XRT75R12DIB-F Exar Corporation, XRT75R12DIB-F Datasheet - Page 109

• 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
Figure 52
the "I" bits designated.
N
During the STS-1 frame that follows the "Byte-Stuffing" event
The "I" bits (within the "pointer-word") will be set back to their normal value; and the contents of the H1 and H2
bytes will be incremented by "1".
If f1 > f2
If frequency f1 is greater than f2, then this means that the STS-1 data is being clocked into the "Slip Buffer" at
a faster rate than is being clocked out. In this case, the "Slip Buffer" will start to fill up. Whenever this occurs,
a typical strategy is to delete (e.g., negative-stuff) a byte from the Slip Buffer. The purpose of this "negative-
stuffing" is to compensate for the frequency differences between f1 and f2; and to attempt to keep the "Slip
Buffer" at a somewhat constant fill-level.
N
Negative-Stuffing and Pointer-Decrementing in a SONET Network
Whenever this "byte negative-stuffing" occurs then the following other things occur within the STS-1 data-
stream.
During the STS-1 frame that contains the "Negative Byte-Stuffing" Event
F
BYTES
b. The "Transmitting" Network Equipment will notify the remote terminal of this byte-stuffing event, by invert-
OTE
OTE
IGURE
b. The remote PTE must be notified of the occurrence of these "negative-stuffing" events. Further, the
a. The "negative-stuffed" byte must not be simply discarded. In other words, it must somehow also be
a. The "Negative-Stuffed" byte will be inserted into the H3 byte position. Whenever an SPE data byte is
ing certain bits within the "pointer word" (within the H1 and H2 bytes) that are referred to as "I" bits.
: At this time the "I" bits are inverted in order to denote that an "incrementing" pointer adjustment event is currently
: This byte, which is being "un-stuffed" does carry valuable information for the user (e.g., this byte is typically a
)
transmitted to the remote PTE with the remainder of the SPE data.
remote PTE must know where to obtain this "negative-stuffed" byte.
inserted into the H3 byte position (which is ordinarily an unused byte), the number of bytes that will exist
between the H3 byte and the J1 byte within the very next SPE will be reduced by 1 byte. As a
consequence, in this case, the J1 byte (and in-turn, the rest of the SPE) will now be "byte-shifted"
towards the H3 byte position.
occurring.
payload byte). Therefore, whenever this negative stuffing occurs, two things must happen.
WITH THE
52. A
presents an illustration of the bit-format within the 16-bit word (consist of the H1 and H2 bytes) with
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
N
MSB
N
I
LLUSTRATION OF THE
"I"
BITS DESIGNATED
N
N
H1 Byte
N
S
B
IT
F
S
ORMAT WITHIN THE
I
D
105
10 Bit Pointer Expression
I
16-
D
BIT WORD
I
H2 Byte
D
(
CONSISTING OF THE
I
D
I
LSB
D
XRT75R12D
H1
AND
H2