Chapter 4 Broadband
46
eircom D1000 modem U
ser’s Guide
Constant Bit Rate (CBR)
Constant Bit Rate (CBR) provides fixed bandwidth that is always available even if no data is being
sent. CBR traffic is generally time-sensitive (doesn't tolerate delay). CBR is used for connections
that continuously require a specific amount of bandwidth. A PCR is specified and if traffic exceeds
this rate, cells may be dropped. Examples of connections that need CBR would be high-resolution
video and voice.
Variable Bit Rate (VBR)
The Variable Bit Rate (VBR) ATM traffic class is used with bursty connections. Connections that use
the Variable Bit Rate (VBR) traffic class can be grouped into real time (VBR-RT) or non-real time
(VBR-nRT) connections.
The VBR-RT (real-time Variable Bit Rate) type is used with bursty connections that require closely
controlled delay and delay variation. It also provides a fixed amount of bandwidth (a PCR is
specified) but is only available when data is being sent. An example of an VBR-RT connection would
be video conferencing. Video conferencing requires real-time data transfers and the bandwidth
requirement varies in proportion to the video image's changing dynamics.
The VBR-nRT (non real-time Variable Bit Rate) type is used with bursty connections that do not
require closely controlled delay and delay variation. It is commonly used for "bursty" traffic typical
on LANs. PCR and MBS define the burst levels, SCR defines the minimum level. An example of an
VBR-nRT connection would be non-time sensitive data file transfers.
Unspecified Bit Rate (UBR)
The Unspecified Bit Rate (UBR) ATM traffic class is for bursty data transfers. However, UBR doesn't
guarantee any bandwidth and only delivers traffic when the network has spare bandwidth. An
example application is background file transfer.
Summary of Contents for eircom D1000
Page 2: ...Copyright 2013 ZyXEL Communications Corporation...
Page 3: ......
Page 12: ...10 eircom D1000 modem User s Guide...
Page 13: ...PART I User s Guide 11...
Page 14: ...12...
Page 18: ...16 eircom D1000 modem User s Guide...
Page 26: ...Chapter 2 Introducing the Web Configurator 24 eircom D1000 modem User s Guide...
Page 27: ...PART II Technical Reference 25...
Page 28: ...26...
Page 78: ...76 eircom D1000 modem User s Guide Chapter 5 Wireless LAN...
Page 110: ...10 8 eircom D1000 modem User s Guide Chapter 6 Home Networking...
Page 126: ...Chapter 8 Quality of Service QoS 124 eircom D1000 modem User s Guide...
Page 136: ...134 eircom D1000 modem User s Guide Chapter 9 Network Address Translation NAT...
Page 148: ...146 eircom D1000 modem User s Guide Chapter 12 Filter...
Page 168: ...Chapter 14 Parental Control 166 eircom D1000 modem User s Guide...
Page 174: ...Chapter 15 Certificates 172 eircom D1000 modem User s Guide...
Page 180: ...178 eircom D1000 modem User s Guide Chapter 17 Traffic Status...
Page 182: ...180 eircom D1000 modem User s Guide Chapter 18 User Account...
Page 184: ...182 eircom D1000 modem User s Guide Chapter 19 System Setting...
Page 187: ...185 eircom D1000 modem User s Guide Chapter 20 Time Setting...
Page 188: ...Chapter 20 Time Setting 186 eircom D1000 modem User s Guide...
Page 196: ...Chapter 23 Backup Restore 194 eircom D1000 modem User s Guide...
Page 210: ...Chapter 25 Diagnostic 208 eircom D1000 modem User s Guide...
Page 216: ...214 eircom D1000 modem User s Guide Chapter 27 LED Descriptions...