Next generation networks




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9.3Service considerations


PSTN/ISDN services which are traditionally provided by Circuit Switching systems whether digital or analogue may be provided by application servers (ASs) in the NGN. It is expected that some or all of the legacy services will be provided by the NGN.

However, there is no guarantee that all services will be provided when PSTN/ISDN is simulated. Use of legacy terminals via adaptation to the NGN is expected in order to support existing services.



  • Bearer services: During the migration process from PSTN/ISDN to the NGN, bearer services should be provided continuously. All bearer services shall be transparent for use of the NGN to connect PSTN/ISDN. NGN should provide same or better QoS for PSTN/ISDN bearer services;

– PSTN/ISDN simulation provides functionality that is similar but not identical to existing PSTN/ISDN bearer services.

– PSTN/ISDN emulation shall be capable of providing all bearer services offered by PSTN/ISDN. However, there is no requirement for the NGN to support all N-ISDN bearer services identified in the ITU T I.230 series Recommendations.



  • Supplementary services: During the migration process from PSTN/ISDN to the NGN, supplementary services should be provided to the extent practical. PSTN/ISDN emulation shall provide support for all supplementary services offered by PSTN/ISDN while PSTN/ISDN simulation provides functionality that is similar but not identical to existing PSTN/ISDN services. The NGN need not support all ISDN supplementary services identified in I.250 series of ITU-T Recommendations. NGN shall appear transparent when used to connect supplementary services between PSTN/ISDN;

  • Service requirements by national regulatory bodies: Following requirements are required by national/regional regulation or law, an NGN service provider shall provide which means in the case of interworking;

  • the basic telephone service with the same or better quality and availability as the existing PSTN/ISDN;

  • the capability for accurate accounting and charging;

  • capabilities to support number portability;

  • the availability of a directory inquiry service for PSTN/ISDN and the NGN users;

  • support of emergency telecommunications;

  • support for all users, including the disabled. Support should provide at least the same capabilities as the existing PSTN/ISDN. NGN offers the opportunity for more advanced support, e.g., network capabilities for text to speech;

  • mechanisms to support lawful interception and monitoring of various media types of telecommunications such as voice, data, video, e-mail, messaging, etc. Such a mechanism may be required of a network provider for providing access to content of telecommunication (CT) and intercept related information (IRI) by law enforcement agencies (LEA), to satisfy the requirements of administrations and international treaties;

  • interoperability between an NGN and other networks e.g., PSTN/ISDN and PLMN (Public Land Mobile Networks).

  • Accounting, charging and billing: During the transition period, maintaining the existing accounting, charging and billing procedures, to the extent practical, may be required. Migration from existing networks to the NGN will also imply replacement of the existing sources of the accounting data generation. The NGN shall support both offline and online charging;

  • Interworking: Interworking is used to express interactions between networks, between end systems, or between parts thereof, with the aim of providing a functional entity capable of supporting an end-to-end telecommunication. PSTN/ISDN migration to the NGN should take the following into consideration:

  • Ability to interwork with legacy networks such as PSTN/ISDN and internet

  • Ability to interwork with IMS-based or call server based networks;

  • Ability for inter-domain, inter-area or internetwork interworking;

  • Support for authentication and authorization;

  • Ability to perform call admission control;

  • Capability to support network performance parameters as defined in ITU-T Recommendation Y.1541;

  • Support for accounting, charging and billing.

  • Call routing: When an NGN coexists with PSTN/ISDN, the routing scheme should allow the carriers to control where their traffic enters and leaves the NGN. This will make it possible for the carrier to optimize use of their network resources and to avoid multiple points of interworking between the NGN and PSTN/ISDN along the media path.

9.4Status of legacy networks


One of the most important factors to be taken into account during the planning process of the migration knows and understands the exact status of legacy networks including related infrastructures supporting networks and services of each country. This has been accomplished through analysis of collected information about the status of legacy networks such as fixed and mobile legacy networks. Issues identified for collection of information are summarized followings:

  • Fixed network infrastructures: status of telecom providers and services, especially for voice service oriented infrastructures such as POTs (Plain Old Telephons) and ISDN over PDH (as well as with SDH);

  • Remaining life time of existing DSS (Digital Switching System): this status is essential factor because there are no more industries to provide DSS any more in the world. Therefore this factor should be used to identify the time to replace of new systems (for example, to support “All IP with NGN capability”);

  • Status of twisted copper cables: this status will used to identify the possibility of providing minimum broadband using xDSL and also the time to provide enhanced medium such as through FTTC and/or FTTH;

  • Status of telecom operators: this factor will be used to identify the plan for enhancement (upgrade) of fixed infrastructures through promotion of completion and collaboration among those telecom providers;

  • Internet and Broadband Infrastructures: currently internet is available almost everywhere, but to know the exact status of using internet including broadband is useful for planning of migration;

  • Status of key access for Internet: many of developing countries used mobile, consequently caused limited quality of services including contents (because it mainly targeted to mobile environment). It is not desirable having serious dependency to mobile. It is recommended to balance between fixed and mobile;

  • Status of fixed Broadband: many of developing countries are in initial stage of providing xDSL and need to expedite but, it needs to improve the deployments taking into account status of twisted pair cables to the subscriber loops;

As a result of the study on infrastructures, it is highly recommended to find out how to get balance between Fixed and Mobile infrastructures because status of most developing countries have too much dependency in mobile, but noting that fixed infrastructures are fundamental parts of both two fixed and mobile.

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