ISO/IEC 10030:1995

INTERNATIONAL
lSO/IEC
STANDARD 10030
Second edition
1995-04-I 5
Information technology -
Telecommunications and information
exchange between systems - End System
Routeing Information Exchange Protocol
for use in conjunction with ISO/lEC 8878
Technologies de I’informa tion - T6kommunica tions et khange
d’information entre systkmes - Pro tocole d ‘6change d ‘in formation pour
le routage d’un systgme d’extrGmit6 9 Wiser conjoin temen t avec
I’lSO/CEI 8878
lSO/lEC 10030: 1995(E)
Page
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1 Scope
. . . . . . . . m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Normative references
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Abbreviations
5 Overview of the Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
SNARE Subnetwork Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8 Configuration Information Subset
System Redirection Information Subset . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .e.m.
10 Address and SNPA Masks
. . . . . . . . . . . . . . . . . . . . . . . .*.*.*.*.
11 SNARE Procedures
Structure and Encoding of PDUs . . . . . . . . . . . . . . . .*.*.
Annex A . . . . . . . .*.
Annex B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annex C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.
0 ISO/lEC 1995
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ii
o lSO/IEC ISO/IEC 10030:1995(E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the Inter-
national Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members of IS0 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. IS0 and IEC technical com-
mittees collaborate in fields of mutual interest. Other international organ-
izations, governmental and non-governmental, in liaison with IS0 and IEC,
also take part in the work.
In the field of information technology, IS0 and IEC have established a joint
technical committee, lSO/IEC JTC 1. Draft International Standards adopted
by the joint technical committee are circulated to national bodies for vot-
ing. Publication as an International Standard requires approval by at least
75 % of the national bodies casting a vote.
International Standard ISO/IEC 10030 was prepared by Joint Technical
Committee lSO/IEC JTC 1, Information technology, Subcommittee SC 6,
Telecommunications and information exchange between systems.
This second edition cancels and replaces the first edition
(IS0 10030:1990), which has been technically revised. It is a consolidation
of Amendments 2 and 3 as well as Technical Corrigenda 1 and 2.
Annexes A and B form an integral part of this International Standard. An-
nex C is for information only.
iii
llntroduction
This International Standard is one of a number of standards concerned with
Network Layer Routeing Protocolsl An overall framework for routeing is
described in ISOIIEC TR 9575. This international Standard specifically relates
to that part of the framework which deals with Single Subnetwork Routeing.
This International Standard is related to ISO/IEC 8878 which specifies the use
of X.25 to provide the IS0 connection-mode Network Service. This Protocol
provides solutions for the following practical problems:
a) How do End Systems discover the reachability of Intermediate Systems
that can route NPDUs to destinations on subnetworks other than the
one(s) to which the End System is directly connected?
b) How do End Systems discover the reachability of other End Systems on
the same subnetwork (when direct examination of the destination NSAP
address does not provide information about the destination subnetwork
address)?
c) How does a Subnetwork Address Resolution Entity discover the
reachability of End Systems on the subnetwork to which it is directly
connected?
d) How does an end System, which has not been pre-configured with its
own Network Address, request the temporary assignment of a Network
Entity Title (NET) and thus, derive the necessary Network Address(
from a SNARE located on a common subnetwork?
e) How do Intermediate systems discover the reachability of End Systems
on the same subnetwork (when direct examination of the NSAP
destination address does not provide information about the destination
subnetwork address)?
The Protocol assumes that:
a) Routeing to a specified subnetwork point of attachment (SNPA) address
on the same subnetwork is carried out satisfactorily by the subnetwork
itself.
b) The subnetwork is not, however, capable of routeing on a global basis
using the NSAP address alone to achieve communication with a
requested destination.
End Systems and Intermediate Systems us ing this protocol require to
Cl
know at least one SNPA address that can be used to access a SNARE.
The protocol is designed to:
minimize the amou nt of a priori state information needed by End
a)
Systems befo re they can begin to co mmunicate with other End Systems;
iV
o lSO/IEC
ISO/IEC looso:1995(E)
b) minimize the amount of memory needed to store routeing information in End Systems; and
c) minimize the computational complexity of End Systems routeing algorithms.
This Protocol .performs similar functions to the ones specified in IS0 9542. However, the characteristics of
environments operating ISO/IEC 8208 (X.2WPLP) and the actual functionality of ISOAEC 8208 (X.2WLP) in itself
invalidate the operation of ISO. 9542 as follows:
a) In general non-broadcast environments, the Configuration subset of IS0 9542 is inadequate.
b) In broadcast environments operating ISOAEC 8208 (X.25/PLP), the Redirection subset of IS0 9542 is
invalidated.
