Intel 480T, Руководство пользователя

Страница: 143 / 367

C H A P T E R 8 Quality of Service (QoS)
141
Configuring DiffServ
Contained in the header of every IP packet is a field for IP Type of
Service (TOS). The TOS field is used by the switch to determine the
type of service provided to the packet. Figure 15 shows the
encapsulation of an IP packet header.
Figure 15: IP packet header encapsulation
Observing DiffServ Information
When a packet arrives at the switch on an ingress port, the first 6 of
8 TOS bits are examined. These bits are called the
code point . The
switch can assign the QoS profile used to subsequently transmit the
packet based on the code point. The QoS profile controls a hardware
queue used when transmitting the packet out of the switch, and
determines the forwarding characteristics of a particular code point.
The observance of DiffServ information can be enabled or disabled.
By default it is disabled. To enable observance of DiffServ
information use the command:
enable diffserv examination ports [<portlist> |
all]
Because the code point uses 6 bits, it has 64 possible values. By
default, the values are grouped and assigned to the default QoS
profiles listed in Table 36.
480t_021
Type-of-service IHL
Data (variable)
0 bits 31
Options (+ padding)
Destination address
Source address
Total length Version
Protocol Time-to-live Header checksum
Flags Identification Fragment offset