Which wireless mode allows for a network connection without a wireless infrastructure in place?

An independent basic service set (IBSS), also known as an ad hoc network, does not require any wireless infrastructure. Clients connect directly to each other over the 802.11 wireless spectrum. A basic service set (BSS) is a small area with wireless coverage and is served by a single WAP. An extended service set (ESS) is a scaled-out BSS, where many WAPs support client roaming between the WAPs and channel selection. The distribution system (DS) is the connection between the wireless network and the wired network.