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PRELIMINARY
XRT79L71
424
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The E3 Overhead bytes supporting each of these purposes are further defined below.
Frame Synchronization Bytes - The Frame Alignment Bytes (FA1 and FA2)
The FA1 and FA2 bytes are known as the Frame Alignment bytes, within a given E3, ITU-T G.832 Frame. A
given Transmitting E3 Terminal Equipment will set the FA1 byte to the value "0xF6" and the FA2 byte to the
value "0x28". The Receiving E3 Terminal Equipment will use these FA1 and FA2 bytes in order acquire and
maintain frame synchronization with the incoming E3 data-stream. For more information on how the Receive
Performance Monitoring Byte - The Error Monitor Byte (EM)
Each E3 frame consists of a single EM byte. This EM byte carries the BIP-8 (Bit Interleaved Parity - 8) value of
the previous E3 frame for performance monitoring. As a Transmitting E3 Terminal assembles an E3 frame
prior to transmitting this E3 signal to the remote terminal equipment, it will compute the Bit-Interleaved-Parity -
8 (BIP-8) over this entire outbound E3 frame. The Transmitting E3 Terminal will then insert the resulting BIP-8
value into the EM byte-position within the very next outbound E3 frame.
As a Receiving E3 Terminal receives a given incoming E3 frame, it will locally compute its value for the EM
byte. Afterwards, this Receiving E3 Terminal will compare its locally-computed BIP-8 value with the value of
the EM byte within the very next incoming E3 frame. If these two EM byte values match, then the Receiving E3
Terminal will presume that the first of these two incoming E3 frames was received in an error-free manner. If
these two EM byte values DO NOT match, then the Receiving E3 Terminal will presume that the first of these
two incoming E3 frames was received in an erred manner.
For information on how the Receive DS3/E3 Framer block handles the EM bytes within the incoming E3 data-
Alarm and Signaling-Related Overhead Bytes
The E3, ITU-T G.832 frame includes numerous bytes that are used to support the handling of alarms/defects
and signaling information. Each of these byte-fields is defined below.
The Trail-Trace Byte (TR)
The Trail-Trace Byte is used to repetitively transmit a Trail-Access Point Identifier value so that a Receiving
Terminal can verify its continued connection to the intended Transmitting Terminal. This Trail-Access Point
Identifier consists of a repeating 16-byte message which consists of 15 ASCII characters and a CRC byte. The
Byte-format of this Trail-Access Point Identifier Message is presented below in Table 53.
Table 53 indicates that the very first byte of this 16-byte string is a Frame Start Marker byte, which is typically
of the form [1, C6, C5, C4, C3, C2, C1, C0]. The "1" in the MSB (Most Significant Bit) of this first byte is used
to identify this byte as the Frame Start Marker (e.g., the very first byte of this Trail Access Point Identifier
Message). The remaining bits within this particular byte (e.g., C0 through C6) are the results of a CRC-7
calculation that was computed over the previous Trail-Access Point Identifier Message. All of the remaining 15
TABLE 53: THE BYTE-FORMAT OF THE TRAIL-TRACE MESSAGE THAT THIS BEING TRANSPORTED VIA AN E3 DATA-
STREAM VIA THE TR BYTE
BYTE NUMBER
BIT 1
(MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
(LSB)
1 (Frame Start Marker)
1
CRC_Value[6:0]
2
0
TTM_Byte_1[6:0]
*
0
TTM_Byte_N[6:0]
15
0
TTM_Byte_15[6:0]
16
0
TTM_Byte_16[6:0]