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ROPE Language Reference - "$ip_tos"

The $ip_tos register contains the type-of-service field from the header of the IP packet being inspected. This is a read-only integer register.

RFC_791 explains this value like this..

Type of Service:  8 bits

 The Type of Service provides an indication of the abstract
 parameters of the quality of service desired.  These parameters are
 to be used to guide the selection of the actual service parameters
 when transmitting a datagram through a particular network.  Several
 networks offer service precedence, which somehow treats high
 precedence traffic as more important than other traffic (generally
 by accepting only traffic above a certain precedence at time of high
 load).  The major choice is a three way tradeoff between low-delay,
 high-reliability, and high-throughput.

    Bits 0-2:  Precedence.
    Bit    3:  0 = Normal Delay,      1 = Low Delay.
    Bits   4:  0 = Normal Throughput, 1 = High Throughput.
    Bits   5:  0 = Normal Relibility, 1 = High Relibility.
    Bit  6-7:  Reserved for Future Use.

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

      Precedence

        111 - Network Control
        110 - Internetwork Control
        101 - CRITIC/ECP
        100 - Flash Override
        011 - Flash
        010 - Immediate
        001 - Priority
        000 - Routine

 The use of the Delay, Throughput, and Reliability indications may
 increase the cost (in some sense) of the service.  In many networks
 better performance for one of these parameters is coupled with worse
 performance on another.  Except for very unusual cases at most two
 of these three indications should be set.

 The type of service is used to specify the treatment of the datagram
 during its transmission through the internet system.  Example
 mappings of the internet type of service to the actual service
 provided on networks such as AUTODIN II, ARPANET, SATNET, and PRNET
 is given in "Service Mappings" [8].

 The Network Control precedence designation is intended to be used
 within a network only.  The actual use and control of that
 designation is up to each network. The Internetwork Control
 designation is intended for use by gateway control originators only.
 If the actual use of these precedence designations is of concern to
 a particular network, it is the responsibility of that network to
 control the access to, and use of, those precedence designations.

ROPE Language Reference - "$ip_tos"

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