Chapter 9 Quality of Service (QoS)
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9.7 QoS Technical Reference
This section provides some technical background information about the topics covered in this
chapter.
9.7.1 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 DS (Differentiated Services) 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.
DSCP (6 bits)
Unused (2 bits)
Summary of Contents for VMG1312-T10C
Page 4: ...Contents Overview VMG1312 T10C User s Guide 4 ...
Page 12: ...Table of Contents VMG1312 T10C User s Guide 12 ...
Page 13: ...13 PART I User s Guide ...
Page 14: ...14 ...
Page 20: ...Chapter 1 Introduction VMG1312 T10C User s Guide 20 ...
Page 28: ...28 ...
Page 34: ...Chapter 4 Connection Status and System Info VMG1312 T10C User s Guide 34 ...
Page 106: ...Chapter 7 Home Networking VMG1312 T10C User s Guide 112 ...
Page 144: ...Chapter 13 Filter VMG1312 T10C User s Guide 152 ...
Page 164: ...Chapter 15 Parental Control VMG1312 T10C User s Guide 172 ...
Page 172: ...Chapter 16 Certificates VMG1312 T10C User s Guide 180 ...
Page 178: ...Chapter 17 System Monitor VMG1312 T10C User s Guide 186 ...
Page 180: ...Chapter 18 User Account VMG1312 T10C User s Guide 188 ...
Page 184: ...Chapter 20 System VMG1312 T10C User s Guide 192 ...
Page 190: ...Chapter 22 Log Setting VMG1312 T10C User s Guide 198 ...
Page 196: ...Chapter 24 Backup Restore VMG1312 T10C User s Guide 204 ...
Page 214: ...Chapter 26 Diagnostic VMG1312 T10C User s Guide 222 ...
Page 232: ...Appendix B Legal Information VMG1312 T10C User s Guide 240 ...