1 qos overview, Introduction to qos, Qos service models – H3C Technologies H3C S5120 Series Switches User Manual
Page 348: Best-effort service model, Intserv model, Qos overview
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QoS Overview
This chapter covers the following topics:
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Introduction to QoS
In data communications, Quality of Service (QoS) is the ability of a network to provide differentiated
service guarantees for diverse traffic in terms of bandwidth, delay, jitter, and drop rate.
Network resources are always scarce. The contention for resources demands that QoS prioritize
important traffic flows over trivial traffic flows. When making a QoS scheme, a network administrator
must consider the characteristics of various applications to balance the interests of diversified users
and fully utilize network resources.
The subsequent section describes some typical QoS service models and widely-used mature QoS
techniques. By appropriately using these techniques, you can improve QoS effectively.
QoS Service Models
This section covers three typical QoS service models:
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Best-Effort Service Model
Best effort is a single service model and also the simplest service model. In the best effort service model,
the network does its best to deliver packets but does not guarantee delay or reliability.
The best-effort service model is the default model in the Internet and applies to most network
applications. It uses the first in first out (FIFO) queuing mechanism.
IntServ Model
The integrated service (IntServ) model is a multiple-service model that can accommodate multiple QoS
requirements. It provides the most granularly differentiated QoS by definitely identifying and
guaranteeing QoS for each data flow.
In the IntServ model, an application must request a specific kind of service from the network before it
sends data. IntServ signals the service request with the Resource Reservation Protocol (RSVP). All
nodes that receive the request reserve resources as requested and maintain state information for the
application flow.
The IntServ model demands high storage and processing capabilities, because it requires that all nodes
along the transmission path maintain resource state information for each flow. The model is suitable for