The capacity and “backhaul structure” of a mesh benefit from a root or relay nodes having multiple downlink radios. 

MD4452 relay node employs two backhaul downlinks to enable branching of the backhaul. It also has one uplink and one service radio.  In the illustration below, the use of multiple downlinks supports two separate mesh branches. If  a wired Ethernet link is attached to it, then the MD4452 configures itself as a root node and can provide up to 44 Mbps TCP/IP data traffic into the mesh.
  
MD4454 root node has all four radios as downlinks. This dictates that the node can only be used as a root node - there are no uplinks so it cannot be used as a relay node also. The primary use of the MD4454 is to provide four separate branches of the mesh tree with each branch using a different type of antenna to support specific range/coverage (see below). Since each radio uses a separate 802.11a channel, the full 22 Mbps of TCP/IP throughput of each radio results in a total of 88 Mbps TCP/IP available for distribution across four separate wireless backhauls.