Lucent Technologies Inc.
Lucent Technologies Inc.
49
Preliminary Data Sheet
October 2000
T7630 Dual T1/E1 5.0 V Short-Haul Terminator (Terminator-II)
LIU-Framer Interface
(continued)
Table 17 shows the encoding of a string of zeros using B8ZS. B8ZS is recommended when ESF format is used. V
represents a violation of the bipolar rule, and B represents an inserted pulse conforming to the AMI rule.
Table 17. DS1 B8ZS Encoding
CEPT: High-Density Bipolar of Order 3 (HDB3)
The line code used for CEPT is described in ITU Rec. G.703 Section 6.1 as high-density bipolar of order 3 (HDB3).
HDB3 uses a substitution code that acts on strings of four zeros. The substitute HDB3 codes are 000V and B00V,
where V represents a violation of the bipolar rule and B represents an inserted pulse conforming to the AMI rule
defined in ITU Rec. G.701, item 9004. The choice of the B00V or 000V is made so that the number of B pulses
between consecutive V pulses is odd. In other words, successive V pulses are of alternate polarity so that no direct
current (dc) component is introduced. The substitute codes follow each other if the string of zeros continues. The
choice of the first substitute code is arbitrary. A line code error consists of two pulses of the same polarity that is not
defined as one of the two substitute codes. Excessive zeros consist of any zero string length greater than four con-
tiguous zeros. Both excessive zeros and coding violations are indicated as bipolar violations. An example is shown
in Table 18.
Table 18. ITU HDB3 Coding
Frame Formats
The supported North American T1 framing formats are superframe (D4, SLC-96, and digital data service-DDS)
and extended superframe (ESF). The device can be programmed to support the ITU-CEPT-E1 basic format with
and without CRC-4 multiframe formatting. This section describes these framing formats.
T1 Framing Structures
T1 is a digital transmission system which multiplexes twenty-four 64 kbits/s time slots (DS0) onto a serial link. The
T1 system is the lowest level of hierarchy on the North American T-carrier system, as shown in Figure 20.
Table 19. T-Carrier Hierarchy
Bit Positions
Before B8ZS
After B8ZS
1
0
0
2
0
0
3
0
0
4
0
V
5
0
B
6
0
0
7
0
V
8
0
B
—
1
B
—
0
0
—
1
B
1
0
0
2
0
0
3
0
0
4
0
V
5
0
B
6
0
0
7
0
V
8
0
B
Input Bit Stream
HDB3-coded Data
HDB3-coded Levels
HDB3 with 5 Double BPVs
1011
1011
–0+–
–0+–
0000
000V
000–
–000
1-BPV
01
01
0+
0+
0000
000V
000+
+00+
3-BPV
0000
B00V
–00–
0–––
5-BPV
0000
B00V
+00+
+00+
0000
B00V
–00–
–00–
T Carrier
T1
T1-C
T2
T3
T4
DS0 Channels
24
48
96
672
4032
Bit Rate (Mbits/s)
1.544
3.152
6.312
44.736
274.176
Digital Signal Level
DS1
DS1C
DS2
DS3
DS4