ETSI I-ETS 300 353 ed.1 (1995-04)

Broadband Integrated Services Digital Network (B-ISDN); Asynchronous Transfer Mode (ATM); Adaptation Layer (AAL) specification - type 1

DI/NA-052617

Širokopasovno digitalno omrežje z integriranimi storitvami (B-ISDN) – Specifikacija prilagodilne plasti (AAL) asinhronega prenosnega načina (ATM), tip 1

General Information

• Status: Published
• Publication Date: 01-May-1995
• Technical Committee: NA 5 - Broadband Networks
• Current Stage: 12 - Completion
• Due Date: 19-May-1995
• Completion Date: 02-May-1995
• Ref Project: SIST I-ETS 300 353 E1:2003 - Broadband Integrated Services Digital Network (B-ISDN); Asynchronous Transfer Mode (ATM); Adaptation Layer (AAL) specification - type 1

Standards Content (Sample)

SLOVENSKI STANDARD
SIST I-ETS 300 353 E1:2003
01-december-2003
âLURNRSDVRYQRGLJLWDOQRRPUHåMH]LQWHJULUDQLPLVWRULWYDPL%,6'1±
6SHFLILNDFLMDSULODJRGLOQHSODVWL$$/DVLQKURQHJDSUHQRVQHJDQDþLQD$70WLS
Broadband Integrated Services Digital Network (B-ISDN); Asynchronous Transfer Mode
(ATM); Adaptation Layer (AAL) specification - type 1
Ta slovenski standard je istoveten z: I-ETS 300 353 Edition 1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
SIST I-ETS 300 353 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST I-ETS 300 353 E1:2003
INTERIM
EUROPEAN I-ETS 300 353
TELECOMMUNICATION April 1995
STANDARD
Source: ETSI TC-NA Reference: DI/NA-052617
ICS: 33.080
B-ISDN, ATM
Key words:
Broadband Integrated Services Digital Network (B-ISDN);
Asynchronous Transfer Mode (ATM)
Adaptation Layer (AAL) specification - type 1
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 - [e-mail]
X.400: Internet:
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 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 .5
Introduction.5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .8
3.1 Definitions .8
3.2 Abbreviations .9
4 AAL type 1.9
4.1 Service primitives provided by AAL type 1.10
4.1.1 AAL-UNITDATA-REQUEST.10
4.1.2 AAL-UNITDATA-INDICATION .10
4.1.3 Definition of parameters .10
4.1.3.1 DATA parameter.10
4.1.3.2 STRUCTURE parameter.11
4.1.3.3 STATUS parameter.11
4.2 Interaction with the management and control planes .11
4.2.1 Management plane.11
4.2.2 Control plane .11
4.3 Functions of AAL type 1.12
4.4 SAR sublayer .12
4.4.1 Functions of the SAR sublayer.12
4.4.2 SAR protocol .13
4.4.2.1 SN field .13
4.4.2.2 SNP field.13
4.5 CS.15
4.5.1 Functions of the CS.15
4.5.1.1 Functions of the CS for circuit transport .16
4.5.1.2 Functions of the CS for video signal transport.17
4.5.1.3 Functions of the CS for voice-band signal transport.18
4.5.2 CS protocol.18
4.5.2.1 SC operations.18
4.5.2.1.1 SC operations at the transmitting end .18
4.5.2.1.2 SC operations at the receiving end.19
4.5.2.2 Source clock frequency recovery method .19
4.5.2.2.1 SRTS method .19
4.5.2.2.1.1 General .19
4.5.2.2.1.2 Choice of parameter .21
4.5.2.2.1.3 Network clocks.21
4.5.2.2.1.4 Transport of the RTS .21
4.5.2.2.1.5 Plesiochronous network operation.22
4.5.2.2.2 Adaptive clock method.22
4.5.2.2.3 Combination of SRTS and adaptive
clock method.22
4.5.2.3 SDT method .22
4.5.2.4 Correction method for bit errors and cell losses for
unidirectional video services.23
4.5.2.5 Partially filled cells.24
Annex A (informative): Illustration of the data unit naming convention .25

