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  • What does the TOS value 160 mean

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Answer

TOS significates "Type of service" and represents the 2nd byte in the IP datagramm. TOS usually refers to "Quality of Service" in packet networks.


Traditionally, the first three IP precedence (-> RFC 791) bits were supposed to be used in TOS Application Routing (RFC 1583-> OSPF, IS-IS) but no application really supports it. The TOS field has then been redefined as the Differentiated Services Code Point (DSCP-> RFC 2474) which consists of the first 6 bits and 2 bits used for a TCP mechanism called Explicit Congestion Notification (ECN) defined in RFC 3168.


The value 160 (Binary 10100000) means IP precedence 5 (Binary 101) or DSCP Class Selector 5 (Binary 101000 = 0x28).
In order to obtain low-delay, low-jitter, low-loss service Expedited Forwarding should be used instead (= 184):

IP PrecIP Prec BinDSCP ClassDSCP BinDSCP HexDCSP DecTOS value (snom)
0000Best Effort0000000x0000
1001CS 10010000x08832
AF11-Low0010100x0A1040
AF12-Medium0011000x0C1248
AF13-High0011100x0E1456
2010CS 20100000x101664
AF21-Low0100100x121872
AF22-Medium0101000x142080
AF23-High0101100x162288
3011CS 30110000x182496
AF31-Low0110100x1A26104
AF32-Medium0111000x1C28112
AF33-High0111100x1E30120
4100CS 41000000x2032128
AF41-Low1000100x2234136
AF42-Medium1001000x2436144
AF43-High1001100x2638152
5101CS 51010000x2840160
Expedited Fwdg1011100x2E46184