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Network Working Group                                          J. PostelRequest for Comments:  795                                           ISI                                                          September 1981                            SERVICE MAPPINGS                            ----------------This memo describes the relationship between the InternetProtocol (IP) [1] Type of Service and the service parameters of specificnetworks.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 - RoutineThe individual networks listed here have very different and specificservice choices.Postel                                                          [Page 1]

                                                          September 1981RFC 795                                                 Service MappingsAUTODIN 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   errorPostel                                                          [Page 2]

                                                          September 1981RFC 795                                                 Service MappingsARPANET   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       errorPostel                                                          [Page 3]

                                                          September 1981RFC 795                                                 Service MappingsPRNET   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      yesSATNET   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]