Next generation networks




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7.3Interworking between Emulation and Simulation capability


Voice service whether over PSTN, ISDN or mobile should be reached to any others as soon as possible, because this is the fundamental and essential telecommunication service to connect the people. Thus the telecommunication world identified voice service is as the universal service. By considering such importance of voice service, voice service of the NGN should be communicated with voice service in PSTN/ISDN environment as well as mobile. Supporting this as maximum as possible, NGN emulation and simulation are used jointly wherever possible, for example interworking between the NGN and PSTN and/or ISDN.

Figure 18 shows an example of interworking between the NGN and legacy PSTN/ISDN. Simulation is used in the NGN side while interworking with legacy side is using emulation. Service features in this case are characterized as following:



  • Service interworking between the NGN and PSTN/ISDN is required;

  • Only PSTN/ISDN-like services available, and;

  • User experience in legacy terminal cannot be fulfilled for end-to-end connection.



Figure 18 – Interworking between NGN Emulation and Simulation

Following Figure 19 shows another example of interworking between the NGN and legacy IP based network which support voice service (e.g. VoIP). Simulation is used in the NGN side while emulation is used in legacy side but connected by interworking. Service features in this case are characterized as following:



  • Service interworking between the NGN and IP network is required, and;

  • Both the NGN and IP network user experiences may not be fulfilled for end-to-end connection.



Figure 19 – Interworking NGN Simulation with Legacy IP

8Migration scenarios


ITU-T Recommendation Y.2261 defines “Evolution to the NGN (same as Migration to the NGN)” as a process in which whole or parts of the existing legacy networks are replaced or upgraded to the corresponding NGN components providing similar or better functionality, while attempting to maintain the services provided by the original network and the possibility of additional capabilities. [5] Thus, there are many of ways about migration from legacy networks to the NGN which would be derived various ways according to the given environments, future vision and adoption of candidate technology. This section introduces various migration scenarios showing high level directions for helping detailed migration design.

8.1Generic migration scenarios


One of the fundamental facts about migration to the NGN is that the result should be changed of all the network elements fitting to the NGN, that is, IP based. IP is one of transport technologies which use in layer 3 (network layer). But IP has been featured with “Everything over IP” as well as “IP over Everything” which request careful thinking where identify best place for replacing legacy systems to IP based systems. In this sense, changing TDM based to IP based should be the 1st step.

Next step should be taken into account the network configurations and possession portions in each country, for example between "Access network vs. Core network" and “Transport network vs. Service network”. In general, migration in “Core network” is easier than "Access network" because less impact on the service provision. Therefore it is generally recommended to introduce the NGN capability into Core network first, and then expand to the Access networks as shown in Figure 20. And it is also noted that service networks have significant dependency with transport capabilities, so migration plan for both transport and service networks should be considered together.

There are various ways of migration from legacy network to the NGN, so choosing NGN emulation and/or NGN simulation in the NGN side should be decided according to the specific scenario, for example according to each country or provider situation. NGN will be deployed and operate jointly with PSTN/ISDN. NGN will occupy more portions while PSTN/ISDN will continuously decrease and finally migration to the NGN. Thus at the beginning stage which legacy networks are majority, both NGN simulation and emulation capabilities should be provided together to the users who want to use advanced features supported by the NGN as shown in Figure 20. With growing of user demands, simulation will cover more users and areas with advanced services while emulation covers PSTN/ISDN users waiting until the time to replace their legacy networks to the NGN.

These two aspects of migration “Core network vs. Access network” and “Emulation vs. Simulation” should be considered together during the set-up of specific migration scenarios. There are, in general, two scenarios of migration: Overlay and Replacement. In any case, it is not expected to replace a network to other network at one shot. Thus it is recommended to set up long term plan rather than short term, and proper combinations among various available solutions. Followings jointly with Figure 20 should be considered as a process for identifying general aspects of migration scenario:



  • Expand the core transmission capacity;

  • Develop a core NGN overlay with call servers and media gateways, then interconnect or interworking with PSTN;

  • Install NGN access nodes (e.g., MSANs: Multi-Service Access Nodes) at legacy access network sites, stop buying more legacy access system;

  • Migrate those customers who want advanced features, or fast Internet, or new NGN services onto the NGN access nodes;

  • May need to use a number portability technology for call routing if number is not going to change, since number block is normally related to the Remote Concentrator Unit, unless whole unit is replaced, and;

  • When number of subscribers on legacy access nodes is small, then the remainder migrate to NGN nodes.



Figure 20 – General views of migration scenario
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