19216811.liveVoIP SIP
VoIP SIP Servers, Users & the Forwarding Data-
iMG/RG Software Reference Manual (Voice Service)
6-22
Detaching a user from a port by means of the VOIP SIP USER REMOVE command, or, by deletion of the port
itself will result in a SIP de-registration transaction with the location server (assuming the user is registered
with the location server).
6.2.2.3 Forwarding database (FDB)
The forwarding database is a component of the iMG that is used to redirect calls to a different destination
address based on the called party number.
The signalling end-point layer uses the Forwarding DataBase every time the called end-point cannot be found
among the local users. It is used both for incoming calls from the VoIP network or for outgoing calls generated
locally and directed to a remote end-point.
The forwarding database may contain up to 100 entries (including users).
Forwarding entries are defined by the VOIP SIP FDB CREATE command.
Each FDB entry is uniquely identified by a name and defines the conditions that calls must satisfy in order to be
routed to the end point specified by FDB entry parameters.
•
When the signalling end-point layer receives a call it retrieves the called end-point address (called number).
•
Typically the called number is defined in the call signalling messages received from the network (in the
SIP
To
header).
•
If the call is locally originated the called number address is equal the dialled number (unless the ana-
logue/digital endpoint has the dialmask set to a value different from 0).
•
The Called end-point address is searched for among the local user addresses to establish whether the called
party is a user on the local system.
•
If the called end-point matches the address of a local user, the access port(s) associated with the called user
start ringing (if the port(s) are available).
•
If the called number cannot be found among the local users, the forwarding database is scanned to look for
entries matching the called number.
Note that the forwarding algorithm acts differently depending on whether the call is locally originated, or, is an
incoming call:
6.2.2.3.1 Locally originated calls
If a match is found, the INVITE message is routed to the IP address defined in the CONTACT field of the
matched FDB entry.
The called user domain will be set to the DOMAIN value (optional) or to the CONTACT
value (if no DOMAIN is specified) defined by the DOMAIN and CONTACT fields in the FDB entry respec-
tively.
If the FDB entry has defined the FWADDRESS field, the called number is changed from the dialed number to
the number defined in the FDB entry FWADDRESS field. In this way it's possible to dial short numbers that will
be replaced by full-qualified numbers in outgoing calls.