$4-$ THE NETWORK LAYER: DATA PLANE

R$3.$ We made a distinction between the forwarding function and the routing func$-$

tion performed in the network layer. What are the key differences between

routing and forwarding?

R$4.$ What is the role of the forwarding table within a router?

R$5.$ We said that a network layer's service model "defines the characteristics of

end$-$to$-$end transport of packets between sending and receiving hosts." What is

the service model of the Internet's network layer? What guarantees are made by

the Internet's service model regarding the host$-$to$-$host delivery of datagrams?

SECTION $4\mathrm{.}2$

R$6.$ In Section $4\mathrm{.}2,$ we saw that a router typically consists of input ports, output

ports, a switching fabric and a routing processor. Which of these are imple$-$

mented in hardware and which are implemented in software? Why? Return$-$

ing to the notion of the network layer's data plane and control plane, which

are implemented in hardware and which are implemented in software? Why?

R$7.$ What does each input port of a high speed router store to facilitate fast for$-$

warding decisions?

R$8.$ What is meant by destination$-$based forwarding? How does this differ from

generalized forwarding $($assuming you've read Section $4\mathrm{.}4,$ which of the two

approaches are adopted by Software$-$Defined Networking$)?$

R$9.$ Suppose that an arriving packet matches two or more entries in a router's

forwarding table. With traditional destination$-$based forwarding, what rule

does a router apply to determine which of these rules should be applied to

determine the output port to which the arriving packet should be switched?

R$10.$ Switching in a router forwards data from an input port to an output port.

What is the advantage of switching via an interconnection network over

switching via memory and switching via bus?

R$11.$ What is the role of a packet scheduler at the output port of a router?

R$12.$ What is a drop$-$tail policy? What are AQM algorithms? Which is the most

widely studied and implemented AQM algorithm? How does it work?

R$13.$ What is HOL blocking? Does it occur in input ports or output ports?

R$14.$ In Section $4\mathrm{.}2,$ we studied FIFO, Priority, Round Robin $($RR$),$ and Weighted

Fair Queueing $($WFQ$)$ packet scheduling disciplines? Which of these queueing

disciplines ensure that all packets depart in the order in which they arrived?

R$15.$ Give an example showing why a network operator might want one class of

packets to be given priority over another class of packets.

R$16.$ What is an essential different between RR and WFQ packet scheduling? Is

there a case $($Hint: Consider the WFQ weights$)$ where RR and WFQ will

behave exactly the same?