ISO/IEC TR 9577:1999

Information technology — Protocol identification in the network layer

This Recommendation | Technical Report provides: a) the description of a means to permit a protocol to be identified; b) a record of the structure and allowable ranges of protocol identifier(s) which can be assigned by ITU-T, ISO/IEC and other authorities; c) a record of the values of protocol identifiers used by OSI Network layer protocols and non-OSI protocols occupying a similar position: in particular, protocols with protocol control information commencing in octet 1 of the protocol data unit (header-oriented protocols), and protocols with protocol control information commencing in the final octet of the protocol data unit (trailer-oriented protocols), are covered; and d) a record of the values that are in use as protocol control information in non-Network layer protocols where they impact on Network layer protocol identification. The application of this Recommendation | Technical Report is: a) in the identification of internationally standardized Network layer protocols operating directly above the Data Link service; b) in the identification of protocols used in conjunction with internationally standardized Network layer protocols that operate directly above the Data Link service; and c) to distinguish between Internationally standardized Network layer protocols, and other internationally standardized protocols used in conjunction with internationally standardized Network layer protocols. This Recommendation | Technical Report is for use by ITU-T Study Groups, ISO/IEC Technical Committees and other authorities in applying the principles contained in clause 4, and in selecting an unused value or values from the range of values permitted in clauses 5 or 6, as appropriate. When a new value is selected, that value and its usage should be brought to the attention of ITU-T Study Group 7 or ISO/IEC JTC 1 SC6 so that this Recommendation | Technical Report can be amended.

Technologies de l'information — Identification des protocoles dans la couche réseau

General Information

• Status: Published
• Publication Date: 15-Dec-1999
• ICS: 35.100.30 - Network layer
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6/WG 7 - Network, transport and future network
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 26-May-2015

Relations

• Revises: ISO/IEC TR 9577:1996 - Information technology — Protocol identification in the network layer
• Effective Date: 15-Apr-2008

Standards Content (Sample)

TECHNICAL ISO/IEC
REPORT TR
9577
Fourth edition
1999-12-15
Information technology — Protocol
identification in the network layer
Technologies de l'information — Identification des protocoles dans la
couche réseau
Reference number
ISO/IEC TR 9577:1999(E)
©
ISO/IEC 1999

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ISO/IEC TR 9577:1999(E)
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ii © ISO/IEC 1999 – All rights reserved

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ISO/IEC TR 9577 : 1999 (E)
CONTENTS
Page
1 Scope . 1
2 References . 1
2.1 Identical Recommendations | International Standards. 2
2.2 Paired Recommendations | International Standards equivalent in technical content. 2
2.3 Additional references . 2
3 Abbreviations . 4
4 Protocol identifiers . 4
5 Initial protocol identifier. 5
5.1 General . 5
5.2 Assignment structure for header-oriented protocols .6
5.3 Values assigned to the IPI for header-oriented protocols. 6
5.4 Assignment structure for trailer-oriented protocols. 8
5.5 Values assigned to the IPI for trailer-oriented protocols. 8
6 Subsequent protocol identifier. 9
6.1 General . 9
6.2 Assignment structure for header-oriented protocols .10
6.3 Values assigned to the SPI for header-oriented protocols. 10
6.4 Assignment structure for trailer-oriented protocols. 12
6.5 Values assigned to the SPI for trailer-oriented protocols .12
Annex A The location and use of protocol identifiers in X.25 Packet Layer Protocol . 13
Annex B Guidelines on the processing of protocol identifiers . 15
B.1 Originating systems. 15
B.2 Destination systems. 15
Annex C – Identification of Internet protocols . 17
Annex D – Identification of protocols that are discriminated according to the IEEE-defined SNAP convention. 18
Annex E – Identification of protocols specified by the Frame Relay Forum. 19
© ISO/IEC 1999 – All rights reserved
iii

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ISO/IEC TR 9577:1999(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission)
form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC
participate in the development of International Standards through technical committees established by the
respective organization to deal with particular fields of technical activity. ISO and IEC technical committees
collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in
liaison with ISO and IEC, also take part in the work.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that which is
normally published as an International Standard ("state of the art", for example), it may decide by a simple majority
vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature
and does not have to be reviewed until the data it provides are considered to be no longer valid or useful.
Attention is drawn to the possibility that some of the elements of this Technical Report may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC TR 9577 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 6, Telecommunications and information exchange between systems, in collaboration with ITU-T.
The identical text is published as ITU-T Rec. X.263.
This fourth edition cancels and replaces the third edition (ISO/IEC TR 9577:1996), which has been technically
revised.
iv © ISO/IEC 1999 – All rights reserved

