SIST ETS 300 048 E2:2003

• Abstract:

  Update of the ETS due to changes since publication; especially new and revised ETSs and ITU-T recommendations

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.080 - Integrated Services Digital Network (ISDN)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI ETS 300 048 ed.2 (1997-12) - Integrated Services Digital Network (ISDN); ISDN Packet Mode Bearer Services (PMBS); ISDN Virtual Call (VC) and Permanent Virtual Circuit (PVC) bearer services provided by the B-channel of the user access - basic and primary rate

SIST ETS 300 048 E2:2003 is the SIST adoption of ETS 300 048 Edition 2 from ETSI for Integrated Services Digital Network (ISDN) Packet Mode Bearer Services (PMBS). It specifies the stage-one service description for ISDN Virtual Call (VC) and Permanent Virtual Circuit (PVC) bearer services carried over the B-channel of the user access at basic and primary rate. In practice, it tells service providers, network planners, and equipment suppliers how the service is offered, accessed, and interworked.

What does SIST ETS 300 048 E2:2003 specify?

SIST ETS 300 048 E2:2003 specifies the stage-one requirements for PMBS-B, meaning the user-facing service description for packet-mode bearer services on the ISDN B-channel. It focuses on how the service is provisioned, invoked, and used, and it ties those service needs to the stage-three procedures in ETS 300 007.

The standard covers both public ISDN operation and the base functionality when the service is provided through a private ISDN. It includes the service profile structure, access methods, call handling, interworking, and the attribute set used to describe the bearer service.

It is organized into nine clauses plus three annexes:

Annex	What it covers
Annex A	Standard service profile for PMBS-B
Annex B	User facilities
Annex C	Default service profile for PMBS-B

The foreword notes that Annexes A and B are normative and Annex C is informative.

What are the key requirements of SIST ETS 300 048 E2:2003?

SIST ETS 300 048 E2:2003 sets out how VC and PVC bearer services are offered over the B-channel, what access methods are allowed, and how the user and network control the access connection. The practical effect is that a supplier has to align subscription, signalling, and X.25 packet handling so the service behaves consistently for users.

Provisioning and service profiles

Clause 5.1 says the service may be provided by prior arrangement or on a general basis. When it is generally available, the default service profile in Annex C applies. Users can subscribe per ISDN number to an access profile and an X.25 service profile, and the network shall at least support the standard X.25 service profile in Annex A.

This matters because the network must be able to map each subscriber to the right access method, notification class, and packet-mode parameters. For PVC use, the X.25 profile may need to be customized.

B-channel access methods

Clause 5.1.2 identifies three B-channel access methods: semi-permanent, switched, and switched long-duration. Semi-permanent access is fixed at subscription time, switched access is established and released on demand based on VC use, and switched long-duration access is user-controlled and is not tied to the first or last VC.

This matters in operation because the access method determines who initiates the B-channel, when it is released, and how stable the packet service is. The standard also states that switched long-duration access can reduce blocking compared with switched access, while improving availability compared with semi-permanent access.

Notification class and incoming calls

Clause 5.1.2.4 limits the usable notification classes for B-channel access to no notification and conditional notification. No notification applies to all B-channel access methods, while conditional notification applies only to switched B-channel access.

In practical terms, a network using conditional notification can alert the subscriber before delivering an incoming packet call. The unconditional notification class is not supported.

Access connection procedures

Clause 5.2 defines the access connection procedures between the Data Terminal Equipment (DTE) and the Packet Handler (PH). These procedures combine layer 1 activation, B-channel establishment, and layer 2 activation, with the details depending on whether the access is semi-permanent, switched, or switched long-duration.

This is important because the service does not work as a pure logical packet service - a physical or semi-permanent access path must be present first. For semi-permanent access, the network maintains layer 2; for switched access, the connection is created when needed and normally released after the last VC; for switched long-duration access, the user keeps the connection up and may need to restore it after failure.

