User Guide

USB topology

The USB physical network is a tiered star topology. A hub is at the center of each star. Each wire

segment is a point-to-point connection between the host and a hub or function, or a hub connected to

another hub or function. This figure illustrates the topology of a USB network.

Root

hub

Hub 1

Hub 2

Hub 3 Hub 4

Hub 5

Hub 7Hub 6

Function

Host (Tier 1)

Tier 2

Tier 3

Tier 4

Tier 5

Tier 6

Tier 7

Function

Timing constraints for hub and cable propagation times allow a maximum of seven tiers, including the

root tier. In seven tiers, a maximum of five non-root hubs can be supported in a communication path

between the host and any device. Note that a compound device occupies two tiers; therefore, it

cannot be attached at tier seven where only functions can be used.

A P P E N D I X A

USB 2.0 specification primer