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

[Andrew Dignan]

To route certain prefixes to unregistered gateways, you need to use the
alias static command.  For example, if you would like to route 0* numbers
to one gateway, and 1* numbers to another your config would look like this
on the gatekeeper:

Alias static <gw ip> 1720 gkid HQGK gateway voip ras <gw ip> 1719
Alias static <gw ip> 1720 gkid HQGK gateway voip ras <gw ip> 1719
Gw-type-prefix 0* gw ipaddr <gw ip> 1720
Gw-type-prefix 1* gw ipaddr <gw ip> 1720


> 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 <-
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