Cisco5814 Dial Shelf
Cisco AS5800 Universal Access Server Hardware Installation Guide1-10
Only one common logic is active at any one time, which is identified by the clock (CLK) LED on
the DSC’s front panel. The active common logic is user-selectable and is independent from each
DSC. This assures th at if a DSC needs repla cing or if the slave DSC becomes the master, clo cking
remains stable. The selected common logic should not be changed during normal operation, unless
related hardware failure is suspected or diagnosed.
The configuration commands for the master clock specify the various clock sourc es and a pri ority
for each source. Together these commands define a list , ordered b y priorit y , of t he clock sou rces used
to generate the master clock. The prioritized list, configured on the router shelves, is passed to and
stored by the DSC providing the active clock. In the event of failure of the highest-priority clock
source, the DSC switches to the source with the next highest priority.
With a split dial shelf, the clock sources can be configured on either of the router shelves. Typically
a router configures clock sources only from the slots that it owns; clock s ources can be configured
from other slots, but they are ignored. On the dial shelf, all valid clock source configurations need
to be known to the DSC providing the clock, i ncludin g th e cloc k sour ce con f igurati ons on the router
connected to the other DSC.
In a typical Cisco AS5800 configuration (wit hout a s plit dia l s helf), cloc k sour ce conf igu rat ion li nes
that specify an external clock are sent directly from the router shelf to both DSCs. In the split dial
shelf configuration, a router can send the clock source configuration only to the DSC to which it is
connected, not to both DSCs. If an external clock is used in a split dial shelf configuration, it must
be configured identically on both router shelves and must be physically connected to both DSCs.
An error condition can arise if a clock input on one router is configured to have the same priority as
a clock input configured on the other router. However, the command is not rejected, because the
values configured on the other router may not be known. Warning messages are issued to both
routers when this condition is detected. Two clock inputs specified with identical priorities both go
into the ordered list of clock sources, but the one recei ve d first by the DSC pr oviding the acti ve cloc k
is assigned a higher priority.
The show dial-shelf clocks command shows all configured clock sources, even those from
non-owned trunk cards. Only one DSC can provide the master cloc k; howe ve r, ba ckup clock so urces
might need to be configured for all trunk cards present (regardless of which DSC owns them).
Dial Shelf OIR Events
Each DSC needs to know whether it is to operate in split mode or normal mode, and in s plit m ode it
needs to know which slots are owne d by its connected router. Currently the DSCs receive inventory
messages from the r outer shelves, informin g them which cards t he routers think are present in the
dial shelf. In split mode operation, these messages have been extended to inform the DSC which
mode is current and the set of slots it owns.
Split dial shelf configurations are managed by having the sl ots that are owned by one router
appearing to the other router as empty slots. A router shelf is informed of dial shelf OIR events by
messages that are se nt to the router shelf when a card is inser ted in or removed from a slot. In the
split dial shelf configuration, once a DSC i s informe d b y the c onnect ed route r whi ch sl ots it o wns, it
sends messages only for dial shelf OIR events that occur in those slots. Thehub on each DSC is
configured to ignore traffic from cards in non-owned slots.
Dial Shelf Card Bootup
When a dial shelf card starts running, it sends a message to the DSC. The DSC determines whether
it is the master for that slot. In the split dial shelf mode, only the DSC whose connected route r o wns
the slot containing the dial shelf card responds to the message. The dial shelf card accepts firmware
and a bootstrap image from that DSC and configures its elf t o communic at e throu gh th at DSC’s hub.