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PRELIMINARY
XRT79L71
62
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Figure 18 presents an illustration of two DS3 Boards that are connected to each other via a System Back-
Plane. Each of these DS3 Boards contains a Receive DS3 Framer and a Transmit DS3 Framer entity. In one
of these boards, the Receive DS3 Framer declares the LOS (Loss of Signal) Defect condition with the DS3
signal that it is receiving from the remote terminal equipment. In this particular system, the correct thing to do
is for the System-Level Software to respond to this declaration of the LOS Defect condition, by commanding
the Transmit DS3 Framer block on the other DS3 Board to transmit the DS3 AIS indicator in the down-stream
direction.
This transmission of the AIS indicator serves the following two purposes.
a. It fills a given DS3 data-stream, in which the contents have been wiped-out by the up-stream defect
condition, such as LOS, with a defined pattern.
b. It notifies the down-stream circuitry of this service-affecting defect condition.
The transmission of the AIS indicator would also be appropriate if the Receive DS3 Framer (in Figure 18) were
to declare the LOF/OOF or AIS defect conditions.
The XRT79L71 can be configured to transmit and receive the following types of DS3 AIS patterns.
The Bellcore GR-499-CORE Compliant DS3 AIS Pattern
This particular AIS pattern has the following characteristics
Valid M-bits, F-bits and P-bits
All C-bits are set to "0"
All X-bits are set to "1"
FIGURE 18. AN ILLUSTRATION OF A CONDITION IN WHICH AIS WOULD NEED TO BE TRANSMITTED
Receive DS3
Framer
Receive DS3
Framer
Transmit DS3
Framer
Transmit DS3
Framer
Receive DS3
Framer
Receive DS3
Framer
Transmit DS3
Framer
Transmit DS3
Framer
Incoming DS3 signal
From “Source” Terminal
Equipment
Outbound DS3 signal
To “Sink” Terminal
Equipment
Incoming DS3 signal
From “Source” Terminal
Equipment
Outbound DS3 signal
To “Sink” Terminal
Equipment
System Back-
Plane
LOS
Defect
AIS