Introduction to Differentiated Services (DiffServ) and HP-UX IPQoS

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What is Quality of Service (QoS)?
Many of today’s IP networks provide what is referred to as “Best Effort Service”. Delivery of an IP
packet is accomplished without differentiating between the requirements of specific traffic flows such
as voice, video, or data. Voice and video, for example, require minimal interruptions in packet flow
to avoid jitter and delays during communication. Data, on the other hand, may only require that it
reaches its destination within a reasonable timeframe. Quality of Service (QoS) was designed to
provide a mechanism to allocate different levels of service or priority based on application needs of
the application or on organizational requirements. The type of mechanism used to provide these
levels of service can vary from one QoS implementation to another and can include dedicated
bandwidth allocation and VLAN marking.
Practical application of QoS can have a wide range of uses that can classify and condition traffic
flows based on an organization’s operational goals as well as the time-critical exchange of
information such as 9-1-1 emergency, communication between remote hospitals an ocean apart,
Homeland Security, and National Defense.
This white paper focuses on the Differentiated Services (DiffServ) model of QoS.
Differentiated Services (DiffServ)
Overview
The Differentiated Services (DiffServ or DS) model classifies and, if needed, conditions traffic streams
to conform to specified levels of service as defined by Service Level Agreements (SLAs). A DS Domain
is defined by a contiguous set of nodes provisioned with the same service policies and PHB
definitions. The classification and conditioning of packets occurs on DS boundary nodes (or interior
nodes - with limited conditioning) within the organization’s core network and other DS Domains. The
packets are marked and conditioned by the DS nodes to receive a specific level of service as they
traverse the network to their final destination.
The following sections use an example scenario to illustrate DiffServ QoS concepts, classification,
conditioning, and operation.
Example – XYZ Corporation
The XYZ Corporation has recently included Voice Over IP (VoIP) in their corporate network.
Unfortunately, the VoIP traffic also shares the wire with day-to-day traffic on a “Best Effort” network.
Within a “Best Effort” environment, all traffic is treated equally and there is no differentiation in
network service. In this environment, VoIP traffic would be sensitive to delays in packet transmission
and packet loss often found with “Best Effort” delivery, resulting in poor voice quality between source
and destination.
After careful examination of XYZ’s network traffic and hardware/software resources, a plan of action
was developed. Upgrades in hardware/software revisions as required by their manufacturers and
reconfiguration of portions of the network topology helped to improve transmission. However, XYZ’s
network traffic still relied on “Best Effort” service and their VoIP applications continued to fall victim to
network congestion during peak times.
Quality of Service (QoS) will offer the XYZ Corporation a way to provide a higher level of bandwidth
to VoIP applications and other time-sensitive communication, while still providing delivery of the