

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.










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