SIST-TP ETSI/ETR 257 E1:2005

SLOVENSKI STANDARD
01-januar-2005
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V interfaces at the digital Service Node (SN); Identification of the applicability of existing
protocol specifications for a VB5 reference point in an access arrangement with Access
Networks (ANs)
Ta slovenski standard je istoveten z: ETR 257 Edition 1
ICS:
33.040.40 Podatkovna komunikacijska Data communication
omrežja networks
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

ETSI ETR 257
TECHNICAL March 1996
REPORT
Source: ETSI TC-SPS Reference: DTR/SPS-03040
ICS: 33.020, 33.080
V interface, VB5 interface, SN, AN
Key words:
V interfaces at the digital Service Node (SN);
Identification of the applicability of existing
protocol specifications for a V reference point
B5
in an access arrangement with Access Networks (ANs)
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
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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 1996. All rights reserved.

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ETR 257: March 1996
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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ETR 257: March 1996
Contents
Foreword .7
1 Scope .9
2 References.10
3 Definitions and abbreviations .11
3.1 Definitions .11
3.2 Abbreviations .12
4 Electrical, physical and procedural interface requirements.13
5 Services and architecture aspects and requirements .13
5.1 General discussion on services .13
5.2 General requirements for broadband access networks.15
5.3 General architectural requirements for the V reference point .15
B5
5.4 Applicability of the connection types .21
5.4.1 Connection characteristics .21
6 ATM functionality required over a V reference point.22
B5
6.1 General concepts relating to the V reference point .22
B5
6.2 The V reference point.24
B5.1
6.3 The V reference point.25
B5.2
7 Narrowband accesses: Conclusions for implementations at the V reference point.26
B5
7.1 Conclusions on ATM caused speech path delays for narrowband services.26
7.2 Narrowband services: Speech path delay considerations .26
7.3 AAL1 definition for the support of narrowband services .26
8 Broadband access: The B-ISDN access requirements and V implementation .27
B5
8.1 Discussion - The B-ISDN access.27
8.2 The preferred B-ISDN signalling protocol .27
8.3 The data link layer for the B-ISDN signalling protocol .27
9 Broadband accesses: The LAN interconnect service requirements and V implementation.27
B5
9.1 LAN interface support - Type 1.27
9.2 LAN interface support - Type 2.27
10 Broadband accesses: The broadcast TV service requirements and V implementation .28
B5
10.1 Discussion - The broadcast TV service .28
11 Broadband accesses: Signalling bandwidth allocation.29
11.1 Signalling bandwidth allocation - General discussion .29
11.1.1 Dynamic signalling bandwidth allocation - for ATM bearers.29
12 Broadband accesses: Bearer channel bandwidth allocation and concentration .30
12.1 Bearer channel bandwidth allocation and concentration - General discussion .30
12.2 Establishment of signalling virtual channels .30
13 Implementing dynamic bearer connection allocation on a V reference point .30
B5
13.1 Functionality of a B-BCC protocol for use at a V reference point.31
B5
13.2 The data link protocol for the B-BCC protocol .31
14 Broadband accesses: Control protocol .31
14.1 Control protocol - General discussion.31

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ETR 257: March 1996
15 Broadband accesses: Link control protocol. 32
15.1 Link control protocol - General discussion . 32
15.1.1 Link control protocol - V . 32
B5.1
15.1.2 Link control protocol - V . 32
B5.2
16 Broadband accesses: Multiplexing cells for individual users onto a common transmission system
- General. 32
17 Broadband accesses: Conclusions for implementations at the V reference point. 33
B5
17.1 Conclusions on ATM caused speech path delays for broadband services:. 33
17.2 Conclusions on the preferred protocol to support narrowband services. 33
17.2.1 The preferred protocol to support a POTS or pseudo POTS service. 33
