This read-write string, specific to the ISDN BRI Voice card, holds the third ISDN number on which the port will accept an incoming connection request, applying only when ifwanTerminating is TE and ifwanTeiMode is set to Dynamic. An administrator configures this as a third accepted MSN, letting the port answer incoming calls for yet another subscriber number under dynamic TEI negotiation. For example, a BRI port shared across three separate subscriber numbers in TE dynamic mode would have this field set to the third of those numbers.