ETSI ETS 300 278 ed.1 (1994-03)

Network Aspects (NA); Support of existing services with guaranteed constant bit rate and specified transfer delay on Metropolitan Area Network (MAN)

DE/NA-053301

Omrežni vidiki (NA) – Podpora obstoječim storitvam z zagotovljeno konstantno bitno hitrostjo in določeno prenosno zakasnitvijo v velemestnih omrežjih (MAN)

General Information

• Status: Published
• Publication Date: 28-Mar-1994
• Technical Committee: NA 5 - Broadband Networks
• Current Stage: 12 - Completion
• Due Date: 04-Apr-1994
• Completion Date: 29-Mar-1994
• Ref Project: SIST ETS 300 278 E1:2003 - Network Aspects (NA); Support of existing services with guaranteed constant bit rate and specified transfer delay on Metropolitan Area Network (MAN)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 278 E1:2003
01-december-2003
2PUHåQLYLGLNL1$±3RGSRUDREVWRMHþLPVWRULWYDP]]DJRWRYOMHQRNRQVWDQWQR
ELWQRKLWURVWMRLQGRORþHQRSUHQRVQR]DNDVQLWYLMRYYHOHPHVWQLKRPUHåMLK0$1
Network Aspects (NA); Support of existing services with guaranteed constant bit rate and
specified transfer delay on Metropolitan Area Network (MAN)
Ta slovenski standard je istoveten z: ETS 300 278 Edition 1
ICS:
35.110 Omreževanje Networking
SIST ETS 300 278 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 278 E1:2003

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SIST ETS 300 278 E1:2003
EUROPEAN ETS 300 278
TELECOMMUNICATION March 1994
STANDARD
Source: ETSI TC-NA Reference: DE/NA-053301
ICS: 33.080
Service, MAN
Key words:
Network Aspects (NA);
Support of existing services with guaranteed constant bit rate
and specified transfer delay on Metropolitan Area Network (MAN)
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 1994. 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
1 Scope .7
2 Normative references .7
3 Definitions. 7
4 Symbols and abbreviations.9
5 Basic principles . 10
6 DQDB layer service model. 10
7 Functional architecture. 11
7.1 Access method. 11
7.2 Slot generation function at the HOB. 11
7.2.1 Frequency and periodicity . 12
7.2.2 Variability. 12
7.2.3 Basic data rates. 13
7.2.4 Compound data rates. 13
7.3 Functions at a DQDB node supporting a CBR interface. 14
7.3.1 Overview . 14
7.3.2 Common functions block . 14
7.3.3 PA-functions block. 15
7.3.3.1 PA-transmit functions. 15
7.3.3.1.1 Transmit interactions between PA
functions block and common functions
block. 15
7.3.3.1.2 PA segment header validation . 15
7.3.3.2 PA receive functions . 15
7.3.3.2.1 Receive interactions between PA
functions block and common functions
block. 15
7.3.3.2.2 PA segment header validation . 16
7.3.3.2.3 CBR convergence function selection . 16
7.3.4 CBR convergence functions block. 16
7.3.4.1 CBR convergence transmit function. 16
7.3.4.2 CBR convergence receive function . 16
7.3.5 CBR interfaces. 17
8 Protocol data unit format. 17
8.1 PA slot. 17
8.2 PA segment. 17
8.2.1 PA segment header fields . 17
8.2.1.1 VCI. 18
8.2.1.2 Payload_Type. 18
8.2.1.3 Segment_Priority. 18
8.2.1.4 Segment HCS . 18
8.2.2 PA segment payload . 18
9 Protocol performance constraints . 19
9.1 Delay constraints . 19
9.1.1 Delay constraints for voice connections. 19

