Nortel 1000 Description, Installation And Operation Manual page 31

IP Trunk 3.01 (and later) uses the Meridian 1/CS 1000M core switch as the
primary driver, which sends ISDN messages through the ISDN Signaling
Link (ISL) to the IP trunk card for IP Trunk 3.01 (and later) processing. IP
Trunk 3.01 (and later) tandems the Meridian 1/CS 1000M core switch to the
IP network, providing point-to-multipoint connection.
Alternatively, depending on the provisioning and the requested destination, if
a call cannot be resolved locally, IP Trunk 3.01 (and later) can interwork with
the Gatekeeper to identify the destination node before routing directly to that
destination.
Two types of calls can be routed through interworking with the Gatekeeper:
directly-routed calls and Gatekeeper-routed calls.
WARNING
The only Gatekeeper that IP Trunk 3.01 (and later)
officially supports is the CS 1000S
Gatekeeper. Gatekeeper calls made between the
CS 1000S
later) are directly-routed calls.
Directly-routed calls
In directly-routed calls, the Gatekeeper returns the IP address of the call's
actual destination.
Figure 2 on page 32
address is obtained, the originator sends the call directly to the destination
node.
Overview of IP Trunk 3.01
or
CS 1000M system and IP Trunk 3.01 (and
represents a directly-routed call. Once the destination IP
IP Trunk Description, Installation, and Operation
Page 31 of 644
or
CS 1000M