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.
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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
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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
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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]
