
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
32
1.0 SYSTEM DESCRIPTION
The XRT7245 DS3 UNI for ATM consists of the follow-
ing functional sections/blocks.
Transmit Section
– Transmit UTOPIA Interface Block
– Transmit Cell Processor Block
– Transmit PLCP Processor Block
– Transmit DS3 Framer Block
Receive Section
– Receive UTOPIA Interface Block
– Receive Cell Processor Block
– Receive PLCP Processor Block
– Receive DS3 Framer Block
Microprocessor Interface Section
Performance Monitor Section
Test and Diagnostic Section
Line Interface Drive and Scan Section
Each of these functional sections (and the blocks,
within these sections) combine to make a single chip
device that is capable of transmitting and receiving
ATM cell data via a DS3 Transport Medium.
1.1
System Level Interfacing of the XRT7245
DS3 UNI
The system designer, when using the XRT7245 DS3
UNI for ATM, must (at a minimum) interface this chip
to the following entities.
The ATM Switch (or ATM Layer Processor)
A local (housekeeping) microprocessor
The DS3 line
Figure 3 and Figure 4 present two illustrations of the
UNI being interfaced to these three entities. A brief
discussion on how to interface the UNI to these enti-
ties follows.
INTERFACING TO THE ATM SWITCH (ATM LAY-
ER PROCESSOR)
Whenever an ATM switch needs to transmit and
receive ATM cells to and from the UNI, it will typically
use some sort of “ATM Layer” processing entity to
accomplish this processing of cell data. This “ATM
Switch Processing” entity will be referred as the “ATM
Layer Processor” throughout this data sheet. The
ATM Layer processor interfaces with the XRT7245
DS3 UNI via the “UTOPIA Bus” and will write ATM
cell data (in an 8-bit or 16-bit wide parallel format) in-
to the Transmit UTOPIA Interface block (of the UNI).
Additionally, the ATM Layer processor will also re-
ceive ATM cells (in this same 8-bit or 16-bit wide par-
allel format) from the Receive UTOPIA Interface
block (within the UNI IC).
INTERFACING TO THE LOCAL MICROPROCES-
SOR
In contrast to the ATM Layer Processor, the “l(fā)ocal”
microprocessor (
μ
P) interfaces with the UNI via the
Microprocessor Interface. This local “housekeeping”
microprocessor will typically read and write “configu-
ration information” from or into the on-chip registers
within the UNI IC. Further, the local microprocessor
will respond to UNI-generated interrupts, read and
write PMDL (Path Maintenance Data Link) Messages,
FEAC Messages, and OAM cell data to and from the
UNI IC. Finally, the local microprocessor will “monitor”
the performance of the overall system by periodically
reading the contents of the “Performance Monitor”
registers.
Note:
The local
μ
P should not be confused with the ATM
Layer processor. The terms “l(fā)ocal
μ
P” and “ATM Layer
Processor” will be used throughout this data sheet in order
to make the distinction between these two “entities”.
INTERFACING THE UNI TO THE DS3 LINE
The UNI can be interfaced to a DS3 line, that is oper-
ating over a copper or optical medium. If the user in-
tends to interface the UNI to a copper DS3 line, (e.g.,
over coaxial cable), then the user must connect the
dual rail inputs (RxPOS and RxNEG) and the dual
rail outputs (TxPOS and TxNEG) to a DS3 Line Inter-
face Unit (LIU) IC, (which is transformer-coupled to
the DS3 line) in order to reliably transmit and receive
this data over the copper medium. An example of
such an LIU are the XRT7295 (DS3 Line Receiver
IC) and the XRT7296 (DS3 Line Transmitter IC).
Figure 3 presents an illustration of the “System-Level”
interfacing of the XRT7245 DS3 UNI, when the DS3
line signal is transmitted over a copper medium.