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Reliability Options
Issue 4 May 2002 6-3 555-233-123
Reliability Options
Standard, High and Critical reliability systems offer an increased level of reliability
by duplicating various components so that standby components can take over
(interchange) when a failure occurs on an active component. Most interchanges
take place with no disruption of current service and allow for repairs to be made
without disruption. Furthermore, duplication allows for the upgrading and
maintenance of duplicated components and software without service disruption.
The following sections describe which components are duplicated with each
option.
Standard Reliability
On standard reliability systems, the 512-time-slot TDM bus is divided into two
duplicate 256-time-slot buses, A and B. Call traffic is shared between the two
buses. The first five time slots on each bus are reserved for the control channel,
which is active on only one of the two buses at a time. Likewise, the next 17 time
slots are reserved for carrying system tones. The tone time slots are not
necessarily on the same bus (A or B) as the control channel. If any failure that
affects the ability of the active control channel or the tone time slots to function
takes place, the other bus becomes active for those time slots. For more
information, see TDM-BUS Maintenance section in
Chapter 10, ‘‘Maintenance
Object Repair Procedures’’ , and the set tdm command in Chapter 8,
‘‘Maintenance Commands and Trouble-Clearing Aids’’ .
High Reliability
High Reliability systems duplicate components that are critical to the viability of
the system as a whole to prevent a single failure from dropping all service. These
components include the following:
■
PPN control carrier and carrier power units (OLSs)
■
All SPE circuit packs, including the Processor, Memory, Network Controller,
Processor Interface, Packet Controller, and Duplication Interface circuit
packs
■
PPN Tone Clock circuit pack (EPN Tone-Clocks are not duplicated)
■
TDM buses (described in the previous section)
NOTE:
In High reliability systems, a TN771 Maintenance/Test circuit pack is
required in the PPN, but is optional in EPNs.
The duplicated SPEs operate in active/standby fashion. Operation of this
duplication is described in the STBY-SPE and DUPINT MO sections in
Chapter
10, ‘‘Maintenance Object Repair Procedures’’ . Interchanges of the SPE and of
PPN Tone-Clocks operate independently unless induced by use of the SPE-select
switches.