SIST ETS 300 399-1 E1:2003

SLOVENSKI STANDARD
01-december-2003
Storitev blokovnega posredovanja – 1. del: Splošni opis
Frame relay services; Part 1: General description
Ta slovenski standard je istoveten z: ETS 300 399-1 Edition 1
ICS:
33.040.01 Telekomunikacijski sistemi Telecommunication systems
na splošno in general
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 300 399-1
TELECOMMUNICATION March 1995
STANDARD
Source: ETSI TC-NA Reference: DE/NA-023216-1
ICS: 33.080
ISDN, frame relay, stage 1
Key words:
Frame relay services;
Part 1: General description
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - secretariat@etsi.fr
X.400: Internet:
Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
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 1995. All rights reserved.
New presentation - see History box

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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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Contents
Foreword .7
Introduction.7
1 Scope .9
2 Normative references.9
3 Definitions.10
4 Symbols and abbreviations .13
5 General definition .13
6 Description of the frame relay service.13
6.1 General description.13
6.1.1 Characteristics of the frame relay service .13
6.1.2 Core functions .14
6.2 Applications.15
7 Service classes .15
7.1 Layer 2 characteristics.15
7.1.1 Layer 2 permanent .15
7.1.2 Layer 2 on-demand case A .15
7.1.3 Layer 2 on-demand case B .15
7.2 Layer 1 characteristics.16
7.2.1 Layer 1 permanent .16
7.2.2 Layer 1 on-demand .16
8 Procedures.16
8.1 Provision/withdrawal .16
8.2 Normal procedures, invocation and operation .16
8.2.1 On-demand virtual circuit procedures .16
8.2.1.1 Originating the service (call set-up) .17
8.2.1.2 Indications during call set-up .17
8.2.1.3 Terminal selection/identification .17
8.2.1.4 Call notification .17
8.2.1.5 Synchronization between C-plane and U-plane.17
8.2.1.6 Terminating the virtual circuit (call clearing) .18
8.2.2 Permanent virtual circuit procedures.18
8.2.2.1 Layer 1 activation/establishment .18
8.2.2.2 Terminal selection/identification .18
8.2.2.3 Virtual circuit establishment.18
8.2.2.4 Terminating the virtual circuit.18
8.2.3 Data transfer.18
8.2.3.1 Regular procedures .18
8.2.3.2 Congestion management and control.19
8.3 Exceptional procedures, invocation and operation .20
8.3.1 On-demand virtual circuit .20
8.3.2 Permanent virtual circuit.20
9 Network capabilities for charging .20
10 Interworking.20
11 Attributes and values of attributes.20

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12 Dynamic description . 21
13 Numbering plan . 21
Annex A (normative): Support of the OSI network layer service . 22
A.1 General. 22
A.2 Connection establishment and release . 22
A.3 Data transfer. 23
A.4 Interworking . 23
A.5 Co-ordination of C-plane and U-plane. 23
Annex B (normative): Core service description . 24
Introduction . 24
B.1 Definitions. 24
B.1.1 OSI reference model definitions. 24
B.1.2 Service conventions definitions. 24
B.2 Definition of the core service . 25
B.2.1 Scope . 25
B.2.2 Overview of the core service. 25
B.2.3 Features of the core service. 25
B.2.4 Model of the core service . 26
B.2.4.1 Core connection endpoint identification. 26
B.2.4.2 Model of the core connection. 26
B.2.4.3 Queue model concepts. 26
B.2.4.4 Core connection establishment . 27
B.2.4.5 Data transfer. 27
B.2.4.6 Core connection release. 27
B.2.5 Sequence of primitives at one core connection endpoint. 27
B.2.6 Data transfer primitives . 27
B.2.6.1 Service primitives and parameters . 28
B.2.6.1.1 Primitives: Core-DATA-request and
Core-DATA-indication . 28
B.2.6.1.2 Parameters . 28
B.2.6.1.2.1 Core-user-data . 28
B.2.6.1.2.2 Congestion . 28
B.2.6.1.2.3 Discard eligibility. 28
B.2.6.1.2.4 Core service user protocol control
information . 29
B.2.6.1.3 Sequence of primitives. 29
B.2.7 Quality of service. 29
B.2.7.1 Throughput . 30
B.2.7.2 Transit delay . 30
Annex C (normative): Congestion management for the frame relay service. 31
C.1 Congestion management principles . 31
C.1.1 Scope . 31
C.1.2 Objectives of congestion management. 31
C.1.3 Requirements of congestion control mechanisms . 32
C.1.4 Congestion management strategy . 32
C.1.4.1 Congestion control mechanisms . 33
C.1.4.1.1 Explicit congestion notification . 33
C.1.4.1.2 Discard eligibility. 33
C.1.4.2 Network response to congestion . 33
C.1.4.3 User response to congestion. 34

