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DS3171/DS3172/DS3173/DS3174
111
10.12 LIU—Line Interface Unit
10.12.1 General Description
The line interface units (LIUs) perform the functions necessary for interfacing at the physical layer to DS3 or E3
lines. Each LIU has independent receive and transmit paths and a built-in jitter attenuator. See
for the
location within the DS317x device of the LIU.
Figure 10-31. LIU Functional Diagram
DS3/E3
Transmit
LIU
IEEE P1149.1
JTAG Test
Access Port
Microprocessor
Interface
HDLC
FEAC
LLB
DLB
DS3 / E3
Transmit
Formatter
DS3 / E3
Receive
Framer
Trail
Trace
Buffer
DS3/E3
Receive
LIU
TAIS
TUA1
Clock Rate
Adapter
TX BERT
RX BERT
PLB
ALB
UA1
GEN
B3ZS/
HDB3
Encoder
B3ZS/
HDB3
Decoder
10.12.2 Features
•
Each Port Independently Configurable
•
Perform Receive Clock/Data Recovery and Transmit Waveshaping
•
Jitter Attenuators can be Placed in Either the Receive or Transmit Paths
•
Interface to 75
Ω
Coaxial Cable at Lengths Up to 380 meters (DS3), 440 meters (E3)
•
Use 1:2 Transformers on TX and RX
•
Require Minimal External Components
•
Local and Remote Loopbacks
10.12.2.1 Transmitter
•
Gapped clock capable up to 52MHz
•
Wide 50
±
20% transmit clock duty cycle
•
Clock inversion for glueless interfacing
•
Unframed all-ones generator (E3 AIS)
•
Line build-out (LBO) control
•
Tri-state line driver outputs support protection switching applications
•
Per-channel power-down control
•
Output driver monitor
10.12.2.2 Receiver
•
AGC/equalizer block handles from 0 to 15dB of cable loss
•
Loss-of-lock (LOL) PLL status indication
•
Interfaces directly to a DSX monitor signal (~20dB flat loss) using built-in preamp
•
Digital and analog loss-of-signal (LOS) detectors (ANSI T1.231 and ITU G.775)
•
Clock inversion for glueless interfacing
•
Per-channel power-down control