asterisk users - Feb 2007 - Help sought: Asterisk H.323, Cisco IOS Gatekeeper(s) intra-zone call routing and TETRA

All,

I'm haveing a bit of trouble getting my head around H.323 and call routing
with Gatekeepers, Zones and intra-zone calls - hopefully someone who is more
informed in things H.323 will be able to point me in the right direction...?

I already have a mature network of Asterisk boxes dotted around the UK and
overseas with hundreds of extensions and our own number-plan/dial-plan in the
form 8EEXXXX where 'EE' is a two digit "exchange number" and
'XXXX' is the four digit extension number, so for example my desk phone
(a Cisco 7970G as it happens) at home is 8202001 and other phones around the
house 8202002, 8202003 etc.

I have a Cisco 2621XM connection to the internet with NM-2V and some
VIC-2E&M cards and have my home Asterisk box hooked up to ham radio and
other interesting audio sources which I use Asterisk ooh323 to make H.323
connections to the Cisco and its simple, reliable and just works.

I'm working on an R&D project with TETRA -- a digital trunked radio
system -- the hardware of which comes from Damm Cellullar (www.damm.dk) and is
called TetraFlex - the system supports point-to-point (half duplex), group
comminication and PABX/PSTN interconnect via H.323.  Further investigation shows
the system controller to be built on Windows-XP embedded and use the OpenH323
stack to provide H.323 connectivity, however the use of a Gatekeeper is
mandatory in their set up.

So, I have the following:

- a network of Asterisk boxes using 8EEXXXX numbering with IAX2 between sites,
hundreds of SIP and SCCP phones

- a TETRA system using 'mobiles' that I have numbered 817XXXX to fit my
number plan, a H.323 setup that requires a Gatekeeper

- an Asterisk box (1.2.14 + asterisk-addons-1.2.5) on the same LAN segment as
the TETRA system with OOH323 compiled up and working

- the devices are as follows:

        192.168.1.5    is the Asterisk box
        192.168.1.6    is the Cisco 2621XM GateKeeper
        192.168.1.7    is the Damm TETRA system


Where I am "stuck" is partly with the H.323 concepts and partly with
the implementation...

First I went in search of a H.323 Gatekeeper and tried to build the GNU GK from
source on another Fedora Core 6 box which turned out to be a nightmare (missing
libraries, the OpenH323 libraries appear to be deprecated in favour of Opal?
conflicting versions of pwlib, problems with yacc/bison building the ASN.1
parser, etc. etc.)  so next I turned to Cisco.  I have a spare 2621XM router
with c2600-jsx-mz.123-22.bin which includes a H.323 gatekeeper... great... so
I've configured it up (all three lines of it :o) so far:

    !
    gatekeeper
     zone local TETRA tubby.org 192.168.1.6
     no shutdown
    !

and can get both Asterisk and the Damm TETRA equipment to register with the
Gatekeeper, like this:


    router-h323-gw#show gatekeeper endpoints

                        GATEKEEPER ENDPOINT REGISTRATION
                        ===============================    CallSignalAddr  Port 
RASSignalAddr   Port  Zone Name         Type    Flags
    --------------- ----- --------------- ----- ---------         ----    -----
    192.168.1.5     1720  192.168.1.5     13030 TETRA             UNKN-GW
        H323-ID: PABX
        H323-ID: Asterisk
        E164-ID: 100
        Voice Capacity Max.=  Avail.=  Current.= 0
    192.168.1.7     1720  192.168.1.7     1085  TETRA             UNKN-GW
        H323-ID: DAMM
        Voice Capacity Max.=  Avail.=  Current.= 0
    Total number of active registrations = 2

    router-h323-gw#


Over at the Asterisk box I have the following in ooh323.conf:

    [general]
    ;Define the asetrisk server h323 endpoint

    bindaddr=0.0.0.0
    port=1720

    gateway=yes

    h323id=Asterisk
    e164=100

    gatekeeper = 192.168.1.6

    [cisco-gk]
    type=peer
    ip=192.168.1.6
    port=1720
    context=from-h323
    disallow=all
    allow=alaw
    allow=ulaw
    allow=gsm
    rtptimeout=60
    dtmfmode=rfc2833
    h323id=PABX


I have the Cisco document "Understanding H.323 Gatekeepers" available
here:

    http://www.cisco.com/warp/public/788/voip/understand-gatekeepers.html

While there is a diagram (top of page 10) in the Cisco document which appears to
show exactly what I want to make there's scant information on how to
configure it and hence its limited help with what I am trying to do, namely
gateway between two different H.323 gateways in a single zone and route calls
between the two gateways - for example:

    Route       Where           Description

    817....     TETRA           to mobiles/portables on the Damm TETRA system
    8......     PABX            to numbers in the rest of my number plan
    0.          PABX            through the PABX on to the PSTN
    9..         PABX            through the PABX to emergency 911/999


I can see how this be acheived if I had two Gatekeepers and two zones, say one
called "tetra" and one called "asterisk" by using zone
prefixes and "zone remote" to route between them and putting one of
the gateways on each of the Gatekeepers - but this appears to be over-the-top
for what I want, ie. two gateways on the same Gatekeeper at the same site, in
the same zone, routing calls between them...


Can anyone give me a clue where to go next with this?


Mike

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