Specifications
166119 8/31/2006
20
Assuming no channel backup switching is required, all channels should be configured for a
failover mode such that they do not seek backup, i.e., their assignment to either Link A or
Link B is fixed, regardless of the state of those links. In such a case, high or low priority will
not matter, since there is no channel switching activity.
2.3.3 Redundant (or Hot Standby) Link Configuration
Another simple configuration example, but quite different than the previous, is that of the
redundant link, shown in Figure 9. In this case, one link, the primary link, carries all channel
traffic under normal conditions. The other link is defined as a backup, or hot standby,
available to accept channels switched over should a failure occur on the primary link.
The backup link does not necessarily need to be of equal rate as the primary, but certainly
should not be greater. If the backup capacity is less than the primary, then some channels
may not be accommodated on the backup should a loss of the primary link occur.
-- No channel data traffic --
Primary LINK A (e.g. 128Kbps)
REDUNDANT LINK CONFIGURATION
Backup LINK B (e.g. 96Kbps)
Channel
Port #s
Channel
Port #s
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Timeslot
Map A
Timeslot
Map B
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Timeslot
Map A
Timeslot
Map B
1) Normal State: Before fault, or after automatic restoral
-- Failed Link --
Primary LINK A (e.g. 128Kbps)
Backup LINK B (e.g. 96Kbps)
Channel
Port #s
Channel
Port #s
2) Backup State: After Link A fault
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Timeslot
Map A
Timeslot
Map B
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Timeslot
Map A
Timeslot
Map B
Figure 9
In the figure above, all channels are assigned to a single primary link, in this case Link A. In
the normal state, both links are in service and all channel traffic is on the primary link. Should
a failure occur on Link A in this example, the system will switch channels to the backup link,
assuming it is operational.
If the backup link has the same rate as the primary link, a switch-over of all channels may
occur. In this example, since Link B has a lower rate and channel capacity, some channels
may not fit in the bandwidth available. As shown, channels 4, 11, and 13 are out of service
and are not switched to the surviving link.