Endpoint A is attempting to call endpoint B. Endpoint A only supports G.711ulaw with a packetization rate of 20 ms, and endpoint B supports…

Transrating fixes packet-size mismatches when the codec itself is identical.

Only IOS-based MTPs (software or DSP-based hardware) can negotiate and repacketize G.711 streams at different sample sizes (10/20/30/40 ms).

The built-in CUCM software MTP is limited to a fixed 20-ms packetization and therefore cannot interwork with a 30-ms endpoint.

Transcoders are irrelevant because no codec change is required.

B. CUCM software MTP supports only 20-ms packets and performs no packetization conversion; cannot interwork with 30-ms endpoint.

C. A transcoder converts between different codecs, not different packet sizes of the same codec; unnecessary here.

D. Hardware transcoder (DSP) again performs codec conversion, not packetization adjustment.

1. Cisco Collaboration SRND 12.x, “Media Termination Point,” Table “Supported Sample Sizes” – CUCM software MTP (20 ms only); IOS Enhanced MTP (10/20/30/40 ms).

2. Cisco IOS Enhanced Media Termination Point White Paper, Doc ID 116076, section “Packetization Conversion,” para 2 – “IOS software or DSP-based MTP can transrate between 10-, 20-, 30- and 40-ms packets.”

3. Cisco Unified CM Features and Services Guide 14, chapter “Media Termination Point,” sub-section “CUCM Software MTP Limitations” – “No support for packetization conversion; fixed at 20 ms.”