Nortel Networks 2500 Series manual High speed flow control, Symmetric mode

78System 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