VC and PVC operation

Clause 5.3 separates Virtual Call procedures from Permanent Virtual Circuit procedures. VC operation uses X.25 packet-layer call setup, data transfer, and clearing, and may trigger B-channel establishment if none exists. PVC operation is tied to the subscription state and, when it uses switched long-duration access, the access connection remains in place independently of individual calls.

This matters because VC traffic can be set up dynamically, while PVC traffic depends on pre-established subscription and channel mapping. The standard also says successive incoming calls to the same ISDN number are multiplexed on an already established B-channel.

Terminal selection, identification, and numbering

Clause 5.3.2.1.2 and Clause 5.3.2.2.2 explain that MSN, DDI, calling party number, and calling party subaddress may be used for terminal selection or user profile selection in certain cases. Public networks conforming to this ETS do not provide channel negotiation.

In practice, this means numbering and subscriber identity are part of the service behavior, not just address decoration. For PVCs on switched long-duration access, the user shall have an E.164 number.

Interworking and service attributes

Clause 7 requires full interworking with existing Packet Switched Public Data Network (PSPDN) services and other ISDN VC and PVC services. Clause 9 then defines the service attributes: packet mode, unrestricted transfer, service data unit integrity, bi-directional symmetric communication, point-to-point configuration, and B-channel access.

This gives implementers the technical profile they must match when configuring networks, terminals, and gateways. Clause 9 also points to the layer 1, layer 2, and layer 3 protocol stack used for the service.

What terms does SIST ETS 300 048 E2:2003 define?

SIST ETS 300 048 E2:2003 defines the terms used to describe the service profile, access behavior, and packet handling roles.

• Integrated Services Digital Network (ISDN) - The digital integrated-services network environment in which the bearer service is provided.
• Virtual Call (VC) - An X.25 virtual call used for packet-mode communication.
• Permanent Virtual Circuit (PVC) - An X.25 permanent virtual circuit that stays provisioned rather than being set up per call.
• Packet Handler (PH) - The network function that provides packet handling to terminals and subscribers.
• PMBS-B - The basic ISDN PMBS provided by the B-channel.
• Semi-permanent B-channel - A B-channel established administratively at subscription time and kept available independently of VC/PVC calls.
• Switched B-channel - A B-channel established on demand and normally released after the last VC.
• Switched long-duration B-channel - A B-channel established on demand but kept up independently of the first or last VC.

Who uses SIST ETS 300 048 E2:2003?

SIST ETS 300 048 E2:2003 is used by public telecommunications operators, Packet Handler operators, and private ISDN operators that offer packet-mode services over ISDN. It is also relevant to terminal and network equipment suppliers that need to implement B-channel VC or PVC support.

In practice, they use it to define subscription profiles, choose access methods, set notification behavior, configure LAPB and X.25 parameters, and plan interworking between public and private ISDN environments. It also helps buyers and system integrators check whether a service or platform is intended for VC, PVC, or both.

What changed in SIST ETS 300 048 E2:2003 from the previous edition?

SIST ETS 300 048 E2:2003 is the second edition of ETS 300 048 and updates the earlier edition. The scope says the update reflects changes since publication, especially new and revised ETSs and ITU-T recommendations.

Which standards are used with SIST ETS 300 048 E2:2003?

The standard depends on several referenced documents to define the surrounding ISDN and X.25 framework.

