XRT75R12DIB-F Exar Corporation, XRT75R12DIB-F Datasheet - Page 101

• Manufacturer Part Number: XRT75R12DIB-F
• Description: Peripheral Drivers & Components (PCIs) 12 Channel 3.3V-5V temp -45 to 85C
• Manufacturer: Exar Corporation

Specifications of XRT75R12DIB-F

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 3.3 V to 5 V
• Package / Case: TBGA-420
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

REV. 1.0.3
Throughout each of these cases, we will discuss how the resulting "bit-stuffing" (that was done when mapping
the DS3 signal into SONET) affects the amount of intrinsic jitter and wander that will be present in the DS3
signal, once it is ultimately de-mapped from SONET.
Let us assume that we are mapping a DS3 signal, which has a bit rate of exactly 44.736Mbps (with no
frequency offset) into SONET. Further, let us assume that the SONET circuitry within the PTE is clocked at
exactly 51.84MHz (also with no frequency offset), as depicted below.
Given the above-mentioned assumptions, we can state the following.
Is there a Problem?
According to
bits". In this case, each STS-1 SPE appears to be three bits "short".
No there is a Simple Solution
three additional bits (for DS3 data) are obtained by using three of these "Stuff Opportunity" bits. As a
consequence, three (3) of these nine (9) "Stuff Opportunity" bits, within each STS-1 SPE, will carry DS3 data-
bits. The remaining six (6) "Stuff Opportunity" bits will typically function as "stuff" bits.
In summary, for the "Ideal Case"; where there is no frequency offset between the DS3 and the STS-1 bit-rates,
once this DS3 data-stream has been mapped into the STS-1 data-stream, then each and every STS-1 SPE will
have the following "Stuff Opportunity" bit utilization.
3 "Stuff Opportunity" bits will carry DS3 data bits.
6 "Stuff Opportunity" bits will function as "stuff" bits
F
No, earlier we mentioned that each STS-1 SPE consists of nine (9) "Stuff Opportunity" bits. Therefore, these
8.2.2.1
IGURE
The Ideal Case (e.g., with no frequency offsets)
The 44.736Mbps + 1 ppm Case
The 44.736MHz - 1ppm Case
The DS3 data-stream has a bit-rate of exactly 44.736Mbps
The PTE will create 8000 STS-1 SPE's per second
In order to properly map a DS3 data-stream into an STS-1 data-stream, then each STS-1 SPE must carry
(44.736Mbps/8000 =) 5592 DS3 data bits.
45. A S
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
Figure
The Ideal Case for Mapping DS3 data into an STS-1 Signal (e.g., with no Frequency
Offsets)
IMPLE
44.736MHz + 0ppm
44, each STS-1 SPE only contains 5589 bits that are specifically designated for "DS3 data
I
LLUSTRATION OF A
DS3_Data_In
DS3 D
ATA
-S
PTE
PTE
97
TREAM BEING
M
APPED INTO AN
STS-1_Data_Out
51.84MHz + 0ppm
STS-1 SPE,
XRT75R12D
VIA A
PTE