SIST ETS 300 467 E1:2003

• Abstract:

  Study & define all aspects necessary to offer FRBS on B-ISDN

• 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 300 467 ed.1 (1998-03) - Broadband Integrated Services Digital Network (B-ISDN); Support of Frame Relay Bearer Service (FRBS) in B-ISDN and frame relay interworking between B-ISDN and other networks

SIST ETS 300 467 E1:2003 is the Slovenian adoption of ETS 300 467 Edition 1, published by SIST from an ETSI European Telecommunication Standard. It specifies how Broadband Integrated Services Digital Network (B-ISDN) supports the Frame Relay Bearer Service (FRBS) and how frame relay interworks between B-ISDN and other networks. It is written for engineers, operators, and implementers who need to design or check B-ISDN access, network-to-network, and interworking functions.

What does SIST ETS 300 467 E1:2003 specify?

SIST ETS 300 467 E1:2003 defines the B-ISDN architectural configuration for providing FRBS. It also covers the service specific convergence sublayer of AAL type 5 and the way it is used for B-ISDN FRBS.

The standard is organized into a foreword, Clause 1 Scope, Clause 2 Normative references, Clause 3 Abbreviations, Clause 4 Service description, Clause 5 Interfaces and protocols, and Annex A.

Annex	What it covers
A	Additional procedures for Frame Relay Permanent Virtual Connections (FR-PVCs) carried on ATM using unnumbered information frame

Clause 4 describes FRBS support in B-ISDN, including the service model and three deployment approaches. Clause 5 then defines the access and network interfaces, FR-SSCS behavior, multiplexing, and congestion management.

What are the key requirements of SIST ETS 300 467 E1:2003?

Service model and architecture

The standard treats FRBS in B-ISDN as a connection-oriented, variable bit rate, non-assured service with no timing relation between sender and receiver. In practice, that means the network carries frame relay traffic over established connections rather than as a timing-sensitive service.

Clause 4.1 gives three ways to support FRBS:

• FRBS provided by a Frame Relay Service Function (FRSF) inside B-ISDN
• FRBS provided by FRSF outside B-ISDN and accessed through ATM bearer capabilities
• frame relay protocol support directly through ATM bearer capabilities

This matters because the same customer-side protocol stack can be used in all three cases, but the network-side function placement changes.

Interfaces and protocol stacks

Clauses 5.1 and 5.2 define the Frame Relay B-ISDN Access Interface (FR-BAI) and the Frame Relay B-ISDN Network-to-Network Interface (FR-BNNI). Both use the B-ISDN physical layer, the ATM layer, AAL5 SAR and CPCS, and FR-SSCS.

The FR-BAI supports direct access to FRSF and indirect access through one or more ATM nodes. The FR-BNNI supports transfer of frame relay service data units within the ATM network. For implementation, this tells you where ATM UNI and ATM NNI behavior applies and where usage parameter control is performed.

FR-SSCS behavior

Clause 5.3 makes FR-SSCS the layer that emulates FRBS in B-ISDN and supports interworking between B-ISDN and frame relay networks. It preserves FR-SSCS-SDU sequence integrity and uses CPCS message mode without the corrupted data delivery option.

Clause 5.3.3 assigns FR-SSCS three main functions:

• multiplexing and demultiplexing of multiple FR-SSCS connections
• inspection of FR-SSCS-PDU length
• congestion control signaling

The standard also defines the FR-SSCS-PDU as a Q.922-style frame relay frame without flags, zero bit insertion, or FCS. The default 2-octet header format is mandatory, while 3- and 4-octet header formats are optional. In practice, equipment must at least accept the default frame format and handle the frame relay fields mapped into ATM transport.

Sender and receiver mapping rules

Clause 5.3.4 specifies how FR-SSCS maps frame relay indicators to CPCS and back again. It covers the handling of DLCI, C/R, FECN, BECN, DE, and the CPCS parameters used at the AAL type 5 boundary.

The important practical point is that some values are negotiated at connection setup or subscription on a per-CPCS-connection basis. That affects provisioning, because the network and terminal have to agree on how discard eligibility and congestion indications are represented across the ATM path.

FR-PVC monitoring and multiplexing

Clause 5.3.5 defines monitoring for Frame Relay Permanent Virtual Connections (FR-PVCs). Management of the ATM layer and FR-PVC monitoring are decoupled, and monitoring messages are transported transparently across the ATM network.

