What codecs are supported by remote phones that communicate with the Cisco Unified PhoneProxy?
A. Because Cisco Unified PhoneProxy does not support media transformations, any codec is supported. However, a problem arises with encrypted media when (RTP payload + RTP header) mod 64 does not equal 43, 44, 45, or 46. Therefore, 20 ms g.711 is acceptable; 30 ms g.711 is not acceptable. In order to calculate this value, use the modulo (mod) operation. The mod operation returns the remainder when one number is divided by another. For example, 13 mod 5 returns 3. For g.711 with an RTP payload of 160 and an RTP header of 12, use these calculations: 160+12=172 172 mod 64 = 44 44 is an acceptable value. Note: Another way to interpret this operation is to find the number closest to 172 that is divisible by 64, which is 128. The remainder of 172 – 128 is 44. Therefore, 172 mod 64 = 44. Note: You can also use Google Calculator in order to determine the results of a mod operation. Enter the mod operation in the search field at Google.com .
