XRT83L314 Datasheet, PDF (41/84 Pages) Exar Corporation – 14-CHANNEL T1/E1/J1 LONG-HAUL/SHORT-HAUL LINE INTERFACE UNIT

XRT83L314
14-CHANNEL T1/E1/J1 LONG-HAUL/SHORT-HAUL LINE INTERFACE UNIT
REV. 1.0.0
4.3 Line Card Redundancy
Telecommunication system design requires signal integrity and reliability. When a T1/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
XRT83L314 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 XRT83L314 reports the alarm to the individual status registers on a
per channel basis. However, for redundancy applications, an RLOS or DMO alarm can be used to initiate an
automatic switch to the back up card. For this application, two global pins RLOS and DMO are used to indicate
that one of the 14-channels has an RLOS or DMO condition.
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
4.3.1 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.
4.3.2 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, T1/E1/J1. A 0.68uF capacitor is used in series with TTIP for blocking DC bias. See
Figure 36. for a simplified block diagram of the transmit section for a 1:1 and 1+1 redundancy.
FIGURE 36. SIMPLIFIED BLOCK DIAGRAM OF THE TRANSMIT INTERFACE FOR 1:1 AND 1+1 REDUNDANCY
Backplane Interface
Primary Card
Tx
Internal Impedence
XRT83L314
1:2
0.68uF
Backup Card
Tx
Internal Impedence
XRT83L314
1:2
0.68uF
T1/E1 Line
4.3.3 Receive Interface with 1:1 and 1+1 Redundancy
The receivers on the backup card should be programmed for "High" impedance. Since there is no external
resistor in the circuit, the receivers on the backup card will not load down the line interface. This key design
feature eliminates the need for relays and provides one bill of materials for all interface modes of operation.
Select the impedance for the desired mode of operation, T1/E1/J1. To swap the primary card, set the backup
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