Nortel Remote Gateway 9110 Reference Manual

Also see for 9110: Reference guide Release note Release note Quick start guide Installation and administration guide

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Nortel Remote Gateway 9110 Reference Manual Manual pdf 5 page image

Remote Gateway 9100 Series Network Engineering Guidelines 5Standard 1.6 June 2005Introduction to packetized voiceThe Public Switched Telephone Network (PSTN) has evolved into a stable, highquality communications medium. When you take a telephone off-hook, dial toneis immediate. Connection time is quite fast and clarity of the audio is excellent.With the development of packetized communications such as Voice overInternet Protocol (VoIP), the same high quality experience can be realized -when engineered properly.To correctly engineer a VoIP system, you must use subjective testing resultsperformed by numerous companies and independent labs to understand thefactors that affect the quality of the VoIP. The main factors are categorized asfollows: audio levelsThe PSTN has been built around clear rules of Loss Level Planning – thelevel of transmitted and received audio. The audio levels are such that theconversation is comfortable and highly intelligible. You can conversewithout having to strain to hear the caller. extra audio (echo, clicks, pops)Extra audio can be created in many ways. The most common extra audio isecho, or a reflection of your own speech. In traditional PSTN telephony,echo is present, but the Loss Level Planning reduces the amplitude, and thesmall amount of echo delay makes it unperceivable. With VoIP systems, theinherent audio processing and network delays can make the echoperceivable, if the echo is not cancelled/managed properly.Clicks and pops can be heard when packet loss is occurring on the network.The severity of the click or pop is determined by the size and duration ofthe packet loss experienced, as well as the audio compression anddecompression scheme (Codec) chosen. A Codec compresses audio,reducing the amount of bandwidth required to have a conversation.— G.711 (64 Kbps data rate - equivalent to a wired telephone [nocompression])— G.726 (32 Kbps data rate - reduces the required bandwidth by one halfin trade for a slightly lower audio fidelity)— G.729A (8 Kbps data rate - high level of compression in trade for loweraudio fidelity)