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Annex B (informative): Functional model for the circuit transport with AAL type 1. 26
B.1 Transmitter . 26
B.2 Receiver. 26
Annex C (informative): Algorithm to detect lost and misinserted cells in AAL 1. 29
C.1 Side effects. 29
C.2 Indications from the SAR sublayer . 29
C.3 Limits of the algorithm . 29
C.4 The algorithm. 29
Annex D (normative): Protocol Implementation Conformance Statement (PICS) proforma for the
AAL type 1. 32
D.1 Introduction. 32
D.2 PICS . 33
D.2.1 SAR sublayer . 33
D.2.1.1 Capabilities . 33
D.2.1.2 PDUs and PDU parameters . 33
D.2.2 CS major capabilities . 33
D.2.2.1 CS for circuit transport. 34
D.2.2.1.1 Capabilities. 34
D.2.2.1.2 Protocol parameters. 35
D.2.2.2 CS for video signal transport . 36
D.2.2.2.1 Capabilities. 36
D.2.2.2.2 Protocol parameters. 36
D.2.2.3 CS for voice band signal transport. 37
D.2.2.3.1 Capabilities. 37
D.2.2.3.2 Protocol parameters. 37
History. 38

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Foreword
This Interim European Telecommunication Standard (I-ETS) has been produced by the Network Aspects
(NA) Technical Committee of the European Telecommunications Standards Institute (ETSI).
NOTE: This I-ETS was submitted to the Public Enquiry phase of the ETSI standards approval
procedure as a draft ETS. Following resolution of the comments received, the
document was converted into an I-ETS. The annex containing Specification and
Description Language (SDL) diagrams for the circuit transport with AAL type 1 has
been removed, and may be re-inserted in a later version of this standard.
An ETSI standard may be given I-ETS status either because it is regarded as a provisional solution ahead
of a more advanced standard, or because it is immature and requires a "trial period". The life of an I-ETS
is limited to three years after which it can be converted into an ETS, have it's life extended for a further
two years, be replaced by a new version, or be withdrawn.
Announcement date
Date of latest announcement of this I-ETS (doa): 31 July 1995
Introduction
The content of this I-ETS is derived from ITU-T Recommendation I.363 [10]. This I-ETS is one of a set of
ETSs describing different Asynchronous Transfer Mode (ATM) Adaptation Layer (AAL) types.
The AAL uses the ATM layer service and offers its layer service to the higher layers. The
connection-oriented transmission methods which provide timing relation between sending and receiving
AAL service users, are described in ITU-T Recommendation I.363 [10], §2. These methods form the AAL
type 1. They check the validity of the cell sequence count, transmit and utilize time stamp information for
source clock recovery at the receiver as a user option, optionally correct data by using Forward Error
Correction (FEC) and offer utilities to transfer structured data. Subtypes are defined for "circuit transport",
"video signal transport" and "voice-band signal transport".

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1 Scope
As ITU-T Recommendation I.363 [10] contains options and describes methods which can be used in
different combinations, this Interim European Telecommunication Standard (I-ETS) minimizes the options
and methods and describes a subset of the Asynchronous Transfer Mode (ATM) Adaptation Layer (AAL)
type 1 to be used in Europe.
In addition, a functional model for the circuit transport transfer of asynchronous data, i.e. Synchronous
Residual Time Stamp (SRTS) method in combination with Structured Data Transfer (SDT), is given in
annex B.
This I-ETS describes the interactions between the AAL and the next higher layer, and the AAL and the
ATM layer, as well as AAL peer-to-peer operations. This I-ETS is based on the classification and the AAL
functional organization described in ITU-T Recommendation I.362 [9].
2 Normative references
This I-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 I-ETS only when incorporated in it by amendment or revision. For undated references the
latest edition of the publication referred to applies.
[1] ITU-T Recommendation G.702: "Digital hierarchy bit rates".
[2] ITU-T Recommendation G.709: "Synchronous multiplexing structure".
[3] ITU-T Recommendation G.711: "Pulse code modulation (PCM) of voice
frequencies".
[4] ITU-T Recommendation G.722: "7 kHz audio-coding within 64 kbit/s".
[5] ITU-T Recommendation G.823: "The control of jitter and wander within digital
networks which are based on the 2048 kbit/s hierarchy".
[6] ITU-T Recommendation G.824: "The control of jitter and wander within digital
networks which are based on the 1544 kbit/s hierarchy".
[7] ITU-T Recommendation I.231: "Circuit-transport-mode bearer service
categories".
[8] ITU-T Recommendation I.361 (1993): "B-ISDN ATM layer specification".
[9] ITU-T Recommendation I.362 (1993): "B-ISDN ATM adaptation layer functional
description".
[10] ITU-T Recommendation I.363 (1993): "B-ISDN ATM adaptation layer
specification".

