- Generation Multi-flex Trunk Voice/Channelized Data T1/E1 Module
- Expansion module
- T1/E1 x 2
- for Cisco 4451-X; Integrated Services Router 4321
The T1/E1 modules contain an onboard Cisco Packet Voice Digital Signal Processor Module 4 (PVDM4) slot, which requires a fourth-generation PVDM4 module. A PVDM4 on the T1/E1 module is necessary for the voice features. The PVDM4 also provides for echo cancellation of up to 128-ms echo-tail length for demanding network conditions.