Cisco's E1 frame service modules (FRSMs) offer high-density native E1 frame service interfaces for the new world of data networking. FRSM cards support multiple HDLC-derivative frame service interfaces, which can be configured on a per-port basis. These service interfaces include the Frame Relay UNI, Frame Relay NNI, ATM FUNI, and frame forwarding - HDLC- transparent, providing "channel extension" support for legacy HDLC-based protocols such as Point-to-Point Protocol (PPP).