Lucent Technologies CAJUN P120, Руководство пользователя

Страница: 20 / 130

Chapter 1 Overview
6 Cajun P120 User’s Guide
Spanning Tree
The Cajun P120 implements the IEEE 802.1D Spanning Tree (SPT) algorithm in
order to allow backup paths and prevent loops throughout the Physical LAN. You
should avoid using Spanning Tree when redundant links are defined or Security is
activated.
Redundant Links
A redundant link (or resilient link) enables you to protect critical links and prevent
network downtime if that link fails. Setting up redundancy ensures that should a
main link fail, a standby duplicate link will immediately and automatically take
over the task of the failed link.
You may set a link (between two switched ports) that will only become operational
when the primary link is down. Up to four redundant link pairs can be configured
for each switch.
Avoid using redundant links when Spanning Tree or Security are enabled.
Congestion Control (Flow Control)
Congestion control is a mechanism designed to reduce the loss of frames.
In full-duplex mode the Cajun P120’s congestion control conforms to the IEEE
802.3x (both sides must conform to this Standard), using PAUSE packets to stop
and auto-restart the transmission of the source of the congestion.
In 10/100M half duplex mode, the Cajun P120 supports forward pressure and
backpressure. These mechanisms reduce the load on the switch and free its buffers
more rapidly without frame loss.
Forward pressure helps to free the switch’s transmit buffers more quickly by
limiting the maximum backoff time that a station waits before transmitting after a
collision.
Backpressure prevents frame loss by causing a carrier sense on the segment when a
frame to be received cannot be handled by Cajun P120 because its input buffer is
full.
On 1000Base Expansion Sub-module ports, Auto-negotiation controls the Flow
Control Mode (Symmetric/Disabled).
Link Aggregation
Link aggregation (or a trunk link) is used to increase bandwidth by connecting two
devices, switches or stations via multiple point-to-point links. Link aggregation also
makes the connection more resilient since traffic on a failed link is supported by the
other link(s) in the Link Aggregation Group (LAG). LAG implementation ensures
traffic load balancing between the links of the LAG and allows load sharing for
resiliency if one of the LAG links fails.