View source for RFC795



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.


















                                                       September 1981



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


























                                                       September 1981



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

























                                                       September 1981



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," [[RFC791|RFC 791]], USC/Information Sciences
     Institute, September 1981.