Function Of The Common Backplane - Nortel Passport 15000 Hardware Description

Chapter 3 Shelf assembly 93

Function of the common backplane

The backplane is referred to as the common backplane because it is the point
across which all processor cards and fabric cards in a shelf intercommunicate.
In a Passport 15000, the backplane provides redundant 3.52 Gbits/s serial
links between the processor cards and the fabric cards to support power and
signal distribution. The high-speed lines on the backplane have a nominal
impedance of 50 ohm and 100 ohm differential to reduce signal ringing and
reflections caused by impedance mismatches. The serial link architecture of
the backplane allows for hot-swapping packs by isolating each card to a single
fabric port, preventing card failures from propagating through the switching
fabric. The backplane also provides links between adjacent FPs for functions
such as sparing, clock distribution, and distribution of -48/-60 V dc.
In a Passport 20000, the backplane provides redundant serial links or
Unilinks between the processor cards and the fabric cards to support power
and signal distribution. The Passport 20000 has the 3.52 Gbits/s link
capability of the Passport 15000 and adds an overlay of 16.0 Gbits/s of link
capability. Only one capability is active per slot. The high-speed lines on the
backplane have a nominal impedance of 50 ohm and 100 ohm differential to
reduce signal ringing and reflections caused by impedance mismatches. The
serial link architecture of the backplane allows for hot-swapping packs by
isolating each card to a single fabric port, preventing card failures from
propagating through the switching fabric.
The backplane also provides links between adjacent FPs for functions such as
sparing and clock distribution. The backplane has layers dedicated to power
distribution of -48/-60 V dc to all plug-in cards and modules.
The backplane can function in dual- or single-fabric mode. Traffic is typically
loadshared through the backplane across both fabrics. Dual-fabric mode is the
standard mode used by the Passport 15000 or 20000. Single-fabric mode
occurs while one of the fabrics is being replaced or upgraded.
Passport 15000, 20000 Hardware Description 5.2S2