Cisco CEoIP network modules provide a virtual circuit through an IP network (similar to a leased line). Transport of data, regardless of the content or structure of the data stream, is entirely transparent to the destination; bits arriving at one end are delivered unchanged to the destination address.The 4-port serial interface network module (NM-CEM-4SER) is a single-width CEoIP network module with 4 serial ports that support the following interfaces: EIA/TIA-232, EIA/TIA-449, EIA-530, EIA-530A, V.35, X.21. The interface type provided by the port is determined by the cable connected to the port.