XRT75L00D Datasheet, PDF (67/92 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

REV. 1.0.2
XRT75L00D
E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
FIGURE 42. THE BIT-FORMAT OF THE 16-BIT WORD (CONSISTING OF THE H1 AND H2 BYTES) WITH THE 10 BITS,
REFLECTING THE LOCATION OF THE J1 BYTE, DESIGNATED
H1 Byte
H2 Byte
MSB
LSB
NNNNS SXXXXXXXXXX
10 Bit Pointer Expression
Figure 43 relates the contents within these 10 bits (within the H1 and H2 bytes) to the location of the J1 byte
(e.g., the very first byte of the STS-1 SPE) within the Envelope Capacity.
FIGURE 43. THE RELATIONSHIP BETWEEN THE CONTENTS OF THE "POINTER BITS" (E.G., THE 10-BIT EXPRESSION
WITHIN THE H1 AND H2 BYTES) AND THE LOCATION OF THE J1 BYTE WITHIN THE ENVELOPE CAPACITY OF AN STS-
1 FRAME
TOH
The Pointer Value “0” is immediately
After the H3 byte
A1 A2 C1/J0 522 523 * * * * * * * * 607 608
B1 E1 F1 609 610 * * * ** ** * * * 694 695
D1 D2 D3 696 697 * * * ** ** * * * 781 782
H1 H2 H3 0
1 * * * ** ** * * * 85 86
B2 K1 K2 87 88 * * * ** ** * * * 172 173
D4 D5 D6 174 175 * * * ** ** * * * 259 260
D7 D8 D9 261 262 * * * ** ** * * * 346 347
D10 D11 D12 348 349 * * * ** ** * * * 433 434
S1 M0 E2 435 436 * * * ** ** * * * 520 521
**
NOTES:
1. If the content of the "Pointer Bits" is "0x00" then the J1 byte is located immediately after the H3 byte, within the
Envelope Capacity.
2. If the contents of the 10-bit expression exceed the value of 0x30F (or 782, in decimal format) then it does not
contain a valid pointer value.
9.3.2 Pointer Adjustments within the SONET Network
The word SONET stands for "Synchronous Optical NETwork. This name implies that the entire SONET
network is synchronized to a single clock source. However, because the SONET (and SDH) Networks can
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