Clause 5.4 allows two multiplexing schemes:

• multiplexing at the FR-SSCS, where several frame relay logical connections share one ATM virtual channel connection using DLCIs
• multiplexing at the ATM layer, where each frame relay logical connection maps to a separate ATM virtual channel connection using VPI/VCI

This matters for provisioning and troubleshooting because the identifiers are locally significant and have to be agreed by subscription on both sides of the interworking function.

Congestion handling

Clause 5.5 gives the congestion management strategy. B-ISDN congestion indications are not mapped directly into the AAL5 CPCS and ATM layer, but they are used when generating FECN and BECN toward frame relay networks.

In practice, the standard expects congestion handling to be coordinated across the B-ISDN and frame relay sides rather than translated mechanically from one layer to another.

What terms does SIST ETS 300 467 E1:2003 define?

• Frame Relay Bearer Service (FRBS) - The frame relay service carried over B-ISDN, described here as connection-oriented, variable bit rate, and non-assured.
• Frame Relay Service Function (FRSF) - The network function that handles frame relay protocols and routing inside B-ISDN or as an external service function.
• Frame Relay Service Specific Convergence Sublayer (FR-SSCS) - The AAL sublayer that adapts frame relay service data for carriage over ATM and supports interworking.
• Frame Relay B-ISDN Access Interface (FR-BAI) - The access interface between user equipment and B-ISDN for frame relay service provision.
• Frame Relay B-ISDN Network-to-Network Interface (FR-BNNI) - The interface used for frame relay service transfer within the ATM network between network nodes.
• Frame Relay Permanent Virtual Connection (FR-PVC) - A permanent virtual connection used for frame relay carriage and monitoring across ATM.
• Data Link Connection Identifier (DLCI) - The identifier used to distinguish frame relay connections and FR-SSCS links locally.

Who uses SIST ETS 300 467 E1:2003?

SIST ETS 300 467 E1:2003 is used by B-ISDN network operators, frame relay service providers, and equipment vendors that implement B-TE, FRSF, IWF, ATM nodes, and related access functions. It is also relevant to engineers working on customer equipment, network interworking points, and FR-PVC monitoring.

Typical tasks include:

• designing direct or indirect FR-BAI access
• implementing AAL5 and FR-SSCS mapping
• configuring FRBS multiplexing over ATM
• setting up interworking between B-ISDN and frame relay networks
• checking congestion signaling and FR-PVC monitoring behavior

Which standards are used with SIST ETS 300 467 E1:2003?

The standard relies on ATM, frame relay, congestion, and interworking references. The most important companion standards and referenced publications are:

Reference	What it contributes
ETS 300 298-2	B-ISDN ATM layer specification
ETS 300 299, ETS 300 300, ETS 300 337	Physical layer and transport options for B-ISDN access
ETS 300 399-1, ETS 300 399-2, ETS 300 399-3, ETS 300 399-4	Frame relay service definitions, including FRBS for ISDN and B-ISDN
ETS 300 428	AAL type 5 SAR and CPCS specification
ETS 300 301	B-ISDN traffic and congestion control
ETS 300 455-1, ETS 300 455-2	Broadband Virtual Path Service options used in the bearer-capability discussion
ITU-T F.811 and I.327	Broadband bearer-service and functional-architecture model
ITU-T I.363 and I.365.1	AAL and FR-SSCS concepts
CCITT Q.922 and Q.933	Frame mode data link format and PVC signaling/management procedures
ITU-T I.370, I.372, I.555	Congestion management, NNI requirements, and frame relay interworking

What does the SIST ETS 300 467 E1:2003 document contain?

The document contains three deployment models in Clause 4, protocol reference architectures for FR-BAI and FR-BNNI in Clause 5, and a detailed FR-SSCS description. It includes figures for the service architectures, protocol stacks, PDU structure, and multiplexing schemes.

Tables 1 to 6 summarize the primitives, mapped parameters, and negotiated connection values used by FR-SSCS. Annex A adds the FR-PVC monitoring procedures for ATM carriage. Overall, the document is focused on U-plane behavior, adaptation, interworking, and monitoring rather than on application profiles.