17.2.2 The preferred protocol to support narrowband ISDN based services . 33
17.3 Conclusions on the preferred B-ISDN signalling protocol . 33
17.4 Conclusions on the preferred B-BCC protocol for bandwidth allocation procedure. 33
17.5 Conclusions on the preferred control protocol . 34
17.6 Conclusions on the preferred link control protocol. 34
17.6.1 Link control protocol - V . 34
B5.1
17.6.2 Link control protocol - V . 34
B5.2
17.7 Conclusions on the preferred method of protection of signalling paths . 34
17.8 Conclusions on resource allocation and policing for a V based system. 34
B5
17.8.1 Conclusions on the use of the GFC field and its implementation in a V
B5
scenario . 34
17.8.2 Conclusion as to the use of the CLP bit of ATM messages at the V
B5
reference point. 35
18 Items for further study. 35
19 Future standardisation requirements for the V reference point. 35
B5
Annex A: Performance parameters associated with an ATM SN . 36
A.1 Introduction. 36
A.2 Measurement experience . 36
A.3 Proposal. 37
Annex B: Delay on the bearer channels associated with PSTN traffic . 38
B.1 Speech path delay considerations when an ATM bearer is used. 38
Annex C: Policing and the UPC/NPC functions . 39
C.1 UPC/NPC definition and description. 39
C.2 UPC/NPC location . 39
C.3 UPC/NPC in an AN-SN configuration. 39
C.3.1 UPC/NPC location. 39
C.4 Consequences. 41
Annex D: Examples of configurations of logical and physical user ports at the UNI. 42
D.1 General principles. 42
D.2 Examples of scenarios at the UNI . 42

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ETR 257: March 1996
D.3 Requirements for operation and maintenance.44
D.3.1 Grouping of blockable objects .44
D.3.2 Different requirements for AN and SN.44
D.3.3 Possible approaches to meet requirements .44
D.4 Conclusion.44
Annex E: General narrowband services discussion .45
E.1 Discussion - The PSTN service .45
E.1.1 The preferred PSTN signalling protocol.45
E.1.2 The data link layer for the PSTN signalling protocol.45
E.2 Narrowband services: The ISDN-BA requirements and V implementation .45
B5
E.2.1 Discussion - The ISDN-BA service.45
E.2.2 The preferred ISDN-BA layer 3 signalling protocol.45
E.2.3 The data link layer (layer 2) for the ISDN-BA signalling protocol.46
E.3 Narrowband services: The ISDN-PRA requirements and V implementation.46
B5
E.3.1 Discussion - The ISDN-PRA service .46
E.3.2 The preferred ISDN-PRA layer 3 signalling protocol .46
E.3.3 The data link layer (layer 2) for the ISDN-PRA signalling protocol .46
E.4 Narrowband services: Signalling bandwidth allocation.46
E.5 Narrowband services: The control protocol.47
E.5.1 Control protocol for narrowband services .47
E.5.2 The data link layer for the control protocol.47
E.6 Narrowband services: Link control protocol layer 3.47
E.7 Narrowband services: Protection of signalling cells at the V reference point .48
B5
Annex F: General discussion on dimensioning of ATM access networks.49
F.1 The V reference point .49
B5.1
F.1.1 The AN is used for broadband UNIs only .49
F.1.2 The broadband AN is used for 2 Mbit/s emulation only .49
F.1.3 The broadband AN with mixed traffic.50
F.2 The V reference point .50
B5.2
F.3 Conclusion on dimensioning of ATM networks .50
Annex G: Examples for the support of LAN interconnect via V .51
B5
G.1 User plane.51
G.1.1 V based access networks.51
B5.1
G.1.2 V based access networks.51
B5.2
G.2 Control plane .51
G.2.1 V based access networks.51
B5.1
G.2.2 V based access networks.51
B5.2
G.3 Management plane.52
History.53

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Foreword
This ETSI Technical Report (ETR) has been produced by the Signalling Protocols and Switching (SPS)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
ETRs are informative documents resulting from ETSI studies which are not appropriate for European
Telecommunication Standard (ETS) or Interim European Telecommunication Standard (I-ETS) status. An
ETR may be used to publish material which is either of an informative nature, relating to the use or the
application of ETSs or I-ETSs, or which is immature and not yet suitable for formal adoption as an ETS or
an I-ETS.
