Dedicated lines, IPLC, and IEPL are actually distinguished by their services and access methods. The hierarchical relationship between these three is mainly defined by different standards and protocols for network connections.
From a broad perspective, "dedicated lines" is actually a category that encompasses all communication lines provided for point-to-point or point-to-multipoint communication, whether temporary or long-term leases. Within this category, IPLC and IEPL can be seen as subsets or more specific implementations of "dedicated lines".
IPLC, or international private leased circuit, is a point-to-point leased service that is based on PDH or SDH technology and complies with G.703, G.704, or G.707 standards. IPLC mainly provides stable line bandwidth between two users and can meet long-distance and high-bandwidth requirements.
Compared to IPLC, IEPL is a dedicated line service based on Ethernet, which is based on the standards of the Metro Ethernet Forum (MEF). One of the major features of IEPL is its transparency, indicating that it can see the business data transmitted on the Ethernet link. IEPL is a shared network access service for point-to-point or multipoint-to-multipoint connections. Basically, IEPL provides the ability to extend a local area network (LAN) from one geographic location to another.
Of course, compared to IPLC, IEPL supports a wider range of business types and better network quality assurance, and also supports a richer variety of services.
For a more intuitive understanding, we can think of IPLC as a relatively traditional, telecom-level point-to-point transmission service. It is mainly based on PDH/SDH technology and provides users with stable dedicated line bandwidth throughout the entire transmission. Therefore, IPLC has high stability and reliability in cross-border data transmission, but it does not involve any network-level routing or data encapsulation issues. So in the OSI model, it should be placed at Layer 1, the physical layer.
IEPL, on the other hand, is a more advanced concept. It is a dedicated line service based on Ethernet and follows the standards of the Metro Ethernet Forum (MEF). IEPL not only provides point-to-point services, but also supports multipoint-to-multipoint communication and a range of Ethernet services. It has stronger network transparency and higher business adaptability. It can transmit data packets such as Ethernet frames and ARP messages, which need to be encapsulated and decapsulated at the data link layer. Therefore, in the OSI model, I would classify it as Layer 2, the data link layer.
With the development of public clouds, enterprises have gradually begun to transition to using software-defined networks such as SDN and SD-WAN. In the future, I can write an article to clarify the relationship between these technologies.