Therefore, this Protocol is developed to perform all the aforementioned functions in harmony with the operation of
ISOAEC 8208 (X.25/PLP).
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ISO/IEC loo3o:1995(E)
INTERNATIONAL STANDARD o ‘so”EC
Telecommunications and
Information technology -
End System
information exchange between systems -
Routeing Information Exchange Protocol for use in
conjunction with ISO/IEC 8878
Statement (PICS), as defined in ISO/IEC 9646-l. This
1 Scope
International Standard provides the PIGS proforma in
This International Standard defines a protocol for the
compliance with the relevant requirements, and in
exchange of routeing information between an End
accordance with the relevant guidance, given in IS0
System and a Subnetwork Address Resolution Entity,
9646-7.
and between an Intermediate System and a Subnetwork
Address Resolution Entity.
2 Normative references
This International Standard is applicable to:
The following standards contain provisions which,
a) End Systems which operate according to the main
through reference in the text, constitute provisions of
body of ISO/IEC 8878 to provide and support the
this International Standard. At the time of publication,
OSI Connection-mode Network Service using
the editions indicated were valid. All standards are
ISO/IEC 8208.
subject to revision, and parties to agreements based on
b) Subnetwork Address Resolution Entities which
this International Standard are encouraged to
operate ISO/IEC 8208.
investigate the possibility of applying the most recent
editions of the standards indicated below. Members of
NOTE - The Subnetwork Address Resolution Entity
IEC and IS0 maintain registers of currently valid
defined in this Intemathal Standard may be associated
with relay functions as defined in ISO/IEC 10028 and International Standards.
ISO/I EC 10177.
ISO/IEC 7498-l : 1994, information technology - Open
systems which operate
c) Intermediate Systems interconnection - Basic Reference Model -
ISO/IEC 8208.
Part I: The Basic Mode/.
End Systems which provide and support the OSI CONS
ISO/IEC 8208 : 1990, information technology - Data
using the fast select 1980 procedures or the alternative - X.25 Packet Layer Protowl for Data
communications
1980 procedures in annex A of ISOIIEC 8878 are
Terminal Equipment.
outside the scope of this International Standard.
: 1991 information
ISO/IEC 8208 : 1990lAmd. 3
This International Standard does not specify any
technology - Data communications - X.25 Packet
protocol elements nor algorithms for facilitating routeing
Layer Protocol for Data Terminal Equipment -
and relaying among SNARES. Such functions are Amendment 3: Conformance reguirements.
intentionally outside the scope of this International
ISO/IEC 8348 : 1993, lnformatrbn technology - Open
Standard.
Systems Interconnection - Network Service Definition.
To evaluate conformance of a particular implementation,
IS0 8648 : 1988, Information processing systems -
it is necessary to have a statement of which capabilities
Open Systems Interconnection - internal organization
and options have been implemented. Such a statement
of the Network Layer.
Implementation Conformance
is called Protocol
o lSO/IEC
lSO/lEC 10030: 1995(E)
IS0 8802-2 : 1989, information processing systems - ISO/IEC 10039 : 1991, Information technology - Open
Systems Interconnection - Local area networks -
Local area networks - Part 2: Logical link control
Medium Access Control (MAC) servcB definitbn.
ISOIIEC 8878 : 1992, lnformation technology -
1993, information technology -
Telecommunicatbns and information exchange ISOAEC 10177 :
Telecommunications and information exchange
between systems - Use of X.25 to provide the OS1
between systems - Provision of the connection-mode
Connection-mode Network Service.
Network internal layer service by intermediate systems
ISOAEC 8880-I : 1990, Information technology -
using /SO//EC 8208, the X.25 Packet Layer Protowl.
Telecommunications and informatbn exchange
between systems - Protocol combinations to provide ISO/IEC TR 10178 : 1992, lnformation technology -
Telecommunications and information exchange
and support the OS1 Network Service - Part I: General
between systems - The structure and wding of Logical
principles.
Link Control addresses in Local Area Networks.
ISOAEC 8880-2 : 1992, information technology -
information exchange
Telecommunicaticns and
Protocol combinations to provide
between systems -
3 Definitions
and support the OS1 Network Service - Part 2:
Provision and suprt of the connection-mode Network
3.1 Reference Model Definitions
Servke.