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ETR 257: March 1996
1 Scope
This ETSI Technical Report (ETR) examines the functional requirements for a broadband reference point
in conjunction with the previously defined V5, Narrowband Integrated Services Digital Network (N-ISDN),
and Broadband Integrated Services Digital Network (B-ISDN) protocols in order to define a useful set of
protocol component parts.
At this stage, the ETR does not attempt to define a unique protocol stack for a V reference point,
B5
because many possible network architectures have been identified, some based on an integrated
narrowband/broadband local exchange and others based on discrete local exchange architectures. All of
these would require different protocol stacks. Within ITU-T Study Group 13 (WP 3) Question 14/13, the
various architectures are being examined and provided in draft new ITU-T Recommendation G.902 [12]. It
might be possible to reduce the options listed in this ETR and come to a definite list of requirements
leading to definitive protocol stacks for the different types of interfaces at V reference points (i.e., V
B5 B5.1
and V ). However, this is left to the development of the individual ETSs.
B5.2
It has been identified that the B-ISDN service will only be provided over an ATM transmission bearer,
although that itself may be provided over a synchronous/plesiochronous data link network (e.g.
Synchronous Digital Hierarchy (SDH)). This somewhat simplifies the possible permutations of options.
New protocols may be identified for the V reference point as required.
B5
Access types so far identified to be supported by the V reference point include:
B5
- analogue telephone access;
- ISDN basic access with a line transmission system conforming to ETS 300 297 [4] for the case with
a NT1 separate from the Access Network (AN);
- ISDN basic access with a user network interface according to ETS 300 012 [2] at the user side of
the AN, (i.e. the interface at the T reference point);
- ISDN primary rate access with a line transmission system conforming to ETS 300 233 [3] for the
case with a NT1 separate from the AN;
- ISDN primary rate access with a user network interface according to ETS 300 011 [1] at the user
side of the AN, (i.e. the interface at the T reference point);
- other analogue or digital accesses for semi-permanent connections without associated out-band
signalling information;
- B-ISDN access;
- Non B-ISDN accesses supporting:
- asymmetric services (i.e. Video on Demand) (if not part of B-ISDN);
- broadcast services (if not part of B-ISDN);
- LAN interconnect functionality (if not part of B-ISDN),
with either:
- flexible (provisioned) Virtual Path Connection (VPC) allocation but without concentration capability
at the Virtual Channel (VC) level within the AN; or
- flexible (provisioned) VPC allocation and flexible Virtual Channel Connection (VCC) allocation on a
connection by connection basis which provides concentration capability at VC level.
This ETR does not specify the implementation of the requirements within the AN and does not constrain
any implementation alternative as long as the functionality at the V reference point as specified in this
B5
ETR is met.
Analysis of network architecture aspects are included. In particular, the relationship between narrowband
and broadband elements (ANs and SNs) are examined.

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ETR 257: March 1996
2 References
This ETR incorporates by dated and undated reference, provisions from other publications. These
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 ETR
only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies.
[1] ETS 300 011: "Integrated Services Digital Network (ISDN); Primary rate user-
network interface; Layer 1 specification and test principles".
[2] ETS 300 012: "Integrated Services Digital Network (ISDN); Basic user-network
interface; Layer 1 specification and test principles".
[3] ETS 300 233: "Integrated Services Digital Network (ISDN); Access digital
section for ISDN primary rate".
[4] ETS 300 297: "Integrated Services Digital Network (ISDN); Access digital
section for ISDN basic rate".
[5] ETS 300 324-1: "Signalling Protocols and Switching (SPS); V interfaces at the
digital Local Exchange (LE); V5.1 interface for the support of Access Network
(AN); Part 1: V5.1 interface specification".
[6] ETS 300 347-1: "Signalling Protocols and Switching (SPS); V interfaces at the
digital Local Exchange (LE); V5.2 interface for the support of Access Network
(AN); Part 1: V5.2 interface specification".
