IP tunnel can be used to carry the ATM service, the CES service or the Ethernet service.
If ATM or CES emulation service that travels through an IP network is required, the PTN equipment can use the IP tunnel to carry the service. Figure 1 shows the protocol stack model of the ATM service. In the case of IP tunnel, the situation is a case where "IP header" replaces the MPLS external label (MPLS tunnel label) to establish a tunnel in the IP network. An ATM emulation service can be provided between NE A and NE B, even though the IP network between NE A and NE B does not support the MPLS.
Figure
1 ATM PWE3 over IP tunnel
