Which service type is needed to bridge an ATM-attached user and an Ethernet-attached user?

Bridging users from two different Layer 2 technologies requires a service that can perform interworking. An E-pipe (Ethernet pipe) on Nokia platforms can be configured to support interworking between different Layer 2 encapsulations. By configuring an ATM SAP on one end and an Ethernet SAP on the other end of an E-pipe, the service edge router performs the necessary translation, including Segmentation and Reassembly (SAR) for the ATM traffic and mapping it to Ethernet frames. This allows seamless communication between the ATM-attached and Ethernet-attached users over a common pseudowire.

A. A-pipe: An A-pipe is a point-to-point ATM service; it can only connect two ATM SAPs and does not perform interworking with other technologies.
B. F-pipe: An F-pipe is a point-to-point Frame Relay service and is used to connect two Frame Relay SAPs only.
C. C-pipe: A C-pipe is a circuit emulation service used to connect two TDM (e.g., T1/E1) circuits and does not interwork with ATM or Ethernet.

Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VLL Services". The section on E-pipe services describes their capability for ATM-to-Ethernet VLL interworking. It details how an ATM SAP can be configured on an E-pipe to transport ATM AAL5 PDUs as Ethernet frames.

Nokia 4A0-104 Course Material, Module 3: Virtual Private Wire Service (VPWS). This course describes I-pipes (Interworking pipes) and also notes that E-pipes can be used for specific interworking scenarios like ATM-to-Ethernet.