The Cisco 2-port T1/E1 multiflex interface cards provide voice and data access to the PSTN domain through TDM ports. They are dual-port trunk interfaces for voice, data, and integrated voice and/or data applications. These cards provide basic structured service for T1 or E1 networks and unstructured service for fractional E1 networks. The cards include an integrated DSU/CSU. Some cards also support the drop-and-insert process, which adds data to a T1 or E1 data stream, or which terminates data from a T1 or E1 data stream to other devices connected to the drop-and-insert equipment.