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FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L54
PRELIMINARY
REV. P1.1.2
146
Table 17 lists the relationship between the value of
the this bit-field and the resulting DS3 Frame Format.
NOTE: This bit setting also configures the frame format for
both the Transmit and Receive Section of the XRT72L54.
Each of the two DS3 Frame Formats, as presented in
full DS3 Frame). Each M-frame consists of 7 - 680 bit
F-frames (sometimes referred to as, subframes). In
the individual rows of payload and overhead bits.
Each F-frame can be further divided into 8 blocks of
85 bits, with 84 of the 85 bits available for payload in-
formation and the remaining one bit used for frame
overhead.
Differences Between the M13 and C-Bit Parity
Frame Formats
The frame formats for M13 and C-bit Parity are very
similar. However, the main difference between these
two framing formats is in the use of the C-bits. In the
M13 Format, the C-bits reflect the status of stuff-op-
portunities that either were or were not used while
multiplexing the 7 DS2 signals into this DS3 signal. If
two of the three stuff bits, within a F-frame, are "1",
then the associated stuff bit, Si (not shown in
Figure 41), is interpreted as being a stuff bit. In the
C-bit Parity framing format, the C bits take on different
Definition of the DS3 Frame Overhead Bits
In general, the DS3 Frame Overhead Bits serve the
following three purposes:
1. Support Frame Synchronization between the
Local and Remote DS3 Terminals
2. Provide parity bits in order to facilitate perfor-
mance monitoring and error detection.
3. Support the transmission of Alarms, Status, and
Data Link information to the Remote DS3 Termi-
nal.
The Overhead bits supporting each of these purpos-
es are further defined below.
4.1.1
Frame Synchronization Bits (Applies to
both M13 and C-bit Parity Framing Formats)
Each DS3 Frame (M-frame) contains a total of 31 bits
that support frame synchronization. Each DS3 M-
frame contains three M-bits. According to
Figure 40and
Figure 41, these M-bits are the first bits in F-
frames 5, 6 and 7. These three bits appear in each
M-frame with the repeating pattern of "010". This fact
contains bit-fields that are designated as: M0, M1,
and M0 (where M0 = "0", and M1 = "1").
Each F-frame contains four F-bits, which also aid in
synchronization between the Local and the remote
x
1x
0
x
xx
x
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6BIT 5BIT 4BIT 3
BIT2BIT 1BIT 0
TABLE 17: THE RELATIONSHIP BETWEEN THE CONTENT
OF
BIT 2, (C-BIT PARITY*/M13) WITHIN THE FRAMER
OPERATING MODE REGISTER AND THE RESULTING DS3
FRAMING FORMAT
BIT 2
DS3 FRAME FORMAT
0
C-Bit Parity
1M13
TABLE 18: C-BIT FUNCTIONS FOR THE C-BIT PARITY DS3 FRAME FORMAT
C - BIT
FUNCTION OF C-BITS WHILE IN THE C-BIT PARITY FRAMING FORMAT
C11
AIC (C-Bit Parity Mode)
C12
NA (Reserved for Network Application)
C13
FEAC (Far End Alarm & Control)
C21, C22, C23
(UDL) User Data Link (undefined for DS3 Frame)
C31,C32, C33
CP (Path) Parity Bits
C41, C42, C43
FEBE (Far End Block Error) Indicators
C51, C52, C53
(DL) Path Maintenance Data Link
C61, C62, C63,
C71, C72, C73
(UDL) User Data Link (undefined for DS3 Frame)