Reference:PBX Locations

Introduction

Locations in the PBX are reworked in v6 for the following reasons:

• In v5 locations which could be addressed only with a prefix could only be administrated locally, so in an installation with many small locations all with prefixes, it was very hard to get an overview over the system in total and backup of the configuration was difficult.
• There is the frequent feature request for group functions not only within one location but for groups of users in different locations. To implement group functions for users which are actually registered in different locations consumes a lot of bandwidth between locations and does not scale very well.

The general idea to solve these problems is to separate the location where a user registers (registration PBX) from the location of the user inside the numbering plan (numbering node) and again from the physical location (physical-location) of the user.

This way call routing can be based on the numbering node and physical-location wheras group functions can be performed for users within a registration PBX.

Locations

The numbering node

Each object is assigned to a node in the numbering tree. All objects within one numbering node can call each other without the use of prefixes. A numbering-node object with the name of the node defines the prefix for the node. The numbering node of the object itself defines where this numbering node is located inside the total numbering plan. There is one implicitly defined numbering node “root” without a prefix. Objects which are configured with a numbering node “root” can be called without prefix. This way a tree of numbering nodes can be defined.

The registration PBX

Each PBX entity running on a gateway is a registration PBX, with a name configured locally on this gateway . Each object is assigned to a registration PBX. If a device registers for an object, this registration is accepted only by the registration PBX defined for the object. By definition, a registration PBX always needs to be assigned to a numbering node as well, so a location object is used to configure it. If there are more than PBXs in a single numbering node, separate pseudo numbering nodes must be created for the PBXs.

The physical-location

The physical-location is not configured but determined for each device on runtime depending on the PBX the original registration was sent to. This physical-location is not necessarily identical to the registration PBX since if the registration is sent first to a PBX which is not the registration PBX for this object, it will be the physical-location anyway, but the registration is redirected to the registration PBX.

GatekeeperId

As GatekeeperId for the registrations of endpoints at the PBX, the registration PBX is used. If a PBX has to redirect a registration, because the user is not defined on this location it is redirected to a gatekeeperId with the form new-location/old-location. This way the incoming GatekeeperId can be used to determin the physical location of an endpoint.

Local Objects

Any object can be marked as “Local”, which means that it can only be called from endpoints with the physical-location being the registration PBX of this object, or by dialing explicitly the prefix of the numbering node of physical location PBX. If routing based on the numbering node fails (which can only determined on the master), it is additionally checked if there is a match for the dialed number within the physical-location of the endpoint.

Routing

The routing of calls works by applying the following rules in this precedence on each PBX the call is handled:

• The dialed number is searched within the numbering node of the calling endpoint.
• If there is no match the call is sent to EXTERN if such a registration exists
• If there is no match in the current or the call to EXTERN fails with “unallocated number” numbering node, the search is continued on the next higher node
• If the destination cannot be resolved locally the call is sent to the respective master.
• If the call is already at the master and a “local-only” object was found, the physical location of the endpoint is searched for a match.
• If there is still no match, the call is terminated with cause “unallocated number”

Objects

Location Definition

Defines the prefix of a numbering node. The numbering node of the location definitions itself defines the location of this node within the complete numbering plan.

Escape

Defines a number which is used to route the call to the next higher numbering node. This way a numbering scheme like in the public telephone network can be established: define a numbering node for each country, inside each country define Escape(0) to access the international numbers, define numbering nodes for each area code, define Escape(0) inside each area code to access the national numbers. This is esspecially useful if a multi-level numbering scheme has to be implemented to avoid conflicts of location prefixes with normal user numbers.

Redundancy

The master of a registration PBX (the PBX where this PBX is registered) always acts as standby for the registration PBX. One registration PBX which is registrated at a given master can be configured as standby to this master. If the physical location of a user is different from the registration PBX this physical location will also act as standby if the connection to the master fails. On the endpoint the physical location has to be configured as primary gatekeeper. As alternate gatekeeper the respective master (where the physical-location is registered) has to be configured, or a PBX which is registered at the physical location and is configured as standby.

Replication

Relpication is done based on the multi-value attribute rep. Each object with an attribute rep matching the location name is replicated to the respective registration PBX. These attributes rep are not configured manually but the master PBX is attaching these attributes to objects so that in each replication PBX the required objects are present. To allow the physical-location to act as standby, the registration PBX adds a rep attribute indicating the physical-location whenever a registration comes in from a physical-location which is not the registration PBX. For the replicator on a given PBX only the location-name has to be configured. On PBXs which are configured as standby for a master, the replicator is configured to replicate the complete database from its master without the configuration of a location.