LXD971L Intel, LXD971L Datasheet - Page 25

• 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
4.0
Question 1
Answer
Question 2
Answer
Question 3
Answer
Question 4
Answer
1+1 Protection without Relays Using Cortina Systems
Frequently Asked Questions
What is redundancy?
In the telecom industry, redundancy means having a back-up board in the system in the
event the primary board fails. Redundancy is the most common method to ensure reliable
and continuous service.
What is HPS 1+1 Protection?
1+1 protection is when every primary board has a back-up board. In this configuration the
equipment is protected from single board failures. Hitless Protection Switching means
having the ability, in the event of a board failure, to be able to switch in the back-up board
before a loss of frame sync.
Why do you need HPS?
Currently, most manufacturers are doing 1+1 protection using relays to switch from the
primary to the back-up board. There are a number of reasons to use Cortina’s HPS
scheme rather than relays. Because the transmitters of the LXT38x family of Line
Interface Units (LIU) can be fast tri-stated and contain constant delay jitter attenuation, the
transmitters and receivers of the primary and back-up boards can be tied together. On an
octal T1/E1/J1 interface card, this saves 8 transformers, 16 mechanical relays and 8 sets
of protection devices. This, in turn, saves money and board space making the end product
more marketable and reliable.
Can I make the primary and back-up boards hot swappable?
Yes. The high impedance of the receiver and the tristated transmitter allow for this. Hot
swapping requires special design considerations.
A system issue for HPS applications is to have the ability to change out a failed card
without taking the system off-line. This means that either the slot be switched and isolated
or simply removed and replaced. A scheme has been tested for doing the latter, saving the
switching and isolation circuitry.
The answer is twofold. First install a Schottky diode between VCC and TVCC ensuring that
both supply pins come up at the same time. The second item is to etch the GND and OE
fingers on the card edge connector longer than the signal pins and to etch the VCC and
TVCC fingers to a length in between the GND/OE and signal pins. If the card is mounted in
a rack and cannot be inserted crooked, the second item is irrelevant.
Figure 21
shows the orientation of the Schottky diode between the power pins.
®
LXT380/1/4/6/8 Hitless Protection Switching
4.0 Frequently Asked Questions
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