Features of the Nortel Ethernet Routing Switch 4500 Series
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corrects the polarity of the received data, if the port detects that the polarity
of the data is reversed due to a wiring error. If autonegotiation is disabled,
auto-polarity is not active.
Autosensing and autonegotiation
The Nortel Ethernet Routing Switch 4500 Series are autosensing and
autonegotiating devices:
•
The term autosense refers to the ability of a port to sense the speed of
an attached device.
•
The term autonegotiation refers to a standard protocol (IEEE 802.3u
or 802.3z or 802.3ab) that exists between two IEEE-capable devices.
Autonegotiation enables the switch to select the best speed and duplex
modes.
Autosensing occurs when the attached device cannot autonegotiate or
uses a form of autonegotiation that is not compatible with the IEEE 802.3z
autonegotiation standard. If it is not possible to sense the duplex mode of
the attached device, the Nortel Ethernet Routing Switch 4500 Series reverts
to half-duplex mode.
When autonegotiation-capable devices are attached to the Nortel Ethernet
Routing Switch 4500 Series, the ports negotiate down from 1000 Mb/s
and full-duplex mode until the attached device acknowledges a supported
speed and duplex mode.
Custom Autonegotiation Advertisements
In the Nortel Ethernet Routing Switch 4500 Series, you can use the Custom
Autonegotiation Advertisements (CANA) feature to control the speed and
duplex settings that each Ethernet port of the device advertises as part of
the autonegotiation process.
Without CANA, a port with autonegotiation enabled advertises all speed
and duplex modes supported by the switch and attempts to establish a link
at the highest common speed and duplex setting. By using CANA, you
can configure the port to advertise only certain speed and duplex settings,
thereby establishing links only at these settings, regardless of the highest
commonly supported operating mode.
CANA provides control over the IEEE802.3x flow control settings advertised
by the port, as part of the autonegotiation process. You can set flow control
advertisements to Symmetric, Asymmetric, or Disabled.
You may not want a port to advertise all supported speed and duplex modes
in the following situations:
•
If a network can support only a 10 Mb/s connection, you can configure
a port to advertise only 10 Mb/s capabilities. Devices that uses
Nortel Ethernet Routing Switch 4500 Series
Overview — System Configuration
NN47205-500
02.01
Standard
5.0
23 February 2007
Copyright © 2007, Nortel Networks
Nortel Networks Confidential
.