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ISO/IEC TR 9577 : 1999 (E)
Introduction
Identifying protocols by information in a uniform part of the protocol control information fulfils two requirements:
a) It enables an entity to verify that the protocol received is of the type and kind expected; and
b) It permits an entity to discriminate among a number of different protocols (both OSI and non-OSI) that
might co-exist in a common environment.
This Recommendation | Technical Report contains a description of the means used to identify protocols and where that
information is located in a protocol, together with a record of those values of protocol identifiers which have been used
by ITU-T and ISO/IEC, and by other authorities. This Recommendation | Technical Report does not attempt to provide
any general architectural principles for the functions of protocol identification, nor does it attempt to provide judgements
as to whether a protocol might have more than one value of protocol identifier.
By reference to this Recommendation | Technical Report, future protocols can be developed to include a protocol
identifier and the values of such protocol identifiers can be chosen on a knowledgeable basis.
© ISO/IEC 1999 – All rights reserved
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ISO/IEC TR 9577 : 1999 (E)
TECHNICAL REPORT
ISO/IEC TR 9577 : 1999 (E)
ITU-T Rec. X.263 (1998 E)
ITU-T RECOMMENDATION
INFORMATION TECHNOLOGY – PROTOCOL IDENTIFICATION
IN THE NETWORK LAYER
1 Scope
This Recommendation | Technical Report provides:
a) the description of a means to permit a protocol to be identified;
b) a record of the structure and allowable ranges of protocol identifier(s) which can be assigned by ITU-T,
ISO/IEC and other authorities;
c) a record of the values of protocol identifiers used by OSI Network layer protocols and non-OSI protocols
occupying a similar position: in particular, protocols with protocol control information commencing in
octet 1 of the protocol data unit (header-oriented protocols), and protocols with protocol control
information commencing in the final octet of the protocol data unit (trailer-oriented protocols), are
covered; and
d) a record of the values that are in use as protocol control information in non-Network layer protocols
where they impact on Network layer protocol identification.
The application of this Recommendation | Technical Report is:
a) in the identification of internationally standardized Network layer protocols operating directly above the
Data Link service;
b) in the identification of protocols used in conjunction with internationally standardized Network layer
protocols that operate directly above the Data Link service; and
c) to distinguish between Internationally standardized Network layer protocols, and other internationally
standardized protocols used in conjunction with internationally standardized Network layer protocols.
This Recommendation | Technical Report is for use by ITU-T Study Groups, ISO/IEC Technical Committees and other
authorities in applying the principles contained in clause 4, and in selecting an unused value or values from the range of
values permitted in clauses 5 or 6, as appropriate. When a new value is selected, that value and its usage should be
brought to the attention of ITU-T Study Group 7 or ISO/IEC JTC 1 SC6 so that this Recommendation | Technical Report
can be amended.
2 References
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | Technical Report. At the time of publication, the editions indicated were
valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | Technical Report are encouraged to investigate the possibility of applying the most recent edition of
the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
ITU-T Rec. X.263 (1998 E) 1

