FAQ/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.

Image:ipdg.gif

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.

Image:dscp.gif

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 Prec IP Prec Bin DSCP Class DSCP Bin DSCP Hex DCSP Dec TOS value (snom)
0000Best Effort0000000x000 0
1 001 CS 10010000x088 32
AF11-Low0010100x0A10 40
AF12-Medium0011000x0C12 48
AF13-High0011100x0E14 56
2 010 CS 20100000x1016 64
AF21-Low0100100x1218 72
AF22-Medium0101000x1420 80
AF23-High0101100x1622 88
3 011 CS 30110000x1824 96
AF31-Low0110100x1A26 104
AF32-Medium0111000x1C28 112
AF33-High0111100x1E30 120
4 100 CS 41000000x2032 128
AF41-Low1000100x2234 136
AF42-Medium1001000x2436 144
AF43-High1001100x2638 152
5 101 CS 51010000x2840 160
Expedited Fwdg1011100x2E46 184
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