Lucent Technologies P550 - Manual (Page 44)

Overview of the P220 Gigabit Switch Family
2 -8 Cajun P550/P220 Switch Operation Guide
Figure 2-4. Spanning Tree
Buffer and Queue Management
Adding gigabit speeds to existing networks means that there can be a huge disparity
between link speeds. For example, anything more than a 1% load on a gigabit link could
easily overwhelm a 10 Mb/s Ethernet link.
Without queue and buffer management, gigabit links might only move congestion in a
network, rather than relieving it. The switch employs the following buffer and queue
management techniques:
❒ Configurable active backpressure:
• Half-duplex ports use active backpressure to jam input ports when their frame
buffers are full.
• Full-duplex links use IEEE 802.3z pause control frames to pause traffic when
buffers are full.
❒ Packed frame buffers for optimal memory utilization. The memory management
allows virtually 100% utilization of buffer memory.
❒ Two Class of Service priority queues that provide flexible queue management
algorithms to meet application requirements.
Single 802.1D Spanning Tree
One Spanning Tree
Longer convergence
One path to and from root for all VLANs
Improper configuration
can shut down Trunk Links
Multi-Level Spanning Tree
Backbone terminates 802.1D STP
Smaller STP Domains
Quicker Convergence
VLAN Load Balancing
Interoperates w/ existing Bridge/Routers Multi-layer Spanning Tree