Nortel 1000 Description, Installation And Operation Manual page 85

System description Page 85 of 644
The ISL interface makes available the flexibility of using ISDN signaling to
analog facilities. When no Primary Rate Interface (PRI) exists between two
Meridian 1/CS 1000M systems, ISL operates in dedicated mode. A dedicated
point-to-point signaling link is established between the two systems. The
signaling information for the selected analog trunks is transported over the
ISDN signaling link. The analog ISL TIE trunks are for user voice transport.
If the D-channel link is down, call control returns to normal in-band analog
trunk signaling.
The ITG is similar to the existing ISL configuration where there is a Virtual
Private Network (VPN) between Meridian 1/CS 1000M systems. Instead of
a one-to-one connection, multiple switches can be networked through a single
ISL interface at each site. Figure 17 on page 86 shows an IP Trunk 3.01 (and
later) trunk configuration with three Meridian 1/CS 1000M systems. The IP
Trunk 3.01 (and later) trunk simulates an analog facility. The ISL interface is
connected to a DCHIP PC Card which provides ISDN to VoIP tandeming. All
IP Trunk 3.01 (and later) IP trunk cards (DCHIP, Leader, and Follower) are
connected through the Embedded Local Area Network (ELAN) subnet. The
IP trunk cards communicate with remote switches through the IP network.
IP Trunk Description, Installation, and Operation