LXD971L Intel, LXD971L Datasheet - Page 5

• Manufacturer Part Number: LXD971L
• Manufacturer: Intel

Specifications of LXD971L

• Lead Free Status / RoHS Status: Not Compliant

LXT38x LIU
Application Note
249464, Revision 2.0
10 August 2007
1.0
1+1 Protection without Relays Using Cortina Systems
Introduction - 1+1 Hitless Protection Switching
Today’s telecommunications customers and international regulatory bodies demand an
extremely high quality of service with little or no periods of service failure or down time. If
your goal is to provide your customers with equipment that has an extremely high
availability, then 1+1 protection is the method to use for T1/E1/J1 line interface cards.
In a 1+1 protection scheme, each primary line card has a backup (or protection) board that
can be switched into the circuit path while the primary line card is isolated in case the
primary line card fails. This is accomplished by having a control circuit card that constantly
monitors each primary line card and preforms switching tasks when necessary. Switching
takes place in a protection switching matrix traditionally constructed with mechanical
relays as switching elements.
From an architectural standpoint, the relay switching matrix is easy to visualize but comes
with some inherent drawbacks:
As can be seen from the previous discussion, relay based protection schemes give rise to
a number of issues. The following sections introduce a scheme designed around
Cortina Systems
Switching (HPS). HPS protects the system from single board failures by utilizing on-chip
fast solid state tri-state drivers to switch in the back-up board before a loss of frame sync.
This eliminates the need for mechanical relays and enhances the overall reliability of the
system.
• Parts Count
• Space
• Switching Speed
• Power
As an example, if each line card has 8 T1/E1/J1 bidirectional ports and is implemented
with a 1+1 protection scheme, a total of 8*2 = 16 DPDT relays would be required.
The typical size for a DPDT telco signal relay is 15 x 7.5 mm. This requires a board
area of 3600 sq. mm. at a parts density of 50%.
The typical switching time for a telco relay, including debounce time, is about 3.5 ms.
On a T1 link running at 1.544 MHz, this corresponds to over 5000 bits of data. This is
well over the time required to cause a loss of frame sync. On E1 links running at
2.048 MHz, the problem is even worse. Since re-framing can take up to 193 frames, a
significant degradation in performance is realized.
Eliminating the need for 16 relays and the associated driver circuitry reduces the
power requirements for the system.
®
LIUs with fast tri-stating transmit drivers utilizing Hitless Protection
®
LXT380/1/4/6/8 Hitless Protection Switching
1.0 Introduction - 1+1 Hitless
Protection Switching
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