Filter
Top Products
ISDN Connection Management
27
Termination Process
When the router has determined that there are no sessions active on an ISDN call, the router will attempt to
close the call. If the partner router 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 router 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 router needs to send data to the partner ISDN router.
If the operator of the router 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 router dependent upon the destination IP address contained within IP traffic received from the local
LAN.
This means that the router continuously monitors IP traffic from the local LAN, as all IP routers do, and makes
ISDN connections to partner routers 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 router 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 router
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 router 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 router observes that one of the devices in the session stops sending
keepalive packets, the router 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 router 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 router, the router will
determine that the device has gone away and the router 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 router will re-
activate the suspended ISDN call and transmit the shut down packet to the remote device. Once the remote
router determines that the TCP session is no longer active, the remote router will stop generating and
responding to the keepalive packets for that TCP session.
RIP—Routing Information Protocol
The P2600 ISDN routers incorporate a 3 second settling time for IP RIP updates. This means that an router
will wait for three seconds after an initial change in the network is reported before transmitting that change on
to the remaining routers connected on the Wide Area Network.