255-700-019
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PacketStar
™
PSAX 20 Access Concentrator User Guide
, Issue 1
Release 6.3.0
Chapter 3 System Features
PSAX 20 Software Features
Table 3-1 details the Access Concentrator system support of defined ATM
quality of service (QoS) classes.
Table 3-2 illustrates the attributes of the classes of service supported by the
Access Concentrator system software.
Table 3-1. Access Concentrator System-Supported Service Classes
ATM Service Class
Description
Constant Bit Rate (CBR)
Service that operates on a connection basis and
offers consistent delay predictability; used for
applications such as circuit emulation, voice,
and video.
Variable Bit Rate—Real
Time (VBR-RT)
Service that operates on a connection basis and
offers very low delay variance but requires
access to a variable amount of network band-
width; used for such applications as packet
video and voice.
Variable Bit Rate—Nonreal
Time (VBR-NRT)
Service that operates on both a connection and
connectionless basis and allows delay variance
between the delivery of cells; used for data
applications that have potentially bursty traffic
characteristics, including LAN interconnect,
CAD/CAM, and multimedia. This class can be
used to support SMDS (switched multimegabit
data service).
Unspecified Bit Rate (UBR) Service that operates on a connection basis and
allows for raw cell or best-effort transport by
the network. In this service, cells are trans-
ported by the network whenever bandwidth is
available and traffic is presented by the user.
Data using UBR service is more apt to be dis-
carded during peak traffic times in deference to
data using other classes of service.
Table 3-2. Class of Service Descriptions
Constant Bit
Rate (CBR)
Real Time
(VBR-RT)
Nonreal Time
(VBR-NRT)
Unspecified Bit
Rate (UBR)
QoS Class
Class 1
Class 2
Classes 3, 4
Class 5
Applications Voice and
video
Packet
video and
voice
Data
Bit Rate
Constant
Variable
Timing
Required
Source/
Destination
Required
Not required
Summary of Contents for PacketStar PSAX 20
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