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ISO/IEC TR 9577 : 1999 (E)
2.1 Identical Recommendations | International Standards
– ITU-T Recommendation X.200 (1994) | ISO/IEC 7498-1:1994, Information technology – Open Systems
Interconnection – Basic Reference Model: The Basic Model.
– ITU-T Recommendation X.224 (1995) | ISO/IEC 8073:1997, Information technology – Open Systems
Interconnection – Protocol for providing the connection-mode transport service.
– ITU-T Recommendation X.233 (1993) | ISO/IEC 8473-1:1994, Information technology – Protocol for
providing the connectionless-mode network service: Protocol specification.
– ITU-T Recommendation X.260 (1996) | ISO/IEC 14765:1997, Information technology – Framework for
protocol identification and encapsulation.
– ITU-T Recommendation X.273 (1994) | ISO/IEC 11577:1995, Information technology – Open Systems
Interconnection – Network layer security protocol.
– ITU-T Recommendation X.633 (1996) | ISO/IEC 14700:1997, Information technology – Open Systems
Interconnection – Network Fast Byte Protocol.
– ITU-T Recommendation X.634 (1996) | ISO/IEC 14699:1997, Information technology – Open Systems
Interconnection – Transport Fast Byte Protocol.
2.2 Paired Recommendations | International Standards equivalent in technical content
– ITU-T Recommendation X.223 (1993), Use of X.25 to provide the OSI connection-mode network service
for ITU-T applications.
ISO/IEC 8878:1992, Information technology – Telecommunications and information exchange between
systems – Use of X.25 to provide the OSI Connection-mode Network Service.
– ITU-T Recommendation X.264 (1993), Transport protocol identification mechanism.
ISO/IEC 11570:1992, Information technology – Telecommunications and information exchange between
systems – Open Systems Interconnection – Transport protocol identification mechanism.
2.3 Additional references
– CCITT Recommendation G.764 (1990), Voice packetization – Packetized voice protocols.
– ITU-T Recommendation I.365.2 (1995), B-ISDN ATM adaptation layer sublayers: Service specific
coordination function to provide the connection-oriented network service.
– ITU-T Recommendation I.365.3 (1995), B-ISDN ATM adaptation layer sublayers: Service specific
coordination function to provide the connection-oriented transport service.
– ITU-T Recommendation Q.931 (1993), ISDN user-network interface layer 3 specification for basic call
control.
– ITU-T Recommendation Q.932 (1993), Generic procedures for the control of ISDN supplementary
services.
– ITU-T Recommendation Q.933 (1995), Signalling specifications for frame mode switched and permanent
virtual connection control and status monotoring.
– ITU-T Recommendation Q.2119 (1996), B-ISDN ATM adaptation layer – Convergence function for
SSCOP above the frame relay core service.
2 ITU-T Rec. X.263 (1998 E)

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ISO/IEC TR 9577 : 1999 (E)
– ITU-T Recommendation Q.2931 (1995), Digital Subscriber Signalling System No. 2 – User-Network
Interface (UNI) layer 3 specification for basic call/connection control.
– ITU-T Recommendation T.70 (1993), Network-independent basic transport service for the telematic
services.
– ITU-T Recommendation X.25 (1996), Interface between Data Terminal Equipment (DTE) and Data
Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public
data networks by dedicated circuit.
– ITU-T Recommendation X.29 (1993), Procedures for the exchange of control information and user data
between a Packet Assembly/Disassembly (PAD) facility and a packet mode DTE or another PAD.
– ITU-T Recommendation X.36 (1995), Interface between Data Terminal Equipment (DTE) and Data
Circuit-terminating Equipment (DCE) for public data networks providing frame relay data transmission
service by dedicated circuit.
– ITU-T Recommendation X.37 (1995), Encapsulation in X.25 packets of various protocols including
frame relay.
– ITU-T Recommendation X.39 (1996), Procedures for the exchange of control information and user data
between a Facsimile Packet Assembly/Disassembly (FPAD) facility and a packet mode Data Terminal
Equipment (DTE) or another FPAD.
– ITU-T Recommendation X.45 (1996), Interface between Data Terminal Equipment (DTE) and Data
Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public
data networks, designed for efficiency at higher speeds.
– ITU-T Recommendation X.48 (1996), Procedures for the provision of a basic multicast service for Data
Terminal Equipments (DTEs) using Recommendation X.25.
– ITU-T Recommendation X.49 (1996), Procedures for the provision of an extended multicast service for
Data Terminal Equipments (DTEs) using Recommendation X.25.
– CCITT Recommendation X.610 (1992), Provision and support of the OSI connection-mode network
service.
– ISO/IEC 8208:1995, Information technology – Data communications – X.25 Packet Layer Protocol for
Data Terminal Equipment.
– ISO/IEC 8802 (All parts), Information technology – Telecommunications and information exchange
between systems – Local and metropolitan area networks.
1)
– ISO 9542:1988 , Information processing systems – Telecommunications and information exchange
between systems – End system to Intermediate system routeing exchange protocol for use in conjunction
with the Protocol for providing the connectionless-mode network service (ISO 8473).
– ISO/IEC 10030:1995, Information technology – Telecommunications and information exchange between
systems – End System Routeing Information Exchange Protocol for use in conjunction with
ISO/IEC 8878.
– ISO/IEC 10589:1992, Information technology – Telecommunications and information exchange between
systems – Intermediate system to Intermediate system intra-domain routeing information exchange
protocol for use in conjunction with the protocol for providing the connectionless-mode Network Service
(ISO 8473).
– ISO/IEC 10747:1994, Information technology – Telecommunications and information exchange between
systems – Protocol for exchange of inter-domain routeing information among intermediate systems to
support forwarding of ISO 8473 PDUs.
– ISO/IEC 11572:1997, Information technology – Telecommunications and information exchange between
systems – Private Integrated Services Network – Circuit mode bearer services – Inter-exchange
signalling procedures and protocol.
– ISO/IEC 11582:1995, Information technology – Telecommunications and information exchange between
systems – Private Integrated Services Network – Generic functional protocol for the support of
supplementary services – Inter-exchange signalling procedures and protocol.
_______________
1)
Currently under revision.
ITU-T Rec. X.263 (1998 E) 3

