á
XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
342
Equipment will interpret this signaling as an indication that the E3 frames that it is transmitting back out to the
Local Receive E3 Framer block are erred.
Conversely, if the Local Receive E3 Framer block does not detect any errors in the EM byte, within the
incoming E3 frame, then it will also inform the Remote Terminal Equipment of this fact by commanding the
Local Transmit E3 Framer block to set the FEBE bit-field of an Outbound E3 frame (which is destined for the
Remote Terminal Equipment) to “0”.
N
OTE
:
A detailed discussion into the practical use of the FEBE bit-field is presented in
Section 6.2.4.2.1
.
Bits 5 - 3 Payload Type
These bit-fields indicate to the Remote Terminal Equipment, what kind of data is being transported in the 530
bytes of E3 frame payload data. Some of the defined payload type values are tabulated in
Table 66
.
Bits 2 - 1 Payload Dependent
To be provided later.
Bit 0 - Timing Marker
This bit-field is set to “0” to indicate that the timing source is traceable to a Primary Reference Clock.
Otherwise, this bit-field is set to “1”.
6.1.1.5
The Network Operator (NR) Byte
The NR byte or the GC byte can be configured to transport LAP-D Message frame octets from the LAPD
Transmitter to the LAPD Receiver (of the Remote Terminal Equipment) at a data rate of 64kbps (1 byte per E3
frame).
If the user opts not to use the NR byte to transport these LAPD Message frames, then the Transmit E3 Framer
block will read in the contents of the TxNR Byte Register (Address = 0x37), and insert this value into the NR
byte-field of each Outbound E3 frame. The Receive E3 Framer block will read in the contents of the NR byte-
field within each incoming E3 frame and will write it into the RxNR Byte register. Consequently, the user can
determine the value of the NR byte, within the most recently received E3 frame by reading the Rx NR Byte
Register (Address = 0x1A).
6.1.1.6
The General Purpose Communications Channel (GC) Byte
The NR byte or the GC byte can be configured to transport LAPD Message frames from the LAPD Transmitter
to the LAPD Receiver (of the Remote Terminal Equipment) at a data rate of 64kbps (1 byte per E3 frame).
If the user opts not to use the GC byte to transport these LAPD Message frames, then the Transmit E3 Framer
block will read in the contents of the Tx GC Byte Register (Address = 0x35), and insert this value into the GC
byte-field of each Outbound E3 frame.
The Receive E3 Framer block will read in the contents of the GC byte-field, within each incoming E3 frame, and
will write it into the RxGC Byte register. Consequently, the user can determine the value of the GC byte, within
the most recently received E3 frame, by reading the Rx GC Byte register (Address = 0x1B).
6.2
The Transmit Section of the XRT72L50 (E3 Mode Operation)
When the XRT72L50 has been configured to operate in the E3, ITU-T G.832 Mode, the Transmit Section of the
XRT72L50 consists of the following functional blocks.
T
ABLE
66: A L
ISTING
OF
THE
V
ARIOUS
P
AYLOAD
T
YPE
V
ALUES
AND
THEIR
CORRESPONDING
M
EANING
P
AYLOAD
T
YPE
V
ALUE
M
EANING
000
Unequipped
001
Equipped
010
ATM Cells
011
SDH TU-12s