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3 Definitions and abbreviations
3.1 Definitions
For the purposes of this I-ETS, the following definitions apply:
ATM Adaptation Layer (AAL): The AAL uses the ATM layer service and includes multiple protocols to fit
the need of the different AAL service users. In AAL type 1 source timing recovery is provided at the
receiver.
Convergence Sublayer Indication (CSI): The CSI is a part of the Protocol Control Information (PCI) in
the SAR sublayer; it indicates a special event in the sending Convergence Sublayer (CS) entity in
combination with the Sequence Count (SC) and depending on the AAL subtype used: it supports source
clock timing recovery using the SRTS method, data structure indication using the SDT method and bit
error and cell loss recovery using Forward Error Correction (FEC).
Forward Error Correction (FEC): The FEC method is adapted to the error conditions at the ATM layer.
non-P format: Format of the SAR-PDU (Protocol Data Unit) payload, which does not carry a pointer of
the SDT method.
P format: Format of the SAR-PDU payload which carries a pointer of the SDT method.
Residual Time Stamp (RTS): The SRTS method uses the RTS value to measure and convey information
about the frequency differences between a common reference clock (derived from the network) and a
service clock. The same derived network clock is assumed to be available at both the transmitter and the
receiver.
Sequence Count (SC): This 3-bit field counts the SAR-PDUs from 0 to 7 (modulo 8).
Sequence Number (SN): The SN field consists of the 1-bit indication called CSI and a 3-bit SC in the
SAR-PDUs.
Sequence Number Protection (SNP): The SNP protects the SN by Cyclic Redundancy Check (CRC)
and parity check.
Structured Data Transfer (SDT): The SDT method supports the transmission of structured data (blocks
of user data organized in octets) by using a pointer to the start of a block.
Synchronous Residual Time Stamp (method) (SRTS): This method uses the RTS values (transferred
peer-to-peer) to recover the source service clock at the receiver side.

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3.2 Abbreviations
For the purposes of this I-ETS, the following abbreviations apply:
AAL ATM Adaptation Layer
ATM Asynchronous Transfer Mode
CRC Cyclic Redundancy Check
CS Convergence Sublayer
CSI Convergence Sublayer Indication
FEC Forward Error Correction
PCI Protocol Control Information
PDU Protocol Data Unit
PICS Protocol Implementation Conformance Statement
RPOA Recognized Private Operating Agency
RTS Residual Time Stamp
SAP Service Access Point
SAR Segmentation And Reassembly (sublayer)
SC Sequence Count
SDH Synchronous Digital Hierarchy
SDL Specification and Description Language
SDT Structured Data Transfer
SDU Service Data Unit
SN Sequence Number
SNP Sequence Number Protection
SRTS Synchronous Residual Time Stamp (method)
STM-1 Synchronous Transfer Mode - 1
4 AAL type 1
The AAL enhances the service provided by the ATM layer to support functions required by the next higher
layer. The AAL performs functions required by the user, control and management planes and supports the
mapping between the ATM layer and the next higher layer. The functions performed in the AAL depend
upon the higher layer requirements.
The AAL supports multiple protocols to fit the needs of the different AAL service users. The service
provided by the AAL type 1 protocol to the higher layer and the functions performed are specified in this
I-ETS.
Details of the data unit naming convention used in this I-ETS can be found in annex A.
This I-ETS describes the interactions between the AAL and the next higher layer, and the AAL and the
ATM layer, as well as AAL peer-to-peer operations. This I-ETS is based on the classification and the AAL
functional organization described in ITU-T Recommendation I.362 [9].
Different combinations of SAR sublayers and CS provide different Service Access Points (SAPs) to the
layer above the AAL. In some applications the SAR and/or CS may be empty.
The AAL receives from the ATM layer the information in the form of a 48 octet ATM Service Data Unit
(ATM-SDU). The AAL passes to the ATM layer information in the form of a 48 octet ATM-SDU. See ITU-T
Recommendation I.361 [8] for definition of ATM layer services and description of primitives provided by
the ATM layer.

