icall VoIP (User Agent) Configuration

Transcription

1 icall VoIP (User Agent) Configuration

2 1 General 1.1 Topic General Document summarizing the general requirements for the configuration of VoIP hardware and / or software to utilize the icall service. 1.2 Configuration VoIP (Voice over Internet Protocol when you write out the whole thing it basically tells you what it is) is a technology that allows you to make telephone calls using the Internet, instead of a regular phone line. The VoIP Service from iburst, icall, allows subscribers the opportunity to make calls using many different VoIP/Voice devices i.e VoIP Phone, VoIP Router with analogue phone, SoftPhone etc. icall will operate with any compatible SIP phone/user agent. Each option however requires specific setup in order to access the service. The following parameters are mandatory and need to be configured as a minimum: SIP (Registration/Proxy) Server: sip.iburst.co.za SIP Account ID: Provided on signup SIP Account password: Provided on signup iburst Page 2 5/4/2007

3 The following fields are optional and are device/configuration specific: upnp: yes STUN: stun.iburst.co.za Codec: G.729 preferred (see more on this below) Outbound Proxy: Do not use (or leave blank) 1.3 More on Codec s & Call Quality A very critical component of the setup process is to ensure that the configuration in use is set to utilize the appropriate codecs. A codec basically converts analogue signals (Voice) into digital ones (data) and vice versa for transport or storage utilizing a specific algorithm. The packets of data that are created following processing by the codec, have the following factors that need to be considered. Codecs are used to save the data bandwidth (compression) by reducing the transmission rate required to carry the voice conversation, using a complex algorithm. The level of compression used by the codec affects the quality of the transmitted voice. This means that the wider the data bandwidth (the higher the transmission rate), the higher the voice transmission quality. The voice transmission quality is measured by the MOS (Mean Opinion Score) which is a qualitative measurement of the quality of the voice provided by the codec, where 1 means the worst and 5 the best quality. The data stream carrying the voice then needs to be packaged in an IP format for routing across the internet. This adds IP overhead which increases the data/ip bandwidth needed or utilized by the VoIP stream. iburst Page 3 5/4/2007

4 For a list of commonly supported codecs together with their coding rates, IP bandwidth used and MOS s, see the table below: Coding algorithm Codec Bandwidth (kbps) IP Bandwidth (kbps) MOS G.711 PCM G.723.1r56 ACELP G.723.1r64 MP-MLQ G.726 ADPCM G.728 LD-CELP G.729a CS-ACELP G.711 provides a quality equivalent to a traditional fixed line phone (under ideal conditions). The factors listed above make for an interesting tradeoff e.g. a smaller packet size will turn result in call of lesser quality. You will see from the above that the G.729 codec offers the best tradeoff of bandwidth efficiency and quality of call. Generally, most VoIP devices support a combination of codecs. The specific codec used during a VoIP call negotiated between the two VoIP gateways originating and terminating the call respectively. The icall system is ideally suited and is optimized to utilize the G.729 codec. Calls terminating locally in South Africa for GSM and landline calls support the G.729 codec exclusively. Furthermore, calls made to these local destinations from devices utilizing other codec s will terminate via international gateways. As the G.729 codec is a licensed codec, generally the free softphones do not support this. Therefore a call made from a free softphone will terminate via an international gateway and may lead to reduced voice quality. iburst Page 4 5/4/2007

5 It is essential to ensure that the devices or software utilised for the icall service support the G.729 codec. During the configuration process, of the icall service, one should ensure that this preferred codec is set in order to ensure an enhanced experience. iburst Page 5 5/4/2007