XRT83SL28
xr
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
REV.1.0.0
3.2
Line Card Redundancy
Telecommunication system design requires signal integrity and reliability. When an E1 primary line card has a
failure, it must be swapped with a backup line card while maintaining connectivity to a backplane without losing
data. System designers can achieve this by implementing common redundancy schemes with the
XRT83SL28 LIU. EXAR offers features that are tailored to redundancy applications while reducing the number
of components and providing system designers with solid reference designs.
RLOS and DMO
If an RLOS or DMO condition occurs, the XRT83SL28 reports the alarm to the individual status registers on a
per channel basis. However, for redundancy applications, RLOS and DMO pins can be used to initiate an
automatic switch to the back up card.
Typical Redundancy Schemes
• 1:1 One backup card for every primary card (Facility Protection)
• 1+1 One backup card for every primary card (Line Protection)
• ·N+1 One backup card for N primary cards
3.2.1
1:1 and 1+1 Redundancy Without Relays
The 1:1 facility protection and 1+1 line protection have one backup card for every primary card. When using
1:1 or 1+1 redundancy, the backup card has its transmitters tri-stated and its receivers in high impedance. This
eliminates the need for external relays and provides one bill of materials for all interface modes of operation.
For 1+1 line protection, the receiver inputs on the backup card have the ability to monitor the line for bit errors
while in high impedance. The transmit and receive sections of the LIU device are described separately.
3.2.2
Transmit Interface with 1:1 and 1+1 Redundancy
The transmitters on the backup card should be tri-stated. Select the appropriate impedance for the desired
mode of operation, E1 75Ω or 120Ω. A 0.68uF capacitor is used in series with TTIP for blocking DC bias. See
Figure 21. for a simplified block diagram of the transmit section for a 1:1 and 1+1 redundancy.
FIGURE 21. SIMPLIFIED BLOCK DIAGRAM OF THE TRANSMIT INTERFACE FOR 1:1 AND 1+1 REDUNDANCY
Backplane Interface
Primary Card
XRT83SL28
1:2
0.68uF
Tx
E1 Line
Internal Impedance
Backup Card
XRT83SL28
1:2
0.68uF
Tx
Internal Impedance
26
EXAR [ EXAR CORPORATION ]
