ent types of peripheral interfaces (parallel ports, serial ports, PS/2, MIDI, etc.) for devices such as joysticks, scanners, keyboards and printers. The maximum bandwidth of USB 1.0 was 12 Mbps, but this has since increased to a FireWire matching 480 Mbps with USB 2.0. USB uses a host-centric architecture, with a host controller dealing with the identification and configuration of devices connected either directly to the host or to intermediate hubs (Figure 2-11). The USB specification supports both isochronous and asynchronous transfer types over the same connection. Isochronous transfers require guaranteed bandwidth and low latency for applications such as telephony and media streaming, while asynchronous transfers are delay-tolerant and are able to wait for available bandwidth. USB control protocols are designed specifically to Wireless Network Logical Architecture Device Device Device Device Device Device Root Hub Tier 1 Device Device Tier 2 Device Device Tier 3 Device Device Device Figure 2-11: USB Network Topology: Daisy-chain and Tree Structures give a low protocol overhead, resulting in highly effective utilisation of the available bandwidth. This available bandwidth is shared among all connected devices and is allocated using "pipes", with each pipe representing a connection between the host and a single device. The bandwidth for a pipe is allocated when the pipe is established, and a wide range of different device bit rates and device types can be supported concurrently. For example, digital telephony devices can be concurrently accommodated ranging from 1 "bearer" plus 1 "demand" channel (64 kbps - see ISDN above) up to T1 capacity (1.544 Mbps). USB employs NRZI (Non Return to Zero Inverted) as a data encoding scheme. In NRZI encoding, a 1-bit is represented by no change in output voltage level and a 0-bit is represented by a change in voltage level (Figure 2-12). A string of 0-bits therefore causes the NRZI output to toggle between states on each bit cycle, while a string of 1-bits causes a period wit