XRT83VSH28IB datasheet(39/74 Pages) EXAR

39 / 74 page

PRELIMINARY

XRT83VSH28

REV. P1.0.0

8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT

4.2.4

N+1 Redundancy Using External Relays

N+1 redundancy has one backup card for N primary cards. Due to impedance mismatch and signal contention,

external relays are necessary when using this redundancy scheme. The relays create complete isolation

between the primary cards and the backup card. This allows all transmitters and receivers on the primary cards

to be configured in internal impedance, providing one bill of materials for all interface modes of operation. The

transmit and receive sections of the LIU device are described separately.

4.2.5

Transmit Interface with N+1 Redundancy

For N+1 redundancy, the transmitters on all cards should be programmed for internal impedance. The

transmitters on the backup card do not have to be tri-stated. To swap the primary card, close the desired

relays, and tri-state the transmitters on the failed primary card. A 0.68uF capacitor is used in series with TTIP

for blocking DC bias. See Figure 26 for a simplified block diagram of the transmit section for an N+1

redundancy scheme.

FIGURE 26. SIMPLIFIED BLOCK DIAGRAM OF THE TRANSMIT INTERFACE FOR N+1 REDUNDANCY

Backplane Interface

Primary Card

XRT83VSH28

Line Interface Card

0.68uF

E1 Line

0.68uF

Primary Card

0.68uF

Primary Card

0.68uF

Backup Card

E1 Line

Internal

Impedence

1:2

XRT83VSH28

Internal

Impedence

Internal

Impedence

Internal

Impedence

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