routed to the gateway that
also happens to be the gatekeeper) and the remaining numbers (must be
routed to the CCM). They are easy to differentiate from each other, the
PSTN directed ones all start with 0 (this is not the NANP), but I don't
find a way to tell this to the gatekeeper. I could direct them to another
zone easily, but they are not going to another GK, they are simply to
leave the IP world alltogether.

Now what I did for a partial solution:

1) The gateway with the PSTN dialpeer registers with another tech
   prefix than the CCM. Say CCM registers with 1#* while the gateway
   registers with 2#*
2) In every route pattern on the CCM that routes 0-starting numbers
   towards the gatekeeper trunk, I prefix the called party number
   with 2#
3) On the gateway, the dialpeer destination is changed from 0T to 2#0T

The good thing: This works. It routes exactly as intented.

The bad thing: The phones change the display of the called party number
from 0xxxxx to 2#0xxxxx which looks weird and disturbing. It is correct
and more of a cosmetic issue, but I can't deploy it this way. So is there
a way to do this without having the display change? Ideally there would
be a special tech-prefix option in the route pattern as is in the voip
dialpeer on IOS, but I only found the explicit prefix.

Long question, but I spent hours on it, either. Any comments are
welcome. This includes comments on whether a setup as described
(GK for dynamic routing to SRST gateways) is feasible or going
to work at all...

TIA,
Andre.
-- 
                  The _S_anta _C_laus _O_peration
  or "how to turn a complete illusion into a neverending money source"

-> Andre Beck    +++ ABP-RIPE +++    IBH Prof. Dr. Horn GmbH, Dresden <-