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ISDN Connection Management
2-6 — Orbitor 3000 Reference Manual
Idle Timer
In order to determine the criteria for suspending an ISDN call, an Idle Timer is defined. The Idle Timer
defines the period of time that LAN traffic is monitored to determine when the ISDN call will be put in
suspension and disconnected. When Interesting Traffic is observed once again, the call is reconnected.
The Idle Timer is common to all ISDN calls and may be defined from 6 seconds to 5 minutes in 1 second
increments. The Idle Timer may be disabled so that only the partner Orbitor determines when the ISDN call
will be suspended.
Orbitor Session Participation (Spoofing)
While an ISDN call is up and connected, all traffic within the sessions will be considered interesting and
will be transferred to the partner Orbitor across the ISDN call. When the Orbitor determines that the ISDN
call is to be suspended, the Orbitor will consider keepalive and routing information packets to now be non-
interesting and will begin to generate and respond to keepalive and RIP packets.
When the Orbitor receives a keepalive packet from the LAN for one of the sessions, the Orbitor will not
activate the ISDN call and will not pass the keepalive packet to the remote LAN. The Orbitor will generate a
response to the keepalive packet and send it to the originator of the packet. In this way, the Orbitor will keep
the ISDN call suspended and will also keep the local side of the session active. The Orbitor at the remote
site will also be participating in the keepalive process with the remote side of the session.
Figure 2—4 Session Keepalive Messages
While an ISDN call is suspended, if the Orbitor observes that one of the devices in the session stops sending
keepalive packets, the Orbitor will begin to generate keepalive packets and send them to the device in order
to determine the status of the device. The length of time the Orbitor waits before beginning to generate
keepalive packets is definable by the operator.
Orbitor routers incorporate a settling time for routing updates. This means that an Orbitor will wait after an
initial change in the network is reported before transmitting that change on to the remaining Orbitor routers
connected on the Wide Area Network.
The Orbitor will resume the suspended ISDN call in order to transmit routing messages to partner Orbitors.
If the ISDN call cannot be resumed, or has been closed, the routes will be aged out of the routing table.