XRT72L56 Datasheet, PDF(390/486 Page) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L56 Datasheet, PDF (390/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L56

SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

REV. P1.1.2

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PRELIMINARY

FIGURE 169. SIMPLE ILLUSTRATION OF THE TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK

TxOHFrame

TxOHEnable

TxOH

TxOHClk

TxOHIns

TTrraannsmsmitit

OOvveerrhheeaadd

DDaatataInInppuut t

InInteterrfafacceeBBlolocckk

To Transmit E3 Framer Block

The E3, ITU-T G.832 Frame consists of 537 bytes.

Of these bytes, 530 bytes are payload bytes and the

remaining 7 are overhead bytes. The XRT72L56 has

been designed to handle and process both the pay-

load type and overhead type bits for each E3 frame.

Within the Transmit Section within the XRT72L56, the

Transmit Payload Data Input Interface has been de-

signed to handle the payload data. Likewise, the

Transmit Overhead Input Interface has been designed

to handle and process the overhead bits.

The Transmit Section of the XRT72L56 generates or

processes the various overhead bits within the E3

frame, in the following manner.

The Frame Alignment Overhead Bytes (e.g., the

âFA1â and âFA2â bytes)

The "FA1" and "FA2" bytes are always internally gen-

erated by the Transmit Section of the XRT72L56.

Hence, the user cannot insert his/her value for the

"FA1" and "FA2" bytes into the Outbound DS3 data

stream, via the Transmit Overhead Data Input Inter-

face.

The Error Monitoring (EM) Overhead Byte

The EM byte is always internally generated by the

Transmit Section of the XRT72L56. Hence, the user

cannot insert his/her value for the EM byte into the

Outbound E3 data stream, via the Transmit Overhead

Data Input Interface.

The Alarm and signaling related Overhead bytes

Bytes that are used to transport the alarm conditions

can be either internally generated by the Transmit

Section within the XRT72L56, or can be externally

generated and inserted into the Outbound E3 data

stream, via the Transmit Overhead Data Input Inter-

face. The E3 frame overhead bits that fall into this

category are:

â¢ The "MAâ byte

â¢ The "TRâ byte

The Data Link Related Overhead Bits

The E3 frame structure also contains bits which can

be used to transport User Data Link information and

Path Maintenance Data Link information. The UDL

(User Data Link) bits are only accessible via the

Transmit Overhead Data Input Interface. The Path

371

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