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

It is significant as a CCNA Voice prospect to realize the several codecs that are supported by Cisco IP phones and the bandwidth that they each and every use.

Several codecs are supported on Cisco IP Telephones which includes:






G711 supplies toll good quality voice – in other words and phrases, the very best voice high quality. There are two variations of G711 –

-G711ulaw – employed in the United states of america, Canada & Japan (also named g711 mulaw)
-G711alaw – employed in the relaxation of the environment

A genuinely intelligent person named Nyquist labored that if you sample voice at two occasions its highest frequency, you can reproduce voice just on the other stop. Nyquist made the decision that human voice conversation 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 household, a machine in the telco cloud is sampling your voice at 8000 instances a 2nd. Just about every of people samples is represented by an 8 bit code phrase.

So 8000 samples a second X 8 bits per sample = 64000 bps or 64 kbps.

Equally G711ulaw and G711alaw use 64 kbps of bandwidth with out headers.

However, to get a far better sign to sound ratio, logarithmic sampling is applied. This usually means that much more samples are taken closer to zero and much less samples are taken as the audio wave moves absent from zero.


Nevertheless, by making use of clever voice sampling, the voice bandwidth can be reduced from the 64kbps required for G711. An example of this is G729. G729 is the codec that is common in Cisco environments. This utilizes 8 kbps.

The G.729 speech coder is an 8 kbps Conjugate-Composition Algebraic-Code-Fired up Linear Prediction (CS-ACELP) speech compression algorithm approved by ITU-T.

G.729 gives large good quality, strong speech effectiveness at the price tag of complexity. We will not address the information of the algorithm in this article – make sure you refer to other documents for comprehensive explanations.


A variant of G.729 is G.729a which utilizes the same sum of bandwidth, but will take less resources to make. It on the other hand, has a a bit lower high-quality than G729. It also uses 8kbps of bandwidth.


The Internet Very low Bandwidth Codec (iLBC) is a newer codec supported on the new Cisco IP Telephones. It has several advandages in excess of the preceding codecs.

– Was developed for packetized communications

– Is royalty no cost

– Has better excellent than G729

– Enables graceful speech excellent degradation in the situation of missing frames

– 13.3 kbps of bandwidth used

It on the other hand is only supported on new Cisco handsets, so if more mature handsets are in use, it will not be obtainable to these.

Some others

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


Many codecs are supported on Cisco IP telephones. Every single has numerous rewards and negatives. iLBC has many pros over other codecs, but is only supported on more recent Cisco IP telephones.

Resource by David Bombal