• ETS 300 007 - stage-three support of packet-mode terminal equipment by ISDN; it supplies the procedures this stage-one standard refers to.
• ETS 300 049 - the D-channel counterpart for PMBS VC and PVC services.
• ETS 300 011 and ETS 300 012 - layer 1 specifications and test principles for primary rate and basic user-network interfaces.
• ETS 300 402-2 and ETS 300 403-1 - DSS1 data link and basic call control signalling used for B-channel establishment and release.
• ITU-T Recommendation X.25 - defines the packet-mode call and data procedures, LAPB, and service profile elements.
• ITU-T Recommendation X.31 - the broader ISDN support for packet-mode terminal equipment.
• ITU-T Recommendations I.112, I.130, I.210, and I.232 - vocabulary, service characterization, service description principles, and packet-mode bearer service categories.
• CCITT Recommendations E.164 and E.165 - numbering plan and timing for the ISDN numbering environment.
• ITU-T Recommendations X.1 and X.2 - user classes and optional user facilities that frame the service profile.

What does the SIST ETS 300 048 E2:2003 document contain?

SIST ETS 300 048 E2:2003 contains a clause structure that moves from scope and references into definitions, service description, procedures, charging, interworking, supplementary services, and service attributes. It includes a procedure summary table for the different B-channel access methods and a table of service-attribute variations for the bearer service.

Annex A gives the standard PMBS-B service profile, including LAPB and packet-layer defaults for subscribers who use the standard profile. Annex B lists optional user facilities and marks which are essential, additional, not offered, or subject to conditions for VC and PVC use. Annex C gives a proposed default service profile for users who are not registered with the PH.

SLOVENSKI STANDARD
01-december-2003
Digitalno omrežje z integriranimi storitvami (ISDN) – Paketne nosilne storitve
(PMBS) – Nosilne storitve navideznega klica (VC) in stalnega navideznega voda
(PVC) v sistemu ISDN prek B-kanala uporabniškega dostopa, osnovne in primarne
Integrated Services Digital Network (ISDN); ISDN Packet Mode Bearer Services
(PMBS); ISDN Virtual Call (VC) and Permanent Virtual Circuit (PVC) bearer services
provided by the B-channel of the user access - basic and primary rate
Ta slovenski standard je istoveten z: ETS 300 048 Edition 2
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 048
TELECOMMUNICATION December 1997
STANDARD Second Edition
Source: NA Reference: RE/NA-025106
ICS: 33.020
Key words: Basic, packet mode, PMBS, primary, PVC, UNI, VC
Integrated Services Digital Network (ISDN);
ISDN Packet Mode Bearer Services (PMBS);
ISDN Virtual Call (VC) and Permanent Virtual Circuit (PVC)
bearer services provided by the B-channel of the user access -
basic and primary rate
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail]
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1997. All rights reserved.

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ETS 300 048: December 1997
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 048: December 1997
Contents
Foreword .5
Introduction.5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .8
3.1 Definitions .8
3.2 Abbreviations .9
4 Description .10
5 Procedures.10
5.1 Provision and withdrawal .10
5.1.1 General.10
5.1.2 Access method.10
5.1.2.1 Semi-permanent B-channel access .11
5.1.2.2 Switched B-channel access.11
5.1.2.3 Switched long-duration B-channel access.11
5.1.2.4 Notification class.11
5.1.3 X.25 service profile.12
5.2 Access connection procedures.12
5.2.1 Semi-permanent B-channel access .12
5.2.1.1 Establishment .12
5.2.1.2 Release.13
5.2.2 Switched B-channel access .13
5.2.2.1 Establishment .13
5.2.2.2 Release.13
5.2.3 Switched long-duration B-channel access .13
5.2.3.1 Establishment .13
5.2.3.2 Release.13
5.2.4 Summary of access connection procedures .14
5.3 Normal procedures .14
5.3.1 Activation, deactivation and registration.14
5.3.2 Invocation and operation .14
5.3.2.1 Virtual call procedures .14
5.3.2.1.1 Access connection establishment.14
5.3.2.1.2 Terminal selection and identification.15
5.3.2.1.3 Call establishment .15
5.3.2.1.4 Data transfer .15
5.3.2.1.5 Call release.15
5.3.2.1.6 Access connection release.15
5.3.2.2 Permanent virtual circuit procedures.15
5.3.2.2.1 Access connection establishment.15
5.3.2.2.2 Terminal selection and identification.15
5.3.2.2.3 Call establishment .15
5.3.2.2.4 Data transfer .16
5.3.2.2.5 Call release.16
5.3.2.2.6 Access connection release.16
5.3.3 Interrogation and editing.16
5.4 Exceptional procedures .16
5.4.1 Activation, deactivation and registration.16
5.4.2 Invocation and operation .16

