Advantages Of Qos; Understanding Qos - D-Link DAS-3626 User Manual

Advantages of QoS

QoS is an implementation of the IEEE 802.1p standard that allows network administrators a method of reserving
bandwidth for important functions that require a large bandwidth or have a high priority, such as VoIP (voice-over
Internet Protocol), web browsing applications, file server applications or video conferencing. Not only can a larger
bandwidth be created, but other less critical traffic can be limited, so excessive bandwidth can be saved. The Switch
has separate hardware queues on every physical port to which packets from various applications can be mapped to,
and, in turn prioritized.

Understanding QoS

The Switch has eight priority queues. These priority queues are labeled from 0-7, with 7 being the highest priority and
0 the lowest priority queue. The eight priority tags, specified in IEEE 802.1p are mapped to the Switch's priority tags
as follows:
Priority 0 is assigned to the Switch's Q2 queue.
Priority 1 is assigned to the Switch's Q0 queue.
Priority 2 is assigned to the Switch's Q1 queue.
Priority 3 is assigned to the Switch's Q3 queue.
Priority 4 is assigned to the Switch's Q4 queue.
Priority 5 is assigned to the Switch's Q5 queue.
Priority 6 is assigned to the Switch's Q6 queue.
Priority 7 is assigned to the Switch's Q7 queue.
For strict priority-based scheduling, any packets residing in the higher priority queues are transmitted first. Multiple
strict priority queues empty based on their priority tags. Only when these queues are empty, are packets of lower
priority transmitted.
For weighted round-robin queuing, the number of packets sent from each priority queue depends upon the assigned
weight. For a configuration of 8 CoS queues, A~H, with their respective weight value: 8~1. When each queue has 10
outbound packets, they are sent in the following sequence:
A1, B1, C1, D1, E1, F1, G1, H1,
A2, B2, C2, D2, E2, F2, G2,
A3, B3, C3, D3, E3, F3,
A4, B4, C4, D4, E4,
A5, B5, C5, D5,
A6, B6, C6,
A7, B7,
A8,
A9, B8, C7, D6, E5, F4, G3, H2,
A10, B9, C8, D7, E6, F5, G4
B10, C9, D8, E7, F6,
C10, D9, E8,
D10,
E9, F7, G5, H3,
E10, F8, G6,
F9,
F10, G7, H4,
G8,
G9, H5,
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