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]