RELEASED
PM7350 S/UNI DUPLEX
DATA SHEET
PMC-1980581
ISSUE 8
DUAL SERIAL LINK PHY MULTIPLEXER
9.3.4 Protection Switching Protocol
The S/UNI-DUPLEX and its sister device, the S/UNI-VORTEX inherently support
system architectures requiring fault tolerance and 1:1 redundancy of the system’s
common equipment. In point-to-point backplane architectures such as these, the
1:1 protection also includes the associated LVDS links connecting the common
equipment to the line cards. The S/UNI-VORTEX and S/UNI-DUPLEX perform
clock recovery, cell delineation, and header error monitoring for all receive high-
speed serial links simultaneously. The maintained error counts and alarm status
indications may be used by the control system to determine the state and viability
of each LVDS link. See the S/UNI-VORTEX data sheet for additional details.
In these architectures, each S/UNI-DUPLEX will be connected to two S/UNI-
VORTEXs (see Fig. 1) or to two S/UNI-DUPLEXs (see Fig. 5). Upon a failure of
the active card, the spare card becomes the conduit for traffic. The S/UNI-
VORTEX and S/UNI-DUPLEX facilitate link selection upon start-up as well as
switching between links upon failure conditions.
Typically a centralized resource or cooperating distributed microprocessor
subsystems will determine which common card is to be considered active for
each downstream S/UNI-DUPLEX and sets the active indication accordingly.
The current state of the link’s active bit is sent downstream once per transmitted
cell. The active status is debounced and acted upon by the far-end S/UNI-
DUPLEX.
The S/UNI-DUPLEX will only accept data traffic from one of its two LVDS links,
and normally it is the link marked active that is considered the working link
(although this can be overridden locally as discussed below). Thus, although the
far-end S/UNI-VORTEX or S/UNI-DUPLEX may indicate the desired active and
spare links, it is actually the local S/UNI-DUPLEX that must enforce the
protection switching. The link switching mechanism preserves cell integrity on
the high-speed serial link that becomes active. In other words, switching occurs
between cells.
At reset Link 1 is marked as the active link. It is also important to note that a
Loss of Signal (LOS) on the active LVDS link does not automatically affect the
value of the ACTIVE bit. The ACTIVE bit value prior to the LOS condition is
maintained unless the other link’s active indication is asserted (after debouncing)
or until a local override (described below) or device reset is invoked. The value of
the extracted ACTIVE bit is forced to logic 0 when the corresponding link is in
Loss of Cell Delineation (LCD ) state.
If the S/UNI-DUPLEX is auto-selecting its active link status (Master Configuration
register 0x01, RXAUTOSEL = 1) the active bit transmitted on the two LVDS links
will indicate which link is currently chosen as active. This reflected ACTIVE bit
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
72
PMC [ PMC-SIERRA, INC ]
