    Network Working Group                                          J. Postel
    Request for Comments:  795                                           ISI
                                                              September 1981
                                SERVICE MAPPINGS
                                ----------------

    This memo describes the relationship between the Internet
    Protocol (IP) [1] Type of Service and the service parameters of specific
    networks.

    The IP Type of Service has the following fields:

       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  |
       |                 |     |     |     |     |     |
       +-----+-----+-----+-----+-----+-----+-----+-----+

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

    The individual networks listed here have very different and specific
    service choices.

    Postel                                                          [Page 1]

                                                              September 1981
    RFC 795                                                 Service Mappings

    AUTODIN II

       The service choices are in two parts: Traffic Acceptance Catagories,
       and Application Type.  The Traffic Acceptance Catagories can be
       mapped into and out of the IP TOS precedence reasonably directly.
       The  Application types can be mapped into the remaining IP TOS fields
       as follows.

          TA    DELAY    THROUGHPUT    RELIABILITY
          ---   -----    ----------    -----------
          I/A     1           0             0
          Q/R     0           0             0
          B1      0           1             0
          B2      0           1             1

          DTR    TA
          ---   ---
          000   Q/R
          001   Q/R
          010    B1
          011    B2
          100   I/A
          101   I/A
          110   I/A
          111   error

    Postel                                                          [Page 2]

                                                              September 1981
    RFC 795                                                 Service Mappings

    ARPANET

       The service choices are in quite limited.  There is one priority bit
       that can be mapped to the high order bit of the IP TOS precedence.
       The other choices are to use the regular ("Type 0") messages vs. the
       uncontrolled ("Type 3") messages, or to use single packet vs.
       multipacket messages.  The mapping of ARPANET parameters into IP TOS
       parameters can be as follows.

          Type   Size   DELAY    THROUGHPUT    RELIABILITY
          ----   ----   -----    ----------    -----------
            0      S      1           0             0
            0      M      0           0             0
            3      S      1           0             0
            3      M      not allowed

          DTR   Type   Size
          ---   ----   ----
          000     0      M
          001     0      M
          010     0      M
          011     0      M
          100     3      S
          101     0      S
          110     3      S
          111       error

    Postel                                                          [Page 3]

                                                              September 1981
    RFC 795                                                 Service Mappings

    PRNET

       There is no priority indication.  The two choices are to use the
       station routing vs. point-to-point routing, or to require
       acknowledgments vs. having no acknowledgments.  The mapping of PRNET
       parameters into IP TOS parameters can be as follows.

          Routing   Acks    DELAY    THROUGHPUT    RELIABILITY
          -------   ----    -----    ----------    -----------
            ptp      no       1           0             0
            ptp      yes      1           0             1
          station    no       0           0             0
          station    yes      0           0             1

          DTR   Routing   Acks
          ---   -------   ----
          000   station    no
          001   station    yes
          010   station    no
          011   station    yes
          100     ptp      no
          101     ptp      yes
          110     ptp      no
          111     ptp      yes

    SATNET

       There is no priority indication.  The four choices are to use the
       block vs. stream type, to select one of four delay catagories, to
       select one of two holding time strategies, or to request one of three
       reliability levels.  The mapping of SATNET parameters into IP TOS
       parameters can thus quite complex there being 2*4*2*3=48 distinct
       possibilities.

    References
    ----------

       [1]  Postel, J. (ed.), "Internet Protocol - DARPA Internet Program
            Protocol Specification," RFC 791, USC/Information Sciences
            Institute, September 1981.

    Postel                                                          [Page 4]