PRELIMINARY
XRT79L71
294
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
However, the Transmit Section of the XRT79L71 can also be configured to externally accept values (via a
certain input port) and to insert this data into certain user specified overhead bits, within the outbound E3 data-
stream. The XRT79L71 permits the user to implement this overhead E3 data-stream. The XRT79L71 permits
the user to implement this overhead bit insertion by either of the following methods.
By configuring the Transmit Section of the XRT79L71 to accept E3 overhead data via the Transmit Payload
By configuring the Transmit Section of the XRT79L71 to accept E3 overhead data via the Transmit Overhead
Data Input Interface (This approach will be discussed below).
The purpose of the Transmit Overhead Data Input Interface block is to accept overhead data from some
system-side or up-stream source and to overwrite the contents of the overhead bits, within the outbound E3
data-stream with these particular overhead bit values.
In order to accomplish this, the Transmit Overhead Data Input Interface block has numerous input and output
pins. Table 39 presents a list and a brief definition of each of these pins.
TABLE 38: HOW THE TRANSMIT E3 FRAMER BLOCK INTERNALLY GENERATES EACH OF THE OVERHEAD BITS/BYTES -
E3, ITU-T G.751 APPLICATIONS
BIT NAME
BIT/BYTE
DESCRIPTION
HOW OVERHEAD BIT IS INTERNALLY GENERATED BY THE TRANSMIT E3 FRAMER BLOCK
FAS Bits[9:0] Framing Alignment
Bits
These 10 bits are set to the value [1111010000]
A
Alarm Bit
The Transmit E3 Framer block will handle the "A" bit, as described below.
If BIP-4 Insertion/Verification is enabled:
The Transmit E3 Framer block will automatically set the "A" bit to "1" anytime the
corresponding Receive E3 Framer block detects a BIP-4 error within an incoming
E3 frame. Conversely, the Transmit E3 Framer block will automatically set the "A"
bit to "0" anytime the corresponding Receive E3 Framer block DOES NOT detect a
BIP-4 error within an incoming E3 frame.
If BIP-4 Insertion/Verification is NOT enabled:
The Transmit E3 Framer block will set the "A" bit to the appropriate value as dictated
by Software Control.
N
National Bit
The Transmit E3 Framer will handle the "N" bit, as described below.
If the Transmit LAPD Controller block is enabled:
The "N" bits will be used to transport the contents of the outbound LAPD/PMDL
Messages from the local Terminal to the remote Terminal.
If the Transmit LAPD Controller block is DISABLED:
The Transmit E3 Framer block will set the "N" bits to the appropriate value as dic-
tated by Software Control.
BIP-4[3:0]
BIP-4 Bits
The Transmit E3 Framer block will handle the BIP-4 bits, as described below.
If BIP-4 Insertion/Verification is enabled:
The Transmit E3 Framer block will compute the BIP-4 value over a given outbound
E3 frame. The resulting BIP-4 value will be inserted into the BIP-4 bit positions
within the very next outbound E3 frame.
If BIP-4 Insertion/Verification is disabled:
The BIP-4[3:0] bits will be used to carry payload bits that have been accepted via
the Transmit Payload Data Input Interface block.