CTI Products EXB Network Manager - Manual (Page 11)

Hot-Standby EXB / Network Manager Software Manual Hot Standby
CTI Products, Inc. EXB Operation
7
68-11707-100
2.4 Open Forward (Probe) Link Condition
Figure 3 Open Forward (Probe) Link
With an open Forward (Probe) Link Condition:
1. The Main EXB Control Neuron issues a Probe packet to the Standby EXB
Control Neuron
2. There is a break in the path. It is shown at point A, but it could occur at Point B
or C.
3. The Main EXB Control Neuron does not receive a Probe ACK.
4. The Main EXB Control Neuron does not issue a Holdoff packet to the Standby
EXB.
5. Since the Standby EXB Control Neuron does not receive a Probe or Holdoff
packet (timeout), it closes its switch and passes MCN packets back and forth
between the Central site and Remote Site on the bottom path.
6. If the break was at Point A (as shown), or the top Remote EXB was bad, all MCN
traffic would pass through the bottom path.
7. If break was at Point B, both EXBs would be passing data.
MCN traffic to/from the In port of the top Remote EXB would pass via the top
pair of EXBs. MCN traffic to/from the Out port of the bottom Remote EXB
would pass via the bottom pair of EXBs.
8. If the break was at Point C, the standby EXB would still close its switch, but there
would be no traffic over the bottom path. The Standby EXB would know that the
link was down because of its link layer diagnostics.
9. Since the Main EXB does not receive a Holdoff Acknowledge, it informs the
EXB Network Management Software of a problem.
Central EXBs Remote EXBs
Open Forward (Probe) Loop CB-80600-100
WAN Links
Router
Control Neuron
Port 1
B A
Switch
In
Out
Router
Control Neuron
Port 1
B A
5. Switch Closes
In
Out
Router
Control Neuron
Port 1
B A In
Out
Router
Control Neuron
Port 1
B A In
Out
Main
Standby
1. Probe Packet
3. No Probe ACK Received
A
B D
C
4. No Holdoff Packet
2. Break in Line
X
4. No Holdoff Packet