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9.2 Jitter constraints.19
9.3 Synchronisation constraints .19
9.4 Reconfiguration constraints .19
10 DQDB layer management interface in support of CBR service .20
Annex A (informative): Applications .24
A.1 Identified applications .24
A.1.1 Interconnection of CBR terminals.24
A.1.2 Video applications .24
A.1.3 Voice applications .24
A.1.4 Multi-application support .24
A.1.5 Multimedia applications.24
A.2 Delay considerations.25
A.2.1 Delay in network components.25
A.2.1.1 Transmission delay.25
A.2.1.2 Delay in the CBR Access Unit (CAU).25
A.2.1.3 Delay in a DQDB-DQDB bridge. 26
A.2.1.4 DQDB-ATM gateway.27
A.2.2 End-to-end delays for CBR connections - some examples .27
A.2.3 Access delay for CBR connections at 2 048 kbit/s .28
A.3 Feasibility of bandwidth allocation.29
A.3.1 Frame groups .29
A.3.2 Valid connections in a frame group .30
A.3.3 Bandwidth allocation algorithms.31
Annex B (normative): Protocol implementation conformance statement .32
B.1 Introduction.32
B.1.1 Instructions for completing this PICS proforma .32
B.1.2 Definitions.33
B.1.2.1 Status column notation.33
B.1.2.2 Support column notation.33
B.2 Identification of the Implementation.33
B.3 Identification of the protocol .34
B.4 Global statement of conformance .34
B.5 Major capabilities and features . 35
B.5.1 Properties of the PLCP.35
B.5.2 Slot generation function at the HOB .35
B.5.3 Functions at a DQDB node supporting a CBR interface .36
B.5.4 Protocol Data Unit (PDU) format.37
B.5.5 DQDB layer management service in support of CBR connection type.37
Annex C (informative): Bibliography.38
History .39

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Foreword
This European Telecommunication Standard (ETS) has been prepared by the Network Aspects (NA)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
The need has been identified for the support of applications that require guaranteed constant bandwidth
and specified transfer delay on a Distributed Queue Dual Bus (DQDB) subnetwork.
Therefore, the DQDB protocol has to be enhanced for the provision of Constant Bit Rate (CBR) connection
types.
This final draft ETS addresses the use of pre-arbitrated functions as defined in IEEE Standard 802.6 [1] to
support CBR connection types.

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1 Scope
This European Telecommunication Standard (ETS) details enhancements to the Distributed Queue Dual
Bus (DQDB) access method as defined in IEEE Standard 802.6 [1] in order to provide Constant Bit Rate
(CBR) connection types for the support of existing services (guaranteed constant bandwidth, specified
transfer delay) on MANs, using semi-permanent connections in the range of n x 64 kbit/s to 2 Mbit/s bit
rate capability. Therefore, signalling protocol specifications are outside the scope of this ETS.
This ETS does not cover the broadband specific aspects and the interworking of MANs with broadband
networks. For the broadband related aspects the CBR services are defined in CCITT Recommendations
I.362 and I.363 and the protocol reference model to be used in the Asynchronous Transfer Mode (ATM)
based networks to support these services is included in CCITT Recommendation I.321.
Annex B provides the Protocol Implementation Conformance Statement (PICS) proforma for this ETS, in
compliance with the relevant requirements, and in accordance with the relevant guidance, given in ISO/IEC
9646-2.
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 below. For dated
references, subsequent amendments to or revisions 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] IEEE Standard 802.6 (1990): "Distributed Queue Dual Bus (DQDB) Subnetwork
of a Metropolitan Area Network (MAN)".
[2] CCITT Recommendation G.101 (1988): "The transmission plan".
[3] CCITT Recommendation G.114 (1988): "Mean one-way propagation time".
[4] CCITT Recommendation G.131 (1988): "Stability and Echo (General
characteristics of the 4-wire chain formed by the international circuits and
national extension circuits)".
[5] CCITT Recommendation G.823 (1988): "The Control of jitter and wander within
digital networks which are based on the 2 048 kbit/s hierarchy".
3 Definitions
For the purposes of this ETS, the definitions defined in IEEE Standard 802.6 [1] apply.
In addition, this Clause contains those definitions that are considered to be essential for the understanding
of this ETS.
Access delay: the time which an octet spends in the transmit queue of a CBR access unit before it can
gain access to the bus.
Basic data rate: a data rate out of the following list:
- 64 kbit/s;
- 192 kbit/s;
- 384 kbit/s;
- 768 kbit/s;
- 1 536 kbit/s;
- 2 048 kbit/s.

