You can enable many other services that are not as common but could play a large role in your network. We will briefly discuss these services here, but you should consult the router or PIC documentation at http://www.juniper.net/techpubs for more detailed configuration information.
L2TP is a tunneling protocol that tunnels PPP packets across a network, acting like a Layer 2 data link tunneling protocol. L2TP headers and payload are actually sent in a UDP datagram, so maybe people claim it to be a Layer 5 or Layer 4.5 protocol. Each endpoint of the tunnel has its own designation, one being an LNS and the other an LT2P Access Concentrator (LAC). A Juniper Networks router can act as an LNS.
Only M7i and M10i routers support LT2P.
RPM is a feature for tracking and monitoring your network by sending network probes to other devices. These probes could be ICMP, UDP, or TCP depending on the configuration. You can use these probes to measure packet round-trip times, jitter, delay, and packet (probe) loss. You also can use RPM to verify the path toward Border Gateway Protocol (BGP) neighbors.
RPM does not require an ASP or Multiservices PIC, unless you are configuring RPM timestamping, which was released in Junos 8.1 for the sender and in Junos 8.3 for the responder.
You can configure probes with a variety of parameters, such as the type or contents of the probe. Also, you can set thresholds ...