Cisco CCNA Voice Certification Examination Tutorial – Codecs Spelled out – G711, G729, G729a, ILBC

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It is essential as a CCNA Voice prospect to recognize the many codecs that are supported by Cisco IP phones and the bandwidth that they every use.

Various codecs are supported on Cisco IP Telephones such as:

-G711

-G729

-G729a

-ILBC

G711

G711 provides toll good quality voice – in other phrases, the most effective voice good quality. There are two versions of G711 –

-G711ulaw – made use of in the Usa, Canada & Japan (also known as g711 mulaw)
-G711alaw – used in the rest of the planet

A seriously intelligent person called Nyquist worked that if you sample voice at two periods its optimum frequency, you can reproduce voice specifically on the other conclusion. Nyquist made the decision that human voice dialogue on telephones is in the assortment to 4000 Hz.

Thus 2 x 4000 Hz = 8000 samples a 2nd. When you get in touch with from an analog landline at property, a device in the telco cloud is sampling your voice at 8000 periods a second. Just about every of those samples is represented by an 8 bit code phrase.

As a result 8000 samples a 2nd X 8 bits per sample = 64000 bps or 64 kbps.

Equally G711ulaw and G711alaw use 64 kbps of bandwidth with no headers.

Nevertheless, to get a far better sign to sound ratio, logarithmic sampling is made use of. This implies that much more samples are taken closer to zero and less samples are taken as the sound wave moves absent from zero.

G729

Having said that, by working with intelligent voice sampling, the voice bandwidth can be lessened from the 64kbps demanded for G711. An case in point of this is G729. G729 is the codec that is popular in Cisco environments. This works by using 8 kbps.

The G.729 speech coder is an 8 kbps Conjugate-Framework Algebraic-Code-Enthusiastic Linear Prediction (CS-ACELP) speech compression algorithm accepted by ITU-T.

G.729 presents superior quality, strong speech functionality at the price of complexity. We will not protect the facts of the algorithm here – you should refer to other paperwork for in depth explanations.

G729a

A variant of G.729 is G.729a which employs the exact same quantity of bandwidth, but requires much less sources to generate. It having said that, has a somewhat decrease quality than G729. It also works by using 8kbps of bandwidth.

iLBC

The Online Very low Bandwidth Codec (iLBC) is a more recent codec supported on the new Cisco IP Phones. It has many advandages over the previous codecs.

– Was built for packetized communications

– Is royalty absolutely free

– Has much better good quality than G729

– Permits sleek speech excellent degradation in the scenario of dropped frames

– 13.3 kbps of bandwidth employed

It nevertheless is only supported on new Cisco handsets, so if more mature handsets are in use, it will not be available to those.

Other individuals

There are other may well other codecs accessible, but these are not automatically supported on the Cisco IP Handsets.

Summary

Numerous codecs are supported on Cisco IP telephones. Every single has numerous advantages and disadvantages. iLBC has many pros about other codecs, but is only supported on more recent Cisco IP telephones.

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