Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:ORPL also outperforms other stateof-the-art solutions such as the Collection Tree Protocol (CTP) [21], Opportunistic Routing for WSN (ORW) [26] or the Low-Power Wireless Bus (LWB) [18].
Category: