
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
264
where: a—bit is available for use by the ATM layer entity
z—Any VCI value other than 0
As far as the XRT7245 DS3 UNI IC is concerned,
whether an OAM cell is an F4 or F5 type OAM cell,
is rather unimportant. The Receive Cell Processor
circuitry has been designed to recognize both types
of OAM cells, based upon their header byte pattern.
However, whether an OAM cell is a “Segment type”
or an “End-to-End type” is more important in regards
to UNI IC operation. The manner in which the
Receive Cell Processor handles “Segment” and
“End-to-End” OAM cells is described below.
7.3.2.4.1
Segment type OAM cells are only intended for point-
to-point transmission. In other words, a segment type
OAM cell will be created at a source node, transmis-
sion across a single link, to a destination node; and
then terminated at the destination node. This Segment
OAM cell is not intended to be read or processed by
any other nodes within the ATM Network.
Segment Type OAM Cells
How the Receive Cell Processor handles Segment
Type OAM Cells
The Receive Cell Processor has been designed to
recognize incoming OAM cells, based upon their
header byte pattern. Further, the Receive Cell
Processor is also capable of reading the header byte
patterns, in order to determine if the OAM cell is a
“Segment” type or an End-to-End type OAM cell. If
the incoming OAM cell is a “Segment” type OAM cell,
then the Receive Cell Processor will not write this cell
to the Rx FIFO, within the Receive UTOPIA Interface
block and will discard this cell. This act of discarding
the OAM cell terminates it and prevents it from prop-
agating to other nodes in the network.
Note:
If the user configures the User Cell Filter to pass
cells with header bytes pattern ranges that includes that of
the “Segment”-type OAM Cell, then the User Cell Filter
settings will take precedence and allow the “Segment”-type
OAM Cell to be written to the Rx FIFO, within the Receive
UTOPIA Interface Block.
Although the Receive Cell Processor will discard this
“Segment” OAM cell, the user can configure the
Receive Cell Processor to have the contents of this
cell written into the Receive OAM Cell Buffer, where it
can be read out and processed by the local μP/μC.
If the user writes a “1” to bit 3 (OAM Check Bit) within
the “Rx CP Configuration” register (Address = 4Ch),
then all OAM cells that are received by the Receive
Cell Processor will be written into the Receive OAM
Cell buffer (located at 161h through 1A1h, in the UNI
chip address space).
Once the Receive Cell Processor has written the
OAM cell into the “Receive OAM Cell” buffer, then the
Receive Cell Processor will alert the local μP/μC of
this fact, by generating the “Received OAM Cell”
interrupt. If the user write a “0” to bit 3 of the “Rx CP
Configuration” register, then the Receive Cell
Processor will not write the contents of the OAM cells
that it receives, to the “Receive OAM Cell” buffer.
T
ABLE
59: T
HE
H
EADER
B
YTE
P
ATTERN
FORMATS
FOR
THE
V
ARIOUS
T
YPES
OF
OAM C
ELLS
OAM C
ELL
O
CTET
1
O
CTET
2
O
CTET
3
O
CTET
4
F4 End-to-End
0000aaaa
aaaa0000
00000000
01000a0a
F4 Segment
0000aaaa
aaaa0000
00000000
00110a0a
F5 End-to-End
0000aaaa
aaaazzzz
zzzzzzzz
zzzz101a
F5 Segment
0000aaaa
aaaazzzz
zzzzzzzz
zzzz100a
RxCP Configuration Register (Address = 4Ch)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
RxLCD
RDPChk
Pattern
RDPChk
Pattern Enable
Idle Cell
Discard
OAM Check
Bit
De-Scramble
Enable
RxCoset
Enable
HEC Error
Ignore
RO
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
x
x
x
x
x
x
x