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4.1 Service primitives provided by AAL type 1
The layer service capabilities provided by AAL type 1 to the AAL user are:
- transfer of service data units with a constant source bit rate and the delivery of them with the same
bit rate;
- transfer of timing information between source and destination;
- transfer of structure information between source and destination;
- indication of lost or errored information which is not recovered by AAL type 1, if needed.
At the AAL-SAP, the following primitives are used between the AAL type 1 and the AAL user. They
represent an abstract model of the interface and they are not intended to constrain implementations:
- from an AAL user to the AAL,
AAL-UNITDATA-REQUEST;
- from the AAL to an AAL user,
AAL-UNITDATA-INDICATION.
An AAL-UNITDATA-REQUEST primitive at the local AAL-SAP results in an AAL-UNITDATA-INDICATION
primitive at its peer AAL-SAP.
4.1.1 AAL-UNITDATA-REQUEST
AAL-UNITDATA-REQUEST:
(DATA [mandatory],
STRUCTURE [optional]).
The AAL-UNITDATA-REQUEST primitive requests the transfer of the AAL-SDU, i.e. contents of the DATA
parameter, from the local AAL entity to its peer entity. The length of the AAL-SDU is constant and the time
interval between two consecutive primitives is constant. These two constants depend upon the specific
AAL service provided to the AAL user.
4.1.2 AAL-UNITDATA-INDICATION
AAL-UNITDATA-INDICATION:
(DATA [mandatory],
STRUCTURE [optional],
STATUS [optional]).
An AAL user is notified by the AAL that the AAL-SDU from its peer is available (i.e. via the contents of the
DATA parameter). The length of the AAL-SDU shall be constant and the time interval between two
consecutive primitives shall be constant. These two constants depend upon the specific AAL service
provided to the AAL user.
4.1.3 Definition of parameters
4.1.3.1 DATA parameter
(Mandatory).
The DATA parameter carries the AAL-SDU to be sent or delivered. Its size depends on the specific AAL
service used.

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4.1.3.2 STRUCTURE parameter
(Optional use).
The STRUCTURE parameter can be used when the user data stream to be transferred to the peer AAL
entity is organized into groups of octets. The length of the structured block is fixed for each instance of the
AAL service. The length is an integer multiple of one octet. An example of the use of this parameter is to
support circuit mode bearer services of the 64 kbit/s based ISDN. If the optional parameter is present, the
two values of the STRUCTURE parameter are:
START; and
CONTINUATION.
The value START is used when the DATA is the first part of a structured block which can be composed of
consecutive DATA. In other cases, the STRUCTURE parameter is set to CONTINUATION. The use of the
STRUCTURE parameter depends upon the specific AAL service provided. The use of this parameter is
agreed prior to or at the connection establishment between the AAL user and the AAL.
4.1.3.3 STATUS parameter
(Local optional use).
The STATUS parameter identifies that the DATA is judged to be non-errored or errored. The STATUS
parameter has two values:
VALID; and
INVALID.
The INVALID status can also indicate that the DATA is a dummy value. The use of the STATUS
parameter and the choice of dummy value depend upon the specific AAL service provided. The use of this
parameter is agreed prior to or at the connection establishment between the AAL user and the AAL.
4.2 Interaction with the management and control planes
Currently no interactions are standardized.
4.2.1 Management plane
For example, the following indications may be passed from the user plane to the management plane:
- errors in the transmission of user information;
- lost and misinserted cells;
- cells with errored AAL-PCI;
- loss of timing and synchronization;
- buffer underflow and overflow.
4.2.2 Control plane
Currently no interactions are standardized.

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4.3 Functions of AAL type 1
The following functions may be performed in the AAL type 1 in order to enhance the ATM layer service:
a) blocking and deblocking of user information;
b) handling of cell delay variation;
c) handling of cell payload assembly delay;
d) handling of lost and misinserted cells;
e) source clock frequency recovery at the receiver;
f) recovery of the source data structure at the receiver;
g) monitoring of AAL-PCI for bit errors;
h) handling of AAL-PCI bit errors;
i) monitoring of user information field for bit errors and possible corrective action.
4.4 SAR sublayer
4.4.1 Functions of the SAR sublayer
The SAR sublayer functions are performed on an ATM-SDU basis:
a) mapping between CS-PDU and SAR-PDU:
- the SAR sublayer at the transmitting end accepts a 47 octet block of data from the CS, and
then prepends a one octet SAR-PDU header to each block to form the SAR-PDU;
- the SAR sublayer at the receiving end receives the 48 octet block of data from the ATM layer,
and then separates the SAR-PDU header. The 47 octet block of SAR-PDU payload is passed
to the CS;
b) indication of existence of CS function:
- the SAR sublayer has the capability to indicate the existence of a CS function. Associated
with each 47 octet SAR-PDU payload, it receives this indication from the CS and conveys it
to the peer CS entity. The use of this indication by the CS is optional;
c) sequence numbering:
- associated with each SAR-PDU payload, the SAR sublayer receives a SC value from the CS.
At the receiving end, it passes the SC value to the CS. The CS may use these SC values to
detect lost or misinserted SAR-PDU payloads (corresponding to lost or misinserted ATM
cells);
d) error protection:
- the SAR sublayer protects the SC value and the CS indication against bit errors. It informs
the receiving CS when the SC value and the CS indication are errored and can not be
corrected.

