Cisco Systems AS5800

Cisco AS5800 Product Overview 1-11

Cisco5814 Dial Shelf

The first time a router shelf sen ds an inventory response to the DSC , it includes a flag indicatin g that

all dial shelf cards should be reloaded. In split mode, the final dial shel f card image is downloaded

by each DSC from the router she lf th a t owns it.

The DSCs communicate between themselves to determine which one is to be active, where “being

active” implies being th e maste r for all t he di al shel f car d slo ts. In split mode, eac h DSC is t he ma ster

for the set of dial shelf cards in the slots owned by it s connec ted router. Additional messages indicate

when DSCs are in split mode and what set of slots they control.

A DSC that is already in split mode simply advertises tha t it is in split mode and which slots it is

claiming. When a second DSC receives an indic ation that t he f irst DSC is i n spli t mode , its b eha vior

depends on the current configuration of its attached router.

•If the attached router is not configured for split mode, the second DSC sends error messages to

its connected router and indicates its router’s state to the first DSC. The first DS C issue s the sa me

error messages to its router.

•If one attached router is configured in split mode and the ot her is in norma l mode, the rout er that

is in normal mode stops claiming ownership of any slots and does not respond to boot requests

from any of the dial shelf cards. The router that is in split mode responds to boot requests only

from dial shelf cards in the slots that it owns. Howe ver , it doe s not tak e ove r (restart) th e dial shel f

cards in its slots until the normal mode router is removed or is also configured in split mode.

In normal mode, both DSCs are connected to the same router shelf. The active DSC monitors the

status of its link to the router shelf and, in the event of link fail ure, requests the other DSC to take

over. When operating in split mode, eac h DS C is connected to a different router shelf, so the DSCs

do not send or respond to link failure messages. If one DSC’s link fails, the other DSC cannot

transparently take over.

Trunk cards and modem cards are tied together across a time-division multi plexing (TDM) bus on

the dial shelf backplan e. T i me sl ots f or t he TD M bus are all ocate d by the rout er sh elf on a cal l-by- cal l

basis. This is implemented by initializing a queue at start up with one element for each usable time

slot (currently 14*128 = 1,792 time slot s are used). Time slots for a call are allocated from the front

of the queue and replaced at the end of the queue when the call is completed. For split dial she lf

operation, time slots are add e d to the queue dynamically, as they ar e ne ed e d . W h en a T DM slot is

required and the queue is empty, a chunk of TDM slots is allocated to the queue.

In normal mode, the router shelf connected to the DSC in slot 12 allo ca tes tim e slo ts star tin g from 0

going up, and the router shelf connected to the DSC in slot 13 alloca tes ti me slots s tarting from 1,791

going down. For split dial shelf operation each router is assigned half of th e usable s et of time slot s.

The router shelf connected to the DSC in slot 12 controls the first half of the time sl ots (0 to 895).

The router shelf connected to the DSC in slot 13 controls the second half of the time slots (896 to

1791).