An important function of the Trai, by section 11 of the Trai (Amendment) Act 2000, is to lay down the standards of quality of service (QoS) for telecom operators.

Accordingly, Trai has laid down norms for 2 nd cellular mobile telephone services in July 2000.

2G cellular mobile systems (GSM/CDMA) employ circuit switching techniques, ideal for carrying real time voice calls. The task of the regulator was relatively easy as circuit switched networks have been in operation for a hundred years. The characteristics of voice traffic have been modelled by tele-traffic experts for dimensioning such networks based on QoS norms. The same is not true for bursty multimedia traffic. Therefore, dimensioning and QoS enablement in an IP-based multimedia network pose a real challenge for network designers, globally.

Last month saw the launch of the first 3G cellular mobile service by Tata Teleservices. Other operators like Bharti Airtel and Vodafone Essar will follow suit soon. Based on Tata Teleservices’ tariff plans for voice calls (49 paise per minute), it is fair to assume that the 3G networks will be mainly used for carriage of real time voice traffic, for quite sometime, as voice remains the killer application in India. Data traffic is yet to pick up due to poor PC penetration.

The latest version of 3G GSM system called UMTS (Universal Mobile Telecom System) has a subsystem called the IP Multimedia Subsystem (IMS). The IMS conform to the functional specifications of Next Generation Network (NGN) of UN agency ITU. However, the framework for QoS enablement in NGN is yet to be completed by the ITU Study Group 13.

The task of the study group is difficult as the Internet Protocol (IP) was not designed for carriage of real time traffic like voice and video. It is only a ?best effort? protocol, which does not guarantee any QoS particularly for real time voice & video traffic. Although a number of enhancements have been designed and incorporated in IP networks, end-to-end QoS at the application level is still difficult to achieve, in a large heterogeneous network.

Quality of services is the main performance indicator of a telephone network and of the degree to which it conforms to the stipulated norms. The subscribers? perception of the QoS is determined by several performance criteria.

These have been specified in Trai’s QoS regulation 2 of 2000 for 2G circuit switched network.

These are not applicable to 3G IP-based networks. Therefore, to safeguard the interest of the subscribers, the Trai should revisit its earlier regulation and come out with a separate section on QoS relating to 3G networks. The subscriber?s expectation from these next generation networks is quite high.

Unlike 2G GSM networks, for which GSM MOU?an international body?had finalised several performance parameters, for IP-based 3G networks, the ITU study group 13 is yet to finalise its recommendations despite about five years of study. The earlier study period, which ended in 2009, has been extended up to 2012. The task is complex since different types of applications/services (e.g., Web services, IP telephony and IPTV ) have varied QoS requirements, all of which are required to be supported by a common IP-based packet network, which is the basis of NGN.

Mechanisms are needed to ensure the required levels of QoS, especially for applications that are delay and loss-sensitive. These are real time applications such as voice and video, for which delay and variability of delay called jitter are difficult to keep within certain bounds, such as less than 100 milliseconds one-way delay for international calls, and its variability within 5 milliseconds.

In circuit switched calls, these are 50 milliseconds & zero. These parameters affect the voice quality of an IP-based network adversely. In the absence of recommendations of international bodies like ITU, the task of setting the QoS norms for 3G multimedia networks is challenging. However, the Trai must rise to the challenge.

A large part of the 3G traffic will be used to access the public Internet as the network is supposed to provide ultra fast internet access and broadband downloads. If the Internet is to give the so-called ?carrier grade? QoS to customers, it will need to be upgraded to deliver voice & video packets within certain bounds of delay. The variability of delay called jitter will also need to be bounded. This is a difficult task given the heterogeneous nature of the public Internet, whose control is vested in a large number of Internet Service Providers.

Another important parameter concerning subscribers is voice quality. Voice quality measurements have always been subjective. The leading subjective measurement of voice quality is the MOS (Mean Opinion Score) as described in the ITU recommendations P.800. Recently to make the quality measurement more objective, ITU has defined the E-Model. The output of an E-model calculation is a single score, called ?R Factors? derived from delays and equipment impairment parameters. Once an R factor is obtained, it can be mapped on to an estimated MOS. R factor values range from 100 (excellent) down to 0 (poor). MOS can range from 5 (excellent) down to 1 (poor). MOS can be directly calculated from the E-model?s R Factor. The 3G operators should carry out objective measurements of R factor of their networks before loading their networks with real traffic. A R factor of > 90 is easily achievable in PSTN networks. The corresponding MOS will be in the range of 4.5.

Another area of concern relates to the higher radiation levels from 3G base stations mounted on telecom towers. Electromagnetic emissions of mobile towers are required to conform to the guidelines issued by ICNIRP. However, these guidelines mainly relates to 2G systems. For the latest 3G systems, fresh norms should be set, considering the higher levels of radiation from 3G systems. Trai should also get the biological effect of long-term exposure to radiation examined by the Indian Council of Medical Research. The regulator should also prescribe the maximum emitted power for various types of 3G/4G systems in the licence.

?The writer is a former member of Trai / Telecom Commission