This International Standard makes use of the following
ISOAEC 8881 : 1989, Information processing systems
terms defined in ISOAEC 7498-l:
- Use of the X.25 packet level
- Data communications
a) Network Layer
protocol in local area networks.
b) Network Service Access Point
c) Network Service Access Point address
1992, lnformation technology -
ISO/IEC 8886 :
d) Network Entity
information exchange
Telecommunications and
e) Routeing
Data link service definition for
between systems -
f) Network Protocol
Open Systems Interconnection.
g) Network Relay
IS0 9542 : 1988, Information processing systems -
h) Network Protocol Data Unit
Telewmmunicatbns and information exchange
3.2 Network Layer Architecture Definitions
between systems - End system to lntermediate system
routeing exchange protowl for use in conjunction with
This International Standard makes use of the following
the Protocol for providing the wnnectionless-mode
terms defined in IS0 8648:
network service (IS0 8473).
a) Subnetwork
ISOAEC TR 9575 : 1990, Information technology -
b) End System
Telecommunications and information exchange
c) Intermediate System
- OS1 Routeing Framework.
between systems
d) Subnetwork Service
e) Subnetwork Access Protocol
ISOAEC TR 9577 : 1993, lnformatibn technology -
information exchange
,TelecgmmunEcations and
3.3 Network Layer Addressing Definitions
Protocol identification in the
between systems -
This International Standard makes use of the following
network layer.
terms defined in ISO/IEC 8348:
ISOAEC 9646-l : 1994, lnformation technology - Open
a) Network Entity Titles
Systems lnterwnnection - Conformance testing
b) Subnetwork address
methodology and framework - Part I: General
c) Subnetwork Point of Attachment
concepts.
3.4 Local Area Network Definitions
ISOAEC 9646-7 : ‘, information technology -
Open Systems Interconnection - Conformance testing
This international Standard makes use of the following
methodology and framework - Part 7: lmplementation
terms defined in IS0 8802-2:
conformance statements.
Multicast address
ISO/IEC 10028 : 1993, Information technology -
Broadcast address
W
Telecommunications and information exchange
3.5 Additional Definitions
- Definition of the relaying functions
between systems
of a Network layer intermediate system. purposes of the International Standard, the
For the
definitions
following
apply:
3.5.1 configuration Information: Information about
published.
1. Tobe
the collection of End Systems and Intermediate
Systems attached to a subnetwork defined in
ISO/IEC 1 oom 1995(E)
o lSO/IEC
4.3 Miscellaneous
terms of the system types, Network Addresses
present, Network Entity Titles present, and the
BCD . Binary Coded Decimal
between systems, SNPA
correspondence
LLC Logical Link Control
addresses, and potential routes.
MAC Medium Access Control
3.5.2 redirection information: Information supplied
NA Network Address
a Call Request fails to achieve
when
NPDU Network Protocol Data Unit
establishment of a Network Connection, indicating
QOS Quality of Service
an SNPA which could be used to establish such a
SNPA Subnetwork Point of Attachment
connection.
resolution
3.5.3 subnetwork address
information concerning
entity: Supplier of
5 Overview of the Protocol
routeing within a single subnetwork.
The protocol specified in this International Standard
3.6 PIGS Definitions
comprises two subsets:
This International Standard makes use of the following
a) The Configuration Information subset
terms defined in ISO/IEC 9646-7.
b) The Redirection Information subset
a) Protocol Implementation Conformance Statement
The functions of the Configuration Information subset
(PIGS)
are:
b) PICS proforma
To enable ESs to notify a SNARE of the existence
and reachability of their Network Addresses (NAs).
4 Abbreviations
To enable ESs to discover, for certain remote
W
NAs, the SNPA addresses of systems on the
4.1 Systems
subnetwork via which communications may
DTE Data Terminal Equipment
potentially be routed.
ES End System
To enable ESs to obtain their own Network
Cl
IS Intermediate System
Addresses without manual intervention.
Subnetwork Address Resolution Entity
SNARE
To enable ISs to obtain, for NAs identifying NSAPs
d)
4.2 Protocol Data Units
located within End Systems directly attached to
ECQ PDU End/Intermediate System Configuration
the same subnetwork, the SNPA address of these
Query Protocol Data Unit
systems.
Notification
ENC PDU End/Intermediate System
The function of the Redirection Information subset is to
Complete Protocol Data Unit
enable ESs which are attempting to establish a
ERA PDU End System Request Address Protocol
connection to be directed to a specific appropriate
Data Unit
SNPA address via which the connection should be
System Connect
ESC PDU End/Intermediate
routed and to permit ISs which are attempting to
Protocol Data Unit
establish a connection to an ES on the subnetwork to be
ESH PDU End/Intermediate System Hello Protocol
directed to the appropriate SNPA address via which the
Data Unit
connection can be established.