SLOVENSKI STANDARD
01-december-2003
Širokopasovno digitalno omrežje z integriranimi storitvami (B-ISDN) – Nosilna
storitev blokovnega posredovanja (FRBS) v B-ISDN in meddelovanje sistema B-
ISDN z drugimi omrežji
Broadband Integrated Services Digital Network (B-ISDN); Support of Frame Relay
Bearer Service (FRBS) in B-ISDN and frame relay interworking between B-ISDN and
other networks
Ta slovenski standard je istoveten z: ETS 300 467 Edition 1
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 300 467
TELECOMMUNICATION March 1998
STANDARD
Source: NA Reference: DE/NA-053204
ICS: 33.020
Key words: Broadband, frame relay, interworking, ISDN, B-ISDN, frame mode, Bearer
Broadband Integrated Services Digital Network (B-ISDN);
Support of Frame Relay Bearer Service (FRBS) in B-ISDN and
frame relay interworking between B-ISDN and other networks
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
Internet: [e-mail] - http://www.etsi.fr - http://www.etsi.org
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 1998. All rights reserved.

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ETS 300 467: March 1998
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 300 467: March 1998
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Abbreviations.8
4 Service description.10
4.1 Functional architecture.10
4.1.1 FRBS provided by FRSF inside B-ISDN .10
4.1.2 FRBS provided by FRSF outside B-ISDN, accessed via ATM bearer
capabilities.11
4.1.3 Frame relay protocol support via ATM bearer capabilities.12
5 Interfaces and protocols.13
5.1 Frame Relay B-ISDN Access Interface (FR-BAI) .13
5.1.1 Physical Layer .14
5.1.2 ATM layer .14
5.1.3 AAL.14
5.1.3.1 AAL5 SAR and CPCS.14
5.1.3.2 FR-SSCS.14
5.2 Frame relay B-ISDN Network-to-Network Interface (FR-BNNI) .14
5.2.1 Physical Layer (PL) .15
5.2.2 ATM layer .15
5.2.3 AAL.15
5.2.3.1 AAL5 SAR and CPCS.15
5.2.3.2 FR-SSCS.15
5.3 FR-SSCS .15
5.3.1 Service provided by FR-SSCS .15
5.3.1.1 Primitives .16
5.3.1.2 Description of connections .17
5.3.2 Interaction with the management and control plane.17
5.3.3 Functions, structure and coding of FR-SSCS .17
5.3.3.1 Functions in FR-SSCS.17
5.3.3.2 FR-SSCS-PDU structure and coding .18
5.3.4 Procedures for the FR-SSCS.18
5.3.4.1 State variable.18
5.3.4.2 Procedures at the sender side.18
5.3.4.3 Procedures at the receiver side.19
5.3.4.4 Summary of parameters and values on the FR-SSCS
connections.21
5.3.5 Frame Relay Permanent Virtual Connection (FR-PVC) monitoring .21
5.4 Multiplexing of FRBS connections over B-ISDN.22
5.5 Congestion management strategy.23
Annex A (normative): Additional procedures for Frame Relay Permanent Virtual Connections
(FR PVCs) for the carriage on ATM using unnumbered information frame.24
History.25

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ETS 300 467: March 1998
Foreword
This European Telecommunication Standard (ETS) has been produced by the Network Aspects (NA)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
This European Telecommunication Standard (ETS) defines the B-ISDN architectural configuration for
providing the FRBS service.
Transposition dates
Date of adoption of this ETS: 20 February 1998
Date of latest announcement of this ETS (doa): 30 June 1998
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 December 1998
Date of withdrawal of any conflicting National Standard (dow): 31 December 1998

