X.25 Facility Handling in Datagram Transport Virtual Circuits
A router either originates or accepts datagram transport (encapsulation) switched virtual circuits (SVCs) to transport LAN traffic through an X.25 network.
When the router originates a call for LAN traffic encapsulation, the facilities in the call are controlled by the facilities configured for the interface and the map statement that specifies the LAN and X.25 encapsulation. Because a router can be attached to a public data network (PDN), the interface and map configurations allow a number of facilities to be specified in outgoing calls. These facilities are specified in all originated calls relating to the given interface and map, with one exception: the incoming and outgoing maximum packet sizes proposed are lowered if the LAPB cannot support the specified data packet size.
When the router accepts an encapsulation call, many facilities are simply ignored. The maximum packet sizes are lowered if the LAPB cannot support the sizes proposed. A reverse-charge call is cleared if neither the interface nor the map allows it. A call that specifies a network user identification (NUID) is cleared if the user authentication fails.
If an interface is configured as a DCE that is subscribed to closed user group (CUG) services, datagram encapsulation calls that originate and terminate on the interface will be subject to the requirements of CUG security.