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The use of the term "basic data rate" implies that the Pre-Arbitrated (PA) slot generation process for a
CBR connection at a basic data rate is based on the frequency parameter pairs (M, N) where M=1 and
N=2, 4, 8, 16, 48 or M=2 and N=3.
CBR Access Unit (CAU): a DQDB node supporting a CBR interface.
CBR Convergence Functions (CCF) block: consists of the CCF transmit functions block and the CCF
receive functions block.
CBR Service User (CSU): sends and receives octets at a constant bit rate across a CBR interface of a
DQDB subnetwork.
CCF receive functions block: receives octets from the PA functions block and stores them in a buffer. It
forwards the octets to the CBR service user at precisely regular intervals according to the rate of the CBR
service.
CCF transmit functions block: receives service octets from the CBR interface. It stores these octets in
a buffer until they are requested by the PA functions block. Then they are passed on to the PA functions
block.
Common Functions (CF) block: provides functions which are needed by some or all of the other
functional blocks in the local DQDB layer subsystem. It provides the DQDB layer function of relaying the
slot octets and management information octets between the service access points to the local physical
layer subsystem.
Composite slot-switching: the service octets of a CBR connection may gain access to an offset in the
payload of a PA slot on one of the busses if, and only if, the pair virtual channel identifier of the PA slot,
offset is contained in a list of such pairs associated at connection set-up with the CBR connection on that
bus.
Compound data rate: is a (necessarily unique) sum of two or more basic data rates. The use of the term
"compound data rate" implies that the PA slot generation process for a CBR connection at a compound
data rate consists in generating the PA slots for the basic data rates of which it is the sum.
Constant Bit Rate (CBR): the time characteristic of an event or signal recurring at known periodic time
intervals, i.e. guaranteed constant bandwidth, specified transfer delay.
NOTE: The term for this characteristic which is used in IEEE Standard 802.6 [1] is "CBR".
CBR Service Data Unit (CSDU): are presented by the CSU at the specified rate for the CBR connection.
Similarly, the CBR service periodically delivers a CSDU to a CSU at the rate specified for the connection.
Dedicated slot-switching: the service octets of a CBR connection may gain access to an offset in the
payload of a PA slot on one of the busses if, and only if, the Virtual Channel Identifier (VCI) of the PA slot
has been associated at connection set-up with the CBR connection on that bus.
Delay end-to-end, one way: the time it takes for a CBR service octet to be transferred between two
corresponding terminal equipments.
Frame: refers to the 125 μs transmission frame of the Physical Layer Convergence Procedure (PLCP).
Frequency: is a pair of positive integer numbers (M, N). It implies that the PA slot generation for a CBR
connection is required to maintain the frequency of M slots every N frames.
PA functions block: controls the transfer in PA segment payloads of CBR service octets received from
the CBR convergence functions block. For this purpose it maintains one transmit table and one receive
table.

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Receive table: is part of the PA receive functions block. It associates a CBR connection end-point
identifier with the bus and with the VCI of the PA slots on which the service octets of the connection are
received.
Slot number: slots in a frame are numbered by starting with the first slot fully contained in the frame and
numbering from 1 to the last slot fully contained in that frame.
Transmit table: is part of the PA transmit functions block. It associates a CBR connection end-point
identifier with the bus and with the VCI of the PA slots on which the service octets of the connection are
transmitted.
Variability: is the maximum difference in the slot number between the k-th and the (k+M)-th PA slots
allocated to a connection with slot generation frequency = (M, N).
4 Symbols and abbreviations
For the purposes of this ETS, the symbols and abbreviations defined in IEEE Standard 802.6 [1] apply.
In addition, those symbols and abbreviations that are essential for the understanding of this ETS are listed:
CAU CBR Access Unit
CBR Constant Bit Rate
CCF CBR Convergence Functions
CF Common Functions
CRC Cyclic Redundancy Check
CSDU CBR Service Data Unit
CSU CBR Service User
DQDB Distributed Queue Dual Bus
HCS Header Check Sequence
HOB Head Of Bus
ISPBX Integrated Services Private Branch Exchange
LM-ACTION Layer Management Action
MAC Media Access Control
MSS MAN Switching System
NMP Network Management Process
PA Pre-Arbitrated
PBX Private Branch Exchange
PDU Protocol Data Unit
PICS Protocol Implementation Conformance Statement
PLCP Physical Layer Convergence Procedure
QA Queued Arbitrated
SDH Synchronous Digital Hierarchy
VCI Virtual Channel Identifier
V default Variability
def