[7] ETS 300 125: "Integrated Services Digital Network (ISDN); User-network
interface data link layer specification; Application of CCITT Recommendations
Q.920/I.440 and Q.921/I.441".
[8] ETS 300 102-1: "Integrated Services Digital Network (ISDN); User-network
interface layer 3; Specifications for basic call control".
[9] ETS 300 443-1: "Broadband Integrated Services Digital Network (B-ISDN);
Digital Subscriber Signalling System No. two (DSS2) protocol; B-ISDN user-
network interface layer 3 specification for basic call/bearer control; Part 1:
Protocol specification [ITU-T Recommendation Q.2931 (1995), modified]".
[10] ITU-T Recommendation G.804 (1993): "ATM cell mapping into plesiochronous
digital hierarchy (PDH)".
[11] ITU-T Recommendation G.841 (1995): "Types and characteristics of SDH
network protection architectures".
[12] Draft new ITU-T Recommendation G.902: "Framework recommendation on
functional access networks. Access networks; Architecture, services,
management and service node aspects".
[13] ITU-T Recommendation I.356 (1993): "B-ISDN ATM layer cell transfer
performance".
[14] Draft ITU-T Recommendation I.363.1 (July 1995): "B-ISDN ATM adaptation
layer (AAL) specification, Types 1 and 2".
[15] Draft ITU-T Recommendation I.371 (July 1995): "Traffic control and congestion
control in B-ISDN".
[16] Draft ITU-T Recommendation I.432 (Nov 1994): "B-ISDN user-network interface
- Layer 1 specification".
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ETR 257: March 1996
[17] Draft ITU-T Recommendation I.610 (Nov 1995): "B-ISDN operation and
maintenance principles and functions".
[18] CCITT Recommendation X.731 (1992) | ISO/IEC 10164-2 (1993): "Information
technology - Open systems interconnection - Systems management: State
management function".
[19] ITU-T Recommendation I.361 (1993): "B-ISDN ATM layer specification".
[20] ITU-T Recommendation I.150 (1993): "B-ISDN asynchronous transfer mode
functional characteristics".
[21] Draft new ITU-T Recommendation I.432.1 (July 1995): "B-ISDN user-network
interface - Physical layer specification for 155 520 kbit/s and 622 080 kbit/s".
[22] Draft new ITU-T Recommendation I.432.2 (July 1995): "B-ISDN user-network
interface - Physical layer specification for 1 544 kbit/s and 2 048 kbit/s".
[23] Draft new ITU-T Recommendation I.432.3 (July 1995): "B-ISDN user-network
interface - Physical layer specification for 51 840 kbit/s".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETR, the following definitions apply, in addition to those given in the referenced
standards:
Access Network (AN): An implementation comprising those entities (such as cable plant, transmission
facilities, etc.) which provide the required transport bearer capabilities for the provision of
telecommunications services between a Service Node Interface (SNI) and each of the associated User
Network Interfaces (UNIs). An AN can be configured and managed through a Q3 interface. In principle
there is no restriction on the types and the number of UNIs and SNIs which an AN may implement. The
AN does not interpret (user) signalling (see ITU-T Recommendation G.902 [12]).
asymmetric services: Services requiring different bandwidths in each direction at the same point in time.
complete user port: The sum of the physical links at an ATM UNI.
logical user port: The set of VPs at the UNI carried on one or several physical access links associated
by provisioning to one single VB5 reference point.
(semi)permanent connection: This is a connection which is set up via management (i.e. triggered via
Q3 and/or Q3 ).
AN SN
NOTE: There may be connections through the AN which are established via management
(Q3) which bypass the service node and which are routed e.g. to a dedicated "leased
line service network". These connections shall have no impact on the V specification
B5
and are out of scope of the ETR and the future V ETSs.
