Ethernet Private Line
Ethernet Private Line (EPL) is a data service defined by the Metro Ethernet Forum, providing a point-to-point Ethernet Virtual Connection (EVC) between a pair of dedicated User–network interfaces (UNIs), with a high degree of transparency.
EPL service is categorized as an E-Line service type, with an expectation of low Frame Delay, Frame Delay Variation and Frame Loss Ratio. EPL is implemented using a point-to-point (EVC) with no Service Multiplexing at each UNI (physical interface), i.e., all service frames at the UNI are mapped to a single EVC (a.k.a. All-to-one bundling).
Due to a high degree of transparency, EPL is often used to provide point-to-point Transparent LAN Service (TLS), where the Service Frame’s header and payload are identical at both the source and destination UNI. Some implementations tunnel most Ethernet Layer 2 Control Protocols (L2CPs) except for some link layer L2CPs such as IEEE 802.3x Pause frames.
Ethernet Virtual Private Line
Ethernet Virtual Private Line (EVPL) is a data service defined by the Metro Ethernet Forum, providing a point-to-point Ethernet connection between a pair of User–network interfaces (UNIs).
EVPL service is specified using an E-Line service type, very similar to a Ethernet Private Line (EPL) service, via a point-to-point Ethernet Virtual Connection (EVC). However, unlike EPL, EVPL allows for Service Multiplexing, i.e., multiple EVCs or Ethernet services per UNI.
The other difference between the EVPL and EPL is the degree of transparency - while EPL is highly transparent, filtering only the Pause frames, EVPL is required to either peer or drop most of the Layer 2 Control Protocols.