 When we look at the Metro Ethernet network, instantly it comes to our mind what kinds of services and what modes would this carrier Ethernet have to provide certain diversity to different kinds of users. So in this module, we'd look at the service types which are offered for the users in terms of the types of users, number of users and their specific data requirements. So we'd look at the service types and the modes through which these users can connect to the Ethernet network. So first, the carrier Ethernet actually provides Ethernet-based services in metropolitan. So it means the Ethernet technology as such does not change significantly. However, since we are talking about very large distance and over this large distance we have two endpoints, which means we have the customer premises equipment and we have the central office. So we actually need to provide some means to identify these endpoints and that is done through Ethernet virtual connection. If you recall, we had VPCs, VCCs in ATM and frame relay. It is something similar, but here it is based on the Ethernet technology. The network providers actually use Ethernet connectivity to provide Ethernet services by using these virtual connections. What are these virtual connections? We'd look at them in the next slide. These Ethernet virtual connections or service types are meant to cater for the needs of users depending upon point-to-point, point-to-multipoint or even a routed arrangement where different users of a certain network are now distributed across a routed domain. Routed domain means now the endpoints are not directly connected. They are connected through an intermediate router. So we have the Ethernet line. It is point-to-point virtual connection. It's known as E-line. It could be physical and it could be virtual, we shall see. Then we have Ethernet local area network. Although we know about local area network that is already there based on Ethernet technology, LAN is based on Ethernet. However, this Ethernet local area network essentially means that two endpoints actually have hosts which have computers or the hosts of the same network. So it is interesting. It's going to be point-to-multipoint Ethernet virtual connection. Then we have a tree. Tree actually means not only do we have only two endpoints, we have multiple endpoints. forming a tree across a routed network. So we have routed multi-point Ethernet virtual connection. For these different service types or the virtual connections, the connectivity modes are the subscriber or the individual computers and the switches are going to attach to this network that is Metro Ethernet network or the carrier Ethernet through the UNI that is the user-to-network interface because these are individual hosts. So they can adopt any standard. So it means there is a provision for 10 base T, 100 base T, 1000 base F or even 10 gigabytes per second. Any Ethernet standard. Now each of these services can be provided on either a port, physical port bases or a virtual service base. So we shall see what is exactly we mean by port based and virtual service based. If you look at the service types, these are the three service types that we've already discussed and these can be provided either on a port by port base or on a VLAN base. Now port-based Ethernet service actually means that you have a switch on one end say on the customer premises and then you have another switch on the central office and you actually provide a one-on-one connectivity between two hosts. So this forms a line. You can scale it up for multi-points and you call it a LAN and if you do it across a routed network, you call it a tree. But interestingly, whatever can be achieved through physical ports can actually also be achieved through VLAN, the virtual local area network. So interestingly, whatever we have seen in port-based Ethernet service would now also be provided through virtual service. For instance, virtual private line on for E-line, virtual private LAN for E-LAN and virtual private tree for E-tree. So we are going to have the same kind of service but in a virtualized way. We talk about it in more detail.