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Introduction

E-NIT-CTC-20041213-0013 v0.5

2.2 Relative versus Guaranteed QoS

Types of QoS

There are two different approaches to achieve QoS:

:

Measurable connection parameters are specified for certain data or for a 
connection, for example a guaranteed amount of bandwidth or delay across the 
network. This allows for an exact specification and measurement of the Quality 
of Service of data or a connection. 
Examples of “guaranteed QoS” are Integrated Services (IntServ) and ATM QoS 
like VBR and CBR connections.

 (also referred to as differentiated QoS):

A priority indication is given as connection parameter to certain data or to a 
connection, so that this data or connection will be handled with precedence 
over data or connections with less priority. Obviously this approach guarantees 
no specified bandwidth or latency, but it is the easiest approach to achieve 
some level of QoS for high priority data. 
Examples of “relative QoS” are Differentiated Services (DiffServ, DS) and 
Ethernet VLAN user priority indication.

The guaranteed QoS approach is slightly more complicated than Relative 
QoS because the connection parameters have to be specified and may be 
verified throughout the entire network. 

In case of relative QoS, data is often specified to belong to a certain Class of 
Service (CoS) instead of QoS. Treatment and priority of data throughout the 
network is configured for each supported CoS.