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10.6.2.2 Receive Framer

Programmable DS3 or E3 framer – Accepts a DS3 (M23 or C-bit) or E3 (G.751 or G.832) signal and performs

DS3/E3 overhead termination.

Arbitrary framing format support – Accepts a signal with an arbitrary framing format. The Line overhead/stuff

periods are removed from the data stream using an overhead mask signal.

Detects alarms and errors – Detects DS3 alarm conditions (SEF, OOMF, OOF, LOF, COFA, AIS, AIC, RDI,

and Idle) and errors (framing, parity, and FEBE), or E3 alarm conditions (OOF, LOF, COFA, AIS, and RDI/RAI)

and errors (framing, parity, and REI).

Serial DS3/E3 overhead extraction port – Extracts all DS3 or E3 overhead and outputs it on a serial

interface.

HDLC overhead extraction – An HDLC channel can be extracted from the DS3 or E3 data stream.

FEAC extraction – A FEAC channel can be extracted from the DS3 or E3 data stream.

Trail Trace extraction – Extracts and outputs the G.832 E3 TR byte.

10.6.3 Transmit Formatter

The Transmit Formatter receives a DS3 or E3 data stream and performs framing generation, error insertion,

overhead insertion, and AIS/Idle generation for C-bit DS3, M23 DS3, G.751 E3, or G.832 E3 framing protocols.

The bits in a byte are transmitted MSB first, LSB last. When they are input serially, they are input in the order they

are to be transmitted. The bits in a byte in an outgoing signal are numbered in the order they are transmitted, 1

(MSB) to 8 (LSB). However, when a byte is stored in a register, the MSB is stored in the highest numbered bit (7),

and the LSB is stored in the lowest numbered bit (0). This is to differentiate between a byte in a register and the

corresponding byte in a signal.

10.6.4 Receive Framer

The Receive Framer receives the incoming DS3, or E3, line/tributary data stream, performs appropriate framing,

and terminates and extracts the associated overhead bytes.

The Receive Framer processes a C-bit format DS3, M23 format DS3, G.751 format E3, or G.832 format E3 data

stream, performing framing, performance monitoring, overhead extraction, and generates downstream AIS, if

necessary.

The bits in a byte are received MSB first, LSB last. When they are output serially, they are output MSB first, LSB

last. The bits in a byte in an incoming signal are numbered in the order they are received, 1 (MSB) to 8 (LSB).

However, when a byte is stored in a register, the MSB is stored in the highest numbered bit (7), and the LSB is

stored in the lowest numbered bit (0). This is to differentiate between a byte in a register and the corresponding

byte in a signal.

Some bits, bit groups, or bytes (data) are integrated before being stored in a register. Integration requires the data

to have the same new data value for five consecutive occurrences before the new data value will be stored in the

data register. Unless stated otherwise, integrated data may have an associated unstable indication. Integrated data

is considered unstable if the received data value does not match the currently stored (integrated) data value or the

previously received data value for eight consecutive occurrences. The unstable condition is terminated when the

same value is received for five consecutive occurrences.

10.6.4.1.1 Receive DS3 Framing

DS3 framing determines the DS3 frame boundary. In order to identify the DS3 frame boundary, first the subframe

boundary must be found. The subframe boundary is found by identifying the subframe alignment bits FX1, FX2, FX3,

and FX4, which have a value of one, zero, zero, and one, respectively. See Figure 10-14. Once the subframe

boundary is found, the multiframe frame boundary can be found. The multiframe boundary is found by identifying

the multiframe alignment bits M1, M2, and M3, which have a value of zero, one, and zero respectively. The DS3

framer is an off-line framer that only updates the data path frame counters when either an out of frame (OOF) or an

out of multiframe (OOMF) condition is present. The use of an off-line framer reduces the average time required to

reframe, and reduces data loss caused by burst error. The DS3 framer has a Maximum Average Reframe Time

(MART) of approximately 1.0 ms.

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