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C.1.4.3.1 Terminals employing destination controlled transmitters.35
C.1.4.3.2 Terminals employing source controlled transmitters .35
Annex D (informative): Bibliography.38
History.39

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Foreword
This European Telecommunication Standard (ETS) has been produced by the Network Aspects (NA)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
The content of this ETS is adapted from the CCITT Recommendation I.233.1 [2].
This ETS consists of 4 parts as follows:
Part 1: "Part 1: General description".
Part 2: "Part 2: Integrated Services Digital Network (ISDN); Frame relay bearer service; Service
definition".
Part 3: "Part 3: Integrated Services Digital Network (ISDN); Frame relay data transmission service;
Service definition".
Part 4: "Part 4: Broadband Integrated Services Digital Network (B-ISDN); Frame relay bearer
service; Service definition".
Transposition dates
Date of latest announcement of this ETS (doa): 30 June 1995
Date of latest publication of new National Standard 31 December 1995
or endorsement of this ETS (dop/e):
Date of withdrawal of any conflicting National Standard (dow): 31 December 1995
Introduction
The purpose of this ETS is to describe the frame relay service. The definition and description of this
service forms the basis to define the network capabilities required for the support of the service. The
prose description begins with clause 5, the static description begins with clause 11. No dynamic
description is provided.
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1 Scope
This European Telecommunication Standard (ETS) specifies the general aspects of the frame relay
service that is common to all frame relay services independent of the network on which the service is
offered.
This ETS is applicable for all network-specific frame relay service definitions.
This ETS should be complemented with standards for the network-specific part of the frame relay service.
2 Normative references
This ETS incorporates by dated and 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] CCITT Recommendation E.164: "Numbering plan for the ISDN era".
[2] CCITT Recommendation I.233.1: "ISDN frame relaying bearer service".
[3] ITU-T Recommendation I.500: "General structure of the ISDN Interworking
Recommendations".
[4] CCITT Recommendation Q.922: "ISDN data link layer specification for frame
mode bearer services".
[5] ITU-T Recommendation Q.933: "Layer 3 signalling specification for frame mode
bearer service".
[6] ITU-T Recommendation X.25: "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".
[7] ITU-T Recommendation X.31: "Support of packet mode terminal equipment by
an ISDN".
[8] CCITT Recommendation X.121: "International numbering plan for public data
networks".
[9] ITU-T Recommendation X.134: "Portion boundaries and packet layer reference
events: basis for defining packet-switched performance parameters".
[10] ITU-T Recommendation X.140: "General quality of service parameters for
communication via public data networks".
[11] CCITT Recommendation X.200: "Reference Model of Open Systems
Interconnection for CCITT applications".
[12] ITU-T Recommendation X.210: "Open Systems Interconnection layer service
definition conventions".
[13] ITU-T Recommendation X.213: "Information technology - Network service
definition for Open Systems Interconnection".
[14] CCITT Recommendation X.300: "General principles for interworking between
public networks and between public networks and other networks for the
provision of data transmission services".
[15] Addendum 1 to ISO 8348 (1987): "Connectionless mode transmission".

