You can measure bandwidth usage by IP address or by application in a network, using one of the flow protocols.

You can also use packet sniffing for bandwidth monitoring if your hardware does not support any of these xFlow versions. sFlow uses statistical sampling of the traffic at defined intervals to achieve scalability for high volume interfaces.

sFlow : Short for sampled flow, introduced by HP.jFlow : Traffic sampling technology introduced by Juniper networks.NetFlow v5/v9 and IPFIX : Originally introduced by Cisco and supported by several vendors.This way, they determine which machine, protocol, or user is consuming bandwidth. You can use them to monitor where and how much data is traveling to and from. XFlows are monitoring data pushed from network devices to PRTG. In PRTG, you can view Toplists for all xFlow sensors. Using Flow (NetFlow, jFlow, sFlow, IPFIX) protocols, you can monitor the bandwidth usage of all packets going through a device. PRTG Manual: Monitoring Bandwidth via Flows

Network flow analyzer