Qos、Tos、Cos、DSCP

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1、由于最近要用到tos，ipprecedence和dscp，找了一些资料，现在明白了tos，ipprecedence和dscp这三者的关系。网上流传的版本众多，其实都是正确的，只是分别被不同的标准定义，因而让人莫名其妙。IPPrecedence和ToS都位于IP头中，共占一个字节，8bits，关于这几个字节的作用被不同的标准定义过，分别是RFC791，RFC1122，RFC1349；RFC1349废除了之前两个RFC的定义，现在大多设备都使用RFC1349中的定义，所以对于tos，有如下版本，分别说明如下

2、； 下面是RFC1349中的原话：InthepasttherehasbeensomeconfusionaboutthesizeoftheTOSfield.RFC-791defineditasathreebitfield,includingbits3-5inthefigureabove.Itincludedbit6intheMBZfield.RFC-1122addedbits6and7totheTOSfield,eliminatingtheMBZfield.This memo redefinestheTO

3、Sfieldtobethefourbitsshowninthefigureabove. 一、RFC1349中的TOS、IPprecedenceRFC1349中定义的ToS格式如下：TypeofService(TOS)XXXXXXX076543210 可表示如下：         0                1                2                3                4                5                6           

4、     7+------------+-----------+------------+------------+------------+-----------+-----------+------------+

5、     PRECEDENCE                       

6、                                                                   

7、                 

8、

9、       优先权         

10、                       

11、                          TOS                                  

12、  MBZ     

13、

14、                                                     

15、                                                                   

16、                 

17、+------------+

18、-----------+------------+------------+------------+-----------+-----------+------------+（MBZ：mustbezero） 对应的优先级如下：BitsMeaning7-5IPPrecedence:111NetworkControl110InternetworkControl101Critic/ECP100FlashOverride011Flash010Immediate001Priority000Routine41=L

19、owDelay;0=NormalDelay31=HighThroughput;0=NormalThroughput21=HighReliability;0=NormalReliability11=Minimisemonetarycost(RFC1349)0Mustbe0整理成表格为：PROPERTYCLIENTVIEWSETTINGBITMASK/BINARYVALUEPrecedenceROUTINE(DEFAULT)000 PRIORITY001 IMMEDIATE010 FLASH011 FLAS

20、HOVERRIDE100DelayNormalLow01ThroughputNormalHigh01ReliabilityNormalHigh01CostNormalLow01CongestionN/A0 二、RFC791中的TOS、IPprecedenceTheIPTypeofServiceByte:Bits0-2:Precedence.Bit3:Delay(0=NormalDelay,1=LowDelay)Bit4:Throughput