Perle Systems P840 User Manual download pdf (Page 20)

ISDN Connection Management

P840 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 P840 across the ISDN call. When the P840 determines that the ISDN call is to be

suspended, the P840 will consider keepalive and routing information packets to now be non-interesting and will

begin to generate and respond to keepalive and RIP packets.

When the P840 receives a keepalive packet from the LAN for one of the sessions, the P840 will not activate the

ISDN call and will not pass the keepalive packet to the remote LAN. The P840 will generate a response to the

keepalive packet and send it to the originator of the packet. In this way, the P840 will keep the ISDN call

suspended and will also keep the local side of the session active. The P840 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 acknowledge

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 P840 observes that one of the devices in the session stops sending

keepalive packets, the P840 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 P840 waits before beginning to generate keepalive

packets is definable by the operator.

P840 routers incorporate a settling time for routing updates. This means that a P840 will wait after an initial

change in the network is reported before transmitting that change on to the remaining P840 routers connected

on the Wide Area Network.

The P840 will resume the suspended ISDN call in order to transmit routing messages to partner P840s. If the

ISDN call cannot be resumed, or has been closed, the routes will be aged out of the routing table.

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Perle Systems P840 User Manual Page 20