User manual

Product Description
Low-Speed (LS) Redundancy
2-22 July 2004 Wide Bank 28 DS3 - Release 2.4
Low-Speed (LS) Redundancy
 Low-Speed Automatic Switchover ... 2-22
 Low-Speed Circuit Groups ... 2-22
 Switchover Lockouts Within Groups ... 2-22
 Maintenance Service Option (MSO) ... 2-24
 Failures that Cause a Low-Speed Switchover ... 2-26
 Enabling and Disabling Low-Speed Switchovers ... 2-26
 Restoring to Original Status (Revertive Switching) ... 2-27
 Hot-Swapping a Failed Standard Low-Speed Card ... 2-27
 Hot-Swapping a Failed MSO Low-Speed Card ... 2-27
Low-Speed Automatic Switchover
The Wide Bank provides low-speed circuit monitoring and automatic switchover to a spare low-
speed circuit card when an error is detected. When an error is detected, traffic is automatically
switched to a spare low-speed circuit in the same circuit group. The status LED indicator on the
spare circuit will change from yellow to green, and the LED on the failed circuit will turn off. When
the failed circuit is replaced (see Hot-Swapping a Failed Standard Low-Speed Card on page 2-27)
the traffic is switched back to the original circuits, leaving the spare card available for subsequent
error switching.
Any traffic carried by the spare circuits will be dropped when a failed standard low-speed circuit
card is removed. Any traffic carried by the spare circuits will not be dropped when a failed MSO
Electronics card is removed, provided that the spare is not already in use before pulling failed MSO
card.
Low-Speed Circuit Groups
The Wide Bank 28 DS3 employs a one to seven (1:7) electronics redundancy scheme using four
spare DS1 circuits (or three spare E1 circuits) to protect up to 28 active DS1 circuits (or 21 active
E1 circuits). Circuit groups are arranged so that each of the circuits on the spare card can replace a
corresponding circuit on each of the seven active cards (see Figure 2-1 Functional Block Diagram
on page 2-4 and Table 2-3 Low-Speed Circuit Groups for Spare Switching on page 2-23).
Switchover Lockouts Within Groups
A resource conflict occurs when more than one circuit fails in the same low-speed circuit group.
Because redundancy is limited to one spare per circuit group, a second failed circuit within the same
group is not covered, so it will be locked out.
 If a second failure occurs in the same circuit group, automatic switchover will not occur and
the second failed circuit will not be spared. A minor failure alarm will be activated for the
second failed circuit, and its card status LED will turn red.