--> CODEC is a software algorithm that performs compression and decompression of speech and audio signals.
--> Selection of CODEC in CUCM depends upon:
i) Quality
ii) Endpoint Support
iii) Network Latency and Reliability
iv) Transcoder Avoidance
v) Bandwidth
--> The following are the most used CODECS by Cisco IP Phones:
1) G.711
--> Supported by Most of the Endpoints.
--> Predominantly used between Endpoints in LAN network.
--> Uses the bandwidth of 64 kbps per call ( Every second of analog call is converted into 64 kbps of data).
--> G.711 comes in two forms:
i) G.711ulaw: Used by America and Japan
ii) G.711Alaw: Used by Rest of the World
--> If one IP Phone is using G.711ulaw and another IP Phone is using G.711Alaw then they are not going to communicate directly with each other without the help of CUCM or Transcoder.
2) G.722
--> Predominantly used between Endpoints in LAN network.
--> Provides Enhanced Audio Quality Compared to G.711
--> CUCM prefers G.722 over G.711 while choosing the codec between the IP Phones as long as both IP Phones support the codec
--> Uses the bandwidth of 64 kbps per call ( Every second of analog call is converted into 64 kbps of data).
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