Pan-European broadband standardization

standardization

Pan-European b r o a d b a n d standardization Brian Moore

reviews

standardization activities for broadband in Europe and

In themid-1980s, when the basic concepts of a narrowband Integrated Services Digital Network (ISDN) carrying bit rates up to 2Mbit/s had been agreed and the detailed specification work was underway, attention turned to Broadband ISDN

worldwide, and (B-ISDN). describes the The main feature of the achievements ISDN concept is the supto date

port of a wide range of audio, video and data applications in the same network. A key element of service integration for an ISDN is the provision of a wide range of services to a broad variety of users utilizing a limited set of connection types and multipurpose user-network interfaces, B-ISDNs will support both non-switchedconnections and switched connections for circuit-mode

ANNEX 1: CCITTB-ISDN Draft Recommendations Recommendationl.113 Vocabulary of Terms for Broadband Aspects of lSDN Consists primarily of terms and definitions considered essential to the understanding and application of the principles of B-ISDN.

Recommendation 1.121 Broadba:ndAspec~s oflSDN includes the basic principles of B-ISDN and indicates further: developments of the ISDN network capabilities to support more advanced services and applications. The Recommendations take into account the:

• emerging demand.for broadband services: • availability of high speed transmission, switching and signal processing technologies; • improved data and u~nageprocessing capabilities availabie to the user; • advances in software application processing in the computer and telecommunication industries; • need to integrate bolh interactive and distribution services; • need to integrate both circuit and packet transfer mode into one universal broadband network: • need to provide flexibility in satisfying the

vol 14 no 5 june 1991

and packet-mode services, They will contain intelligence for the purpose of providing service features, maintenance and network management functions, perhaps for some new services supplemented by either additional intelligence within the network, or possibly compatible intelligence in the user terminals. Extensive collaborative R&D activities such as RACE have been examining the technologies likely to be available to realize broadband networks, and the standardization bodies in Europe and worldwide have been studying the 'target' network infrastructures that will be necessary to provide broadband services. These have culminated in an agreement that Asynchronous Transfer Mode (ATM) switching and Synchronous Digital Hierarchy (SDH)-based transmission networks will be among the key enabling technologies. Standardization of networks, interfaces, transmission systems, etc., based on ATM and SDH is now well underway,

The standardization picture

Worldwide The CCITT (Consultative Committee for International Telegraphy and Telephony), during its 1985-88 Study Period, established in Study Group XVIII a Broadband Task Group. The studies resulted in a CCITT

Recommendation 1.121 published in the CCITT Blue Book, and a status report on broadband aspects of ISDN. These have formed the basis of the work programme for the current 1989-92 Study Period. Broadband studies have continued in Study Group XVlII, which at its meeting in November 1990 agreed 13 draft Recommendations to be submitted to the accelerated approval procedure. If all has gone well, these should have reached full Recommendation status by May 1991. (These Recommendations are outlined in Annex 1.) Work will now concentrate on developing the Recommendations further, and the agreed objective is that the 1992 Recommendations should be sufficiently detailed to allow the initial support of commercial B-ISDN services using standardized procedures and interfaces. To extend the 1990 BISDN Recommendations to reflect these objectives, particular attention in the next two years will be required on: • signalling aspects of B-ISDN; • resource management procedures and specification; • description of initial B-ISDN services; • adaptation layer procedures and specification to support a range of B-ISDN services; • operation and maintenance capabilities sufficlent to support initial commercial services; • full specification of ATM aspects, including access flow control and ATM layer management; • finalization of user-

313

standardization network interface aspects, In addition to the standards for B-ISDN, the CCITT has been developing a number of standards which concern the Synchronous Digital

meeting in November 1 990 agreed three draft Recommendations on SDH which, along with the BISDN Recommendations mentioned above, have been submitted for accelerated approval. (An outline

Hierarchy (SDH). Recommendation G.702 specifies a number of digital hierarchy bit rates for 1544 kbit/s and 2048 kbit/s based digital networks, and these have conventionally been interconnected by means of digital multiplexing

of the SDH Recornmendations is given in Annex 2.)

employing justification methods. However, more recently there has been a growing interest in the use of synchronous digital multiplexing and a related Synchronous Digital Hierarchy (SDH). This offers advantages such as:

band standards, In 1984 the CEPT (Conference on European Posts and Telecommunications Administrations) established a special group to study broadband. The work of the group has laid the foundation for much of what is now included in the

• simplified multiplexing/ demultiplexing techniques; • direct access to lower speed tributaries, without the need to multiplex/ demultiplex the entire high speed signal; • enhanced ()AM capabilities; • easy growtl~ to higher bit rates in step with evolution of transmission technology, The Synchronous Digital Hierarchy bit rates have been chosen to both accommodate the Recommendation G.702 bit rates and those of broadband networks. The first level of the synchronous digital hierarchy is 155.52 Mbit/s. Higher levels are based on integer multiples of the first level. So far, multiples of 4 and 16 have been included (i.e. bit rates of 622.08 and 2,488.32 Mbit/s). Study Group XVIII at its

