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Atheros Communications, Inc. AR8031 Integrated 10/100/1000 GB Ethernet Transceiver • 17
COMPANY CONFIDENTIAL January 2010 • 17
Figure 3-6 shows a block diagram of external
remote PHY loopback.
NOTE: AR8031-1L1E does not support.
AR8031-1L1A supports Remote PHY Loopback.
3.6 Cable Diagnostic Test
The Cable Diagnostic Test (CDT) feature in the
AR8031 device uses Time Domain Reflectometry
(TDR) to identify remote and local PHY
malfunctions, bad/marginal cable or patch cord
segments, or connectors. Some of the possible
problems that can be diagnosed include opens,
shorts, cable impedance mismatch, bad connectors,
termination mismatch, and bad magnetics. The CDT
can be performed when there is no link partner or
when the link partner is auto-negotiating.
3.7 Fiber Mode Support
Besides standard 10/100/1000Base-T copper port
support, Both AR8031 and AR8033 provide
additional IEEE 1000Base-X and 100Base-FX
support in fiber applications through integrated
SERDES. Both the AR8031 and the AR8033 can
work in RGMII mode to fiber or 10/100/1000Base-
T to fiber.
Besides 1000Base-X and 100Base-FX support,
Both devices will support IEEE 802.3 remote Fault
Indication and fault propagation in fiber application.
3.7.1 IEEE 802.3 Remote Fault Indication
Support
Remote Fault allows stations on a fiber optic link to
know when there is a problem on the link. Without
Remote Fault, a station can not detect a problem that
affects only one fiber (Transmit, for example).
With Remote Fault, the loss of a Receive signal
(Link) causes the Transmitter to send a special
pattern of data indicating that a fault has occurred.
84 '1's followed by a single '0' is sent three times, in-
band, and is readily detectable by the remote station,
but is constructed so as to not satisfy the 100BASE-
X carrier sense criterion, so the message will not be
interpreted as normal traffic. If the remote station
has Remote Fault, the link is dropped. If the remote
station does not have Remote Fault, the special data
pattern is ignored.
The AR8031 indicates whether or not a Remote
Fault pattern has been received from the remote
station using the "Remote Fault Status Bit". This
"Remote Fault Status Bit" can be "Propagated" (see
below) to the copper links on both ends of a fiber
link. In the event of a detected fault, both ends of the
link can be notified of the failure in this way. This is
particularly useful given the distances fiber links are
generally used over.
3.7.2 Fault Propagation
The AR8031 supports Fault Propagation - this
allows the fiber link fault to be propagated to the
Twisted-pair copper connections where the "link
down" status can be easily and quickly detected.
The following steps describe Fault Propagation (for
both 100Base-FX and 1000Base-X):
The AR8031 supports Fault Propagation - this
allows the fiber link fault to be propagated to the
Twisted-pair copper connections where the "link
down" status can be easily and quickly detected.
The following steps describe Fault Propagation (for
both 100Base-FX and 1000Base-X):
n The Twisted-pair transmit path will be OFF
when the Receive path of the Fiber link has no
signal detected or is link down. The two Fiber
media types are then handled as described
below:
n The Media Converter (in 100Base-FX mode)
will transmit Far-End Fault message, on the TX
pair, when the Receive path of Fiber has no
signal detected or is link down. This alerts the
Media Converter on the remote end of the link.
n The Transmit Twisted-pair will then be switched
OFF on the remote end of the link.
n The Media Converter (in 1000Base-X mode)
will restart auto-negotiation when the Receive
path of the Fiber detects no signal or is link
down.
n Auto-negotiation will carry remote fault
indications from the Transmit fiber and the local
station will restart auto-negotiation when its'
Receive path has no detected signal or is link
down.
Figure 3-6. Remote PHY Loopback
MAC/
Switch
RGMII/
SGMII
PHY
Digital
PHY
AFE
RJ-45