Redirect Protocol Data Unit
RD PDU
SNARE Assign Address Protocol Data
SAA PDU
The two subsets are complementary in that the
Unit
information obtained from the Redirection Information
SCC PDU SNARE Configuration Complete Protocol
associated Configuration
subset implicitly carries
Data Unit
Information, and in that the information obtained from
SCR PDU SNARE Configuration Response Protocol
the Configuration Information subset may be used to
Data Unit
derive a suitable SNPA address and so avoid the need
SHL PDU SNARE Hello Protocol Data Unit
for use of the Redirection Information subset. The
SNC PDU SNARE Notification Complete Protocol
choice of which subset to use to obtain Routeing
Data Unit
Information for any individual instance of communication
SRH PDU SNARE Request Hello Protocol Data Unit
is a local ES or IS decision, which may be different for
SNARE Received Notification Protocol
SRN PDU
different instances of communication and may be varied
Data Unit
freely during ES or IS operation without impacting the
ability to interwork.
The name of the PDU should not be construed as
NOTE -
implying a definition of the PDU’s function. For example an
5.1 The SNARE Function
ECQ PDU can be transmitted by an IS.
A SNARE is an entity which collects configuration
information from ESs, and which distributes
ISO/IEC 10030: 1995(E)
o lSO/IEC
configuration and redirection information to them. The protocol exchanges begin with the IS establishing
an X.25 connection to a SNARE by issuing an X.25 Call
The SNARE also distributes configuration and
Request. When the SNARE accepts the call, the IS
redirection information to the ISs.
may request information about one or several Network
- A SNARE may also interact with Intermediate
NOTE
Addresses. For each requested Network Address the
Systems for the purpose of collecting configuration information
SNARE supplies details of the SNPA (or SNPAs) of the
but the details of such interactions are outside the scope of this
system at which the Network Address resides. Having
International Standard.
received information about one Network Address, the IS
The function of a SNARE may be carried out by one or more can request information about another. When it has all
ESs or ISs attached to the subnetuvork. Where the subnetwork
the information it requires, the IS clears the call.”
is one which itself acts on the X.25 protocol, it is also possible
5.3 Overview of Redirection Information
that some or all of the SNARE operations may be performed
by functions integrated with the subnetwork itself.
The redirection information functions can be considered
In order for an ES (or IS) to use this protocol, it requires as two parts.
knowledge of at least one SNPA address which can be used to
The first part takes place when an ES (or IS) is about to
access a SNARE. In general, this address is pre-configured in
establish a Network Connection according to
the ESs (or ISs). Annex A describes techniques which may be
ISO/IEC 8878, but does not have the information
used in certain circumstances to avoid the need for such pre-
necessary to determine the appropriate subnetwork
configuration.
address to which the Call Request should be
5.2 Overview of Configuration Information
transmitted. The action of the ES (or IS) in this case is
The protocol exchanges which constitute the
simply to use the address of a SNARE. The Call
Configuration Information subset begin with the ES
Request packet is constructed exactly in accordance
establishing an X.25 connection to a SNARE by issuing
with ISO/IEC 8878 and is transmitted to the SNARE.
an X.25 Call Request. The first octet of the call user
The ES (or IS) subsequently continues to operate the
data contains a protocol identifier indicating the protocol
connection in accordance with ISO/IEC 8878. In the
defined in this International Standard. When the
event that the SNARE is an ES or IS attached to the
SNARE accepts the call, the ES may then transmit to
subnetwork, rather than having functionality integrated
the SNARE details of its Network Addresses. Once the
with the subnetwork itself, it may:
information concerning all of its Network Addresses is
transmitted the ES explicitly notifies the SNARE that the
use the X.25 Call Deflection facility to deflect the call
notification is complete so that the SNARE can ensure
to an appropriate ES or IS;
that all the information received is secure to the extent
clear the call, supplying information about the
required for its use. Optionally, following acceptance of
appropriate SNPA which should be used for future
the call by the SNARE, a non-configured End System
attempts; or
may request a NET for itself. Once it obtains this
information it may derive additional Network addresses
if it contains relay functions, accept the call itself and
for subsequent interactions with other End Systems.
take part in the connection as a relay.
