XRT75R03D_06 Datasheet, PDF (33/135 Pages) Exar Corporation – EXAR DATA SHEET FORMAT TEMPLATES

XRT75R03D
REV. 1.0.4
THREE CHANNEL E3/DS3/STS-1 LINE
1.0 R³ TECHNOLOGY (RECONFIGURABLE, RELAYLESS REDUNDANCY)
Redundancy is used to introduce reliability and protection into network card design. The redundant card in
many cases is an exact replicate of the primary card, such that when a failure occurs the network processor
can automatically switch to the backup card. EXAR’s R³ technology has re-defined E3/DS-3/STS-1 LIU design
for 1:1 and 1+1 redundancy applications. Without relays and one Bill of Materials, EXAR offers multi-port,
integrated LIU solutions to assist high density agregate applications and framing requirements with reliability.
The following section can be used as a reference for implementing R³ Technology with EXAR’s world leading
line interface units.
1.1 Network Architecture
A common network design that supports 1:1 or 1+1 redundancy consists of N primary cards along with N
backup cards that connect into a mid-plane or back-plane architecture without transformers installed on the
network cards. In addition to the network cards, the design has a line interface card with one source of
transformers, connectors, and protection components that are common to both network cards. Wtih this
design, the bill of materials is reduced to the fewest amount of components. See Figure 3 for a simplified
block diagram of a typical redundancy design.
FIGURE 3. NETWORK REDUNDANCY ARCHITECTURE
Framer/
Mapper
0.01µF
Rx _0.01µF
LIU
Tx
31.6Ω
31.6Ω
Primary Line Card
Framer/
Mapper
0.01µF
Rx _0.01µF
LIU
Tx
31.6Ω
31.6Ω
Redundant Line Card
GND
37.5Ω
37.5Ω
1:1
1:1
Line Interface Card
Back
Plane
or
Mid
Plane
1.2 Power Failure Protection
EXAR’s "High" impedance circuits protect the LIU and preserve the line impedance characteristics when a
power failure occurs. As the power supply decreases to a pre-determined voltage, the I/O pads are
automatically switched to "High" impedance. This effectively removes the LIU, preventing a line impedance
mismatch or system degradation. Power failures or network card hot swapping change the network circuit. It
is critical that under these circumstances, that the primary card still behaves according to network standards.
The three sensitive specifications are pulse mask conformance, receive sensitivity and return loss. Each must
be carefully characterized to ensure network integrity and reliability.
1.3 Software vs Hardware Automatic Protection Switching
The implementation of R³ technology can be controlled through programming the internal registers or through
the use of the TxON hardware pin available within the LIU. To use software to tri-state the transmitters, first
the TxON pin must be pulled "High". Once the pin is pulled "High", the individual register bits can be used to
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