Specifications

TD 92326GB
2009-03-10 / Ver. E
Installation and Operation Manual
VoIP Gateway
134
The source and destination of the call do not necessarily have to use the same gatekeeper,
figure 123 on page 135 shows the sequence of a call which is forwarded via two
gatekeepers.
The sequence of the call is the same for the destination and source as illustrated by figure
122 on page 133. The more complex infrastructure is fully concealed by the gatekeepers.
Only two gatekeepers now have to be known to one another. This again can be done via
the RAS protocol, either by one gatekeeper logging on to the other or by both
gatekeepers logging on to the other (step 1). The incoming call from the VoIP client is now
forwarded by the first gatekeeper to the second, which in turn forwards it to the
destination gateway. In this way, very complex structures can be set up involving a number
of gatekeepers.
The devices are managed dynamically by means of “Registration” in the RAS (Registration,
Admission and Status) protocol. First of all the registering device finds out which
gatekeeper is responsible. During this procedure, referred to as Gatekeeper discovery, the
terminal searches the network for a gatekeeper with the desired gatekeeper ID, a logical
name for the gatekeeper.
A number of gatekeepers can be operated in a network and found by “their” respective
devices by means of the gatekeeper ID. However, many external gatekeepers do not
support the gatekeeper ID.
The device transmits its identity and IP address once the gatekeeper has been identified.
This can be a logical name, a telephone number or both. The device is ready for operation
Tip: Many gatekeepers (and also some VoIP devices) do not support the Discovery
procedure. In this case the gatekeeper's IP address has to be configured in the
device to be registered. Likewise, multicasts of routers are not usually transmitted.
That is why the IP address of the gatekeeper also has to be registered if it is
separated from the registering device by a router.