Manual background

Design Guide

A scenario wherein BPDUs are lost may be caused by unidirectional links, which can cause Layer 2 loops. To prevent this problem, use Loop Guard and UDLD. Loop Guard prevents a port from forwarding as a result of missed BPDUs, which might cause a Layer 2 loop that could bring down the network.

UDLD allows devices to monitor the physical configuration of fiberoptic or copper Ethernet cables and detect when a unidirectional link exists. When a unidirectional link is detected, UDLD shuts down the affected port and generates an alert. BPDU Guard prevents a port from being active in a spanning-tree topology as a result of an attack or a misconfigured device connected to the switch port. The port that sees unexpected BPDUs is automatically disabled and must then be manually enabled, giving the network administrator full control over port and switch behavior.

The Cisco Catalyst Blade Switch 3020 supports Per VLAN Spanning Tree (PVST) and a maximum of 128 spanning- tree instances. RPVST+ is a combination of Cisco PVST Plus (PVST+) and RSTP, provides the flexibility of one spanning-tree instance per VLAN and the fast convergence benefits of IEEE 802.1w. MST allows the switch to map several VLANs to one spanning-tree instance, reducing the total number of spanning-tree topologies the switch processor must manage. A maximum of 16 MST instances is supported. In addition, MST uses IEEE 802.1w for rapid convergence. MST and RPVST+ create a more predictable and resilient spanning-tree topology, while providing downward compatibility for integration with devices that use IEEE 802.1d and PVST+ protocols.

Figure 4 illustrates an example of Spanning Tree Protocol when using two switches in the crossover configuration. Each blade switch is dual homed to each aggregation switch through a 2- port Cisco EtherChannel interface. In this figure the blocked links are indicated in red. In this example, only four of the eight uplinks from each blade switch are used. The network designer can make those EtherChannel uplinks more robust (up to four 4 ports each), or use them to connect other devices such as intrusion detection systems (IDSs) or standalone servers.

Figure 4. Spanning-Tree Example with the HP c-Class Enclosure and Cisco Catalyst Blade Switch 3020s

© 2008 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.

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NAD 3020 manual Design Guide
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3020 specifications

The NAD 3020 is a classic integrated amplifier that has gained a legendary status among audiophiles since its launch in 1978. Known for its incredible sound quality and value for money, the NAD 3020 has become a reference point in the realm of affordable audio equipment.

One of the main features of the NAD 3020 is its high current design, allowing it to drive a wide range of speaker impedances. This capability ensures that the amplifier can deliver a dynamic sound, characterized by a robust bass response and clear treble. With a power output of 20 watts per channel into 8 ohms, the NAD 3020 is often underestimated due to its modest specifications. However, it can produce remarkable sound pressure levels and handle transient peaks with ease.

The amplifier utilizes a simplified circuit design, which is one of its defining characteristics. This minimalist approach reduces potential signal distortion, enabling the amplifier to maintain sonic integrity. The use of discrete components rather than integrated circuits contributes to its rich, detailed audio reproduction, making it a favorite among purists.

Another key technology featured in the NAD 3020 is its unique power supply design. NAD engineers incorporated a toroidal transformer, which is known for its compact size and low electromagnetic interference. This results in cleaner power delivery, which is essential for maintaining audio clarity and depth.

The NAD 3020 is also equipped with multiple inputs, including phono, line-level, and tape inputs, making it versatile for various audio sources. The built-in phono stage supports moving magnet cartridges, allowing vinyl enthusiasts to connect their turntables directly to the amplifier without needing a separate phono preamplifier.

In terms of build quality, the NAD 3020 features a sturdy chassis that minimizes vibrations, ensuring that audio performance remains stable. The user-friendly design includes a straightforward control layout, allowing users to adjust volume and tone settings with ease.

Throughout its decades-long legacy, the NAD 3020 has influenced countless audio products and remains a benchmark for entry-level amplification. Its combination of power, clarity, and affordability makes it a beloved choice for both new listeners and seasoned audiophiles seeking a dependable amplifier that doesn't compromise on sound quality. The NAD 3020 exemplifies how great engineering can lead to remarkable audio experiences, solidifying its place in the history of hi-fi audio.
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