However, it is not necessary or even permitted for an
If the SNARE function is integrated with the subnetwork
End System to use a NET obtained in this manner
itself, then in addition to the above it may be able to
indefinitely. The ES may also request information about
deliver the call to an appropriate SNPA by other means
remote Network Addresses. For each requested
which are outside the scope of this International
Network Address the SNARE supplies details of the
Standard (for example, by invoking the X.25 Call
SNPA or SNPAs on the subnetwork via which the
Redirection facility).
Network Address can be reached, and the associated
potential Quality of Service. Having received
Since, therefore, the connection establishment may now
information about one Network Address, the ES can
be going to proceed satisfactorily without the originating
request information about another. When it has all the
ES (or IS) doing any further routeing operations, the ES
information it requires, the ES clears the call.
(or IS) continues to process the Network Connection in
accordance with ISO/IEC 8878 unless a Clear Indication
An IS also may request information about Network
is received.
Addresses. In the present context this request will
strictly take place within the realm of Single Network
Receipt of a Clear Indication in response to a Call
Routeing, as defined in ISO/TR 9575, and is thus
Request causes the second part of the redirection
hierarchically placed under any IS-IS routeing activity.
information procedure to take place. At this point,
Therefore this request can only occur for Network
provided the cause and diagnostic codes in the clear
Addresses corresponding to End Systems directly
indication packet show that the disconnection was not
attached to the subnetwork. However, this protocol
initiated by the Network Service user, the ES (or IS)
contains no provisions to ensure that this is so, and checks whether there is user data in the packet
relies instead on the processes effected above it in the
containing information encoded according to this
routeing hierarchy.
International Standard indicating an appropriate
o lSO/lEC ISWIEC loo3o: 1995(E)
SNARE can be reached. Local methods may be
subnetwork address via which a Network Connection
provided for determining such an address; alternate
equivalent to that being rejected could be established.
methods described in Annex A may be used where they
An equivalent Network Connection is one between the
are available.
same NSAPs with the same Quality of Service
parameters. The ES (or IS) may use this information
In the event that an ES is aware of more than one
either to retry the connection establishment, according
SNPA at which a SNARE can be reached, the choice
to the provisions of ISO/IEC 8878, or in establishing
between them is a local matter.
future equivalent network connections.
8 Configuration Information Subset
6 Conformance
8.1 Protocol Parameters
6.1 Static Conformance Requirements
This clause defines parameters used in this protocol
An ES for which conformance to this International
and, where applicable, specifies which values of these
Standard is claimed shall implement one or more of the
parameters are required to be supported by all
following:
conforming end systems. The ability to support values
other than those specifically required, and the means of
a) The procedures of the system Configuration
identifying that such a value is to be used in any
Information Subset, specified in clause 8, that
particular instance, are local matters.
apply to an ES.
8.1.1 Response Time
b) The procedures of the system Redirection
Information Subset, specified in clause 9, that
This is the time limit used by an ES (or IS) during
apply to an ES.
operation of the protocol.
An IS for which conformance to this International
Any implementation of the Configuration Information
Standard is claimed shall implement one or more of the
subset shall be capable of supporting a response time
following:
value of 180 s, accurate to within * 30 s.
a) The procedures of the system Configuration
8.1.2 Notification Retry Time
Information Subset, specified in clause 8, that
This is the time interval at which an ES shall retry a
apply to an IS, in particular 8.2.3.3.
failed attempt to convey its configuration to a SNARE.
b) The procedures of the system Redirection
Any implementation of the Configuration Information
Information Subset, specified in clause 9, that
subset shall be capable of supporting a Notification
apply to an IS.
Retry Time value of 900 s, accurate to within & 120 s, if
A SNARE for which conformance to this International
it supports any values of the Notification Required
Standard is claimed shall implement those procedures
parameter other than that which indicates that
which clause 11 prescribes as requirements.
notification is never required and that which indicates
that no specific value is being suggested.
- Therefore a SNARE is required to process
NOTE
Configuration and Redirection Information.
NOTE - There are no requirements on the support of
Notification Retry Time by an implementation which does not
6.2 Dynamic Conformance Requirements
support such values of the Notification Required parameter.
A system for which conformance to this International
8.13 Not if ication Required
Standard is claimed shall exhibit external behavior
consistent with having implemented:
This parameter indicates the circumstances in which an
ES shall attempt to notify its configuration to a SNARE.
a) for each supported function, the corresponding
procedures and the encoding of any transmitted
Any implementation of the Configuration Information
Protocol Data Units, as specified in the relevant
subset shall be capable of supporting a value of this
subclauses of clauses 8,9,10, 11 and 12;
parameter which indicates that notification is never
required.
b) the X.25 Packet Layer Protocol in conformance
Notification Required parameter
with the requirements of ISO/IEC 8208 Amd. 3, NOTE - Examples of other
be supported include:
values which might optionally
and in conformance with the procedures invoked
by IS0 8880 for the relevant environment.
l A value indicating that notification is required each time the
ES is initialized and subsequently at the expiry of the time
specified by the SNARE at the end of each preceding
notification.