314

Europe

In parallel with the CCITT's studies, a number of European manufacturers and operators have been actively pursuing broad-

CCITT Recommendations on B-ISDN. It produced two status reports, one in 1986 and a second in 1988. The first report considered a number of technical aspects of broadband networks, and surveyed the broadband activities and plans of the CEPT administrations. The second report of the group issued at the end of 1988 after the CEPT work had been transferred into the new ETSI (European Telecommunications Standards Institute)laid the foundation for the B-ISDN standards. The broadband standardization activities have continued in ETSI in Sub Technical Committee NA5 of the Network Aspects Technical Committee. STC NA5 is active in the areas:

currently following

• broadband network and user interfaces;

requirements of both users and operators; • need to cover broadband aspects of SDN n CCITT Recommendations. Recommendation 1.150 B-ISDN ATA4 Functional Characteristics

AddressesATM layer functions. This layer is common to all services including signalling and OAM. ATM is the transfer mode solution for implementing a BISDN. It influences the standardization of digital hierarchies, multiplexing structures, switching and interfaces for broadband signals. ATM is a specific packet-oriented transfer mode using asynchronous time division multiplexing techniques The multiplexed information flow is organized into blocks of a fixed size called cells. A cell consists of an information field and a header. The primary role of the header is to identify cells belonging to the same virtual channel within the asynchronous time division multiplex. Transfer capacity Js assigned by negotiat on, and is based on the source requirements and the available capacity. Cell sequence integrity on a virtual channel connection is preserved by the ATM layer.

RecommendationL211 B-fSDN Service Aspects This is a guide to the objective of providing detailed recommendations on specific standardized services to be supported by a B-ISDN. The purpose is to: (i) provide a classification of such serwces; (ii) provide some considerations on the means for the description of such services; (iii) give a basis for the definition of the network capabilities required by B.ISDN. The Recommendation takes into accounl some of the known and relevant aspects of the B-ISDN including: • capabilities for increased flexibility to both user and network operator, including independent call and connection control; • the Quality of Service implications of information being structured and transported in cells; • capabilities for flexible bandwidth allocation: • capabilities to provide service.timing information; • the overall interface capabilities, The Recommendation also gives guidance on video coding, taking into account characteristics of the ATM-based network, and recommends a common approach to video coding for visual services including both interactive and distribution type services, Recommendation 1,311 B+lSDNGeneral Network Aspects

Describesnetworking techniques, signalling principles, traffic control and resources management for B-ISDN. Recommendation !.321 B+ISDNProtocol Reference Model and iLs Application

Basedon the general fSDN protocol RM as defined in Recommendatior~ 1.320. This Recommendation takes accoLull of the functionalities of B-fSDN as an expansion of the ISDN protocol RM. In this Recommendation the protocol RM is called 'B-ISDN PRM'.

computer communications

standardization Recommendation 1.327 [Y-fSDN Functional Architecture The objective of this Recommendation is to provide a bas:ic functional architecture of the B-ISDN to cornplement the general functional architecture rnodel for ISDN as described in Recommendation 1.324. The concepts and associated definitions adopted in Recommendation 1.324 also apply to the B-ISDN, i.e. Reference Configurations, Functional Groups, Reference Points. The mode is nol intended to require or exclude any specific implementation of the B-fSDN, but io provide a guide for the specification of B-ISDN capabilities, Recommendation 1.361 B.ISDNATL Layer Specification Addresses the cell structure, the ATM cell coding and the ATM protocol procedures.

Recommendations !.362 and l.363 B-tSDNATMAdaptationLayer(AAL) Functional Descriptionfl.362) and Specification (I,363) The AAL enhances the services provided by the ATM layer to support the functions required by the next highest layer. The AAL performs functions required by the user, control and management planes and supports mapping between the ATM and next highest l a y e r .

Recommendation 1.413 B.tSDNUser-Network Interface Gives reference configuration for B-ISDN UserNetwork Interface (UNI), and examples of physical realizations. Describes Physical Laver information flows according to the B-ISDN protocol RM, and identifies interface functions. Also addresses operation and maintenance issues as they relate to the reference configuration at the user access and to the interface specifications, Recommendation 1.432 B-ISDN User-Network Interface - Physical Layer This defines a limited sol of Physical Layer interface structures to be applied to the B-1SDN UNI. tt addresses separately the physical rnedia and the transmission systern structure thai may be used at these interfaces, and also addresses the implementation of the UNI-related OAM functions. The selection of the physical mediurn for the interfaces should take into account thai optical fibre is the agreed preferred medium to cable customer equipment. To accommodate existing cabling of customer equipment, other transmission media (e.g. coaxial) are not precluded, Also. irnptementation will allow terminal interchangeability.