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5 Basic principles
The CBR capability shall provide for the following data rates defined by CCITT:
- 64 kbit/s;
- 384 kbit/s;
- 1 536 kbit/s;
- 2 048 kbit/s.
The CBR capability provides for these basic data rates and combinations thereof, e.g. n x 64 kbit/s.
The PLCP of a DQDB subnetwork providing CBR capability shall have a 125 μs frame structure. In order
to allow for simple and efficient bandwidth allocation/management algorithms, the Head Of Bus (HOB)
node shall generate slots used for CBR services which fit as a whole into a single 125 μs frame.
Therefore, the use of a 1,5 Mbit/s or 2 Mbit/s transmission system for the DQDB subnetwork is excluded.
All other standardised PLCPs are supported.
6 DQDB layer service model
The CBR service provided by the DQDB layer is described abstractly by means of the service primitives
notation defined in ISO/TR 8509.
NOTE: The abstract description does not constrain an implementation in any way. For
example, an implementation might use a service data unit consisting of a number of
octets or only a single bit.
The primitives used to describe the service are the following:
- CSU-DATA request;
- CSU-DATA indication.
CSDUs to be sent via the CBR service are presented by the CSU at the specified rate for the constant bit
rate connection. Similarly, the CBR service periodically delivers a CSDU unit to a CSU at the rate specified
for the connection.
CSU-DATA request
Function:
- this primitive requests the transfer of a CSDU over an established CBR connection.
Semantics of the Service Primitive:
- CSU-DATA request;
- the CSDU parameter conveys a single CSDU.
When generated:
- this primitive is generated by an CSU whenever a CSDU is required to be transferred over a
connection.
Effect on receipt:
- the receipt of this primitive by the DQDB layer results in the DQDB layer attempting to transfer the
CSDU over the established connection. CSDUs are transferred in the same order in which they are
submitted by the CSU.

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CSU-DATA indication
Function:
- this primitive indicates the arrival of a CSDU over an established CBR connection.
Semantics of the service primitive:
- CSU-DATA indication (CSDU).
The CSDU parameter conveys a single CSDU.
When generated:
- this primitive is generated by the DQDB Layer to deliver a CSDU that has arrived over an
established CBR connection.
Effect on receipt:
- the effect of receipt of this primitive is dependent upon the CSU;
- the CSDUs shall be received by the receiving CSU in the same order in which they were sent by the
sending CSU.
7 Functional architecture
7.1 Access method
CBR service octets will be carried in the payload of PA slots. For the format of PA slots see Clause 8. In
particular, the payload of PA slots contains 48 octets. PA slots are generated by the slot generation
function at the HOB according to algorithms which are discussed in subclause 7.2.
Dedicated slot-switching shall be used for the nodes to gain access to CBR bandwidth in the payload of
the PA-slots on a DQDB bus.
In dedicated slot-switching, the octets of the payload of a PA-slot are associated with only one connection,
and there is a one-to-one correspondence between CBR connections and VCIs in the headers of PA-slots
on each bus.
NOTE: This is in contrast to "composite slot-switching" where different octet positions in one
PA slot may be associated with different connections. There is no contradiction
between the two access methods as dedicated slot-switching may be viewed as just a
particular way to use composite slot-switching.
7.2 Slot generation function at the HOB
In order to achieve interoperability of equipment it has to be specified how the PA slots associated with a
CBR connection (i.e. with a particular VCI) are generated by the HOB. The bandwidth provided by all PA
slots with a particular VCI defines a CBR connection on a DQDB subnetwork.
For a PLCP based on CCITT Recommendation G.703 at 34 Mbit/s or at 140 Mbit/s, all slots are fully
contained in a frame and may be used as PA slots.
For certain PLCPs, however, slots can cross frame boundaries. Furthermore, the number of slots which
are fully contained in a frame varies between Max and Max+1 where Max is an integer. In this case, in
order to simplify PA slot generation procedures, only the first Max complete slots in a frame may be used
as PA slots.

