remove non-standard reference to 3-tier

Author: drbruced12

uses.rst

@@ -199,7 +199,7 @@ brief introduction.
 
 A datacenter switching fabric is a network often designed according to
 a *leaf-spine* topology. The basic idea is illustrated by the small
-4-rack/3-tier example shown in :numref:`Figure %s <fig-leaf-spine>`.
+4-rack example shown in :numref:`Figure %s <fig-leaf-spine>`.
 Each rack has a *Top-of-Rack
 (ToR)* switch that interconnects the servers in that rack; these are
 referred to as the *leaf* switches of the fabric. (There are typically
@@ -208,7 +208,7 @@ only one for simplicity.) Each leaf switch then connects to a subset
 of available *spine* switches, with two requirements: (1) that there
 be multiple paths between any pair of racks, and (2) that each
 rack-to-rack path is two-hops (i.e., via a single intermediate spine
-switch). Note that this means in 3-tier design like the one shown in
+switch). Note that this means in leaf-spine designs like the one shown in
 :numref:`Figure %s <fig-leaf-spine>`, every server-to-server path is
 either two hops (server-leaf-server in the intra-rack case) or four
 hops (server-leaf-spine-leaf-server in the inter-rack case).