7 SNARE Subnetwork Address
. A value indicating that notification is required each time the
The use of this protocol requires an ES (or an IS) to be
ES is attached to a different subnetwork.
aware of at least one subnetwork address at which a
ISO/IEC 10030: 1995(E) o lSO/IEC
It is emphasized that these are only examples - other values
not continue for longer than the value of the Response
are permitted.
Time parameter. When it has finished retrying, the ES
(or IS) shall proceed as specified in 8.2.2.
8.1.4 Address Holding Time
8.2.2 Connection Establishment Failure Procedure
This is the time for which the End System may continue
to use an NET that has been assigned to it by the
When an attempt to establish a connection fails, if the
SNARE. ES (or IS) has knowledge of any alternative SNARE
subnetwork address, it shall attempt to establish a
8.2 Protocol Operation
connection to one which it has not previously tried in this
This clause specifies the protocol making use of the
establishment attempt.
X.25 Packet Layer Procedures specified in ISO/IEC
When all known SNARE addresses have been tried
8208. Subject to the provisions of ISO/IEC 8208, the
unsuccessfully:
choice of values for X.25 fields which are not specified
in this clause is a local matter.
If the ES (or IS) needed to obtain Configuration
a)
Information from the SNARE, the time at which a
8.2.1 Connection Establishment
further attempt is made (if any) or the invocation of
An ES (or an IS) shall attempt to establish a connection
other forms of action (e.g., fallback to default
whenever it needs to obtain configuration information
configuration, or use of Redirection subset as a
from a SNARE. In addition, an ES shall attempt to
basis for routeing) is a local matter.
establish connection to a SNARE when conditions
If according to the provisions of 8.1.3 the ES was
b)
specified in 8.1.3 make it necessary to notify
due to notify its configuration to a SNARE, the
configuration information to a SNARE. The ES shall
attempt at notification shall be considered to have
attempt to establish a connection to a SNARE when it
failed. Another attempt shall be made after the
needs to obtain a NET when initially connecting to the
expiry of the Notification Retry Time.
subnetwork or upon expiration of the Address Holding
Time value. However, neither an ES nor an IS shall
attempt to establish a connection that have already a If the ES needed to obtain a NET, the time at
Cl
connection established or being established for the use which a further attempt is made (if any) is a local
for configuration information, and neither an ES nor an
matter.
IS shall attempt to establish more than one connection
Data Transfer Procedure
8.2.3
to SNARES from any one one system SNPA at any one
time.
This clause specifies the transfer of data once an
acceptable connection to a SNARE has been achieved.
An ES (or an IS) shall attempt to establish a connection
to the SNARE by originating a virtual call in accordance
This clause requires transmission of a number of PDUs.
with the procedures for virtual call setup specified in
Each PDU shall be transmitted as a single M-bit
lSO/IEC 8208. The SNPA address to which the Call sequence without the Q-bit set, according to the
Request shall be transmitted shall be one applicable to procedures for data transfer specified in ISO/IEC 8208.
the SNARE, as described in clause 7. The Fast Select
This clause also requires, in some circumstances, that
facility shall be specified, indicating no restriction on
the connection be abandonded before completion. This
response. The User Data to be transmitted with the Call
shall be done by clearing the call according to the
Request packet shall contain an ESC PDU.
procedures for virtual call clearing specified in
If the virtual call setup procedure succeeds, the ES (or
ISO/IEC 8208, using a cause code of 0 and a diagnostic
IS) shall examine the User Data received with the Call
code of 242.
Connected packet.
In the event that the virtual call is cleared (whether by
If this contains a valid SNC PDU, then the ES (or IS) the ES (or IS) itself abandoning the connection
shall proceed to perform data transfer as specified in according to the provisions of this International
8.2.3. Otherwise the ES (or IS) shall clear the call
Standard, or as a consequence of the operation of
according to the procedures for virtual call clearing ISO/IEC 8208 procedures) before the normal
specified in ISO/IEC 8208 using a cause code of 0 and completion of the data transfer procedure specified in
a diagnostic code of 242, and shall then act according to
this clause, the ES shall follow the procedure for failed
the procedure for failed connection establishment in
connection specified in 8.2.4.