B5
Service Node (SN): A network element that provides access to various switched and/or permanent
telecommunication services. In case of switched services the SN is providing access call and connection
control signalling, and access connection and resource handling.
switched connection: This is a connection which is set up in response to user-to-network signalling.
user port function: This function adapts the specific UNI requirements into the core and system
management functions (see ITU-T Recommendation G.902 [12]).

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ETR 257: March 1996
V : The VB5 reference point.
B5
V : The VB5 reference point with flexible (provisioned) VPC allocation but without concentration
B5.1
capability at VC level within the AN.
V : The VB5 reference point with flexible (provisioned) VPC allocation and flexible VCC allocation on a
B5.2
connection by connection basis which provides concentration capability at VC level.
3.2 Abbreviations
For the purposes of this ETR, the following abbreviations apply:
AAL ATM Adaptation Layer
AN Access Network
ATM Asynchronous Transfer Mode
BA Basic Access
BCC Bearer Channel Connection
B-AN Broadband Access Network
B-BCC Broadband BCC
B-ISDN Broadband ISDN
CBR Constant Bit Rate
CLP Cell Loss Priority (bit)
ET Exchange Termination
GFC Generic Flow Control
HDLC High level Data Link Controller
ILMI Interim LMI
ISDN Integrated Services Digital Network
LAN Local Area Network
LAPD Link Access Protocol for the D-channel
LE Local Exchange
NB Narrowband
N-ISDN Narrowband ISDN
NNI Network Node Interface
NPC Network Parameter Control
NT Network Termination
PDH Plesiochronous Digital Hierarchy
PNOs Public Network Operators
POTS Plain Old Telephony Service
PRA Primary Rate Access
PSTN Public Switched Telephone Network
QOS Quality Of Service
SAAL Signalling ATM Adaptation Layer
SDH Synchronous Digital Hierarchy
SN Service Node
SNI Service Node Interface
TE Terminal Equipment
TMN Telecommunications Management Network
TV Television
UNI User Network Interface
UPC Usage Parameter Control
VC Virtual Channel
VCC Virtual Channel Connection
VCI Virtual Channel Identifier
VC Sw Virtual Channel Switching function
VP Virtual Path
VPC Virtual Path Connection
VPCI Virtual Path Connection Identifier
VPI Virtual Path Identifier
VP XC Virtual Path Cross Connect function
XC Cross Connect
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ETR 257: March 1996
4 Electrical, physical and procedural interface requirements
It is outside the scope of this ETR to specify the electrical and physical interfaces for the V reference
B5
point. The physical interface shall however be a standard interface (e.g. SDH or PDH). Future ETSs may
provide a limited list of options for physical interfaces in order to restrict the choice of the physical interface
to a reasonable number of possibilities. This is to avoid unnecessary diversity of physical implementations,
which would increase development costs and would threaten connectivity in multi-vendor environments.
This will allow manufacturers and purchasers to develop the most flexible designs from the standards
without having to modify the European standards every time a new access mechanism across the V
B5
reference point is specified.
It has been accepted that an indication of the range of rates to be supported should be indicated as this is
likely to affect the addressing range required by V -related protocols.
B5
It is suggested that the V reference point should be applicable for data rates in the range 1,5 Mbit/s to
B5
2,488 Gbit/s (STM16) although other rates are not excluded.
Draft new ITU-T Recommendations I.432.x ([21] to [23]) provide in a flexible form the B-ISDN user-
network (UNI) physical layer specifications which cover:
a) cell based and SDH-based UNIs at 155 520 kbit/s and 622 080 kbit/s (ITU-T Recommendation
I.432.1 [21]);
b) PDH based UNIs at 1 544 kbit/s and 2 048 kbit/s (ITU-T Recommendation I.432.2 [22]);
c) UNIs at S reference point at 51 840 kbit/s (ITU-T Recommendation I.432.3 [23]).
B
Reference is made to ITU-T Recommendation G.804 [10] for other interfaces, for national use. ITU-T
Recommendation G.804 [10] covers the PDH-based physical layers which are defined for ATM
transmission.
