Overview

The SMDS trunk interface supports SMDS framed in standard High-Level Data Link Control (HDLC). This interface is like other layer 2 interfaces, such as PPP, Frame Relay, and ATM, with the exception that the system does not de-encapsulate the packet and route the traffic as it does for the other layer 2 interfaces.

A HSSI physical interface maps one-to-one with an SMDS logical interface. The data received on an SMDS interface is forwarded to the destination interface in the E-series device, which has an associated generic routing encapsulation (GRE) tunnel interface defined. If a (connection-based forwarding) CBF interface does not exist for the SMDS interface, all received traffic is dropped. In addition, the connection must be to another HSSI or to a GRE tunneled interface and never to a purely routed interface.

The SMDS trunk interface supports only CBF to another SMDS trunk-encapsulated interface; that is, to a GRE tunnel.