D-Link DSA-3200 Technical Information download pdf (Page 64)

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DGS-3200 Series Layer 2 Managed Gigabit Ethernet Switch Web UI Reference Guide

Section 3

L2 Features

VLAN

Layer 2 Protocol Tunneling Settings

Egress Filter Settings

L2 Multicast Control

Multicast Filtering

Port Mirroring

Spanning Tree

Link Aggregation

Forwarding & Filtering

LLDP

NLB FDB Settings

VLAN

802.1Q VLAN

Understanding IEEE 802.1p Priority

Priority tagging is a function defined by the IEEE 802.1p standard designed to provide a means of managing traffic on a network

where many different types of data may be transmitted simultaneously. It is intended to alleviate problems associated with the

delivery of time critical data over congested networks. The quality of applications that are dependent on such time critical data,

such as video conferencing, can be severely and adversely affected by even very small delays in transmission.

Network devices that are in compliance with the IEEE 802.1p standard have the ability to recognize the priority level of data

packets. These devices can also assign a priority label or tag to packets. Compliant devices can also strip priority tags from

packets. This priority tag determines the packet’s degree of expeditiousness and determines the queue to which it will be assigned.

Priority tags are given values from 0 to 7 with 0 being assigned to the lowest priority data and 7 assigned to the highest. The

highest priority tag 7 is generally only used for data associated with video or audio applications, which are sensitive to even slight

delays, or for data from specified end users whose data transmissions warrant special consideration.

The Switch allows you to further tailor how priority tagged data packets are handled on your network. Using queues to manage

priority tagged data allows you to specify its relative priority to suit the needs of your network. There may be circumstances where

it would be advantageous to group two or more differently tagged packets into the same queue. Generally, however, it is rec-

ommended that the highest priority queue, Queue 7, be reserved for data packets with a priority value of 7. Packets that have not

been given any priority value are placed in Queue 0 and thus given the lowest priority for delivery.

Strict mode and weighted round robin system are employed on the Switch to determine the rate at which the queues are emptied of

packets. The ratio used for clearing the queues is 4:1. This means that the highest priority queue, Queue 7, will clear 4 packets for

every 1 packet cleared from Queue 0.

Remember, the priority queue settings on the Switch are for all ports, and all devices connected to the Switch will be affected.

This priority queuing system will be especially beneficial if your network employs switches with the capability of assigning

priority tags.

VLAN Description

A Virtual Local Area Network (VLAN) is a network topology configured according to a logical scheme rather than the physical

layout. VLANs can be used to combine any collection of LAN segments into an autonomous user group that appears as a single

LAN. VLANs also logically segment the network into different broadcast domains so that packets are forwarded only between

ports within the VLAN. Typically, a VLAN corresponds to a particular subnet, although not necessarily.

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D-Link DSA-3200 Technical Information Page 64

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