E-LAN vs. E-TREE

Metro Ethernet Forum (MEF) has defined 4 types of service, namely;

1. E-LINE (Ethernet Line) - Point to Point
2. E-LAN (Ethernet Local Area Network (LAN)) - Multipoint to Multipoint
3. E-TREE (Ethernet Tree) - Point to Multipoint
4. E-Access (Ethernet Access)

The lack of E-TREE implementations/support on Communication Service Providers (CSP) networks today make the customers buy Virtual Private LAN Service (VPLS) (Multi Protocol Label Switching (MPLS) bases E-LAN implementation) services for point-to-multipoint applications such as 3G back-hauling to Radio Network Controller (RNC), Head Quarters (HQ) to branch communication on corporates. 

If the resources required to E-LAN and E-TREE are compared, when the E-TREE requires N number of Pseudo Wires (PW)s for N locations, E-LAN requires N*(N-1)/2=> N^2. If the Media Access Control (MAC) learning is considered, in E-TREE leafs learn only the root MACs and root learns all the root and leaf MACs (2 if there's only one root exists). In E-LAN, all the points in the VPLS (Virtual Switching Instance (VSI)) will learn all the MACs (N). 

Note that MAC table size is a limited resource for a Network Element (NE). Number of PWs, number of Label Switch Path (LSP)s, number of VSI instances and number of Virtual LAN (VLAN)s are also limited resources.