Though there are many kinds of Internet architectures, there is a generally accepted hierarchy of Access, Edge, and Core. Here is a quick review of the key elements in a Hierachical Network.

Access usually connects the customer or CPE (Customer Provided/Premise Equipment). Access circuits are multiplexed, integrated, or aggregated to Edge routers.

At the Edge, a myriad of different protocols are combined by the carrier depending on their architecture into Core protocols such as IP (Internet Protocol) or ATM (Asynchronous Transfer Mode). In order to reduce the number and types of different routing and switching systems, the next-generation Edge device is often called a BRAS (Broadband Remote access Aggregation Server) or MSSS (Multi-Service Switching System). MSE (Multi-Service Edge) system provides protocol conversion from Access protocols to one or more Core protocols.

The MSE will connect the customer with POTS (Plain Old Telephone Service), DSL (Digital Subscriber Line), Cable modem, Wi-Fi (Wireless Fidelity), satellite, T-1 (Transmission Level One) transmission lines. Over these transmission lines is Ethernet, ATM, Frame Relay or IP. These services are organized by the SP (Service Providers, also known as ISP [Internet SP], WISP [Wireless Internet SP], and others). These carriers (or SPs) call their products by their own brand names such as Metro Ethernet, Leased Access, Special Access, L2 (Layer 2 Access), VPN (Virtual Private Network), VPLS (Virtual Private Lan Services), VPWS (Virtual Private Wire Services, which are private line services using a Layer 2 protocol such as ATM, Frame Relay or Ethernet [also known as private line Ethernet]), NMLI (Native Mode LAN [Local Area Network] Interconnection), BRAS (Broadband Remote access Aggregation Server), and other names.

[Thomas B. Cross of TECHtionary]