Recommendation 1.610 OAM Principles of the B-15DNAccess OAM functions for B-ISDN are based on OAM principes applied to the narrowband ISDN. Primarily coyers the maintenance of the B-tSDN UNI and the customer access controlled by the network. It follows the maintenance principles as defined in the CCITT's M.20 Recommendation.

vol 14 no 5 june 1991

duction of telecommunications networks and services • among the European telecommunications operators, the CEPT has developed a • number of Memoranda of Under~anding(MOU). The MOUs are open for • signature by any of the CEPT operators who wish • to abide by the conditions laid down. MOUs have so far been developed in the areas of ISDN, cellular • radio, radio paging and one-stop shopping. Two In the area of SDH, the ETSI further MOUs in the area Technical Committee on of broadband networks transmission systems (TM) and services, namely EBIT has been developing and METRAN, have been European views, and con- the subject of recent tributing to CCITT's work. debate. The intention is that ETSI will develop a set of European European Broadband

•

B-ISDN operational and maintenance aspects; protocol Reference Models and signalling principles; ATM Adaptation Layer and coordinationfor ATM studies in ETSI; network architecture and evolution; traffic control and resource management and ATM matters relating to traffic control; video coding,

Telecomms Standards (ETS) on B-ISDN and SDH which will refer to the CCITT Recommendations where they are applicable to the European environment. ETSI will only develop additional specifications in areas where the CCITT Recommendations are incomplete, or contain options which have to be closed,

Interconnection Trial The general aim of the EBIT project was to provide during 1991 a broadband switched network capability throughout Europe, in a timescale consistent with Part III of the RACE programme, to be used for RACE Application Pilots. It was also the aim of the project to obtain an indica-

• In order to maximize the suitability of the CCITT Recommendations, ETSI has been collaborating with the T1 standards organization in the US, and with the Japanese standards body. The aim has been to share objectives and proposals in

tion of likely future demands for broadband services, and possibly to act as a market stimulus for these services. The EBIT network was to have been based on existing technology and standards in order to provide a broad-

support of the CCITT studies, Currently, STC NA5 and TC TM are developing some 55 draft ETSs and Technical Reports in the areas of BISDN and SDH, most of which should be available by the end of 1991.

band communications infrastructure as a basis for a trial Europewide 1920 kbit/s network with calls being connected on demand or by a reservation service. However, since the original drafting of the MOU a number of uncertainties have led to a reap-

European initiatives

praisal of the objectives. At the present time, the project is going ahead, although with objectives dif-

In order to assist in the harm()nization of plans for the intro-

315

standardization ferent from the original concepts. A number of European operators have signed an agreement to collaborate on the provision on n x 64 kbit/s services on a commercial basis, and this is being progressed under the auspices of EBIT. M a n a g e d European Transmission N e t w o r k

The MOU on METRAN is intended to lead to the implementation of a trans-

mission network which is service independent and flexible enough to meet the cost and quality needs of all current and anticipated emerging service networks, The networkwill connect designated national gateways, and will provide access into the national networks. It will be an optimized network, planned to common rules and principies agreed on a pan-

ANNEX 2: CCITT Recommendations on SDH

Recommendation G.707 Synchronous Digital Hierarchy Bit Rates

Provides an outline of the set of Recommendations on SDH and details the bit rates of the SDH.

Recommendation G.708 NNI for the Synchronous Digital Hierarchy

This describes the frame structure for multiplexed digital signals at the Network Node Interface of a synchronous digitat network (including ISDN). Recommendation G.709 Synchronous A4ultiplexing Structure

This describes the formats for multiplexing and mapping information and overhead elements at the NNI

European basis, and it will be based on ETSI and CCITT standards. It is anticipated that METRAN will take advantage of the remotely controlled automatic flexibility of SDH-based cross-connect and line systems, and will include automatic network management. Primarily, optical fibre will be used, but radio and satellite links will be incorporated on consideration of cost and quality. Cross-connects are anticipated to be in service by the mid-1990s, and later possible enhancements of the network, to include" ATM switching, are to be considered. Plans for METRAN are currently progressing well. A number of European telecommunications operatOtS have already signed the Memorandum Of Understanding, and management and project leadership structures are being put into place.

A version of this paper was presented at Blenheim's Broadband '91 Conference. Proceedingsfrom BlenhemOnline, Ash Hill Drive, Pinner,Middlesex HA5 2AE, UK Tel: 081 868 4466

::::::::::::~::~:::;::::::::::::~:::~::::::::::::::::::::::::::::::~:::~:~::::~::~:::~::::::::::::::::::::::::::::::::::::~;~;:::5::~:~::~:::::::::::::::::::::::::::::::::::::~:~:::::::::::::::::::::::::::::::::::::::::

316

computer communications