It could be appropriate to have maximum commonality between the physical layer functions at the V
B5
SNIs (and NNIs) and the physical layer functions at the UNI defined in ITU-T Recommendations I.432.x
([21] to [23]).
No V specific protection switching mechanism will be defined for the V reference point or interface.
B5 B5
Existing or future mechanisms defined for the physical layer shall be used for V (see e.g. ITU-T
B5
Recommendation G.841 [11]).
5 Services and architecture aspects and requirements
5.1 General discussion on services
The broadband architectures defined for use under the general title of B-ISDN should become the
predominant telecommunications services at some point in the future. At present, the narrowband
services such as Public Switched Telephone Network (PSTN), ISDN-BA and ISDN-PRA are the
predominant service offerings by telecommunications operators. There will need to be an interim
changeover period when broadband and narrowband services co-exist over the same Access Network
infrastructure. It was originally anticipated that V would only be of use during this interim period although
B5
this assumption is under review.
What is more certain is that there is now a need for Access Networks supporting both narrowband and
broadband services over common transmission systems and that this situation is likely to persist for some
time.
The services to be supported across the V reference point include all those supported by V5.2 with the
B5
addition of symmetrical and asymmetric broadband services, broadcast services, and a LAN interconnect
function. However, it is not the intention of this reference point specification to restrict any implementation
of ANs or SNs to support the full set or a subset of the services listed in this ETR.

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ETR 257: March 1996
It is anticipated that many of the principles developed for the V5 interfaces will also apply here. The most
fundamental of which are:
1) That signalling for N-ISDN and B-ISDN services should be handled as near to transparently as
possible. This means that the contents of signalling messages should not be checked unless it is
unavoidable.
2) That tones and announcements should be generated in the service node(s) and not in the access
networks themselves.
3) Charging information is only provided by the service node. This information may be passed over the
V reference point when a user requires it as part of the service to which he has subscribed and is
B5
not passed over the V reference point as a means of providing information for use by the access
B5
network itself.
4) That it is not a requirement for local switching to be carried out within the Access Network itself,
either under SN control or under local control.
5) That the architecture should be designed in such a way as to minimise the costs of implementing
the architecture.
6) Concentration shall be supported across a V reference point as an option (although it shall
B5
always be possible to guarantee bandwidth for user ports who require such a facility such as the
security services).
7) In order to support non-ATM interfaces at the AN, semi-permanent virtual connections originating at
the user ports have to be provided (for further study).
8) The V reference point shall not be limited to a single physical interface (for redundancy and to
B5
allow more user ports to be connected).
9) The AN shall perform the UPC function prior to cross connecting different traffic sources towards
the V reference point (to ensure that errant users do not cause miss-operation at the V
B5 B5
reference point which could affect other user ports).
10) Technology specific functions, such as control of echo cancellers which might be required in a radio
based access network, shall not be supported unless they are already supported by either V5 (in
the case of narrowband services) or B-ISDN (in the case of broadband services).
11) Selection of the service provider (i.e. service node) by the user using the control plane (signalling)
shall not be possible in the access network. This would require service node functionality in the
access network. However, at the UNI different VPs could be statically provisioned such that they
are assigned to different V interfaces belonging to different service node. This would allows the
B5
user of a B-ISDN terminal to choose the service provider by selecting dynamically a certain VP.
NOTE: No equivalent functionality is provided by V5 interfaces.
12) If multicasting in the AN is used to support broadcast services, this shall be allowed to be performed
in the SN to AN direction only. Otherwise multicasting is presumed to be a service provided by the
service node functionality.
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ETR 257: March 1996
5.2 General requirements for broadband access networks
Many of the requirements for access systems have been well defined and have already been discussed at
depth. Additional functionality may be required for access networks incorporating broadband functionality.
In particular, the following principles can be identified:
An access network is used in order to multiplex the signalling and data streams from user/network
interfaces (UNIs) together in the most cost effective manner and then to present the multiplexed
information stream so formed back to the local exchange or service node (SN) in a manner such that the
SN can determine the source UNI from which it originates. The aims of the reference point between the
SN and the access network (AN) is to reduce the costs of the reference point and to reduce the amount of
equipment/cabling etc. needed in order to support multiple UNIs over the case when each of the UNIs
were directly connected to the SN over dedicated equipment (whether optical, copper or other).