8.2.2.
In the event that a Reset Indication, an Interrupt packet,
If the virtual call setup procedure fails, the ES (or IS) or Q-bit data is received at any time during the operation
may retry it provided that the failure was due to a cause of the data transfer procedure, the ES (or IS) shall
which, if it occurred in an attempt to establish a Network abandon the connection.
Service connection, would have been interpreted
The data transfer procedure consists of 3 parts --
according to ISO/IEC 8878 as “connection rejection -
address assignment, configuration notification and
However, attempts to retry shall
transient condition”.
o lSO/IEC
ISO/IEC 10030: 1995(E)
configuration collection. When the address assignment 8.23.2 Configuration Collection by End Systems
procedure is applicable, it shall be carried out
The configuration collection procedure is an optional
immediately following connection establishment. When
procedure and, when implemented, its operation is
the configuration notification procedure is applicable, it
applicable whenever the ES requires to obtain
shall be carried out after completion of the address
information from a SNARE about the SNPAs of systems
assignment procedure (or immediately if the address
which may be used to reach remote Network
assignment procedure is not applicable). When the
Addresses. This International Standard does not
configuration collection procedure is applicable, it shall
impose any constraints on how often an ES attempts to
be carried out after completion of the address
collect configuration information.
assignment and/or configuration notification procedures
(or immediately if the address assignment and The ES shall transmit an ECQ PDU specifying a
configuration notification procedures are not applicable). Network Address for which it requires information. In
After completion of all applicable parts, the ES shall response it may receive a number of SCR PDUs,
follow the procedure for normal completion as specified containing information about SNPAs through which the
in 8.3. specific Network Address may be reached. The SCR
PDU may include an Address Mask parameter and a
8.23.1 Configuration Notification
SNPA Mask parameter. These parameters may be
used as described in 8.1.4 and 8.1.5, respectively.
The configuration notification procedure is an optional
procedure and, when implemented, its operation is
The receipt of an SCC PDU indicates that the
controlled by the setting of the Notification Required
information is complete; if no SCR PDUs are received
parameter.
before the SCC PDU this indicates that no information is
available for the specified Network Address. If the ES
This procedure is applicable when (and only when) the
requires information about further Network Addresses, it
following conditions are satisfied:
may then repeat the process provided that the Query
a) The Notification Required parameter is set to a
Limit field in the SCC PDU specifies that another query
value which indicates that the ES should notify its
is allowed. lf the Query Limit field specifies that no
configuration to a SNARE at this time.
more queries are allowed, the ES shall not transmit any
more ECQ PDUs. When the ES has information for all
b) An attempt to notify configuration has not failed
the Network Addresses it requires, or the Query Limit
within the duration specified by the Notification
disallows further queries, the configuration collection
Retry Time parameter.
function is successfully complete.
The ES shall start the procedure by transmitting one
If a time greater than the Response Time parameter
ESH PDU for each Network Address reachable through
elapses after transmission of an ECQ PDU and before
its SNPA. Following the ESH PDUs it shall transmit an
receipt of the corresponding SCR or SCC PDU, the
ENC PDU. It shall then wait to receive an SRN PDU. If
connection shall be abandoned.
the received SRN PDU contains the Notification
Required parameter then the ES shall extract and use
The following shall also cause the connection to be
this value as the next time interval prior to notification to
abandoned:
the SNARE. On receipt of the SRN PDU, the
a) Receipt of any data which does not contain a valid
configuration notification procedure is successfully
SCR or SCC PDU.
completed.
b) Receipt of any PDU before transmission of the first
NOTE 1 - After such successful completion, the value of the
Notification Required parameter determines if and when this ECQ PDU, or between receipt of an SCC PDU
procedure will subsequently again be applicable. and transmission of the next ECQ PDU.
After the transmission of the first ESH PDU, if the SRN c) Receipt of a PDU relating to a Network Address
PDU has not been received within a time equal to the other than that for which the ES has transmitted
Response Time parameter, the connection shall be an ECQ PDU on the connection and not received
abandoned. an SCC PDU.
NOTE 2 - The expiry of this time may be a result either of
8.233 Configuration Collection by Intermediate
delays in transmitting the PDlJs (e.g., because of flow control),
Systems
or delay in response by the SNARE.
