cx28250 Mindspeed Technologies, cx28250 Datasheet - Page 64

• Manufacturer Part Number: cx28250
• Description: Cx28250 Atm Physical Interface Phy Devices
• Manufacturer: Mindspeed Technologies

2.0 Functional Description
2.3 SONET/SDH Framer and Overhead Processor
2.3.5 SONET Frame Scrambler
2-28
Each SONET Network Element (NE) must have the capability to derive the clock
timing from the incoming OC-3c signal. All transmitted OC-3c signals are timed
from this clock. Therefore, it is important to maintain the 1s density in the data
stream to ensure enough data transitions for robust clock recovery. The technique
commonly used with modems, called scrambling and descrambling, is used in
SONET to make the data appear to be more random.
127, operating at the line rate. The generating polynomial is 1+x
scrambler is reset to 1111111 on the most-significant bit of the J1 byte. This bit
and all the subsequent bits to be scrambled are added, modulo 2, to the output
from the x
overhead is scrambled. This scrambling occurs just before the signal is passed to
the PMD sublayer. Scrambling can be disabled by setting bit 7 in register TXSEC
(0x0C). All 0s can be sent after scrambling for diagnostic purposes.
This process uses a frame synchronous scrambler with a sequence length of
Mindspeed Technologies
7
position of the scrambler. Everything but the first row of the section
™
ATM Physical Interface (PHY) Devices
28250-DSH-002-C
6
+x
7
. The
CX28250