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PRELIMINARY
XRT79L71
464
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
NOTE: The shaded rows designate those Overhead bits that the XRT79L71 can be used to insert into the outbound E3
data-stream via the Transmit Overhead data Input Interface block. The un-shaded rows designate those Overhead
bits that the XRT79L71 CANNOT insert into the outbound E3 data-stream.
TASK # 3: After the System-Side Terminal Equipment has waited the appropriate number of clock edges from
the TxOHFrame signal being sampled "High", it should assert the TxOHIns input signal by pulling it "High".
Concurrently, the System-Side Terminal Equipment should also place the appropriate value of the overhead bit
to be inserted into the outbound E3 data-stream onto the TxOH input signal. The Transmit Overhead Data
Input Interface block will sample and latch the data residing on the TxOH input pin upon the very next falling
edge of the TxOHClk output signal.
TASK # 4: The System-Side Terminal Equipment should hold the TxOHIns input pin "High" and also hold the
value of the TxOH signal stable until the next rising edge of TxOHClk is detected. Afterwards, the System-Side
Terminal Equipment should toggle the TxOHIns input pin "Low" and wait until another appropriate TxOHClk
period come up, for inserting an overhead bit into the outbound E3 data-stream.
CASE STUDY: The System-Side Terminal Equipment intends to insert the appropriate overhead bits
into the Transmit Overhead Data Input Interface using Method 1 in order to transmit the FERF/RDI
indicator to the remote terminal equipment.
For E3, ITU-T G.82 applications, the FERF/RDI indication is transmitted by setting the FERF/RDI bit-field (Bit 1
within the MA-byte, of each outbound E3 frame) to "1".
If we were to assume that the connection between the System-Side Terminal Equipment and the XRT79L71
Transmit Overhead Data Input Interface block is as illustrated in Figure 222, then Figure 223 presents an
illustration of the signaling that must go on between the System-Side Terminal Equipment and the Transmit
Overhead Data Input Interface, when using Method 1.
50
GC Byte, Bit 3
YES
51
GC Byte, Bit 4
YES
52
GC Byte, Bit 5
YES
53
GC Byte, Bit 6
YES
54
GC Byte, Bit 7
YES
55
GC Byte, Bit 8 (LSB)
YES
TABLE 60: THE RELATIONSHIP BETWEEN THE NUMBER OF RISING CLOCK EDGES IN THE TXOHCLK SIGNAL, SINCE
THE
TXOHFRAME SIGNAL WAS LAST SAMPLED "HIGH" TO THE E3 OVERHEAD BIT THAT IS BEING PROCESSED BY THE
TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK
NUMBER OF RISING EDGES IN
TXOHCLK SINCE TXOHFRAME
BEING SAMPLED
"HIGH"
THE OVERHEAD BIT TO BE PROCESSED BY THE TRANSMIT
OVERHEAD DATA INPUT INTERFACE BLOCK
CAN THIS OVERHEAD BIT BE
ACCEPTED BY THE
XRT79L71,
AND INSERTED INTO THE
OUTBOUND
E3 DATA-STREAM?