$1.$ The textbook explains the three layers that exist in a backbone network. The diagram above has several labeled computers, switches, and routers that are part of these layers. For all labeled devices, identify their layer, and explain the function the device plays in this backbone network.

$2.$ The textbook describes three types of backbone networks $$ switched, routed, and a mixture of the two. What type of backbone network does this diagram illustrate? Explain your answer.

$3.$ Imagine that Computer $1$ broadcasts a data$-$link layer frame.

$.$ Would other computers or devices on LAN $1$ receive this broadcast? Explain your answer.

$.$ Would this broadcast be restricted only to a single LAN, or to multiple LANs? Explain your reasoning.

$4.$ Imagine that Computer $1$ generates an IPv$4$ packet that is destined for Computer $3.$ Assume that Computer $1$ knows the IPv$4$ address of Computer $3,$ and also assume that the forwarding and routing tables of all switches and routers respectively are fully populated to ensure readily available end$-$to$-$end communication between any two devices. Explain step$-$by$-$step how that IPv$4$ packet will travel the network to arrive at its destination. In your answer, make sure to identify the source and destination MAC and IPv$4$ addresses by labeling them with the attached device name, for example, $$Computer $3$s MAC address$$ or $$Computer $3$s IP address$.$

$5.$ Imagine that all of the routers except for Router B and Router C are replaced with switches.

$.$ What would the new backbone architecture be $($switched$,$ routed, or hybrid$)?$ Explain.

$.$ If Computer $1$ broadcasts a data$-$link layer frame with this new architecture, which LANs and devices would receive this broadcast?

$.$ Suppose that a total of few hundred employees work in Building $1$ and Building $2$ with many more LANs than what is illustrated in the diagram. What would be the advantages and disadvantages of this new architecture as compared to the old?