The illustration has two areas bordered by dotted lines. The area on the 
left is labelled "Cluster 1"; the area on the right is labelled "Cluster 2".

The Cluster 1 area has five boxes--one by itself on the left side, 
and the other four in a vertical stack on the right. The box by itself and 
the top and bottom boxes in the stack are each labelled "Balancer3". The 
two boxes in the middle of the stack are labelled "Firewall server 1" and 
"Firewall server N" respectively. 

The Balancer3 box by itself has a double-headed arrow labelled "z1" 
extending away from it. Two more unlabelled double-headed arrows connect 
it to the Firewall server 1 box and to the Firewall server N box. The 
points at which these arrows touch the Firewall boxes are labelled "i1".

The Balancer3 box at the top of the stack has a double-headed arrow labelled 
"z2" extending away from it and is connected to the Firewall server 1 box 
by an unlabelled double-headed arrow. The point at which this arrow touches 
the Firewall box is labelled "i2". An unlabelled single-headed arrow extends 
from the Firewall box to the Balancer3 box.

The Balancer 3 box at the bottom of the stack has a double-headed arrow labelled 
"z3" extending away from it and is connected to the Firewall server N box 
by an unlabelled double-headed arrow. The point at which this arrow touches 
the Firewall box is labelled "i3". An unlabelled single-headed arrow extends 
from the Firewall box down to the Balancer3 box.

Between the two Firewall boxes are two unlabelled single-headed arrows, one 
pointing up and the other pointing down. The point at which an arrow head 
touches the Firewall server 1 box is labelled "i3"; the corresponding point 
for Firewall server 2 is labelled "i2".

The Cluster 2 area has four boxes--one by itself on the left side, and 
the other three in a vertical stack on the right. The box by itself is 
labelled "Balancer4. The bottom box in the stack is labelled "Balancer3". 
Above it is a box labelled "Firewall server N", and above that box is one 
labelled "Firewall server 1".

The Balancer4 box has three double-headed arrows extending away from it. 
One is labelled "z1", and the other two are each labelled "z2". 
Two more unlabelled double-headed arrows connect it to the Firewall 
server 1 box and to the Firewall server N box. The points at which these 
arrows touch the Firewall boxes are each labelled "i1".

The Balancer3 box has a double-headed arrow labelled "z3" extending away 
from it and an unlabelled double-headed arrow connecting it to the Firewall 
server N box. The point at which the latter touches the Firewall box is 
labelled "i2". An unlabelled single-headed arrow extends from the Firewall 
server N box down to the Balancer3 box.

Between the two Firewall boxes is an unlabelled single-headed arrow extending 
from the Firewall server N box up to the Firewall server 1 box. The point at 
which it touches the Firewall server 1 box is labelled "i2".