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ETS 300 048: December 1997
5.4.2.1 Invalid invocation. 16
5.4.2.2 Virtual call. 16
5.4.2.3 Permanent virtual circuit . 17
5.4.3 Interrogation and editing . 17
6 Network capabilities for charging. 17
7 Interworking . 17
7.1 Interworking between public networks . 17
7.2 Interworking between private and public ISDNs. 17
7.2.1 Private ISDN providing own PH-Function. 17
7.2.2 Private ISDN not providing own PH-Function. 18
8 Interaction with supplementary services. 18
9 Attributes and values of attributes (including the provision of individual bearer services). 18
9.1 Attributes and values. 18
9.2 Provision of individual bearer services. 20
Annex A (normative): Standard service profile for PMBS-B . 21
Annex B (normative): User facilities. 22
Annex C (informative): Default service profile for PMBS-B . 25
History. 26

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ETS 300 048: December 1997
Foreword
This European Telecommunication Standard (ETS) has been produced by the Network Aspects (NA)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
Annexes A and B are normative, annex C is informative.
Transposition dates
Date of adoption: 19 December 1997
Date of latest announcement of this ETS (doa): 31 March 1998
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 September 1998
Date of withdrawal of any conflicting National Standard (dow): 30 September 1998
Introduction
In accordance with CCITT Recommendation I.130 [13], the following three level structure is used to
describe the supplementary telecommunication services as provided by European public
telecommunications operators under the pan-European Integrated Services Digital Network (ISDN):
- stage 1: is an overall service description, from the user's stand-point;
- stage 2: identifies the functional capabilities and information flows needed to support the service
described in stage 1; and
- stage 3: defines the signalling system protocols and switching functions needed to implement the
service described in stage 1.
This ETS describes the stage one requirements of the ISDN Packet Mode Bearer Services (PMBS)
provided on the B-channel of the user access. Services using the D-channel are covered in
ETS 300 049 [4].
The requirements described in this ETS are applicable only to those services within Europe and are based
upon ITU-T Recommendation I.232 [17].This service description corresponds to case B (B-channel) of
ETS 300 007 [1] (the European equivalent to ITU-T Recommendation X.31 [11]).
The requirements for stage three of these services are contained in ETS 300 007 [1].

