What Happens if a Call Spreading Route Goes Down

When a call has been dialed, the call spreading function will check the state of LAPB for the port selected by the round robin process.

• If the port is in the LAPB Information Transfer State, the call will be routed through that port.
• If the port is not in the LAPB Information Transfer State, the call will be routed to the other port configured with the same DNA.

The following illustration shows the effect of call spreading encountering a port not being in the LAPB Information Transfer State (a broken path).

In the above example, the route from Passport 4400 unit A port 161 to DNA 111* at Passport 4400 unit B is not in the LAPB Information Transfer State. In this case, all calls to DNA 111* will be routed over the path from Passport 4400 unit A port 167 to DNA 111* at Passport 4400 unit C.

LAPB is polled by the Passport 4400 unit every three seconds. Each time the unit polls LAPB, the unit records the status of each port. This is the status that is checked when a call is dialed to a DNA assigned to two ports (the two ports are configured for call spreading).