3. Main protocols involved

Before describing the main protocols involved in each of the packet transport technologies, it is important to understand the difference between the transport layer and the service layer. Each type of mobile traffic (e.g. telephony, Internet, video) is encapsulated in a service tunnel based on a traffic identifier. For example, encapsulation may be based on VP/VC for 3G traffic (ATM), on a physical port for 2G traffic (TDM), or on a priority level (DSCP) for LTE traffic. The service layer thus enables different services to be multiplexed in a transport tunnel. This service layer will not be handled by intermediate transport equipment (known as P, Provider ), but only by terminal equipment (T-PE, Terminating Provider Edge ) or, in the case of transport tunnel aggregation as part of scaling (see § ...