CS6250, Chapter 5 Exam with Questions
and Correct Answers 100% Pass
GRADED A+
What are the basic components of a router? - CORRECT ANSWERS-the input/output
ports,
the switching fabric,
the routing processor.
Explain the forwarding (or switching) function of a router - CORRECT ANSWERS-This is
the router's action to transfer a packet from an input link interface to the appropriate output
link interface.
Forwarding takes place at very short timescales (typically a few nanoseconds), and is
typically implemented in hardware.
What are the functionalities of the input ports? - CORRECT ANSWERS-i. Physically
terminate the incoming links to the router
ii. The data link processing unit decapsulates the packets
iii. Perform the lookup function. At this point the input ports consult the forwarding table to
ensure that each packet is forwarded to the appropriate output port through the switching
fabric.
What are the functionalities of the output ports? - CORRECT ANSWERS-receive and
queue the packets which come from the switching fabric and then send them over to the
outgoing link
What is the purpose of the router's control plane? - CORRECT ANSWERS-implementing
the routing protocols,
maintaining the routing tables,
computing the forwarding table.
All these functions are implemented in software in the routing processor, or by a remote
controller.
What tasks occur in a router? - CORRECT ANSWERS-1. Lookup
2. Switching
3. Queueing
4. Header validation and checksum
5. Route processing
6. Protocol Processing.
, Explain the lookup task of a router - CORRECT ANSWERS-Time Sensitive, when a packet
arrives at the destination IP and determines the output link by looking at the forwarding
table or forwarding information base (FIB). The
Explain the switching task of a router - CORRECT ANSWERS-Time Sensitive, after
lookup, the switching system takes over to transfer the packet from the input link to the
output link. Modern fast routers use a crossbar for this task. Scheduling can be difficult
because multiple inputs may want to send to the same output.
Explain the Queuing task of the router - CORRECT ANSWERS-Time Sensitive, After the
switch has been switched to a specific output, it will need to be queued (if the link is
congested). Queue may be FIFO or other.
Explain the Header validation and checksum task of the router - CORRECT ANSWERS-
Time insensitive, the router checks the packets version number, it decrements the time to
live field and recalculates the header checksum. Data Plane
Explain the route processing task of the router - CORRECT ANSWERS-Time insensitive,
the router builds their forwarding table using routing protocols such as RIP, OSPF and
BGP. These protocols are implemented in routing processors. Control Plane
Explain the protocol processing task of the router - CORRECT ANSWERS-Time
insensitive, the routers, in order to implement their functions, need to implement the
following protocols (Control Plane):
i. SNMP - Remote inspection
ii. TCP and UDP - remote communication with the router
iii. ICMP - for sending error messages when time to live time is exceeded.
Explain switching via memory - CORRECT ANSWERS-a. Input/Output ports operate as
I/O devices in an operating system, and they are controlled by the routing processor. When
an input port receives a packet, it sends an interrupt to the routing processor and the
packet is copied to the processor's memory. Then the processor extracts the destination
address and looks into the forward table to find the output port, and finally the packet is
copied into that output's port buffer.
Explain switching via bus - CORRECT ANSWERS-a. the routing processor does not
intervene as we saw the switching via memory. When an input port receives a new packet,
it puts an internal header that designates the output port, and it sends the packet to the
shared bus. Then all the output ports will receive the packet, but only the designated one
will keep it. When the packet arrives at the designated output port, then the internal header
is removed from the packet. Only one packet can cross the bus at a given time, and so the
speed of the bus limits the speed of the router.
Explain switching via interconnection network (Crossbar) - CORRECT ANSWERS-
Connects N input ports to N output ports using 2N buses. Horizontal buses meet the
vertical buses at crosspoints which are controlled by the switching fabric. For example,
and Correct Answers 100% Pass
GRADED A+
What are the basic components of a router? - CORRECT ANSWERS-the input/output
ports,
the switching fabric,
the routing processor.
Explain the forwarding (or switching) function of a router - CORRECT ANSWERS-This is
the router's action to transfer a packet from an input link interface to the appropriate output
link interface.
Forwarding takes place at very short timescales (typically a few nanoseconds), and is
typically implemented in hardware.
What are the functionalities of the input ports? - CORRECT ANSWERS-i. Physically
terminate the incoming links to the router
ii. The data link processing unit decapsulates the packets
iii. Perform the lookup function. At this point the input ports consult the forwarding table to
ensure that each packet is forwarded to the appropriate output port through the switching
fabric.
What are the functionalities of the output ports? - CORRECT ANSWERS-receive and
queue the packets which come from the switching fabric and then send them over to the
outgoing link
What is the purpose of the router's control plane? - CORRECT ANSWERS-implementing
the routing protocols,
maintaining the routing tables,
computing the forwarding table.
All these functions are implemented in software in the routing processor, or by a remote
controller.
What tasks occur in a router? - CORRECT ANSWERS-1. Lookup
2. Switching
3. Queueing
4. Header validation and checksum
5. Route processing
6. Protocol Processing.
, Explain the lookup task of a router - CORRECT ANSWERS-Time Sensitive, when a packet
arrives at the destination IP and determines the output link by looking at the forwarding
table or forwarding information base (FIB). The
Explain the switching task of a router - CORRECT ANSWERS-Time Sensitive, after
lookup, the switching system takes over to transfer the packet from the input link to the
output link. Modern fast routers use a crossbar for this task. Scheduling can be difficult
because multiple inputs may want to send to the same output.
Explain the Queuing task of the router - CORRECT ANSWERS-Time Sensitive, After the
switch has been switched to a specific output, it will need to be queued (if the link is
congested). Queue may be FIFO or other.
Explain the Header validation and checksum task of the router - CORRECT ANSWERS-
Time insensitive, the router checks the packets version number, it decrements the time to
live field and recalculates the header checksum. Data Plane
Explain the route processing task of the router - CORRECT ANSWERS-Time insensitive,
the router builds their forwarding table using routing protocols such as RIP, OSPF and
BGP. These protocols are implemented in routing processors. Control Plane
Explain the protocol processing task of the router - CORRECT ANSWERS-Time
insensitive, the routers, in order to implement their functions, need to implement the
following protocols (Control Plane):
i. SNMP - Remote inspection
ii. TCP and UDP - remote communication with the router
iii. ICMP - for sending error messages when time to live time is exceeded.
Explain switching via memory - CORRECT ANSWERS-a. Input/Output ports operate as
I/O devices in an operating system, and they are controlled by the routing processor. When
an input port receives a packet, it sends an interrupt to the routing processor and the
packet is copied to the processor's memory. Then the processor extracts the destination
address and looks into the forward table to find the output port, and finally the packet is
copied into that output's port buffer.
Explain switching via bus - CORRECT ANSWERS-a. the routing processor does not
intervene as we saw the switching via memory. When an input port receives a new packet,
it puts an internal header that designates the output port, and it sends the packet to the
shared bus. Then all the output ports will receive the packet, but only the designated one
will keep it. When the packet arrives at the designated output port, then the internal header
is removed from the packet. Only one packet can cross the bus at a given time, and so the
speed of the bus limits the speed of the router.
Explain switching via interconnection network (Crossbar) - CORRECT ANSWERS-
Connects N input ports to N output ports using 2N buses. Horizontal buses meet the
vertical buses at crosspoints which are controlled by the switching fabric. For example,