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ETS 300 467: March 1998
1 Scope
This ETS defines the Broadband Integrated Services Digital Network (B-ISDN) architectural configuration
for providing the Frame Relay Bearer Service (FRBS) service.
B-ISDN FRBS is defined in ETS 300 399-1 [5] and ETS 300 399-4 [8].
This ETS specifies service specific convergence sublayer of AAL type 5 and its use for B-ISDN FRBS.
The B-ISDN FRBS belongs is a connection-oriented, variable bit rate, non assured operation broadband
services with no timing relation between the sender and receiver.
This ETS also describes the network interworking between B-ISDNs supporting FRBS and other ISDNs
and Public Data Networks (PDNs) supporting FRBS as defined in ETS 300 399-1 [5], ETS 300 399-2 [6]
and ETS 300 399-3 [7].
It describes also access configurations to networks supporting FRBS or FRDTS.
This ETS defines only the U-plane procedures for FRBS supported on Permanent Virtual Connections
(PVCs).
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] ETS 300 298-2: "Broadband Integrated Services Digital Network (B-ISDN);
Asynchronous Transfer Mode (ATM); Part 2: B-ISDN ATM layer specification
[ITU-T Recommendation I.361 (1995)]".
[2] ETS 300 299: "Broadband Integrated Services Digital Network (B-ISDN); Cell
based user network access for 155 520 kbit/s and 622 080 kbit/s; Physical layer
interfaces for B-ISDN applications".
[3] ETS 300 300: "Broadband Integrated Services Digital Network (B-ISDN);
Synchronous Digital Hierarchy (SDH) based user network access; Physical layer
User Network Interfaces (UNI) for 155 520 kbit/s and 622 080 kbit/s
Asynchronous Transfer Mode (ATM) B-ISDN applications".
[4] ETS 300 337: "Transmission and Multiplexing (TM); Generic frame structures
for the transport of various signals (including Asynchronous Transfer Mode
(ATM) cells and Synchronous Digital Hierarchy (SDH) elements) at the
ITU-T Recommendation G.702 hierarchical rates of 2 048 kbit/s, 34 368 kbit/s
and 139 264 kbit/s".
[5] ETS 300 399-1: "Frame relay services; Part 1: General description".
[6] ETS 300 399-2: "Frame relay services; Part 2: Integrated Services Digital
Network (ISDN); Frame relay bearer service; Service definition".
[7] ETS 300 399-3: "Frame relay services; Part 3: Frame relay data transmission
service; Service definition".
[8] ETS 300 399-4: "Frame relay services; Part 4: Broadband Integrated Services
Digital Network (B-ISDN); Frame relay bearer service; Service definition".
[9] ETS 300 428: "Broadband Integrated Services Digital Network (B-ISDN);
Asynchronous Transfer Mode (ATM) Adaptation Layer (AAL) specification -
type 5".
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ETS 300 467: March 1998
[10] ETS 300 455-1: "Broadband Integrated Services Digital Network (B-ISDN);
Broadband Virtual Path Service (BVPS); Part 1: BVPS for Permanent
communications (BVPS-P)".
[11] ETS 300 455-2: "Broadband Integrated Services Digital Network (B-ISDN);
Broadband Virtual Path Service (BVPS); Part 2: BVPS for Reserved
communications (BVPS-R)".
[12] ITU-T Recommendation F.811 (1993): "Broadband connection-oriented bearer
service".
[13] ITU-T Recommendation G.804 (1994): "ATM cell mapping into plesiochronous
digital hierarchy (PDH)".
[14] ITU-T Recommendation G.832 (1994): "Transport of SDH elements on PDH
networks - Frame and multiplexing structures".
[15] CCITT Recommendation I.233.1 (1992): "ISDN frame relaying bearer service".
[16] ITU-T Recommendation I.363 (1994): "B-ISDN ATM Adaptation Layer (AAL)
specification".
[17] ITU-T Recommendation I.365.1 (1994): "Frame relaying service specific
convergence sublayer (FR-SSCS)".
[18] CCITT Recommendation I.370 (1992): "Congestion management for the ISDN
frame relaying bearer service".
[19] ETS 300 301, Edition 2 (1997): "Broadband Integrated Services Digital Network
(B-ISDN); Traffic control and congestion control in B-ISDN [ITU-T
Recommendation I.371 (1996)]".
[20] ITU-T Recommendation I.372 (1993): "Frame relaying bearer service network-
to-network interface requirements".
[21] ITU-T Recommendation I.555 (1994): "Frame relaying bearer service
interworking".
[22] CCITT Recommendation Q.922 (1992): "ISDN data link layer specification for
frame mode bearer services".
[23] ITU-T Recommendation Q.933 (1994): "Digital Subscriber Signalling System
No.1 (DSS1) - Signalling specification for frame mode basic call control".
[24] ITU-T Recommendation I.327 (1993): "B-ISDN functional architecture".
3 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
AAL ATM Adaptation Layer
AAL5 AAL type 5
ATM Asynchronous Transfer Mode
ATM-VCC Asynchronous Transfer Mode-Virtual Circuit Connection
B-ISDN Broadband Integrated Services Digital Network
B-TE B-ISDN Terminal
BECN Backward Explicit Congestion Notification
BVPS Broadband Virtual Path Service
C/R Command/Response bit
CBR Constant Bit Rate
CEB Congestion Encountered Backward
CEF Congestion Encountered Forward