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4.4.2 SAR protocol
The SAR-PDU header together with the 47 octets of the SAR-PDU payload comprises the 48 octet ATM-
SDU (cell information field). The size and positions of the fields in the SAR-PDU are given in figure 1.
Cell header SN field SNP field SAR-PDU payload
4 bits 4 bits 47 octets
SAR-PDU header
SAR-PDU (48 octets)
Figure 1: SAR-PDU format of AAL type 1
4.4.2.1 SN field
The SN field is divided into two subfields as shown in figure 2. The SC field carries the SC value provided
by the CS. The CSI bit carries the CS indication provided by the CS. The default value of the CSI bit is "0".
The least significant bit of the SC value is right justified in the SC field.
CSI bit Sequence count field (3 bits)
SN field (4 bits)
Figure 2: SN field format
4.4.2.2 SNP field
The SNP field provides error detection and correction capabilities over the SAR-PDU header. The format
of this field is given in figure 3. A two step approach is used for the protection:
1) the SN field is protected by a 3 bit CRC code;
2) the resulting 7 bit code word is protected by an even parity check bit.
Even parity
CRC field (3 bits)
bit
SNP field (4 bits)
Figure 3: SNP field format

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The receiver is capable of either single-bit error correction or multiple-bit error detection:
a) operations at transmitting end:
- the transmitter computes the CRC value across the first 4 bits of the SAR-PDU header and
inserts the result in the CRC field;
- the notation used to describe the CRC is based on the property of cyclic codes. The
elements of an n-element code word are thus the coefficients of a polynomial of order n-1. In
this application, these coefficients can have the value 0 or 1 and the polynomial operations
are performed using modulo 2 operations. For example a code vector such as 1011 can be
3
represented by the polynomial P(x)=x +x+1. The polynomial representing the content of the
SN field is generated using the left most bit of the SN field as the coefficient of the highest
order term;
- the CRC field consists of three bits. It shall contain the remainder of the division (modulo 2)
3 3
by the generator polynomial x +x+1 of the product x multiplied by the content of the SN field.
2
The coefficient of the x term in the remainder polynomial is left justified in the CRC field;
- after completing the above operations, the transmitter inserts the even parity bit (i.e. the sum
of the eight bits shall be even);
b) operations at receiving end:
- the receiver has two different modes of operation: correction mode and detection mode.
These modes are related as shown in figure 4. The default mode is the correction mode,
which provides for single-bit error correction. At initialization, the receiver is set up in this
default mode;
No error detected Error detected
(valid SN) (invalid SN)
No error detected (valid SN)
Correction Detection
Mode Mode
Single-bit error detected
(valid SN after correction)
Multi-bit error detected
(invalid SN)
Figure 4: SNP - receiver modes of operation
- the receiver examines each SAR-PDU header by checking the CRC and the even parity. If a
header error is detected, the action taken depends on the state of the receiver. In the
"Correction Mode", only single-bit errors can be corrected and the receiver switches to
"Detection Mode". In "Detection Mode", all SAR-PDU headers with detected errors are
declared to have an invalid SN; however, when a SAR-PDU header is examined and found
not to be in error, the receiver switches to "Correction Mode";
- tables 1 and 2 give the detailed mandatory operations of the receiver in the "Correction
Mode" and "Detection Mode", respectively. The operation is based on the combined validity
of the CRC and the parity bit;
- the receiver shall convey the sequence count and the CS indication to the CS together with
SN check status (valid or invalid).

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Table 1: Operations in Correction Mode
CRC syndrome Parity Action on current SN+SNP Reaction for next SN+SNP
Zero No violation No corrective action. Continue in Correction Mode
Declare SN valid.
Non-zero Violation Single bit correcti
...