The SN needs to know the transforms allied to the information streams in order to correctly demultiplex
these data streams and then to process them as if they where UNIs directly connected to the exchange
from a service point of view.
In the other direction, the SN needs to be able to route signalling and data to the UNIs individually over the
multiplexed reference point.
Figure 1 shows the general case of n UNIs being connected to one access network. On the other side of
the access network, there is only one multiplexed connection back into the SN.
Access Network
UNI 1
Service Node
AN to SN
UNI 2
reference point
(VB5)
UNI n
Figure 1: Multiple UNIs hosted back to one service node port
5.3 General architectural requirements for the V reference point
B5
The architecture of the V reference points from a service point of view is as yet undefined. It has been
B5
identified that the way that the architecture of the Local Exchange(s) is designed can significantly affect
the protocol stacks in order to serve them. In order to identify the protocol component parts, it is hence
necessary to define the architectures of interest. A generalised model is first presented as figure 2, and
then more detailed cases are shown:

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ETR 257: March 1996
ACCESS NETWORK
SN (function)
(5)
(5)
BB AN
BB SN
BB
(function)
Accesses (function)
For the circuit emulation
(4) (4)
function reference should
be made to the
Transmission
appropriate clause
Node
in this ETR
circuit
circuit
(function)
emulation emulation
function
function
(3)
(3)
NB AN NB SN
NB
(function)
(function)
Accesses
(2) (2)
(1)
(1)
(1) V5 Interface between NB AN and SN
(2) V5 Interface over (possibly shared) transmission node function
Note: Scenario 1 : VB5 only for BB services
(3) V5 functionality but physical layer provided by ATM circuit emulation
Scenario 2: VB5 for BB services and also for NB
(4) BB over (possibly shared) transmission node function
(2Mbit/s circuit emulation)
(5) BB Interface between AN and SN
Figure 2: General architectural scenarios
Access Network (AN)
PSTN Access
TE
broadband
VB5
ISDN-BA
Service
Node
TE
ISDN-PRA
TE
Analogue Leased Line
TE
Digital Leased Line
TE
narrowband
V5
Service
B-ISDN
Node
TE
LAN Interconnect
TE
B/CAST Rx
TE
Leased Line
Service
Network
Figure 3: V service architecture (separate broadband/narrowband SNs)
B5
In the case of figure 3, the V5 interface (either V5.1 (ETS 300 324-1 [5]) or V5.2 (ETS 300 347-1 [6])) shall
apply to the narrowband interface between the SN and the AN and shall not be considered further.

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ETR 257: March 1996
For the architectural scenario presented in figure 3, taking into account the V5.2 interface only, the
protocol stacks given in figures 4 and 5 are relevant:
Application
64kbit/s Services
(eg POTS, ISDN-BA,
ISDN-PRA)
PSTN L3
BCC
Q931
Protection
(ISDN-BA
Control and/or
SDN-PRA)
link control
LAP V5 DL
LAPD B channels
LAPV5-EF LAPV5-EF 28-31 * 64Kbit/s
V5 L1 (1 to 16)
NOTE: One frame relay and one LAP V5 DL instance per above protocol.
Figure 4: V5.2 Protocol Stack related to figure 3
VB5
Application
ATM
(eg BISDN)
VB5-specific
L3
Broadband Q2931
SAAL
Bearer SAAL
ATM layer
Physical Layer (e.g. SDH)
Figure 5: VB5 reference point protocol stack related to figure 3

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ETR 257: March 1996
In the case of figure 6, separate narrowband and broadband SNs co-exist in the network. The narrowband
SNs may be the old, legacy networks whilst the broadband SNs are likely to be new additions into the
network. It is possible that this network architecture would be of use in the short term in order to support
both narrowband and broadband services.