The configuration collection procedure is an optional
If any data is received by the ES before transmission of
procedure and, when implemented, its operation is
the ENC PDU, or if any data is received which does not
applicable whenever the IS requires to obtain
contain a valid SRN PDU, the connection shall be
information from a SNARE about the SNPAs of End
abandoned.
Systems directly attached to the same subnetwork at
which are located certain Network Addresses. This
International Standard does not impose any constraints
on how often an IS attempts to collect configuration
o lSO/IEC
b) Any Configuration information received in SCR
information.
PDUs for which no corresponding SCC PDU has
The IS shall transmit an ECQ PDU specifying a Network
been received is incomplete.
Address for which it requires information. Because of
the hierarchical fashion after which routeing is organized
NOTE - It is a local matter whether the system (ES or IS) will
within OSI, this request takes place under the umbrella
make use of incomplete data or whether it will discard it.
of an IS-ES exchange. Therefore the SCR PDUs that
Whether and when to make another attempt to obtain the
the IS may receive in response from the SNARE can
remainder of incomplete data, or information still required for
only contain information on SNPAs of End Systems
other Network Addresses, is also a local matter.
directly attached to the subnetwork. The SNPA
8.3 Normal Completion Procedure
correspond to system at which the NSAPs are located.
The SCR PDU may include an Address Mask
When the applicable data transfer procedures have
parameter, and a SNPA Mask parameter which may be
been successfully completed, if the Query Limit field
used as described in 10.1 and 10.2 respectively.
contained in the SCC PDU indicated that no more query
requests are allowed, then the ES (or IS) shall clear the
The receipt of an SCC PDU indicates that the
call according to the virtual call clearing procedure
information is complete; if no SCR PDUs are received
specified in ISO/IEC 8208, using cause code 0 and
before the SCC PDU this indicates that no information is
diagnostic code 241. If the Query Limit field does permit
available for the specified Network Address. tf the ES
another request, then the ES (or IS) shall do either (a)
requires information about further Network Addresses, it
or (b) below:
may then repeat the process provided that the Query
Limit field in the SCC PDU specifies that another query
a) it may clear the call immediately, using cause
is allowed. tf the Query Limit field specifies that no
code 0 and diagnostic code 241.
more queries are allowed, the ES shall not transmit any
b) It may retain the call for a time and subsequently
more ECQ PDUs. When the ES has information for all
use it for further data transfer functions as
the Network Addresses it requires, or the Query Limit
specified in 8.2.3 when these functions again
disallows further queries, the configuration collection
become applicable. The maximum time for which
function is successfully complete.
a call may be retained without such further data
tf a time greater than the Response Time parameter
transfer taking place is half the value of the
elapses after transmission of an ECQ PDU and before
Request Time parameter received in the SNC
receipt of the corresponding SCR or SCC PDU, the
PDU. Once this time has elapsed the system (ES
connection shall be abandoned.
or IS) shall clear the call with a cause code 0 and
a diagnostic code 241. The ES is not required to
The following shall also cause the connection to be
retain calls for this maximum time period; instead it
abandoned:
may, as a local choice, clear the call at any
Receipt of any data *Jhich does not contain a valid
a) convenient earlier time, still using cause code 0
SCR or SCC PDU.
and diagnostic code 241. During the time that the
call is retained, the system (ES or IS) shall
Receipt of any PDU before transmission of the first
W
continue to operate it according to the procedures
ECQ PDU, or between receipt of an SCC PDU
specified in ISO/IEC 8208. If a Data, Reset, or
and transmission of the next ECQ PDU.
Interrupt packet is received, it shall clear the call
Receipt of a PDU relating to a Network Address
c) with cause code 0 and diagnostic code 242. in the
other than that for which the ES has transmitted
event that this occurs, or in the event that a Clear
an ECQ PDU on the connection and not received
Indication is received or the operation of
an SCC PDU.
iSO/IEC 8208 procedures results in the call being
cleared, it is a local matter whether and when to
NOTE - A procedure identical to the Configuration Collection
attempt to establish another call according to the
procedure could conceivably be used by an IS-IS protocol. It is
procedures specified in 8.2.1.
not within the scope of this document to discuss this matter.
The choice between (a) and (b), and the length of time
8.2.4 Failed Connection Procedure
for which calls are retained if action (b) is chosen, are
purely local matters and the ES may freely vary them
When a connection fails:
according to internal conditions without impact on
a) If the configuration notification procedure is
interworking.
applicable, then it shall be considered that the
8.4 Use of Configuration Information
notification attempt has failed. (Consequently it
will again be applicable when the time indicated by
This clause applies applies identically to End Systems
the Notification Retry Time paramete
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