1. first you know which brand ? (Cisco, Nortel, Alcatel ?)
2. there are some configurable parameters such as LMI type (Cisco, Ansi AnnexD, AnnexG), CIR, EIR, BC, DLCI no ... these are the most common parameters. Other parameters changes to switch type.
3. For Cisco look for product type IGX, IPX, BPX .