Thus, isochronous devices are of particular interest because they are allowed to request as much bandwidth as they need (up to the percent allowed before system reserved for control) and the host allocates the bandwidth on a first-come, first-served basis. USB Mouse and keyboard devices often use the interrupt protocol, while storage devices typically use the bulk protocol for data transfer. The USB 2.0 specification reserves approximately 10% of the available bandwidth for control protocol operations (commands and handshaking). Many devices need the consistent allocation of bandwidth that isochronous enables, including most USB cameras, speakers, and other audio/video USB devices. Each protocol has distinct bandwidth allocation properties. Isochronous, bulk, interrupt, and control are each different protocols within USB.
įigure 2: In the multi-TT hub architecture each port has a dedicated TT, thus allowing each client to have access to a dedicated 12-Mbps pipe.Īnother concept that is crucial to understanding the value of multi-TT technology is the types of transfer protocols within the USB specification.
#Multi port usb hub 2.0 full#
However, if the same configuration is used with a multi-TT hub with one TT per port, each device would receive a full 12-Mbps pipe for each port (Figure 2). įigure 1: In single-TT hubs, client devices must share a common 12-Mbps pips. Thus, when three full-speed USB 1.1 devices are attached to a Single-TT hub, each would device share a single 12-Mbps pipe created by the single TT (Figure 1). Single-TT hubs require that all ports share a 12-Mbps pipe.
USB 2.0 specification allows for two varieties of HS hubs: ones with a single TT for all ports and others with multiple TT's with up to one TT for each port. The TT is a dedicated processor within USB 2.0 hubs that services classic speed devices by translating their traffic from either low-speed or full-speed into a high-speed data stream that gets sent to the host. The USB 1.1 spec, on the other hand, calls for devices to operate at either a full-speed data rate of 12 Mbps and/or a low-speed data rate of 1.5 Mbps collectively referred to as “classic speed”. The USB 2.0 specification calls for hubs to operate in a native high-speed mode that delivers 480-Mbps data rates. In the discussion that follows, we'll layout why the mult-TT approach is a better option when designing USB 2.0 hubs. Currently, there are two flavors of these TT-enabled hubs on the market: multi-TT and single-TT. To solve this problem, designers have created transaction translators (TTs) that serve as a mechanism for converting lower-speed USB traffic into higher speed USB 2.0 streams.
But, for these hubs to be truly successful, they must equally support existing USB 1.0 and 1.1-enabled devices while also supporting emerging USB 2.0 systems.
#Multi port usb hub 2.0 portable#
With that in mind, designers must develop high-speed USB 2.0-compliant hub architectures that provide connectivity to portable devices. Since the adoption of the 2.0 specification, there has been renewed interest in using USB as a means for linking portable devices together.