Nortel 1000 Description, Installation And Operation Manual page 35

Depending on the Gatekeeper type (for example, Gatekeepers other than
CS 1000S or CS 1000M), if the Gatekeeper flag in the dial plan file indicates
the need for multiple IP Trunk 3.01 card IP addresses (flag value = 0), the
RRQ includes all IP addresses for the node. These additional IP addresses are
reserved exclusively for calls to the Gatekeeper. By sending all the IP
addresses in the RRQ, the Gatekeeper is able to determine the origin of the
admission requests. These addresses are used when the Gatekeeper considers
the endpointIdentifier sent to the gateway in the RRQ confirmation to be
insufficient to confirm that the Admission Request (ARQ) belongs to a
gateway registered with that Gatekeeper. The Gatekeeper rejects any ARQ
from an unknown end-point.
Note: CS 1000S or CS 1000M require an endpointIdentifier match and
does not care about the IP addresses. Therefore, the Gatekeeper flag is
unnecessary for CS 1000S or CS 1000M.
On startup, the message flow between the IP trunk card serving as the
IP Trunk 3.01 (and later) Active Leader and the Gatekeeper is as follows:
1 Gatekeeper Request (GRQ) – From the Active Leader to the
Gatekeeper, using the provisioned Gatekeeper IP address. The Optivity
Telephony Manager (OTM) configuration indicates where the IP Trunk
3.01 (and later) node must look for its Gatekeeper, but this is not
necessarily the actual Gatekeeper address the node uses for call
processing.
Some Gatekeepers use a "virtual IP address" to screen the fact that the
Gatekeeper with which the gateway registers has internal standby
controllers. In this case, the request might go to a Gatekeeper server that
determines the correct virtual IP address. The Gatekeeper's internal
Message Forwarding process sends the messages to the current active
Gatekeeper node.
Note: CS 1000S or CS 1000M do not require a Gatekeeper Request
from IP Trunk 3.01 (and later); therefore, no Request or Confirm is sent.
2 Gatekeeper Confirm (GCF) – From the Gatekeeper to the Active
Leader, with the functional Gatekeeper IP address. This address is used
for all call control messaging and registration messages between the IP
Trunk 3.01 (and later) cards and the Gatekeeper.
Overview of IP Trunk 3.01
IP Trunk Description, Installation, and Operation
Page 35 of 644