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ISO/IEC TR 9577 : 1999 (E)
– ISO/IEC TR 13532:1995, Information technology – Telecommunications and information exchange
between systems – Protocol combinations to provide and support the OSI Network Service.
– RFC 791, Internet Protocol. J. Postel (September 1981).
– RFC 1548, The Point-to-Point Protocol (PPP). W. Simpson (December 1993).
– RFC 2460, Internet Protocol, Version 6 (IPv6) Specification (December 1998).
– FRF.9 (Frame Relay Forum), Data Compression over Frame Relay Implementation Agreement
(January 1996).
– FRF.12 (Frame Relay Forum), Fragmentation over Frame Relay Implementation Agreement
(December 1997).
– FRF.priv (Frame Relay Forum), Frame Relay Privacy Implementation Agreement.
– FRF.OA&M (Frame Relay Forum), Frame Relay Operations, Administration and Maintenance (OA&M)
Protocol and Procedures Implementation Agreement.
3 Abbreviations
For the purposes of this Recommendation | Technical Report, the following abbreviations apply:
GFI General Format Identifier
IPI Initial Protocol Identifier
NCMS Network Connection Management Subprotocol
OSI Open Systems Interconnection
PDU Protocol Data Unit
SPI Subsequent Protocol Identifier
TPDU Transport Protocol Data Unit
4 Protocol identifiers
The protocol operating directly over the Data Link layer is termed the initial protocol and is identified by the Initial
Protocol Identifier (IPI).
The protocol carried by the initial protocol is termed the subsequent protocol and is identified by a Subsequent Protocol
Identifier (SPI).
The subsequent protocol can carry further subsequent protocols, identified by further SPIs, iteratively.
For the purposes of this Recommendation | Technical Report, the octets referred to as IPI and SPI are viewed as protocol
identifiers. In some cases the protocol itself gives other names to these octets, and might also view the function of the
octets as being distinct from protocol identification. ITU-T Rec. X.25 and ISO/IEC 8208 provide an example (see Annex
A). It is possible to identify such protocols by the means described in this Recommendation | Technical Report. It is also
possible for a given protocol to be identified in more than one way, in different contexts.
ITU-T Rec. X.260 | ISO/IEC 14765 contains a more detailed specification of the framework for protocol identification
on which the above concepts are based.
NOTE – Guidelines for the processing of protocol identifiers are given in Annex B.
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ISO/IEC TR 9577 : 1999 (E)
5 Initial protocol identifier
5.1 General
The location of the IPI for a header-oriented protocol is the first octet of the protocol control information; this is depicted
in Figure 1. The value of the IPI unambiguously identifies the initial protocol within the set of header-oriented protocols.
Data Link service data unit
Octet 1
Network layer
protocol control information
Location of the IPI
TISO7040-96/d01
Figure 1 – Location of the IPI
FIGURE 1/X.263.[D01]
The location of the IPI for a trailer-oriented protocol is the final octet of the protocol control information; this is depicted
in Figure 2. The value of the IPI unambiguously identifies the initial protocol within the set of trailer-oriented protocols.
It is not possible in general to mix header-oriented and trailer-oriented protocols on the same data link: a priori
knowledge is needed of the nature of the protocols to be received at a particular Data Link service access point.
Data Link service data unit
Last octet
Network layer
protocol control information
Location of the IPI
TISO8740-98/d02
Figure 2 – Location of the IPI for trailer-oriented protocols
ITU-T Rec. X.263 (1998 E) 5
Initial Protocol
Identifier
Initial Protocol
Identifier

