Preliminary Data Sheet
October 2000
T7630 Dual T1/E1 5.0 V Short-Haul Terminator (Terminator II)
48
L Lucent Technologies Inc.
LIU-Framer Interface
(continued)
DS1: Alternate Mark Inversion (AMI)
The default line code used for T1 is alternate mark inversion (AMI). The coding scheme represents a one with a
pulse (mark) on the positive or negative rail and a zero with no pulse on either rail. This scheme is shown in
Table 15.
Table 15. AMI Encoding
The T1 ones density rule states that:
In every 24 bits of information to be transmitted, there must be at least three pulses, and no more than 15 zeros
may be transmitted consecutively [AT&T TR62411 (1988), ANSI T1.231 (1997)].
Receive ones density is monitored by the receive line interface as per T1M1.3/93-005, ITU G.775, or TR-TSY-
000009.
The receive framer indicates excessive zeros upon detecting any zero string length greater than 15 contiguous
zeros (no pulses on either RPD or RND). Both excessive zeros and coding violations are indicated as bipolar viola-
tions.
DS1: Zero Code Suppression (ZCS)
Zero code suppression is a technique known as pulse stuffing in which the seventh bit of each time slot is stuffed
with a one. The line format (shown in Table 16) limits the data rate of each time slot from 64 kbits/s to 56 kbits/s.
The default ZCS format stuffs the seventh bit of those ALL-ZERO time slots programmed for robbed-bit signaling
(as defined in the signaling control registers with the F and G bits).
The receive framer indicates excessive zeros upon detecting any zero string length greater than fifteen contiguous
zeros (no pulses on either RPD or RND). Both excessive zeros and coding violations are indicated as bipolar viola-
tions.
Table 16. DS1 ZCS Encoding
DS1: Binary 8 Zero Code Suppression (B8ZS)
Clear channel transmission can be accomplished using Binary 8 Zero Code Suppression (B8ZS). Eight consecu-
tive zeros are replaced with the B8ZS code. This code consists of two bipolar violations in bit positions four and
seven and valid bipolar marks in bit positions five and eight. The receiving end recognizes this code and replaces it
with the original string of eight zeros.
The receive framer indicates excessive zeros upon detecting a block of eight or more consecutive zeros (no pulses
on either RPD or RND). Both excessive zeros and coding violations are indicated as bipolar violations.
Input Bit Stream
AMI Data
1011
–0+–
0000
0000
0111
0+–+
1010
–0+0
Input Bit Stream
ZCS Data (Framer Mode)
T7630 Default ZCS
00000000
00000010
00000010
01010000
01010010
01010000
00000000
00000010
00000000
00000000
00000010
00000010
(data time slot remains clear)