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[16] ISO 8473: "Information processing systems - Data communications - Protocol
for providing the connectionless-mode network service".
3 Definitions
For the purposes of this ETS, the following definitions apply:
access rate: The data rate of the physical connection at the user-network interface. The speed of the
physical connection determines how much data (maximum rate) the end-user can inject into the network.
Forward Explicit Congestion Notification (FECN): See CCITT Recommendation Q.922 [4] for the full
definition.
Backward Explicit Congestion Notification (BECN): See CCITT Recommendation Q.922 [4] for the full
definition.
Consolidated Link Layer Management Message (CLLM): See CCITT Recommendation Q.922 [4] for
the full definition.
Committed Burst size (B ): The maximum committed amount of data a user may offer to the network
C
during a time interval T . B is negotiated at virtual circuit establishment.
C C
Committed rate measurement interval (T ): The time interval during which the user is allowed to send
C
only the committed amount of data (B ) and the excess amount of data (B ). T is computed.
C E C
Committed Information Rate (CIR): The information transfer rate which the network is committed to
transfer under normal conditions. The rate is averaged over a minimum increment of time T . CIR is
C
negotiated at virtual circuit establishment.
congestion management: This includes: network engineering; Operation, Administration and
Maintenance (OAM) procedures to detect the onset of congestion; and real time mechanisms to prevent
or recover from congestion. Congestion management includes, but is not limited to; congestion control,
congestion avoidance and congestion recovery, as defined below:
- congestion control: this refers to real-time mechanisms to prevent and recover from congestion
during periods of coincidental peak traffic demands or network overload conditions (e.g. resource
failures). Congestion control includes both congestion avoidance and congestion recovery
mechanisms;
- congestion avoidance: congestion avoidance procedures refer to procedures initiated at or prior
to the onset of mild congestion in order to prevent congestion from becoming severe. Congestion
avoidance procedures operate around and within the regions of mild congestion and severe
congestion;
- congestion recovery: congestion recovery procedures refer to procedures initiated to prevent
congestion from severely degrading the end-user perceived Quality of Service (QoS) delivered by
the network. These procedures are typically initiated when the network has begun to discard frames
due to congestion. Congestion recovery procedures operate around and within the region of severe
congestion.
core service: See CCITT Recommendation Q.922 [4], annex A for the full definition.
C-plane: The C-plane refers to the data exchanged across a user-network interface for establishment,
release, monitoring, etc. of virtual circuits that are carried out outside the virtual circuits' data transmission.
delivered duplicated frames: A frame D received by a particular destination user is defined to be a
duplicated frame if both of the following conditions are true:
- frame D was not generated by the source user;
- frame D is exactly the same as a frame that was previously delivered to that destination.