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ETS 300 048: December 1997
1 Scope
This European Telecommunication Standard (ETS) defines the stage one of the Packet Mode Bearer
Service (PMBS) provided by the B-channel of the user access for the pan-European Integrated Services
Digital Network (ISDN) as provided by European public telecommunications operators. Stage one is an
overall service description from the user's point of view (see CCITT Recommendation I.130 [13]), but
does not deal with the details of the human interface itself.
This ETS makes use of ETS 300 007 [1], which is a stage three ETS, in order to provide a description of
the procedures. This mechanism would not normally be used in a stage one standard.
In addition this ETS specifies the base functionality where the service is provided to the user via a private
ISDN.
This ETS does not define details of the interworking requirements of private ISDNs with the public ISDN.
This ETS does not specify the additional requirements where the service is provided to the user via a
telecommunications network that is not an ISDN but does include interworking requirements of other
networks with the public ISDN.
Charging principles are outside the scope of this ETS.
The ISDN Virtual Call (VC) and Permanent Virtual Circuit (PVC) bearer service category provides the
unrestricted transfer (without alteration) of user information in a packetized manner over a virtual circuit
between reference points via the basic and primary rate access. Each of the reference points can be
either an S or coincident S and T reference point.
NOTE: Network operators can also provide information transfer with the same attributes
where the reference point is T.
The ISDN VC and PVC bearer service category is described in ITU-T Recommendation I.232 [17].
This ETS is applicable to the stage three standards for the ISDN PMBS. The term "stage three" is also
defined in CCITT Recommendation I.130 [13]. Where the text indicates the status of a requirement,
(i.e. as strict command or prohibition, as authorization leaving freedom, as a capability or possibility), this
shall be reflected in the text of the relevant stage three standards.
Furthermore, conformance to this ETS is met by conforming to the stage three standards with the field of
application appropriate to the equipment being implemented. Therefore no method of testing is provided
for this ETS.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to, or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] ETS 300 007 (1991): "Integrated Services Digital Network (ISDN); Support of
packet-mode terminal equipment by an ISDN".
[2] ETS 300 011 (1992): "Integrated Services Digital Network (ISDN): Primary rate
user-network interface - Layer 1 specification and test principles".
[3] ETS 300 012 (1992): "Integrated Services Digital Network (ISDN): Basic user-
network interface; Layer 1 specification and test principles".
[4] ETS 300 049 (1992): "Integrated Services Digital Network (ISDN); ISDN Packet
Mode Bearer Service (PMBS); ISDN Virtual Call (VC) and Permanent Virtual
Circuit (PVC) bearer services provided by the D-channel of the user access -
basic and primary rate".
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ETS 300 048: December 1997
[5] ETS 300 099 (1992): "Integrated Services Digital Network (ISDN); Specification
of the Packet Handler access point Interface (PHI)".
[6] ETS 300 402-2 (1995): "Integrated Services Digital Network (ISDN); Digital
Subscriber Signalling System No. one (DSS1) User-network interface data link
layer; Part 2: General application protocol specification [ITU-T
Recommendation Q.921 (1993), modified]".
[7] ETS 300 403-1 (1995): "Integrated Services Digital Network (ISDN); Digital
Subscriber Signalling System No. one (DSS1); User-network interface layer 3
specification for basic call control; Part 1: Protocol specification [ITU-T
Recommendation Q.931 (1993), modified]".
[8] ITU-T Recommendation X.1 (1993): "International user classes of service in
public data networks and Integrated Service Digital Networks (ISDNs)".
[9] ITU-T Recommendation X.2 (1993): "International data transmission services
and optional user facilities in public data networks and ISDNs".
[10] ITU-T Recommendation X.25 (1993): "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".
[11] ITU-T Recommendation X.31 (1993): "Support of packet mode terminal
equipment by an ISDN".
[12] ITU-T Recommendation I.112 (1993): "Vocabulary of terms for ISDNs".
[13] CCITT Recommendation I.130 (1988): "Method for the characterization of
telecommunication services supported by an ISDN and network capabilities of
an ISDN".
[14] CCITT Recommendation E.164 (1991): "Numbering plan for the ISDN era".
[15] CCITT Recommendation E.165 (1988): "Timetable for co-ordinated
implementation of the full capability of the numbering plan for the ISDN era
(E.164)".
[16] ITU-T Recommendation I.210 (1993): "Principles of telecommunication services
supported by an ISDN and the means used to describe them".
[17] CCITT Recommendation I.232 (1988): "Packet mode bearer services
categories"
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply:
Integrated Services Digital Network (ISDN): See ITU-T Recommendation I.112 [12], subclause 2.3,
definition 308.
service; telecommunication service: See ITU-T Recommendation I.112 [12], subclause 2.2,
definition 201.
Supplementary Service: See ITU-T Recommendation I.210 [16], subclause 2.4.
Virtual Call, VC: See ITU-T Recommendation X.25 [10], clause 3. Instead of "virtual call" also the term
"X.25" call is used in this ETS.

