3Com MSR 50 Series, Руководство по настройке

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1628 C
HAPTER
84: T
RAFFIC
C
LASSIFICATION
, P
OLICING
,
AND
S
HAPING
Figure 458 DS field and ToS byte
As shown in Figure 458 , the ToS byte of IP header contains 8 bits: the first three
bits (0 to 2) indicates IP precedence, valued in the range 0 to 7; the following 4
bits (3 to 6) indicates ToS priority, valued in the range 0 to 15. In RFC2474, the ToS
field of IP packet header is redefined as DS field, where the DiffServ code point
(DSCP) priority is indicated by the first 6 bits (0 to 5), valued in the range 0 to 63.
The remaining 2 bits (6 and 7) are reserved.
Traffic Policing and
Traffic Shaping
If no restrictions are imposed on the traffics from the users, bursting data sent by
mass users continuously will make the network become more congested. Thus for
more efficient network function and better network service for more users, the
traffics from the users must be restricted, for example, to restrict a traffic can only
acquire the specific assigned resources in certain time interval so as to prevent the
network congestion caused by excess burst.
Traffic policing and traffic shaping is a traffic monitoring policy to restrict the traffic
and resources through comparing with the traffic specification. To know whether
the traffic exceeds the specification or not is a prerequisite for traffic policing or
shaping. Then based upon the evaluation result you can implement a regulation
policy. Usually, Token Bucket is used to value the traffic specification.
Traffic Evaluation and
Token Bucket
Token bucket features
Token bucket can be regarded as a container capable of holding a certain number
of tokens. The system will put Tokens into the Bucket at a defined rate. In case the
Bucket is full, the extra Tokens will overflow and no more Tokens will be added.
0 7 6
DSCP
M
B
Z
Class Selector
codepoints
Differentiated Services
Codepoint ( DSCP)
RFC 2474
Currently
Unused
RFC 1122
IP Type of Service (ToS)
RFC 791
Must
Be
Zero
RFC 1349
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
IPv4 ToS
byte
1 5 4 3 2 Bits: 0 7 6 1 5 4 3 2 Bits:
Preced
ence
Type of
Service
CU