At the concept level, all networks are simple: They provide services and functions to the users. Examples of popular services include the following:
- Virtual private network (VPN)
- Internet access
- Layer 2 transport
- Voice " video over IP (V"VoIP)
These basic services are addressed by the MPLS network design, and then user-level service software suites (such as email and browsers) ride on top of these basic services.
Let’s take a quick look at these core network services.
- VPN services help fulfill functions such as teleworking and the secure interconnection of geographically dispersed sites. A popular example of an organization using the latter is the so-called virtual organization, made up of home office workers with no headquarters. Such organizations trade expensive office space and commuting for a more flexible and distributed approach, and make heavy use of technologies such as conference services.
- More traditional organizations use centralized VPN and Internet access services. In addition, many large organizations are increasingly demanding IPv6 in their networks because IPv6 provides a large addressing range and advanced features such as neighbor discovery and autoconfiguration. Layer 2 transport can be provided using an MPLS technology called pseudowires, which allows legacy traffic to tunnel into an MPLS core without the need for transport over legacy Layer 2 devices.
- Given that so many networks are migrating to IP, an increasingly important service is Voice " video over IP. These services provide savings (as in VoIP toll bypass and reduced video-equipment needs) as well as flexibility—find a wireless access hotspot, plug in your laptop and IP phone, and you have a mobile office.
Figure 1 illustrates a conceptual service provider network that supplies users with access to a growing range of services and functions.
Figure 1 A service provider network.
The PE routers in Figure 1 are linked to the CE routers that sit on customer premises. In turn, the PE routers are connected to P routers. As Figure 1 shows, we have label switched paths (LSPs) that stretch across the network core between the PE routers. The CEs (that is, the customers) are plain-vanilla IP routers and have no knowledge of MPLS technologies. This simplification helps to reduce the cost of deploying MPLS—the customer side is straightforward, traditional IP routing. The devices in Figure 1 may be routers or switches.