ZL50404GDC ZARLINK [Zarlink Semiconductor Inc], ZL50404GDC Datasheet - Page 31

• Manufacturer Part Number: ZL50404GDC
• Description: Lightly Managed/Unmanaged 5-Port 10/100M Ethernet Switch
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

5.7
Quality of Service (QoS) refers to the ability of a network to provide better service to selected network traffic over
various technologies. Primary goals of QoS include dedicated bandwidth, controlled jitter and latency (required by
some real-time and interactive traffic), and improved loss characteristics.
Traditional Ethernet networks have had no prioritization of traffic. Without a protocol to prioritize or differentiate
traffic, a service level known as “best effort” attempts to get all the packets to their intended destinations with
minimum delay; however, there are no guarantees. In a congested network or when a low-performance
switch/router is overloaded, “best effort” becomes unsuitable for delay-sensitive traffic and mission-critical data
transmission.
The advent of QoS for packet-based systems accommodates the integration of delay-sensitive video and
multimedia traffic onto any existing Ethernet network. It also alleviates the congestion issues that have previously
plagued such “best effort” networking systems. QoS provides Ethernet networks with the breakthrough technology
to prioritize traffic and ensure that a certain transmission will have a guaranteed minimum amount of bandwidth.
Extensive core QoS mechanisms are built into the ZL50404 architecture to ensure policy enforcement and
buffering of the ingress port, as well as weighted fair-queue (WFQ) scheduling at the egress port.
In the ZL50404, QoS-based policies sort traffic into a small number of classes and mark the packets accordingly.
The QoS identifier provides specific treatment to traffic in different classes, so that different quality of service is
provided to each class. Frame and packet scheduling and discarding policies are determined by the class to which
the frames and packets belong. For example, the overall service given to frames and packets in the premium class
will be better than that given to the standard class; the premium class is expected to experience lower loss rate or
delay.
The ZL50404 supports the following QoS techniques:
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In a port-based setup, any station connected to the same physical port of the switch will have the same
transmit priority.
In a tag-based setup, a 3-bit field in the VLAN tag provides the priority of the packet. This priority can be
mapped to different queues in the switch to provide QoS.
In a TOS/DS-based set up, TOS stands for “Type of Service” that may include “minimize delay,” “maximize
throughput,” or “maximize reliability.” Network nodes may select routing paths or forwarding behaviours that
are suitably engineered to satisfy the service request.
In a logical port-based set up, a logical port provides the application information of the packet. Certain
applications are more sensitive to delays than others; using logical ports to classify packets can help speed
up delay sensitive applications, such as VoIP.
Quality of Service
Zarlink Semiconductor Inc.
ZL50404
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Data Sheet