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ISO/IEC TR 9577 : 1999 (E)
5.2 Assignment structure for header-oriented protocols
The structure applied to the values of the IPI for header-oriented protocols is depicted in Table 1.
With the exception of protocol identifiers used by ITU-T Rec. X.25 and ISO/IEC 8208, bits 8, 7, 6, and 5 of the IPI
indicate the administrative authority which is responsible for assigning a combination of the associated bits 4, 3, 2 and 1
to an initial protocol.
Table 1 – Structure of the IPI octet for header-oriented protocols
Bit pattern
Allocation category
87 65 43 21
0 0 0 0 0 0 0 0 Allocation by ISO/IEC
00 00 00 01
through to and including Allocation by ITU-T
00 00 11 11
x x 0 1 x x x x ITU-T Rec. X.25 and ISO/IEC 8208
x x 1 0 x x x x ITU-T Rec. X.25 and ISO/IEC 8208
0 0 1 1 x x x x ITU-T Rec. X.25 and ISO/IEC 8208
0 1 0 0 0 0 x x Allocation by ISO/IEC
0 1 0 0 0 1 0 0 Allocation by ITU-T
01 00 01 01
through to and including Allocation by ISO/IEC
01 00 11 11
0 1 1 1 x x x x Joint allocation by ITU-T and ISO/IEC
1 0 0 0 x x x x Allocation by ISO/IEC
1 0 1 1 x x x x Allocation by ITU-T
1 1 0 0 x x x x Not categorized by this Recommendation | Technical Report (Note)
11 11 00 00
through to and including Joint Allocation by ITU-T and ISO/IEC
11 11 11 10
1 1 1 1 1 1 1 1 Reserved for extension, see Table 2
NOTE – Although not categorized by this Recommendation | Technical Report, the codepoints 1100 1100 and 1100 1111 are in
widespread use (see Table 2 and Annex C).
5.3 Values assigned to the IPI for header-oriented protocols
Table 2 records the values that have been assigned to specific protocols. Values not recorded are reserved and available
for allocation by the administrative authorities specified by the structure depicted in 5.2.
A specific value is reserved to indicate the null Network layer. One value is reserved for future extension to this
Recommendation | Technical Report.
6 ITU-T Rec. X.263 (1998 E)

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ISO/IEC TR 9577 : 1999 (E)
Table 2 – Values assigned to the IPI octet for header-oriented protocols
Bit pattern
Protocol
87 65 43 21
0 0 0 0 0 0 0 0 Null Network layer (Note 1)
0 0 0 0 0 0 0 1 ITU-T Rec. T.70 (Minimum Network layer functionality)
0 0 0 0 0 0 1 1 ITU-T Rec. X.633 (Network layer fast-byte protocol)
0 0 0 0 1 0 0 0 ITU-T Recs. Q.931, Q.932, Q.933, X.36, ISO/IEC 11572, ISO/IEC 11582
0 0 0 0 1 0 1 0 ITU-T Rec. Q.2119
0 0 0 0 1 0 0 1 ITU-T Rec. Q.2931 (Broadband ISDN Signalling protocol)
xx 01 xx xx ITU-T Rec. X.25 and ISO/IEC 8208 – Modulo 8
x x 1 0 x x x x ITU-T Rec. X.25 and ISO/IEC 8208 – Modulo 128
0 0 1 1 0 0 1 0 ITU-T Rec. X.45
0 0 1 1 x x x x ITU-T Rec. X.25 and ISO/IEC 8208 – GFI extension (except value 0011 0010)
0 1 0 0 0 1 0 0 ITU-T Rec. G.764
1 0 0 0 0 0 0 0 IEEE SNAP, see Annex D
1 0 0 0 0 0 0 1 ITU-T Rec. X.233 | ISO/IEC 8473-1 (excluding the inactive subset)
1 0 0 0 0 0 1 0 ISO 9542
1 0 0 0 0 0 1 1 ISO/IEC 10589
1 0 0 0 0 1 0 1 ISO/IEC 10747 (Note 3)
1 0 0 0 1 0 1 0 ISO/IEC 10030
1 0 0 0 1 0 1 1 ITU-T Rec. X.273 | ISO/IEC 11577
1 0 0 0 1 1 1 0 RFC 2460 (see Annex C)
1 0 1 1 0 0 0 0 FRF.9 (Note 4)
1 0 1 1 0 0 0 1 FRF.12 (Note 4)
1 0 1 1 0 0 1 0 FRF.OA&M
1 0 1 1 0 0 1 1 FRF.priv (Note 5)
1 1 0 0 1 1 0 0 RFC 791 (see Annex C)
1 1 0 0 1 1 1 1 RFC 1548 (see Annex C)
1 0 0 0 1 1 1 1 Private Network layer protocols
1 1 1 1 1 1 1 1 Reserved for extension (Note 2).
NOTE 1 – ITU-T Rec. X.233 | ISO/IEC 8473-1 uses this value for the inactive subset.
NOTE 2 – The extension mechanisms will be the subject of joint development between ITU-T and ISO/IEC.
NOTE 3 – IPI assigned but not currently used since current usage of ISO/IEC 10747 PDUs is covered by the ITU-T Rec. X.233 |
ISO/IEC 8473-1 IPI.
NOTE 4 – The first octet of the decompressed PDU, when the IPI indicates Data compression protocol, or of the reassembled
PDU, when the IPI indicates Fragmentation protocol, is itself an IPI octet.
NOTE 5 – Depending upon the protocol(s) that use it, this IPI may be followed by another IPI, an SPI or no Protocol Identifier at
all.
ITU-T Rec. X.263 (1998 E) 7