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delivered errored frames: A delivered frame is defined to be an errored frame when the values of one or
more of the bits in the frame is in error, or when some, but not all, bits in the frame are lost bits or extra
bits (i.e. bits which were not present in the original signal) have been inserted (see
ITU-T Recommendation X.140 [10]).
delivered out-of-sequence frames: Consider a sequence of frames F , F , F , . , F and assume that
1 2 3 n
F is transmitted first, F second, . , F last.
1 2 n
A delivered frame F is defined to be out-of-sequence if it arrives at the destination after any of the frames
i
F , F , . , F .
(i+1) (i+2) n
discard eligibility indicator: This indicates that a frame should be discarded in preference to other
frames in a congestion situation, when frames need to be discarded to ensure safe network operation and
to maintain the committed level of service within the network.
egress node: The node that supports the destination user-network interface.
Excess Burst size (B ): The maximum allowed amount of data by which a user can exceed B during a
E C
time interval T . This data (B ) is delivered in general with a lower probability than B . B is negotiated at
C E C E
virtual circuit establishment.
fairness: An attempt by the network to maintain the committed call parameters which the end-user
negotiated at call set-up time. An example of this would be first discarding the frames in excess of the CIR
and refusing to allow new call set-ups to occur prior to discarding committed data traffic.
information integrity: Information integrity is preserved when for all frames delivered by the network no
transmission errors have been detected.
ingress node: The node that supports the source user-network interface.
lost frames: A transmitted frame is declared to be a lost frame when the frame is not delivered to the
intended destination user within a specified timeout period, and the network is responsible for the non-
delivery (see ITU-T Recommendation X.140 [10]).
misdelivered frames: A misdelivered frame is a frame transferred from a source to a destination user
other than the intended destination user. It is considered inconsequential whether the information is
correct or incorrect in content (see ITU-T Recommendation X.140 [10]).
offered load: Refers to the frames offered to the network, by an end-user, to be delivered to the selected
destination. The information rate offered to the network could exceed the negotiated class of service
parameters.
residual error rate: The residual error rate is defined for frame relay services and the corresponding layer
services. The layer services corresponding to the frame relay services are characterized by the exchange
of Service Data Units (SDUs). For frame relay, SDUs are exchanged at the functional boundary between
the core functions of CCITT Recommendation Q.922 [4] and the end-to-end protocol implemented above
them. The network participates in this exchange by means of FPDUs.
The residual error rate for the frame relay layer service is defined as:
Total correct SDUs delivered
=−1
R
fr
Total offered SDUs
The residual error rate for frame relay is defined as:
Total correct SDUs delivered
=−1
R
fr
Total offered FPDUs
statistical guarantee on traffic parameters: The QoS level for committed traffic characterized by the
CIR, B , and T parameters may be guaranteed with a certain probability. The QoS level for excess traffic
C C
characterized by the supplementary parameter B may also be guaranteed with a certain probability.
E
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The values of these probabilities are network dependent.
These statistical guarantees may only be verified over an observation period which is:
- sufficiently long with respect to T ;
C
- constraining for the network; and
- significant for the user.
As an example, the "busy hour" (in terms of traffic load) of the network may be used for this purpose.
throughput: Throughput for a virtual circuit (see ITU-T Recommendation X.134 [9], figure 1/X.139) is the
number of data bits contained in the SDU of the frame successfully transferred in one direction across the
virtual circuit per unit time. Successful transfer means that, for each frame, no transmission errors have
been detected.
transit delay: Transit delay is defined only between pairs of section boundaries. Transit delay of a Frame
relay Protocol Data Unit (FPDU) starts at the time t at which the first bit of the FPDU crosses the first
boundary, and ends at the time t at which the last bit of the FPDU crosses the second boundary:
transit delay = t - t
2 1.
Transit delay for a virtual circuit is equal to the summation of the section delays.
Figure 1: International reference frame relay connection
U-plane: The U-plane refers to the data exchanged across a user-network interface for the data transfer
on one or more virtual circuits.
virtual circuit: The term "virtual circuit" refers to a layer 2 virtual circuit, i.e. a frame relay virtual circuit.

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4 Symbols and abbreviations
For the purpose of this ETS, the following symbols and abbreviations apply:
BECN Backward Explicit Congestion Notification
B-ISDN Broadband Integrated Services Digital Network
B Committed Burst size
C
B Excess Burst size
E
CEI Connection Endpoint Identifier
CIR Committed Information Rate
CLLM Consolidated Link Layer Management Message
CONS OSI Connection Oriented Network layer Service
CPDU Core Protocol Data Unit
CSAP Core Service Access Point
CSDU Core Service Data Unit
DLCI Data Link Connection Identifier
ECN Explicit Congestion Notification
FECN Forward Explicit Congestion Notification
FPDU Frame relay Protocol Data Unit
ISDN Integrated Services Digital Network
LAN Local Area Network
NSAP OSI Network Service Access Point
OAM Operation, Administration and Maintenance
OSI-NS OSI Network layer Service
PSPDN Packet Switched Public Data Network
QoS Quality of Service
SDU Service Data Unit
T Committed rate measurement interval
C
X.25 DTP ITU-T Recommendation X.25 [6] Data Transfer Protocol
5 General definition
The frame relay service provides the bi-directional transfer of data units (Core-Service Data Unit (CSDU))
from one user-network interface to another. The data units are routed through the network on the basis of
an attached label. This label is a logical identifier with local significance (termed Data Link Connection
Identifier (DLCI) in the protocol description). Per DLCI, the order of the data units is preserved from one
user-network interface to another.
The user-network interface allows for the establishment of multiple on-demand and/or permanent virtual
circuits to many destinations.
This service description shows how the OSI network layer service can be supported (see annex A).
6 Description of the frame relay service
6.1 General description
6.1.1 Characteristics of the frame relay service
The frame relay service has the following characteristics:
1) all C-plane procedures, if needed, are performed in a logically separate manner using protocol
procedures that are network dependent and are specified in the network specific frame relay
service definition (e.g. in ETS 300 399-2);
2) the U-plane procedures at layer 1 are network dependent. Layer 2 procedures are based on the
core functions as defined in annex B (see also subclause 6.1.2). These layer 2 core functions allow
for the statistical multiplexing of user information flows immediately above layer 1 functions.

