Cisco PA-4E1G/120= serial interface cards/adapter

4-Port E1 G.703 Serial Port Adapter, 120ohm, Balanced for 7000 Series The PA-4E1G provides up to four E1 synchronous serial interfaces, which are compatible with and specified by G.703/G.704. The PA-4E1G network interfaces provide a connection between standard serial interfaces such as V.35 to telephone lines or Post, Telephone, and Telegraph (PTT) networks. Each PA-4E1G interface operates in full-duplex mode at E1 (2.048 Mbps) speed.

The PA-4E1G interfaces do not operate in the data terminal equipment (DTE) and data communications equipment (DCE) modes that are typical of data communications interfaces. The PA-4E1G interfaces operate with either a line-recovered or an internal clock signal. The default is for a line clock signal that the interface recovers from the received data stream. The interface can also operate with an internal clock signal. The PA-4E1G generates the internal clock signal; the interface does not use the motherboard or system clock.

The PA-4E1G provides the following features and capabilities:
-Provides framed and unframed service access, E1 (2.048 Mbps) line speeds over unbalanced 75-ohm or balanced 120-ohm cable, with 15-pin, D-shell (DB-15) receptacles on the port adapter.
-Operates over E1 leased-line services, and provides ITU-T G.703 with high-density bipolar of order 3 (HDB3) line encoding.
-Operates with either an external or internal clock signal, and runs at wire speed.
-Provides for local and remote loopback testing services.
-Allows you to fractionalize a data stream into a single channel from 64 kilobits per second (kbps) to 1984 kbps.
-Provides G.704 framing for n x 64-kbps service support (where n = 1 to 31).
-Support for 4-bit cyclic redundancy check (CRC4) to provide and ensure data integrity.
-Support for point-to-point connections to supported platforms.
-Eliminates the need for a separate, external data termination unit that is typically used to convert standard serial interfaces, such as V.35, to E1-G.703/G.704.