From the point of view of the narrowband local exchange the broadband exchange looks like a
transmission system and does not affect the narrowband service in any way. In practise the effect of this
is to change the physical layer as seen at the V reference point.
B5
Access Network (AN)
PSTN Access
TE
broadband narrowband
VB5 V5
ISDN-BA
Service
Service
Node
TE
Node
ISDN-PRA
TE
Analogue Leased Line
TE
Digital Leased Line
TE
B-ISDN
TE
LAN Interconnect
TE
B/CAST Rx
TE
Leased Line
Service
Network
Figure 6: V service architecture (broadband with narrowband SN behind)
B5
The protocol stack associated with the architecture shown (broadband with narrowband SN behind) is
given in figure 7. In this case, the narrowband services are shown as supported within a 2 Mbit/s V5
stream (see details in this ETR).
VB5
Application
Application
Application
64kbit/s Services
ISDN-PRA (V3)
ATM
(V5 equivelent)
(eg BISDN)
(eg POTS, ISDN-BA,
ISDN-PRA)
PSTN L3
BCC
Q931
Protection (ISDN-BA
and/or
Control
link control SDN-PRA) Q931
(SDN-PRA)
LAP V5
LAPD B channels B channels
VB5-specific
LAPV5-EF LAPV5-EF 28-31*64Kbit/s Q921 30 * 64Kbit/s
L3 Broadband Q2931
SAAL Bearer SAAL 2Mbit/s - AAL1 2Mbit/s - AAL1
ATM layer
Physical Layer (e.g. SDH)
NOTE: One frame relay and one LAP V5 DL instance per above protocol.
Figure 7: V reference point protocol stack associated with figure 6
B5
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ETR 257: March 1996
In the case of figure 8, the integrated narrowband/broadband SNs are likely to be completely new. It is
possible that this is a cost-effective manner in which narrowband services can be supported in the
medium time scale of network evolution.
Access Network (AN)
PSTN Access
TE Integrated
broadband/
VB5
ISDN-BA narrowband
Service
TE
Node
ISDN-PRA
TE
Analogue Leased Line
TE
Digital Leased Line
TE
B-ISDN
TE
LAN Interconnect
TE
B/CAST Rx
TE
Leased Line
Service
Network
Figure 8: V service architecture (integrated broadband/narrowband SN)
B5
The protocol stack associated with the architecture shown (integrated broadband/narrowband SN) is given
in figure 9. In this case, the narrowband services are shown as supported within a 2 Mbit/s V5 stream (see
details in this ETR).
VB5
Application Application
Application
64kbit/s Services ISDN-PRA (V3)
ATM
(eg BISDN) (V5 equivelent)
(eg POTS, ISDN-BA,
ISDN-PRA)
PSTN L3
BCC
Q931
Protection
(ISDN-BA
and/or
Control
SDN-PRA)
link control Q931
(SDN-PRA)
LAP V5 DL
VB5-specific LAPD B channels B channels
LAPV5-EF lapV5 - EF 28-31*64Kbit/s Q921 30 * 64Kbit/s
L3 Q2931
Broadband
SAAL Bearer SAAL 2Mbit/s - AAL1 2Mbit/s - AAL1
ATM layer
Physical Layer (e.g. SDH)
NOTE 1: One frame relay and one LAP V5 DL instance per above protocol.
NOTE 2: As figure 7 (the V5 link control and protection protocols are redundant but retained in order to
minimise the number of software variants.
Figure 9: V reference point protocol stack associated with Fig 8.
B5
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ETR 257: March 1996
NOTE: There is some question as to whether there is any value in maintaining either the link
control protocol or the protection protocol for the case of figure 9 (see clauses later
within the ETR).
Figure 10 shows the case when narrowband services are no-longer supported. In this case V will only
B5
be used if it gives advantages to the operation/support of the broadband exchanges.
Access Network (AN)
B-ISDN
TE
Broadband
VB5
Service
LAN Interconnect
Node
TE
Digital Leased Line
TE
B/C
...