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The frame relay service:
a) preserves the order of SDUs transmitted at one user-network interface when they are delivered at
the other end;
NOTE: Since the network does not support any procedure above the core functions, the
network cannot use information in the frame to preserve the order of SDUs.
Nevertheless, networks are implemented in such a way that the frame order is
preserved.
b) detects transmission, format, and operational errors (e.g. frames with an unknown label);
c) transports frames transparently, only the label and, hence, the bit error detection information may
be modified by the network;
d) does not acknowledge frames.
The functions above are based on the core functions. It provides service quality that is characterized by
the values of the following parameters:
- throughput;
- access rate;
- CIR;
- committed burst size;
- excess burst size;
- transit delay;
- residual error rate;
- delivered errored frames;
- delivered duplicated frames;
- delivered out-of-sequence frames;
- lost frames;
- misdelivered frames.
6.1.2 Core functions
The core functions are:
- frame delimiting, alignment and transparency;
- frame multiplexing/demultiplexing using the label (DLCI);
- inspection of the frame to ensure that it consists of an integer number of octets;
- inspection of the frame to ensure that it is neither too long nor too short;
- detection of transmission errors;
- congestion control functions.

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6.2 Applications
The frame relay service specified in this ETS aims to support a wide range of data applications and rates
from very low to high (including Broadband Integrated Services Digital Network (B-ISDN)). A typical
application may be the interconnection of Local Area Networks (LANs).
7 Service classes
The service classes are defined per physical connection; not all service classes may be offered
simultaneously on a single physical connection. If a network provides at the user-network interface more
than one physical connection (e.g. more than one B-channel in an Integrated Services Digital Network
(ISDN)), several service classes per physical connection may co-exist at a user-network interface. Not all
service classes are supported on all networks.
The service classes are summarized in table 1.
Table 1: Frame relay service classes
Class Characteristic References
P Layer 2 permanent (permanent virtual call) subclause 7.1.1
1 Layer 1 permanent subclause 7.2.1
a with Q.933, annex A connection monitoring
b with Q.933, annex B connection monitoring
2 Layer 1 on-demand subclause 7.2.2
a with Q.933, annex A connection monitoring
b with Q.933, annex B connection monitoring
A On-demand case A subclause 7.1.2
1 Layer 1 permanent subclause 7.2.1
2 Layer 1 on-demand subclause 7.2.2
B On-demand case B subclause 7.1.3
1 Layer 1 permanent subclause 7.2.1
2 Layer 1 on-demand subclause 7.2.2
Q.933 = ITU-T Recommendation Q.933 [5].
7.1 Layer 2 characteristics
7.1.1 Layer 2 permanent
The layer 2 connection is established for a period of time. No change in the profile is possible. If the layer
1 characteristic is different from "permanent", the layer 2 connection may also be suspended.
7.1.2 Layer 2 on-demand case A
Case A is defined in ITU-T Recommendation Q.933 [5]. It implies a signalling link with a DLCI value "0" on
the same physical connection. Signalling on this data link, defined according to ITU-T Recommendation
Q.933 [5], is deployed to establish and release layer 2 connections.
7.1.3 Layer 2 on-demand case B
Case B is defined in ITU-T Recommendation Q.933 [5]. It implies signalling on a network dependent
physical connection. The network dependent signalling procedures are deployed to establish and release
layer 2 connections.
NOTE: The physical connection used for the case B signalling may also be used to carry
frame relay traffic (e.g. D-channel in ISDN).

