TANDBERG D13691.03 user manual Search Order

TANDBERG Border Controller User Manual

Location Request to all the other Gatekeepers and Border Controllers on the system. Whilst conceptually simple, this sort of flat dial plan does not scale very well: adding or moving a Gatekeeper requires changing the configuration of every Gatekeeper and Border Controller; one call attempt can result in a flood of location requests. With 3 interconnected systems, an unknown alias can result in 28 LRQs, with 4 systems some 50,000 LRQs will be generated.

An alternative deployment would use a structured dial plan: endpoints are assigned an alias based on the system they are registering with. Using E.164 aliases, each Gatekeeper or Border Controller would be assigned an area code. When the Gatekeepers and Border Controllers are neighbored together, each neighbor is configured with its corresponding area code as a prefix. That neighbor will now will only be queried for calls to numbers which begin with its prefix. In a URI based dial plan, similar behaviour may be obtained by configuring neighbors with a suffix to match the desired domain name.

It may be desirable to have endpoints register with just the subscriber number — the last part of the E.164 number. In that case, the Border Controller should be configured to strip prefixes before placing the Location Request.

A structured dial plan will minimize the number of location requests issued when a call is attempted, but, as described above, still requires a fully connected mesh of all Gatekeepers and Border Controllers in your deployment. A hierarchical dial plan can simplify this. One Gatekeeper is nominated as the directory gatekeeper for the deployment. All Border Controllers and public Gatekeepers are neighbored with it and vice versa. There is no need to neighbor the Border Controllers and public Gatekeepers with each other. Adding a new Border Controller or public Gatekeeper now only requires changing configuration on that system and the Directory Gatekeeper.

Failure of the directory gatekeeper could cause significant disruption to communications. Con- sideration should be given to the use of Alternate Gatekeepers (section 3.4) for increased resilience.

Neighbors are added and zones configured through the command line interface using the xconfiguration zones family of command, xCommand ZoneAdd or through the web interface: Border Controller Configuration → Zones as shown in Figure 1. The prefixes and suffixes described above are formed using patterns: each zone may have up to 5 patterns assigned, each of which may be defined as a prefix or a suffix.

3.3.1 Search Order

If a called alias matches a prefix or suffix zone a strong match is achieved. A weak match is achieved if a zone is to be queried only because it has no pattern matching configured.

When an incoming call request is received a Border Controller will first search all of its registered endpoints. If no match is found, all strongly matching neighbor and traversal zones will be queried concurrently. If the target is not found in any of the strongly matching zones, all weakly matching neighbor zones will be queried, then all weakly matching traversal zones. Finally, if a match has still not been found, a DNS query may be attempted as described in section 6.

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