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ETS 300 048: December 1997
Permanent Virtual Circuit (PVC): see ITU-T Recommendation X.25 [10], clause 3.
customized service profile: A set of individual service data allocated per ISDN-number for a period of
time to a subscriber registered at the Packet Handler (PH). This data includes:
- an access profile: ETS 300 007 [1]-related data (e.g. notification class, access method);
- an X.25 service profile: ITU-T Recommendation X.25 [10], layer 2 and 3 related data.
standard service profile: A set of service data predefined at the PH for subscribers not requiring a fully
individual service profile. The standard service profile comprises just the ITU-T
Recommendation X.25 [10]-related data. The other part of the service data (the access profile) can still be
allocated individually at subscription time.
See annex A for the standard service profile applicable for users subscribing to B-channel access.
default service profile: A set of service data which applies for subscribers not registered at the PH. This
default service profile may be network specific, and includes both, the ETS 300 007 [1]-related data
(access profile) and ITU-T Recommendation X.25 [10]-related data (X.25 service profile).
See annex C for the proposed default service profile.
Packet Handler (PH): See ETS 300 007 [1].
PMBS-B: Basic ISDN PMBS provided by the B-channel.
semi-permanent B-channel: A B-channel established by OAM-procedures at subscription, independent
of ITU-T Recommendation X.25 [10] calls; not to be released after last virtual call.
switched long-duration B-channel: A B-channel established by ETS 300 403-1 [7] signalling
procedures, independent of ITU-T Recommendation X.25 [10] calls; not to be released after the last
virtual call.
switched B-channel: A B-channel established on-demand by ETS 300 403-1 [7] signalling procedures,
dependent of ITU-T Recommendation X.25 [10] virtual calls; normally to be released after the last virtual
call.
ISDN number: A number conforming to the numbering plan and structure specified in CCITT
Recommendation E.164 [14].
party number: As ISDN number.
party subaddress: See CCITT Recommendation E.164 [14], subclause 11.2.
3.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
CUG Closed User Group
DDI Direct Dialling In
DTE Data Terminal Equipment
ISDN Integrated Services Digital Network
LAPB Link Access Procedure Balanced
MSN Multiple Subscriber Number
OSI Open Systems Interconnection
PH Packet Handler
PMBS Packet Mode Bearer Services
PSPDN Packet Switched Public Data Network
PTN Private Telecommunication Network
PVC Permanent Virtual Circuit
TA Terminal Adaptor
TE Terminal Equipment
VC Virtual Call
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4 Description
This service is described for both the point-to-multipoint and point-to-point configurations. This covers the
passive bus and NT2 access arrangements.
These packet mode bearer services allow users (e.g. terminals) in a point-to-point communication
configuration to communicate via the ISDN using ITU-T Recommendation X.25 [10] encoding, by means
of procedures over a B-channel in both directions continuously and simultaneously, for the duration of a
call as described in ETS 300 007 [1] (ITU-T Recommendation X.31 [11]). User class 30 as described in
ITU-T Recommendation X.1 [8] is supported.
NOTE: In case of access via a Terminal Adaptor (TA), the following user classes are
supported at the R-reference point: 8-13 (see ITU-T Recommendation X.1 [8]).
5 Procedures
5.1 Provision and withdrawal
5.1.1 General
The ISDN VC and PVC bearer services shall be either provided by prior arrangement with the service
provider or be available on a general basis. In the latter case, a default service profile applies
(see annex C for a PMBS-B default service profile).
Networks may offer either or both B-channel and D-channel VC- and PVC-bearer services on a general
basis.
The user may subscribe, on a per ISDN number basis, to:
- an Access Profile (AP). The AP consists of ETS 300 007 [1] related service data and includes the
access method and the notification class;
an X.25 Service Profile. The X.25 service profile consists of ITU-T Recommendation X.25 [10]
layer 2 and layer 3 related service data. The user may subscribe to a customized (essential for PVC
operation) X.25 service profile or to a standard service profile offered by the network. The network
shall at least support the standard ITU-T Recommendation X.25 [10] service profile as described in
annex A.
NOTE: The subscription to more than one B- or D-channel access method or ITU-T
Recommendation X.25 [10] service profile per ISDN number is recognized as a
possibility, but not described further on in this ETS. Concurrent subscription to the
switched (see subclause 5.1.2.2) and to the switched long-duration
(see subclause 5.1.2.3) access method is not possible as there are no means for the
network to recognize at call setup, which type of access the subscriber is requesting.
5.1.2 Access method
The access method defines the method of establishment and release of a connection between the user
and PH which gives access to the ISDN VC and PVC service.
The network may offer a subset of the access methods using the B- or D-channel, to which the user can
subscribe. Only access methods using the B-channel are within the scope of this ETS For access
methods using the D-channel, refer to ETS 300 049 [4].
Only B-channel access methods according to ETS 300 007 [1] Case B are described in this ETS. Case A
access methods are exclusively described in ETS 300 007 [1].