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ETS 300 467: March 1998
CI Congestion Indication
CPCS Common Part Convergence Sublayer
CPCS-CI CPCS - Congestion Indication
CPCS-LP CPCS - Loss Priority
CPCS-UU CPCS - User-to-User Indication
D/C DLCI or DL-CORE control indicator
DE Discard Eligibility
DLCI Data Link Connection Identifier
DSS1 Digital Subscriber Signalling N°1
DTE Data Terminal Equipment
EA Address Extension bit
FCS Frame Check Sequence
FECN Forward Explicit Congestion Notification
FR Frame Relay
FR-BNNI Frame Relay Broadband Network-to-Network Interface
FR-IWP Frame Relay Interworking Point
FR-SSCS Frame Relay Service Specific Convergence Sublayer
FR-BAI Frame Relay Broadband Access Interface
FR-IAI Frame Relay ISDN Access Interface
FR-INNI Frame Relay ISDN Network to Network Interface
FR-PAI Frame Relay Private Access Interface
FR-PNNI Frame Relay Private Network to Network Interface
FRBS Frame Relay Bearer Service
FRDTS Frame Relay Data Transmission Service
FRSF Frame Relay Service Function
ID Interface Data
ISDN Integrated Service Digital Network
IWF Interworking Function
LME Layer Management Entity
LSB Least Significant Bit
MSB Most Significant Bit
NNI Network Node Interface
PCI Protocol Control Information
PDH Plesiochronous Digital Hierarchy
PDN Public Data Network
PDU Protocol Data Unit
PHY Physical layer
PISN Private Integrated Service Network
PVC Permanent Virtual Connection
SAP Service Access Point
SAR Segmentation and Reassembly Sublayer
SDH Synchronous Digital Hierarchy
SDU Service Data Unit
SSCS Service Specific Convergence Sublayer
TE Terminal Equipment
UNI User Network Interface
UPC Usage Parameter Control
VBR Variable Bit Rate
VC Virtual Channel
VCC Virtual Channel Connection
VCI Virtual Channel Identifier
VP Virtual Path
VPC Virtual Path Connection
VPI Virtual Path Identifier
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ETS 300 467: March 1998
4 Service description
This description of FRBS in B-ISDN is in accordance with:
- ITU-T Recommendation F.811 [12], which provides a service description of a broadband
connection oriented bearer service. ITU-T Recommendation F.811 [12] includes the following
service subcategories:
- sub-category A: Constant Bit Rate (CBR);
- sub-category B: Variable Bit Rate (VBR) with timing;
- sub-category C: VBR without timing:
C1: emulation of packet mode bearer services;
C2: emulation of frame mode bearer services;
C3: others.
- sub-category X: Asynchronous Transfer Mode (ATM) Adaptation Layer (AAL) defined by
user;
- ETS 300 399-2 [6], which defines ISDN FRBS;
- ETS 300 399-1 [5];
- ETS 300 399-4 [8].
4.1 Functional architecture
B-ISDN is capable of supporting data transfer between B-ISDN customers based on frame relay transfer
techniques. The B-ISDN configuration is in line with the functional architecture defined in
ITU-T Recommendation I.327 [24]. It need not directly imply frame relay methods implemented within
B-ISDN. In the B-ISDN, virtual channels are established at the ATM layer by means of the connection
oriented technique. The frame relay protocol can be supported in the U-plane using the B-ISDN in the
following three ways:
a) FRBS provided by Frame Relay Service Function (FRSF) inside B-ISDN;
b) FRBS provided by FRSF outside B-ISDN, accessed via ATM bearer capabilities;
c) frame relay protocol support via ATM bearer capabilities.
In all cases the protocol stack implemented in B-ISDN customer equipment is identical as shown in
figures 1, 2 and 3. The management and control plane functions which need to be provided in the network
in all cases are for further study. The three cases are outlined in the following paragraphs.
4.1.1 FRBS provided by FRSF inside B-ISDN
In this case the FRSF is provided within the B-ISDN. The FRSF handles frame relay protocols and routes
data according to routing information provided during frame relay connection establishment. This case is
illustrated in figures 1a and 1b.
ATM
switched
B-ISDN
capabilities
B-ISDN B-ISDN
customer
customer
S or T
P S or T
using VP or VC
connections
FRSF FRSF
ATM connection
FRSF
FRSF: Frame Relay Service Function
P , S, or T:
Reference points
Figure 1a: FRBS provided by FRSF inside B-ISDN

