CN8223
2.0 Functional Description
ATM Transmitter/Receiver with UTOPIA Interface
2.3 Overhead Generation
2.3 Overhead Generation
The CN8223 automatically receives and generates line overhead. For additional
flexibility, line overhead can be monitored and inserted for STS-3c, STM-1, and
G.832 E3/E4 modes.
2.3.1 Internal DS3 Mode
The transmitter circuitry automatically generates all F and M framing bits. The
transmitter calculates the parity of each M-frame and inserts this data into bits P1
and P2 of the following M-frame. Bits X1 and X2 contain 1s unless Transmit
Alarm Control [bit 6] of CONFIG_2 [0x01] is set. If this bit is set, bits X1 and X2
contain 0s. All C bit positions are generated automatically by the transmitter.
Overhead generation of DS3 values is summarized in Table 2-8.
Table 2-8. DS3 Overhead Values
Overhead Bits
CN8223 Operation
X1, X2
Yellow alarm bits set from CONFIG_2, bit 6.
P1, P2
Calculates and inserts frame parity. No error insertion.
Internally generated 010 pattern. No error insertion.
Internally generated 1001 pattern. No error insertion.
Application ID channel. Internally generated as all 1s.
Network requirement bit. Internally generated as all 1s.
FEAC channel. Internally generated under processor control.
Unused. Internally generated as all 1s.
M123
F1234
C1 Subframe 1
C2 Subframe 1
C3 Subframe 1
C123 Subframe 2
C123 Subframe 3
C123 Subframe 4
Path parity. Same value inserted as P1, P2 in all 3 bits. No error insertion.
FEBE indication. Internally generated as all 1s. If receiver detects a path parity, or M123 or F1234 error,
then non-111 code is inserted for one frame.
C123 Subframe 5
Terminal data link. Data or all 1s from internal HDLC formatter when enabled.
Internally generated as all 1s.
C123 Subframes 6, 7
100046C
Conexant
2-13
CONEXANT [ CONEXANT SYSTEMS, INC ]
