Cisco CCNA Voice Certification Exam Tutorial – Codecs Discussed – G711, G729, G729a, ILBC

It is significant as a CCNA Voice prospect to recognize the several codecs that are supported by Cisco IP telephones and the bandwidth that they just about every use.

Numerous codecs are supported on Cisco IP Phones like:

-G711

-G729

-G729a

-ILBC

G711

G711 gives toll excellent voice – in other phrases, the ideal voice high-quality. There are two versions of G711 –

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

A genuinely clever man termed Nyquist labored that if you sample voice at two periods its optimum frequency, you can reproduce voice specifically on the other conclude. Nyquist decided that human voice dialogue on telephones is in the vary to 4000 Hz.

Consequently 2 x 4000 Hz = 8000 samples a second. When you phone from an analog landline at home, a device in the telco cloud is sampling your voice at 8000 times a next. Every of individuals samples is represented by an 8 bit code word.

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

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

Even so, to get a far better sign to noise ratio, logarithmic sampling is applied. This suggests that more samples are taken nearer to zero and fewer samples are taken as the sound wave moves away from zero.

G729

Nonetheless, by applying intelligent voice sampling, the voice bandwidth can be reduced from the 64kbps necessary for G711. An example of this is G729. G729 is the codec that is prevalent in Cisco environments. This takes advantage of 8 kbps.

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

G.729 provides high high-quality, strong speech overall performance at the selling price of complexity. We will not deal with the information of the algorithm listed here – you should refer to other paperwork for specific explanations.

G729a

A variant of G.729 is G.729a which employs the exact same quantity of bandwidth, but normally takes significantly less sources to create. It on the other hand, has a a little lower excellent than G729. It also makes use of 8kbps of bandwidth.

iLBC

The Net Small Bandwidth Codec (iLBC) is a newer codec supported on the new Cisco IP Phones. It has several advandages about the previous codecs.

– Was built for packetized communications

– Is royalty free of charge

– Has better excellent than G729

– Permits swish speech top quality degradation in the situation of lost frames

– 13.3 kbps of bandwidth used

It nonetheless is only supported on new Cisco handsets, so if older handsets are in use, it will not be offered to all those.

Other individuals

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

Summary

Several codecs are supported on Cisco IP phones. Each individual has many rewards and shortcomings. iLBC has quite a few rewards in excess of other codecs, but is only supported on more recent Cisco IP telephones.