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ISO/IEC TR 9577 : 1999 (E)
5.4 Assignment structure for trailer-oriented protocols
The structure applied to the values of the IPI for trailer-oriented protocols is depicted in Table 3.
Bits 8, 7, and 6 of the IPI indicate the administrative authority which is responsible for assigning a combination of the
associated bits 5, 4, 3, 2 and 1 to an initial protocol.
Table 3 – Structure of the IPI octet for trailer-oriented protocols
Bit pattern
Allocation category
87 65 43 21
0 0 x x x x x x Allocation by ITU-T
0 1 x x x x x x Reserved for future assignment to ITU-T and/or ISO/IEC
1 0 0 x x x x x Allocation by ISO/IEC
1 0 1 x x x x x Allocation by ITU-T
11 00 00 00
through to and including Not categorized by this Recommendation | Technical Report
11 11 11 10
1 1 1 1 1 1 1 1 Reserved for extension, see Table 4
5.5 Values assigned to the IPI for trailer-oriented protocols
Table 4 records the values that have been assigned to specific protocols. Values not recorded are reserved and available
for allocation by the administrative authorities specified by the structure depicted in 5.4.
One value is reserved for future extension to this Recommendation | Technical Report.
Table 4 – Values assigned to the IPI octet for trailer-oriented protocols
Bit pattern
Protocol
87 65 43 21
0 0 0 0 0 0 0 0 ITU-T Recs. I.365.2 and I.365.3
1 1 1 1 1 1 1 1 Reserved for extension (Note).
NOTE – The extension mechanisms will be the subject of joint development between ITU-T and ISO/IEC.
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ISO/IEC TR 9577 : 1999 (E)
6 Subsequent protocol identifier
6.1 General
An initial protocol can make provision for implicit or explicit mechanisms to list and/or negotiate the identity of
subsequent protocols to be carried by it. In the case of an explicit mechanism, the identity of the subsequent protocol is
given by the Subsequent Protocol Identifier (SPI).
For the purposes of this Recommendation | Technical Report, the SPI is the first octet of protocol control information in
each instance of communication of the subsequent protocol. This is depicted in Figure 3 where a subsequent protocol is
operating directly over the initial protocol.
Data Link
service data unit
Octet 1
Protocol control information Next highest sublayer
of the lowest sublayer of the of the Network Layer
Network Layer if present
Location of the SPI
TISO7050-96/d03
NOTE – The term sublayer is used as defined in ITU-T Rec. X.200 | ISO/IEC 7498-1.
Figure 3 – Location of the SPI
FIGURE 3/X.263.[D03]
The value of the SPI:
a) identifies another OSI Network layer protocol;
b) identifies some other non-OSI protocol;
c) identifies that a set of protocols is encapsulated within the initial protocol – the method for identification
of the subsequent encapsulated protocol(s) is defined by the protocol associated with the SPI; or
d) is that which is in use by an OSI Transport layer protocol.
It should be noted that in some cases an SPI might not be present, for example see Figure A.3.
It should also be noted that in case c), for the purposes of the initial protocol, the single-octet SPI defined here can
...