Understanding Gatekeepers, Gatekeeper Call Routing & CUBE - Part 2.1/3

The only document that comes to my mind when trying to decipher Gatekeeper Call Routing would be the "Understanding Cisco IOS Gatekeeper Call Routing" document (Document ID: 24462), especially the "GK Address Resolution on ARQ" flowchart on page 3 of the document; 
So from Part 1 of the document where we understood the functionality, benefits and use of the Gatekeeper in a VOIP Network, this document is going to cover the Gatekeeper Call Routing and the Configuration part of it all: 
For understanding the GK Call Routing Process we will use the following topology: 
• 3 Sites (London, Mumbai, Sydney) and one Gatekeeper Device (basically it’s just a Cisco ISR like the CME routers with an IOS capable of running Gatekeeper commands; I’m using the 2811 with the c2800nm-adventerprisek9_ivs_li-mz.124-24.T8.bin IOS as my Gatekeeper Device), we can have the Gatekeeper be one of the CME’s but I’ve separated it for ease of understanding... 
• All the CME’s are running on the Cisco ISR 2811 platform and the IOS is I’m using is c2800nm-adventerprisek9-mz.124-24.T8.bin 
• All the phones are registered as SCCP so you’ll see them as eFXS ports in the “show voice-port summary” on the CME’s... 
• Site London has a CME (hostname CME_LON) with 2 phones registered to it (Ph1_LON with extension 1001; PH2_LON with extension 1002) 
• Site Mumbai has a CME (hostname CME_MUM) with 2 phones registered to it (PH1_MUM with extension 2001; PH2_MUM with extension 2001) 
• Site Sydney has a CUCM Cluster (Pub & Sub) with 2 phones registered to the subscriber (PH1_SYD with extension 3001; PH2_SYD with extension 3002) 
• The Gatekeeper ISR has a hostname of GK. 
Now from the earlier post (Part 1/3) we mentioned having to register each Endpoint (CME or CUCM) to the gatekeeper before you can send any calls to the Gatekeeper, so the following is the configuration to define the local zones that each endpoint would register in and the configuration to register the endpoints to the GK. 
Define Zones in the Gatekeeper: (You can define multiple local zones in the gatekeeper and logically assign an endpoint to a zone, so for example all the endpoints in the City Sydney belong to the local zone called “Zone_Sydney” or maybe group the endpoints into local zones based on the area code of city, etc... defining what calls are routed to which local or remote zone is done by defining the zone prefix in the gatekeeper configuration) 

On the Gatekeeper: 

GK#conf t 
GK(config)#gatekeeper (switch on the gatekeeper process) 
GK(config-gk)#zone local Zone_London cisco.com (we’ll register all our endpoints located in London to this zone) 
GK(config-gk)#zone local Zone_Mumbai cisco.com (we’ll register all our endpoints located in Mumbai to this zone) 
GK(config-gk)#zone local Zone_Sydney cisco.com (we’ll register all our endpoints located in Sydney to this zone) 
GK(config-gk)#no shut (bring up the gatekeeper process) 

Registering the endpoints 

Registering the CME endpoints to the Gatekeeper: 

CME_LON# 
CME_LON(config-if)# interface loopback0 (choose an interface that would be used to register as an h323 endpoint to the gatekeeper) 
CME_LON(config-if)#h323-gateway voip interface 
CME_LON(config-if)#h323-gateway voip id Zone_London 142.102.64.1 (you can add the endpoint to any local zone that you defined in the gatekeeper configuration above but for our scenario we will register the London CME to the local zone Zone_London, the ip address is the ip address of the gatekeeper device) 
CME_LON(config-if)#h323-gateway voip h323-id CME_LON (this is the name the endpoint would be registered with as shows up later in the “show gatekeeper endpoints” command on the gatekeeper) 
CME_LON(config-if)#tech-prefix 0044 
CME_LON(config)# gateway