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7.2 Layer 1 characteristics
7.2.1 Layer 1 permanent
The layer 1 connection is established for a period of time. The network shall ensure that the physical
connection remains established.
7.2.2 Layer 1 on-demand
The physical connection can be released by the terminal equipment. In addition, the network releases the
physical connection after a timer expiry after the release of the last virtual circuit on the physical
connection; a signalling link, if it exists, is cleared before the release of the physical connection. The
network may also release the physical connection in case of a severe error situation. The network does
not attempt to (re-)establish the physical connection. The timer may be set to "infinity", i.e. it may never
expire.
8 Procedures
8.1 Provision/withdrawal
The frame relay service is offered with several subscription options which apply separately to each
network number (e.g. CCITT Recommendation E.164 [1] or CCITT Recommendation X.121 [8] number)
or group of network numbers on the interface. For each subscription option, only one value can be
selected. Subscription options for the interface are summarized below:
- general subscription to the frame relay service (some networks may not require specific
subscription as the frame relay service may be offered as a default for general subscription);
- subscription to the frame relay service with a user defined profile (the DLCI length and convention is
also agreed at subscription time - a single convention applies per user-network interface);
- subscription to the conveyance of subaddresses for terminal selection and/or conveyance of NSAP
addresses for support of the OSI network layer service;
- subscription to supplementary services as may be required for terminal selection purposes.
In general, there will be a limit on the number of virtual circuits available at the user-network interface:
- maximum number of total virtual circuits present per user-network interface;
- maximum number of total virtual circuits present per physical connection.
8.2 Normal procedures, invocation and operation
All user-network signalling takes place using logically separate messages.
The layer 1 protocol for the U (user) and C (control) planes is network dependent. The C-plane uses either
a separate physical connection dedicated to signalling. It may also share the physical connection with
other virtual circuits; in such cases, C-plane messages are distinguishable from virtual circuits by a
reserved DLCI (label). For permanent virtual circuits, no real time call establishment is necessary and any
parameters are agreed upon at subscription time. Depending on the network, the U-plane may use
different types of physical connections (e.g. D-channels, B-channels, or H-channels on ISDN) on which
the user implements the core functions of annex B.
On-demand and permanent virtual circuit procedures can be invoked and operated concurrently by a
given terminal. However, not all service classes can be supported concurrently on a single user-network
interface.
8.2.1 On-demand virtual circuit procedures
Before procedures for originating the service are invoked, a physical connection and a reliable data link
connection for signalling shall be established.

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8.2.1.1 Originating the service (call set-up)
The call is originated by the subscriber requesting from the network the required service with this request
including a number identifying the called user. Other information required for the service and additional
information (e.g. calling line identification) may also be included.
There are two possible physical channel access arrangements:
- on-demand establishment of the physical connection;
- permanent establishment of the physical connection or use of an already existing physical
connection.
In the first arrangement, if a physical connection is not established, or already established channels have
no free capacity, another physical connection (if available) is established using the network dependent
signalling procedures. Depending on the signalling capabilities of the network, the physical connection
may be requested simultaneously with the establishment of the first virtual circuit.
NOTE: Some networks may only provide for one physical connection per user-network
interface.
In the second arrangement, no dynamic establishment procedure is required.
Once a physical connection has been established either dynamically or permanently then, in the
on-demand virtual circuit case, the values of the logical identifier and the other associated parameters, as
defined in clause 6, shall be negotiated during the call set-up by means of C-plane procedures. Depending
on the parameters requested, the network can either accept or reject the call.
As a network option, the user-network interface shall allow for the establishment of multiple on-demand or
permanent virtual circuits to one or more destinations.
8.2.1.2 Indications during call set-up
If interworking takes place an indication of such interworking is required. The user can then decide
whether to proceed with the interworking or to clear the call (see clause 10 and ITU-T Recommendations
of the I.500 [3] and CCITT Recommendations of the X.300 [14] series).
Annex A provides for indications specific to the support of the OSI network service.
8.2.1.3 Terminal selection/identification
Terminal selection and identification are network dependent. Supplementary services as well as
subaddressing are methods applicable to terminal selection and identification.
NOTE: Some networks may not provide for terminal selection and identification.
8.2.1.4 Call notification
Network dependent signalling procedures are used to notify the user of incoming calls.
NOTE: Some networks allow the called user to request that a call be offered on a specific
physical connection from a choice of physical connections. For load sharing purposes,
networks may also deploy supplementary services, e.g. hunt groups.
8.2.1.5 Synchronization between C-plane and U-plane
In some cases, there is a gap between the time a connection confirmation is received and when the actual
virtual circuit is established. It may be necessary to verify the virtual circuit prior to the beginning of the
data transfer. This should be accomplished end-to-end in the U-plane.

