[RS笔试问题]EPL和EVPL的问题

酌香

题库中有一道题是这样的

然后还有一道题是这样的...


然而我搜索EPL和EVPL的解释是这样的...那么答案是否正确呢?(来自http://en.wikipedia.org/wiki/Ethernet_Private_Line)
Ethernet Private Line[size=0.875em]From Wikipedia, the free encyclopedia

Ethernet private line (EPL) and Ethernet virtual private line (EVPL) are carrier Ethernet data services defined by the Metro Ethernet Forum. EPL provides a point-to-point Ethernet virtual connection (EVC) between a pair of dedicated user–network interfaces (UNIs), with a high degree of transparency. EVPL provides a point-to-point or point-to-multipoint connection between a pair of UNIs.

The services are 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.

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.

Other types of EVC defined for carrier Ethernet networking are the Ethernet Virtual Private LAN and Ethernet Virtual Private Tree.

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我不太懂EPL是什么技术做什么用的求问！！？？？