XRT86SH328_2 Datasheet, PDF (65/159 Pages) Exar Corporation – SONET TO 28-T1/21-E1 PDH MAPPER - VOYAGER PIN AND ARCHITECTURE DESC

XRT86SH328
REV. 1.0.1
SONET TO 28-T1/21-E1 PDH MAPPER - VOYAGER PIN AND ARCHITECTURE DESC
The rxstoh_stat block lets software specify the time interval over which to monitor the B2 error counts and the
thresholds over/under which to set/clear the SF and SD conditions.
SEF FORCE
Software can force the SEF condition in the frame finder in the rxstoh_proc block by writing a "1" to the
appropriate register file bit. This causes the rxstoh_proc block to re-find frame. The bit is cleared after the
rxstoh_proc block has rediscovered frame alignment (after at least 1 frame).
SECTION TRACE (J0) MONITOR
The SONET standard has defined the J0 byte as a 1 byte or 16 byte message in the following manner:
This byte is used to transmit repetitively a Section Access Point Identifier so that a Section receiver can verify
its continued connection to the intended transmitter. Within a national network, or within the domain of a single
operator, this Section Access Point Identifier may use either a single byte (containing the code 0-255) or the
Access Point Identifier format as defined in clause 3/G.831. At international boundaries, or at the boundaries
between the networks of different operators, the format defined in clause 3/G.831 shall be used unless
otherwise mutually agreed by the operators providing the transport.
A 16-byte frame is defined for the transmission of Section Access Point Identifiers where these conform to the
definition contained in clause 3/G.831. The first byte of the string is a frame start marker and includes the result
of a CRC-7 calculation over the previous frame. The following 15 bytes are used for the transport of 15 T.50
characters (international Reference Version) required for the Section Access Point Identifier. The 16 byte
frame description is given in the table below:
TABLE 1: 16-BYTE FRAME FOR TRAIL APID
BYTE #
VALUE (BIT 1, 2, … ,8)
1
1
C1
C2
C3
C4
C5
C6
C7
2
0
X
X
X
X
X
X
X
3
0
X
X
X
X
X
X
X
:
:
:
16
0
X
X
X
X
X
X
X
NOTES:
1. C1 to C7 is the result of the CRC-7 calculation over the previous frame. C1 is the MSB. The description of this
CRC-7 calculation is given in Annex B
2. 0XXXXXXX represents a T.50 character.
.2
In the case of inter-working of equipment implementing the STS identifier functionality and equipment
employing the Section Trace function, the latter shall interpret the pattern "0000001" in J0 as "Section Trace -
unspecified". This unspecified Section Trace can also be used if no use of the Section Trace is made.
The rxstoh_stat block enables software to specify the length of the J0 section trace message. This length could
be 1 or 16 for SONET, and 64 should the SONET standard in the future specify the J0 byte as a Section Trace
Byte. The software also specifies whether to look for an LF or a starting "1" bit when the rxstoh_stat block is
trying to locate the start of the message. The software also specifies the number (3 or 5) of consecutive
consistent Section Trace messages that must be observed before it is accepted.
An interrupt is generated when a new Section Trace message is accepted as valid. The valid Section Trace
message is compared with an expected Section Trace message downloaded to memory by software. A J0
mismatch (J0_MIS) flag is raised if the 2 messages are not identical. The rxstoh_stat block also implements a
J0 unstable counter. The J0 unstable counter is incremented for each byte that differs from the previously
received byte. An invalid J0 condition is declared when the J0 unstable counter reaches 8. The J0 unstable
counter is cleared to 0 when a valid J0 is accepted.
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