Perle Systems IOLINK-PRO IOLINK-520 - Manual (Page 27)

ISDN Connection Management
2.6 — IOLINK-PRO & 520 Reference Manual
When the IOLINK router receives a keepalive packet from the LAN for one of the sessions, the IOLINK
router will not activate the ISDN call and will not pass the keepalive packet to the remote LAN. The IOLINK
router will generate a response to the keepalive packet and send it to the originator of the packet. In this way,
the IOLINK router will keep the ISDN call suspended and will also keep the local side of the session active.
The IOLINK router at the remote site will also be participating in the keepalive process with the remote side of
the session.
This Router will receive the keepalive
frames destined for the Client and generate
a response back to the Server on behalf of the
Client while the ISDN call is suspended.
The Server generates keepalive frames
which are to be sent to the Client and
acknowledged by the Client.
The Client receives the
keepalive frames and
sends an acknowledged
back to the Server.
While the ISDN call is
suspended, this Router
will generate keepalive
frames and send them
to the Client and wait for
an acknowledement from
the Client.
Client
Server
Suspended
Figure 2 - 4 Session Keepalive Messages
While an ISDN call is suspended, if the IOLINK router observes that one of the devices in the session stops
sending keepalive packets, the IOLINK 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 IOLINK router waits before
beginning to generate keepalive packets is definable by the operator.
IOLINK routers incorporate a settling time for routing updates. This means that an IOLINK router will wait
after an initial change in the network is reported before transmitting that change on to the remaining IOLINK
routers connected on the Wide Area Network.
The IOLINK will resume the suspended ISDN call in order to transmit routing messages to partner IOLINK
routers. If the ISDN call cannot be resumed, or has been closed, the routes will be aged out of the routing table.
Termination Process
When the IOLINK router has determined that there are no sessions active on an ISDN call, the IOLINK
router will attempt to close the call. If the partner IOLINK 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 IOLINK 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 IOLINK router needs to send data to the partner ISDN IOLINK router.
If the operator of the IOLINK router performs a link reset, the suspended call will be closed unilaterally.