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ETS 300 467: March 1998
ATM ATM TE
TE ATM FRSF FRSF
FR-SSCS
FR-SSCS FR-SSCS FR-SSCS
CPCS
CPCS
CPCS CPCS
(note) SAR
SAR SAR (note) SAR
(note)
ATM ATM
ATM ATM ATM ATM
ATM
PHY PHY
PHY PHY PHY
PHY PHY
NOTE: The ATM switching capabilities can be integrated with FRSF.
Figure 1 b: Protocol stack of FRBS provided by FRSF inside B-ISDN
The statistical multiplexing can be done at the frame level. In this case the bearer capabilities required
from the ATM network can be met by those provided by the Virtual Path (VP) bearer service already
defined in ETS 300 455 [11], with peak bandwidth allocation. Virtual Channel (VC) bearer capabilities may
also be deployed and the way of mapping the frame relay parameters into ATM transfer capabilities
(e.g. for statistical multiplexing at the ATM layer) is for further study.
4.1.2 FRBS provided by FRSF outside B-ISDN, accessed via ATM bearer capabilities
In this case a transparent connection of the ATM layer, is used between B-ISDN interfaces (at reference
points S /T or M). Frame relay protocols operating on and above the adaptation layer are transparent to
B B
the B-ISDN. The frame relay service and adaptation layer functions are implemented outside the B-ISDN.
This case is illustrated in figures 2a and 2b.
Specialized
service provider
fram e relay FRSF
S pecialized
service
service provider
FRSF
fram e relay
service
M
M
B-ISDN
ATM
customer
sw itched
S or T
B-ISDN
capabilities
customer
S or T
using VP or VC
connection s
B-ISDN
ATM connection
FRSF Frame Relay Service Function
M, S, or T Reference points
Figure 2a: FRBS provided by FRSF outside B-ISDN

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ETS 300 467: March 1998
ATM
TE ATM FRSF FRSF ATM TE
FR-SSCS FR-SSCS
FR-SSCS FR-SSCS
CPCS CPCS
CPCS CPCS
SAR SAR
SAR SAR
ATM
ATM ATM ATM
ATM ATM ATM
PHY
PHY PHY
PHY PHY PHY PHY
Figure 2b: Protocol stack of FRBS provided by FRSF outside B-ISDN
The requirements on the ATM layer are the same as in subclause 4.1.1.
4.1.3 Frame relay protocol support via ATM bearer capabilities
A frame relay protocol may also be carried by ATM bearer capabilities as shown in figures 3a and 3b. In
this case a transparent connection of the ATM layer, is used between B-ISDN UNIs (at reference point
S /T ). Frame relay protocols operating on and above the adaptation layer are transparent to the B-ISDN
B B
and they are implemented in the Terminal Equipments (TEs) at B-ISDN UNIs.
B-ISDN
B-ISDN
ATM
customer customer
switched
S or T
S or T
capabilities
using VP o r VC
connections
ATM connection
S or T Reference points
B-ISDN
Figure 3a: A frame relay protocol carried by an ATM bearer service
TE
ATM ATM TE
FR-SSCS
FR-SSCS
CPCS CPCS
SAR SAR
ATM ATM ATM ATM
PHY
PHY PHY PHY
Figure 3b: Protocol stack of frame relay protocol carried by an ATM bearer service
The switching and statistical multiplexing is done at the ATM level. The preliminary list of requirements for
the used bearer service is as follows:
- Virtual Channel Identifier (VCI) based switching;
- isolation between connections: e.g. usage parameter control, network parameter control;
- delay and delay variation adapted to data applications;
- network congestion: the random discarding of cells can badly impact the frame loss rate. This
impact may be reduced by taking frame boundaries (reflected in the value of the AUU bit in the
ATM cell header) into account when taking discarding decisions;
- a minimum bandwidth requirement per connection has to be met.
NOTE: Optional multiplexing at the frame level is transparent to the B-ISDN.

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5 Interfaces and protocols
5.1 Frame Relay B-ISDN Access Interface (FR-BAI)
Frame relay direct provision is performed through the use of specialized network functions (FRSF). User
equipment may have direct access to the equipment realizing FRSF at the S /T reference points. The
B B
protocol stack includes the UNI physical and ATM layer both in the user equipment on one side of the
FR-BAI and in the network equipment realizing FRSF on the other side. Usage Parameter Control (UPC)
functions, as foreseen for ATM user access, are performed on the network side of the FR-BAI.
Indirect user access to the FRSF through one or more ATM nodes is also possible. In this case the
interface between the user equipment and the adjacent ATM node is defined at the S /T reference
B B
points, while that between the equipment realizing the FRSF and the adjacent ATM node(s) is defined at
the P/M reference points.
At the S /T reference points, the physical and ATM layer of the FR-BAI stack are terminated in the user
B B
equipment and the ATM node(s). They are based on the ATM UNI. UPC functions as foreseen for ATM
user access are performed by the ATM network e
...