USB topology
TheUSB physical network is a tieredstar topology. A hubis at the centerof each star. Each wire
segmentis a point-to-pointconnectionbetween the host and a hub orfunction, or a hub connectedt o
anotherhubor function. This f igureillustrates 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
Function
Function
Function
Function
Function
Timingconstraints for hub and cablepropagationtimes allow a maximum of s event iers, includingthe
roottier. In seven tiers, amaximum of five non-roothubs can besupportedin a communicationpath
betweenthe host and any device. Note that a compounddevice occupies two t iers; therefore,it
cannotbe attached at tier seven whereonly f unctions canbe used.
AP P E N DI X A
USB2.0 specification primer
17