Chapter 10 Quality of Service (QoS)
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DiffServ
QoS is used to prioritize source-to-destination traffic flows. All packets in the flow
are given the same priority. You can use CoS (class of service) to give different
priorities to different packet types.
DiffServ (Differentiated Services) is a class of service (CoS) model that marks
packets so that they receive specific per-hop treatment at DiffServ-compliant
network devices along the route based on the application types and traffic flow.
Packets are marked with DiffServ Code Points (DSCPs) indicating the level of
service desired. This allows the intermediary DiffServ-compliant network devices
to handle the packets differently depending on the code points without the need to
negotiate paths or remember state information for every flow. In addition,
applications do not have to request a particular service or give advanced notice of
where the traffic is going.
DSCP and Per-Hop Behavior
DiffServ defines a new Differentiated Services (DS) field to replace the Type of
Service (TOS) field in the IP header. The DS field contains a 2-bit unused field and
a 6-bit DSCP field which can define up to 64 service levels. The following figure
illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so
that non-DiffServ compliant, ToS-enabled network device will not conflict with the
DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior),
that each packet gets across the DiffServ network. Based on the marking rule,
different kinds of traffic can be marked for different kinds of forwarding. Resources
can then be allocated according to the DSCP values and the configured policies.
IP Precedence
Similar to IEEE 802.1p prioritization at layer-2, you can use IP precedence to
prioritize packets in a layer-3 network. IP precedence uses three bits of the eight-
bit ToS (Type of Service) field in the IP header. There are eight classes of services
(ranging from zero to seven) in IP precedence. Zero is the lowest priority level and
seven is the highest.
DSCP (6 bits)
Unused (2 bits)
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Страница 8: ...Safety Warnings VSG1435 B101 Series User s Guide 8 ...
Страница 10: ...Contents Overview VSG1435 B101 Series User s Guide 10 ...
Страница 20: ...Table of Contents VSG1435 B101 Series User s Guide 20 ...
Страница 21: ...21 PART I User s Guide ...
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Страница 42: ...Chapter 2 The Web Configurator VSG1435 B101 Series User s Guide 42 ...
Страница 71: ...71 PART II Technical Reference ...
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Страница 78: ...Chapter 5 Network Map and Status Screens VSG1435 B101 Series User s Guide 78 ...
Страница 150: ...Chapter 8 Home Networking VSG1435 B101 Series User s Guide 150 ...
Страница 154: ...Chapter 9 Static Routing VSG1435 B101 Series User s Guide 154 ...
Страница 178: ...Chapter 11 Policy Forwarding VSG1435 B101 Series User s Guide 178 ...
Страница 196: ...Chapter 12 Network Address Translation NAT VSG1435 B101 Series User s Guide 196 ...
Страница 202: ...Chapter 13 Dynamic DNS Setup VSG1435 B101 Series User s Guide 202 ...
Страница 228: ...Chapter 16 Firewall VSG1435 B101 Series User s Guide 228 ...
Страница 234: ...Chapter 18 Parental Control VSG1435 B101 Series User s Guide 234 ...
Страница 282: ...Chapter 25 Traffic Status VSG1435 B101 Series User s Guide 282 ...
Страница 286: ...Chapter 26 IGMP Status VSG1435 B101 Series User s Guide 286 ...
Страница 294: ...Chapter 28 Remote Management VSG1435 B101 Series User s Guide 294 ...
Страница 298: ...Chapter 29 Time Settings VSG1435 B101 Series User s Guide 298 ...
Страница 302: ...Chapter 30 Logs Setting VSG1435 B101 Series User s Guide 302 ...
Страница 318: ...Chapter 34 Troubleshooting VSG1435 B101 Series User s Guide 318 ...
Страница 348: ...Appendix A Setting up Your Computer s IP Address VSG1435 B101 Series User s Guide 348 ...
Страница 358: ...Appendix B IP Addresses and Subnetting VSG1435 B101 Series User s Guide 358 ...
Страница 368: ...Appendix C Pop up Windows JavaScripts and Java Permissions VSG1435 B101 Series User s Guide 368 ...
Страница 384: ...Appendix D Wireless LANs VSG1435 B101 Series User s Guide 384 ...
Страница 412: ...Index VSG1435 B101 Series User s Guide 412 ...