Perle Systems IOLINK-PRO IOLINK-520 - Manual (Page 28)

ISDN Connection Management
IOLINK-PRO & 520 Reference Manual — 2. 7
IP Specifics
IP Address Connect
As stated previously, an IP Address Connect connection is an ISDN connection that is established to a specific
destination IOLINK router dependent upon the destination IP address contained within IP traffic received
from the local LAN.
This means that the IOLINK router continuously monitors IP traffic from the local LAN, as all IP routers do,
and makes ISDN connections to partner IOLINK 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 IOLINK 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
IOLINK 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 IOLINK 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 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.
If the device does not respond to five consecutive keepalive packets sent from the IOLINK router, the
IOLINK router will determine that the device has gone away and the IOLINK 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 IOLINK router will re-activate the suspended ISDN call and transmit the shut down packet to the
remote device. Once the remote IOLINK router determines that the TCP session is no longer active, the
remote IOLINK router will stop generating and responding to the keepalive packets for that TCP session.
RIP—Routing Information Protocol
IOLINK ISDN routers incorporate a 3 second settling time for IP RIP updates. This means that an IOLINK
will wait for three seconds 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.