This read-write value assigns the Frame Relay channel to a specific logical port on the card, a value the administrator must explicitly set when creating a new channel, and on the FRSM12 card this field specifically holds the port's ifIndex value rather than an arbitrary port number. An administrator provisioning a new Frame Relay PVC sets this to bind the channel, and its DLCI, to the correct physical port. On an FRSM12 card, an operator would look up the intended port's ifIndex value first before setting chanPortNum to that identifier.