This read-write integer assigns a unique local VP identifier (1-340, though the valid subrange depends on the interface type - up to 100 for STI, 20 for UNI, 340 for NNI, or up to 255 on a 4-port AUSM card) that, combined with the card's slot number, forms an identifier unique across the entire shelf, and it can only be set when the connection is first added. Admins configure this at VP connection setup time so the PXM controller (ASC) can correctly track the connection shelf-wide, being careful to stay within the valid range for the specific interface type in use. For example, an admin adding a new VP connection on an NNI interface could use a value up to 340, but the same admin working on a UNI interface would need to stay within 1-20.