DEFINITY Enterprise Communications Server Release 7
Maintenance for R7r
555-230-126 Issue 4
June 1999
Hardware Configurations
2-17Duplication: Reliability Options
2
Duplication: Reliability Options

Standard Reliability Option

On Standard Reliability systems, the 512-time-slot TDM bus is d ivided into two
duplicate 256-time-slot b uses, A and B. Call traffic is shared between the two
buses. The first 5 time slots on each bus are reserved for the control channel,
which is active on only one of the two b uses at a time. Likewise, the next 17 time
slots are reserved for carrying system tones. The tone times slot are not
necessarily on the same bus (A or B ) as the control channel. If any failure takes
place that affects the ab ility of the active control or tone time sl ots to function, the
other bus becomes active for those time slots.

High Reliability Option

High Reliability systems dup licate components that are c ritical to the viability of
the system as a whole to prevent a single failure from d ropping all servic e:
■PPN control carrier and carrier power units (OLSs)
■All SPE c ircui t pac ks: Pro cess or, Me mory, MSSN ET, Disk , Tape, SYSA M,
Duplication Interface, and carrier power units (OLSs)
■PPN Tone Clock circuit p ack (EPN Tone-Clocks are not duplicated)
■TDM buses (described above)
In addition to the above, the following are duplicated in Center Stage Switch
(CSS) configurations:
■The PPN to CSS fiber link (consisting of the PPN Expansion Interface
circuit packs, t he Switch Node Interface circ uit packs that connec t to the
PPN EIs, and cabling from the PPN EI to the CSS)
■Switch Node Clocks (SNCs) (two; on each Switch N ode carrier)
The du plic ated SPEs ope rate i n act ive/s tandb y fas hion. Interc hang es of the SPE
and of PPN Tone-Clocks operate independently unle ss induced by u se of the
SPE-select switches. The 2 SNCs on each Switch Node carrier also operate in an
active/standby manner.
The duplicated fib er link between the PPN EIs and the CSS (the cable may
actually be metallic) d o not use an active/standby strateg y. Instead, both links
simultaneously carry active c all traffic and control c onnectivity in an equally
distributed load -sharing manner. If a component fails one of these fiber links, all
connectivity over it on it is torn d own, resulting in some droppe d calls and control
and applic ation links. Links and subsequ ent call service is immediat ely
re-established over the other EI fiber link.