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78 System configuration software features
When autonegotiating, the switch selects the highest common operating
mode supported between the switch and its link partner.
In certain situations, it is useful to autonegotiate a specific speed and
duplex value. In these situations, the switch can allow for attachment at an
operating mode other than its highest supported value.
For example, if the switch advertises only a 100 Mbps full-duplex capability
on a specific link, the link goes active only if the neighboring device is also
capable of autonegotiating a 100 Mbps full-duplex capability. This prevents
mismatched speed and duplex modes if customers disable autonegotiation
on the neighboring device.
ATTENTION
The CANA feature is available only for built-in 10/100 Ethernet ports and combo
ports (not available for rear ports).
You can only enable CANA through the CLI. When CANA is enabled on a port,
autonegotiation status is displayed as Custom in the web-based management
interface.
High speed flow control
The high speed flow control feature lets you control traffic and avoid
congestion on the gigabit full-duplex link. If the receive port buffer becomes
full, the Ethernet Routing Switch 2500 Series issues a flow-control signal
to the device at the other end of the link to suspend transmission. When
the receive buffer is no longer full, the switch issues a signal to resume the
transmission. You can choose Symmetric or Asymmetric flow control mode.
High speed flow control cannot be configured unless you set Autonegotiation
to Disabled on the port and the speed/duplex is at 1000/full.
Two high speed flow control modes are available:
Symmetric mode
This mode lets both GBIC port and its link partner to send flow control
pause frames to each other.
When a pause frame is received (by either the GBIC port or its link partner),
the port suspends transmission of frames for a number of slot times specified
in the control frame or until a pause-release control frame is received. Both
devices on the link must support this mode when it is selected.
Nortel Ethernet Routing Switch 2500 Series
Overview — System Configuration
NN47215-500 (323162-B) 02.02 Standard
4.1 19 November 2007
Copyright © 2007, Nortel Networks
.