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8.2.1.6 Terminating the virtual circuit (call clearing)
When the call is cleared all resources used by the call are cleared (e.g. label, call reference value, etc.). In
the on-demand physical connection establishment arrangement, if no calls are present and if the user or
network so desires, either the user or the network may clear the physical connection.
If the network desires, it may deactivate the C-plane layer 2 and layer 1 connections.
NOTE: Not all access arrangements have a defined deactivated state of the user-network
interface.
In the permanent physical connection access arrangement, the network or user may only deactivate the
C-plane layer 2 connection.
The virtual circuit may be cleared by either or both of the users by indicating this to the network. In either
case, an appropriate indication is sent to the other user. The network may terminate the call for several
reasons (e.g. severe congestion, error or failure conditions).
8.2.2 Permanent virtual circuit procedures
For permanent virtual circuits, there is no call set-up or clearing. A physical connection to the network
node needs to be in place. The logical identifier and the other associated parameters for the virtual circuit
are defined by means of administrative procedures.
8.2.2.1 Layer 1 activation/establishment
The layer 1 physical connection may be permanently active. Such a channel is established at subscription
time.
Alternatively, the physical connection may be established on-demand. Either the user and/or the network
may release the physical connection (the network bases this decision on an inactivity timer).
In general, the status of the virtual circuits is monitored either via ITU-T Recommendation Q.933 [5],
annex A or B procedures.
NOTE: ITU-T Recommendation Q.933 [5], annex A procedures are only applicable if no other
signalling procedures are in effect for the physical connection.
8.2.2.2 Terminal selection/identification
No terminal selection or identification procedures are applicable as the terminal has been fixed at
subscription time.
8.2.2.3 Virtual circuit establishment
Not applicable.
8.2.2.4 Terminating the virtual circuit
Not applicable.
8.2.3 Data transfer
8.2.3.1 Regular procedures
Frame relay data units are frames as defined in the core service (annex B). The basic frame relay service
provided by the network is the unacknowledged transfer of frames between two user-network interfaces.
The frame size supported by this service is determined by:
a) the default maximum information field to be supported by all networks is 1 600 octets;

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ETS 300 399-1: March 1995
b) all other values are negotiated between users and networks and between networks;
c) certain physical connections (e.g. D-channel in ISDN) may restrict the maximum information field
size to less than 1 600 octets.
Figure 2 illustrates the U-plane configuration for this service. Protocol functions up to and including layer 3
are shown. The network does not terminate the full layer 2 protocol; it offers the core service as defined in
annex B. The virtual circuits are used to implement the core service; the protocols for the network
dependent implementation are indicated in the network specific frame relay service definition (e.g. in
ETS 300 399-2).
User-network interface User-network interface
User specified User specified
Layer 3 and higher Layer 3 and higher
User specified User specified
(note 1) (note 1)
Layer 2 (upper) CO RE SERVICE CO RE SERVICE Layer 2 (upper)
CSAP CSAP
Core Core Core
Layer 2 (lower) Layer 2 (lower) Layer 2 (lower)
Physical Physical Physical
NOTE 1: CCITT Recommendation Q.922 [4] is one protocol which may be used. Other standard
or proprietary protocols may be used.
NOTE 2: Protocols to support the core service are network dependent. The particular protocol to
be used is defined, for example, in ETS 300 399-2.
Figure 2: U-plane configuration
The core service can be offered on a variety of access arrangements. Frame size restrictions apply, e.g.
when in an end-to-end connection at least one of the access channels is the ISDN D-channel (16 kbit/s or
64 kbit/s).
The data transfer phase of the OSI Connection Oriented Network layer Service (CONS)/(see
ITU-T Recommendation X.213 [13]) can be provided by using ITU-T Recommendation X.25 [6] Data
Transfer Protocol (X.25 DTP), appropriate ISO layer 2/3 protocols or a convergence protocol above
CCITT Recommendation Q.922 [4]. In the latter case, only the mandatory features of the network service
as defined in ITU-T Recommendation X.213 [13] are provided. Even though all these arrangements are
permitted, the combination of CCITT Recommendation Q.922 [4] and X.25 DTP protocol
...