ISDN Connection Management
Orbitor 3000 Reference Manual— 2-7
Termination Process
When the Orbitor has determined that there are no sessions active on an ISDN call, the Orbitor will attempt
to close the call. If the partner Orbitor still has sessions assigned to that call, the call will be maintained until
each side has determined that there are no active sessions using the call.
When the connection to the partner ISDN Orbitor is configured to use Auto-Call, the ISDN call will be
suspended when there are no session in the table. The ISDN call will be re-established to the Auto-Call
number the next time the Orbitor needs to send data to the partner ISDN Orbitor.
If the operator of the Orbitor performs a link reset, the suspended call will be closed unilaterally.
IP Specifics
IP Address Connect
As stated previously, an IP Address Connect connection is an ISDN connection that is established to a
specific destination Orbitor dependent upon the destination IP address contained within IP traffic received
from the local LAN.
This means that the Orbitor continuously monitors IP traffic from the local LAN, as all IP routers do, and
makes ISDN connections to partner Orbitors when IP traffic needs to be sent to remote LANs. Once the IP
traffic is passed to the remote LAN and all sessions are closed, the local Orbitor will then disconnect the
ISDN call and continue to monitor the local LAN for IP traffic.
The IP Address Connect table consists of IP addresses and associated ISDN numbers of remote partner
Orbitor IP Routers. Either one or both of the ISDN calls may be used for IP Address Connect use. When one
of the ISDN calls is defined for Auto-Call purposes, the remaining ISDN call may be used for IP Address
Connect use.
The combination of Auto-Call and Address Connect allows part of the WAN environment to be established
statically and still allow dynamic connections to other networks depending upon destination IP addresses.
Suspension of TCP/IP Sessions
When Connection Management is enabled, TCP sessions that are established across the ISDN calls are
monitored and maintained in a table. The TCP session table may contain up to 256 entries. The Orbitor will
filter all traffic for any TCP/IP session over the 256 limit of the table preventing any new TCP sessions from
being established.
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.
If the device does not respond to five consecutive keepalive packets sent from the Orbitor, the Orbitor will
determine that the device has gone away and the Orbitor will send a packet to each end of the TCP session
to shut down the session. When the shut down packet is generated for the remote device, the Orbitor will re-
activate the suspended ISDN call and transmit the shut down packet to the remote device. Once the remote
Orbitor determines that the TCP session is no longer active, the remote Orbitor will stop generating and
responding to the keepalive packets for that TCP session.
RIP—Routing Information Protocol
Orbitor ISDN routers incorporate a 3 second settling time for IP RIP updates. This means that an Orbitor
will wait for three seconds 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.
