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

It is crucial as a CCNA Voice applicant to fully grasp the several codecs that are supported by Cisco IP phones and the bandwidth that they each use.

Different codecs are supported on Cisco IP Telephones such as:

-G711

-G729

-G729a

-ILBC

G711

G711 delivers toll top quality voice – in other words and phrases, the greatest voice high-quality. There are two variations of G711 –

-G711ulaw – applied in the United states, Canada & Japan (also termed g711 mulaw)
-G711alaw – utilised in the relaxation of the world

A seriously clever man identified as Nyquist worked that if you sample voice at two moments its highest frequency, you can reproduce voice just on the other conclusion. Nyquist made a decision that human voice dialogue on telephones is in the vary to 4000 Hz.

Hence 2 x 4000 Hz = 8000 samples a 2nd. When you call from an analog landline at residence, a equipment in the telco cloud is sampling your voice at 8000 instances a 2nd. Each of those samples is represented by an 8 little bit code phrase.

Consequently 8000 samples a second X 8 bits for each sample = 64000 bps or 64 kbps.

Each G711ulaw and G711alaw use 64 kbps of bandwidth without having headers.

Nonetheless, to get a much better signal to sounds ratio, logarithmic sampling is employed. This indicates that much more samples are taken closer to zero and less samples are taken as the sound wave moves away from zero.

G729

On the other hand, by employing clever voice sampling, the voice bandwidth can be decreased from the 64kbps necessary for G711. An illustration of this is G729. G729 is the codec that is common in Cisco environments. This employs 8 kbps.

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

G.729 delivers large top quality, sturdy speech general performance at the rate of complexity. We will not protect the information of the algorithm in this article – make sure you refer to other files for comprehensive explanations.

G729a

A variant of G.729 is G.729a which works by using the identical total of bandwidth, but will take much less resources to create. It on the other hand, has a a little bit lower high-quality than G729. It also works by using 8kbps of bandwidth.

iLBC

The Internet Minimal Bandwidth Codec (iLBC) is a newer codec supported on the new Cisco IP Telephones. It has numerous advandages in excess of the former codecs.

– Was developed for packetized communications

– Is royalty absolutely free

– Has greater high-quality than G729

– Enables graceful speech top quality degradation in the situation of missing frames

– 13.3 kbps of bandwidth utilized

It even so is only supported on new Cisco handsets, so if older handsets are in use, it will not be readily available to these.

Others

There are other may possibly other codecs out there, but these are not automatically supported on the Cisco IP Handsets.

Summary

Various codecs are supported on Cisco IP telephones. Each and every has a variety of positive aspects and negatives. iLBC has quite a few strengths more than other codecs, but is only supported on newer Cisco IP telephones.