Perle Systems IOLINK-520

ISDN Connection Management

IOLINK-PRO & 520 Reference Manual —

Protocol Awareness

For Connection Management to be effective, each of the IOLINK routers must be aware of the protocols used

within the data being transferred over the ISDN calls between them.

IP and IPX Client-Server sessions are established between devices located on the LANs that are routed by the

IOLINK Router. If the IOLINK router is to manage the ISDN calls between the routed LANs, the IOLINK

routers on each WAN end of the Client-Server session must be aware of the session and also must become

actively involved in the maintenance of the session. When an ISDN call is suspended, both the Client and the

Server must still believe that the session exists.

Suspension Process

The IOLINK router maintains a table for each ISDN call made to a partner ISDN IOLINK router in order to

determine when the ISDN call should be suspended during Connection Management.

Any number of LAN sessions may be currently using the established ISDN call to transfer data between the

client and the server. The IOLINK router monitors the ISDN call for interesting traffic passed on each of the

sessions currently using the ISDN call. If no interesting traffic is observed on the ISDN call for a period of time

greater than the defined Idle Timer value, the ISDN call is suspended and disconnected. While the ISDN call is

suspended, the IOLINK router will monitor the LAN sessions for interesting traffic and re-establish the ISDN

call when required.

A suspended ISDN call may only be re-established by the IOLINK router initiating the suspension or by the

partner IOLINK router that was connected just prior to the call being suspended. This prevents other IOLINK

routers from tying up the ISDN calls and interfering with the suspended calls.

ISDN calls may be connected and disconnected between the two IOLINK routers when required according to

the suspension and re-activation of the ISDN calls. When all of the sessions using the call in the table have been

closed, the call will be terminated and the ISDN B-channel becomes available for use to connect to a different

ISDN IOLINK router. 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 sessions in the table.

Interesting Traffic

Interesting Traffic is defined as normal interactive user data for a session. Certain data exchanged during a

normal session is not considered to be interesting and usually is composed of keepalive messages, watchdog

messages, and routing messages. Non-interesting data is handled differently when Connection Management is

enabled.

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 IOLINK router determines when the

ISDN call will be suspended.

IOLINK 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 IOLINK router across the ISDN call. When the IOLINK router determines that the

ISDN call is to be suspended, the IOLINK router will consider keepalive and routing information packets to

now be non-interesting and will begin to generate and respond to keepalive and RIP packets.