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A detailed analysis of flow classification for IP QoS
[Url]www.net130.com[/url] Date: 2007-11-18 views: 3337
Source: Blog.sina.com.cn/stimwoo Last and colleagues discussed the priority of QoS traffic and protocol traffic. Later found this article. Special forwarding.
In RFC 791, the IP precedence of the TOS bit is divided into 8 priorities, which can be applied to the flow classification, and the higher the number indicates the greater the priority.

0 1 2 3  4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| Precedence | D | T | R | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+

111-network Control
110-internetwork Control
101-critic/ecp
100-flash Override
011-flash
010-immediate
001-priority
000–routine

However, these 8 priorities are far from sufficient in actual deployment on the network, and the TOS is redefined in RFC 2474. The first six digits are defined as DSCP, and the last two bits are retained.

0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| DSCP | CU |
+---+---+---+---+---+---+---+---+

dscp:differentiated Services Codepoin

cu:currently Unused

However, since DSCP and IP precedence coexist, there are some compatibility issues, the DSCP is less readable, such as DSCP 43 We do not know what value corresponds to the IP precedence, and the DSCP is further categorized. The DSCP is divided into 4 categories altogether.

Class Selector (CS) AAA 000
Expedited Forwarding (EF) 101 110
Assured Forwarding (AF) AAA bb0
Default (BE) 000 000

1, the default DSCP is 000 000
2,cs the DSCP after three digits of 0, that is to say CS still used the IP precedence only CS defined Dscp=ip precedence*8, such as cs6=6*8=48,cs7=7*8=56
3,ef meaning is expedited forwarding, can also be considered as IP precedence 5, is a relatively high priority, with a value of 101110 (46), but the RFC is not defined as what the EF value is 46.
4,AF is divided into two parts, A and B, a part of the 3 bit can still correspond to the IP precedence, b part of the 2 bit for the discard, can represent 3 drop priority, can be applied to red or wred. Currently, part A has three bit maximum values of 8, but only 1~4 is used. In order to quickly and 10 conversion, you can use the following methods, the first 10 in addition to 8 of the integer is the AF value, the remainder converted into binary to see the first two are discarded priority, such as the 34/8=4 remainder of 2, 2 converted into binary to 010, Then the conversion can be known 34 represents AF4 discard priority middle datagram.

If you make an arrangement of CS EF AF and be, you can find an interesting phenomenon, such as the following table. This table is the queue that we use most in reality. Depending on the priority of the IP precedence, the CS7 highest order is the lowest. In general, the purpose of these queues is to look at the usage field of this table


Corresponding service IPV4 priority/exp/802.1p DSCP (binary) DSCP (decimal) TOS (hexadecimal) application
Be 0 0 0 0 Internet
AF1 Green 1 1010 Leased Line
AF2 Green 2 10010 IPTV VOD
AF3 Green 3 11010 IPTV Broadcast
AF4 Green 4 100010 ngn/3g singaling
EF 5 101110 B8 ngn/3g Voice
CS6 6 110000 C0 Protocol
CS7 7 111000 E0 Protocol




1,CS6 and CS7 are used by default for protocol messages, such as OSPF messages, BGP messages, and so on, because if these messages cannot be received, the Protocol will be interrupted. It is also the highest priority message in most vendors ' hardware queues.
2,ef is used for carrying voice traffic, because voice requires low latency, low jitter, and low packet loss rate, which is the most important message after protocol message.
3,AF4 is used to host voice signaling traffic, and here you may have questions about why voice here takes precedence over signaling. In fact, the signaling here is the call control of the telephone, you can endure to wait for a few seconds while connecting, but absolutely cannot allow the interruption during the call. So speech takes precedence over signaling.
4,AF3 can be used to carry the live broadcast of IPTV traffic, the real-time live is very strong need for continuity and large throughput guarantee.
5,AF4 can be used to carry the flow of VOD, relative to the live VOD request time is not very strong, allow delay or buffering.
6,af5 can carry not very important line business, because the Green Line business relative to IPTV and voice, IPTV and voice is the operator's most critical business, need the highest priority to ensure. Of course, for the bank and the like business needs diamond level assurance, can be arranged for AF4 even EF.
7, the least important business is the Internet business, which can be placed in the be model for transmission.

And in the hardware queue is how to ensure that the protocol message (CS6 and CS7 data) priority transmission. In the production of routers are generally the data in CS6 and CS7 to do PQ is absolute priority, regardless of whether there is data below is to give priority to pass the data in these two queues. Other EF to AF1 queues are made with WFQ to ensure that all queues can receive bandwidth to transmit