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For the PLCP for CCITT Recommendations G.707, G.708 and G.709 SDH based systems at 155 Mbit/s,
the payload of the PLCP frame is 2 340 = 44 x 53 + 8 octets. Here, the mapping of slots onto PLCP
frames has been defined such that slots are allowed to cross frame boundaries. Any given PLCP frame
will contain either 43 or 44 complete slots, i.e. Max = 43.
The slot generation process for a CBR connection is characterised at a minimum by the parameters of
"frequency" (see subclause 7.2.1) and "variability" (see subclause 7.2.2). The slot generation process is
further characterised by the attributes "basic" or "compound" (which are mutually exclusive). The term
"basic" means that the rate of the channel is a "basic data rate", i.e. a data rate associated with a
particularly simple slot generation process (see subclause 7.2.3). The term "compound" means that the
CBR connection is obtained by combining the bandwidth of two or more connections at basic data rates
(see subclause 7.2.4).
7.2.1 Frequency and periodicity
Frequency
The frequency parameter determines the average rate of the CBR channel. In general, CBR bandwidth
allocations are of the form "M slots every N frames". To make bandwidth allocation simple, M and N may
be constrained. PA slot generation by the HOB shall maintain the frequency of M slots every N frames for
each CBR connection.
NOTE: This definition requires two parameters, M and N, to specify frequency which have to
be included in the LM-ACTION invoke (PA VCI ADD HOB) service primitive (see Clause
10 below).
Periodicity
When frequency = (M, N) the HOB is required to generate the PA slots with a particular VCI periodically
with period N in the following sense: the k-th and the (k + N)-th PLCP frames (125 μs transmission frames)
shall contain the same number of PA slots with that particular VCI for k = 0,1,2,.
7.2.2 Variability
According to the periodicity requirement above the number of PA slots per frame associated with a
connection repeats every N frames. However, nothing is implied about the slot position within each frame,
hence variability is allowed there.
Slots in a frame can be numbered by starting with the first slot fully contained in the frame and numbering
from 1 to the last slot fully contained in that frame. Using this definition of slot number, variability V is
defined as the maximum difference in the slot number between the k-th and the (k + M)-th PA slots
allocated to a connection with slot generation frequency (M, N):
V = max { | S(k) - S(k+M) | }
where S(k) is the slot number of the k-th PA slot allocated to a connection and the max is taken over
k = 0,1,2,.
The minimum variability is V = 0. A default value, V , shall be chosen that all HOB stations will support
def
such that the possibility of CBR connections with no more variability than V can be assured. This default
def
value is chosen to be V = 0.
def

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Minimum variability
For a PLCP based on CCITT Recommendation G.703 at 34 Mbit/s or at 140 Mbit/s, the k-th slot in each
PLCP frame appears with precisely the same offset (i.e. precisely the same number of octets from the
beginning of the frame). Therefore, when V = 0 for a connection, PA slot appearances for that connection
are precisely periodic with period N frames, ignoring PLCP induced jitter.
Minimum variability would be supported for any given CBR connection by allocating to that connection the
same slot number(s) in each frame that contains slots for that connection (not necessarily in every frame).
For the PLCP for CCITT Recommendations G.707, G.708 and G.709 SDH based systems at 155 Mbit/s,
the offset of the k-th complete slot within a PLCP frame varies. It can be shown that the offset of the k-th
complete slot will never be identical between adjacent frames and will occasionally change by as much as
45 octets. Between non-adjacent frames, the change in offset for a given slot number depends on the
distance between frames. In the general case, the offset of a given slot number will vary by up to 52
octets (i.e. one less than the length of a slot).
7.2.3 Basic data rates
A basic data rate is one of the data rates out of the list below. It is associated with a particularly simple
slot generation process based on simple frequency parameter pairs.
For M=1, N may take on the values 1, 2, 4, 8, 16 and 48. For M=2, N=1 or N=3. For all other values of M,
N is equal to 1. These frequency parameter pairs define the basic data rates given in table 1.
Table 1
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