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ETS 300 048: December 1997
5.1.2.1 Semi-permanent B-channel access
The B-channel access connection is permanently available, independent of ITU-T
Recommendation X.25 [10] VC/PVCs.
The user may subscribe to multiple instances of this access method. For each of them:
- a B-channel timeslot on the ISDN access shall be assigned at subscription time;
- a customized Link Access Procedure Balanced (LAPB) profile (see ITU-T
Recommendation X.25 [10], subclause 2.4.8) and logical channel range (ITU-T
Recommendation X.25 [10], annex A) may be subscribed to in addition. This overrules the
corresponding part of the X.25 service profile that relates to the ISDN number.
NOTE: The logical channel range defines the logical channels to be used for PVCs and hence
includes possible subscription to PVC services.
5.1.2.2 Switched B-channel access
The switched B-channel access connection is established (released) on-demand, by means of
ETS 300 403-1 [7] signalling procedures, depending on the first/last virtual call (X.25 virtual call), using
this channel.
Subscription to or general availability of the switched B-channel access method implies subscription to or
general availability of the basic service PMBS-B (as specified in ETS 300 007 [1]).
The user may subscribe to a maximum number N of switched B-channel connections, on a per ISDN
number basis.
5.1.2.3 Switched long-duration B-channel access
The switched long-duration B-channel access connection is established (released), by means of
ETS 300 403-1 [7] signalling procedures, under control of the user and independent of the first/last virtual
call (X.25 virtual call), using this channel.
NOTE: This long-duration access connection:
- reduces the blocking probability of the VC service, as compared to the switched
access, because the connection will in general already exist before any VC is
established;
- increases the availability of the VC service, as compared to the semi-permanent
access, because it does not depend upon administrative intervention in case of
connection failure.
Subscription to the switched long-duration B-channel access method implies subscription to a basic
service, characterized by the B-channel packet mode bearer capability (as specified in ETS 300 007 [1]).
The user may subscribe to a maximum number N of switched long-duration B-channel connections, on a
per ISDN number basis. However, when the X.25 service profile includes PVC subscription, then this
maximum number shall be one.
NOTE: This is necessary because the mapping of PVCs on multiple on-demand access
connections is ambiguous.
5.1.2.4 Notification class
Out of the three notification classes defined in ETS 300 007 [1] for notification of the user of incoming
packet calls, two classes are applicable for use with the B-channel access methods: the "no notification"
and the "conditional notification" classes.

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The "no notification" class applies to all B-channel access methods. No ETS 300 403-1 [7] signalling
procedures are used to notify the user of incoming calls. An incoming call packet will directly be delivered
over an existing access connection.
The "conditional notification" class can be subscribed to for switched B-channel access method only.
ETS 300 403-1 [7] call offering procedures may be used to notify the subscriber of an incoming packet
call. A switched B-channel access connection may then be established before i
...