XRT72L50 Datasheet, PDF (373/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
FIGURE 157. THE TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK
TxOHFrame
TxOHEnable
TxOH
TxOHClk
TxOHIns
Transmit
Overhead
Data Input
Interface Block
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 XRT72L50 has been designed to handle and process both the payload
type and overhead type bits for each E3 frame. Within the Transmit Section within the XRT72L50, the Transmit
Payload Data Input Interface has been designed 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 XRT72L50 generates or processes the various overhead bits within the E3 frame,
in the following manner.
The Frame Alignment Overhead Bytes (e.g., the FA1 and FA2 bytes)
The "FA1" and "FA2" bytes are always internally generated by the Transmit Section of the XRT72L50. Hence,
the user cannot insert his/her value for the "FA1" and "FA2" bytes into the Outbound E3 data stream, via the
Transmit Overhead Data Input Interface.
The Error Monitoring (EM) Overhead Byte
The EM byte is always internally generated by the Transmit Section of the XRT72L50. 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 XRT72L50, or can be externally generated and inserted into the Outbound E3 data stream, via the
Transmit Overhead Data Input Interface. The E3 frame overhead bits that fall into this category are:
• The "MA” byte
• The "TR” 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 Maintenance Data Link (PMDL) bits can either be sourced from the
Transmit LAPD Controller/Buffer or via the Transmit Overhead Data Input Interface.
Table 68 lists the Overhead Bits within the E3 frame. Additionally, this table also indicates whether or not these
overhead bits can be sourced by the Transmit Overhead Data Input Interface or not.
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