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VoIP gateway IP400 version 5.01
keeper's device management. They submit their identity and their current IP
address in the process. This step requires the RAS protocol and therefore
doesn't apply when operating without the RAS protocol.
• The IP telephone initiates a call (3.) and sets up a signalling connection to the
gatekeeper.
• The gatekeeper determines the call destination and sets up a signalling con-
nection to the destination (4.). The IP telephone and the gateway exchange
their IP addresses. Further signalling between the two of them goes via the
gatekeeper.
• The IP telephone and ISDN gateway directly set up the two voice channels
(5. and 6.) between one another.
The source and destination of the call do not necessarily have to use the same
gatekeeper. Fig. 20 on page 71 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 Fig. 19 on page 69. 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 IP telephone 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 device management is configured in the configuration applet in the
VoIP
Interfaces
area.
The devices are managed dynamically by means of
Registration
in the
RAS
(
R
egistration,
A
dmission and
S
tatus) 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 gate-
keepers do not support the gatekeeper ID.