
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
134
Note:
1. The System-side test is not supported by this version
of the XRT7245 DS3 UNI IC.
2. The “UTOPIA Loopback” mode, as depicted in
Figure 29, must be implemented by the user’s
system level hardware.
4.3
Operating the Test Cell Generator/Receiver
Sections 4.1 discussed the various loopback modes
that are available within the UNI device. Section 4.2
discussed Line Side Testing; where the “internal” Test
Cell Generator can be enabled to produce test cells,
and write them into the TxFIFO. These cells will be
read out of the TxFIFO by the Transmit Cell Processor,
and routed towards the DS3 line. Section 4.1 and 4.2
also mentioned that these cells could be “l(fā)ooped”
back into the Receive path (of the UNI), at various
points depending upon the Loopback Mode selected.
When operating the UNI in the Line Side Test Mode,
the following loopback options are available.
PLCP Loopback
Line Loopback
External Loopback
As these test cells proceed through the Receive path
(after traversing the loopback point), they will eventu-
ally arrive at the RxFIFO (within the Receive UTOPIA
Interface); where they will be identified, collected and
analyzed by the Test Cell Receiver.
The next two sections discuss the operation of the
Test Cell Generator and the Test Cell Receiver, with
the UNI Test and Diagnostic Section.
4.3.1
The Test Cell Generator has the following
characteristics:
It allows the user to specify the header byte patterns
of these test cells.
The payload bytes within these test cells will be
filled by an internal Pseudo-Random Byte
Sequence (PRBS) Pattern Generator.
It allows the user to select one of two “Test Cell
Traffic” generating options. These options are:
The “One Shot” Mode
The “Continuous” Mode
It generates Test Cells and writes them into the
TxFIFO (within the Transmit UTOPIA Interface
block), where they will be read from and processed
throughout the UNI.
Characteristics of the Test Cell Generator
1.
2.
Each of these Characteristics of the Test Cell Gener-
ator are described in greater detail below.
4.3.1.1
Specifying the Header Byte Pattern of
Test Cells
The user can specify his/her choice for the header byte
patterns of these Test Cells, by writing the “desired”
header byte patterns into the “Test Cell Header Byte”
F
IGURE
29. I
LLUSTRATION
OF
S
YSTEM
S
IDE
T
EST
,
WHILE
THE
UNI S
YSTEM
IS
CONFIGURED
TO
OPERATING
IN
UTOPIA L
OOPBACK
M
ODE
.
Utopia Loopback
UNI Chip
Tx Utopia
Tx PLCP
Processor
Tx DS3
Framer
Rx DS3
Framer
Rx PLCP
Processor
Rx Utopia
Tx Cell
Processor
Rx Cell
Processor
Test Cell
Receiver
Test Cell
Generator
ATM Layer
Processor