Network Programming Final Othman
Describe why an application developer might choose to run an application over UDP rather than TCP. -
correct answer ✔✔An application developer may not want its application to use TCP's congestion
control, which can throttle the application's sending rate at times of congestion. Often, designers of IP
telephony and IP videoconference applications choose to run their applications over UDP because they
want to avoid TCP's congestion control. Also, some applications do not need the reliable data transfer
provided by TCP.
Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP?
If so, how? - correct answer ✔✔Yes. The application developer can put reliable data transfer into the
application layer protocol. This would require a significant amount of work and debugging, however.
In our rdt protocols, why did we need to introduce sequence numbers? - correct answer ✔✔Sequence
numbers are required for a receiver to find out whether an arriving packet contains new data or is a
retransmission.
Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first
segment has sequence number 90; the second has sequence number 110.
a. How much data is in the first segment?
b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment
that Host B sends to Host A, what will be the acknowledgment number? - correct answer ✔✔The
acknowledgement number is the sequence number of the next byte the receiver expects to receive. The
receiver ack'ing sequence number x acknowledges receipt of all data bytes less than (but not including)
byte number x.
Discuss why each input port in a high-speed router stores a shadow copy of the forwarding table. -
correct answer ✔✔With the shadow copy, the forwarding decision is made locally, at each input port,
without invoking the centralized routing processor. Such decentralized forwarding avoids creating a
forwarding processing bottleneck at a single point within the router.
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? -
, correct answer ✔✔A router uses longest prefix matching to determine which link interface a packet will
be forwarded to if the packet's destination address matches two or more entries in the forwarding table
Three types of switching fabrics are discussed in Section 4.2 . List and briefly describe each type. Which,
if any, can send multiple packets across the fabric in parallel? - correct answer ✔✔Switching via memory:
Fabric switching with the use of Crossbar, and Switching with use of Bus.
Suppose Host A sends Host B a TCP segment encapsulated in an IP datagram. When Host B receives the
datagram, how does the network layer in Host B know it should pass the segment (that is, the payload of
the datagram) to TCP rather than to UDP or to some other upper-layer protocol - correct answer ✔✔The
8-bit protocol field in the IP datagram contains information about which transport layer protocol the
destination host should pass the segment to.
Do routers have IP addresses? If so, how many? - correct answer ✔✔Yes, one per router interface.
What is the 32-bit binary equivalent of the IP address 223.1.3.27? - correct answer ✔✔Each decimal
number represents a byte (8 bits).11011111 00000001 00000011 00011011
Suppose there are three routers between a source host and a destination host. Ignoring fragmentation,
an IP datagram sent from the source host to the destination host will travel over how many interfaces?
How many forwarding tables will be indexed to move the datagram from the source to the destination? -
correct answer ✔✔An IP datagram sent from a source host to a destination host will travel through 8
interfaces. 3 forwarding tables will be indexed to move the datagram from source to destination.
What is a private network address? Should a datagram with a private network address ever be present in
the larger public Internet? Explain. - correct answer ✔✔A network address only meant to be used by
devices in the same network. Never should be present in public internet because it can cause overlap
with devices assigned to the same address.
Name three header fields in an IP datagram that can be "matched" in OpenFlow 1.0 generalized
forwarding. What are three IP datagram header fields that cannot be "matched" in OpenFlow? - correct
answer ✔✔IP source address, TCP source port, and source MAC address. TTL field, datagram length
field, and header checksum can't be matched.
Describe why an application developer might choose to run an application over UDP rather than TCP. -
correct answer ✔✔An application developer may not want its application to use TCP's congestion
control, which can throttle the application's sending rate at times of congestion. Often, designers of IP
telephony and IP videoconference applications choose to run their applications over UDP because they
want to avoid TCP's congestion control. Also, some applications do not need the reliable data transfer
provided by TCP.
Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP?
If so, how? - correct answer ✔✔Yes. The application developer can put reliable data transfer into the
application layer protocol. This would require a significant amount of work and debugging, however.
In our rdt protocols, why did we need to introduce sequence numbers? - correct answer ✔✔Sequence
numbers are required for a receiver to find out whether an arriving packet contains new data or is a
retransmission.
Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first
segment has sequence number 90; the second has sequence number 110.
a. How much data is in the first segment?
b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment
that Host B sends to Host A, what will be the acknowledgment number? - correct answer ✔✔The
acknowledgement number is the sequence number of the next byte the receiver expects to receive. The
receiver ack'ing sequence number x acknowledges receipt of all data bytes less than (but not including)
byte number x.
Discuss why each input port in a high-speed router stores a shadow copy of the forwarding table. -
correct answer ✔✔With the shadow copy, the forwarding decision is made locally, at each input port,
without invoking the centralized routing processor. Such decentralized forwarding avoids creating a
forwarding processing bottleneck at a single point within the router.
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? -
, correct answer ✔✔A router uses longest prefix matching to determine which link interface a packet will
be forwarded to if the packet's destination address matches two or more entries in the forwarding table
Three types of switching fabrics are discussed in Section 4.2 . List and briefly describe each type. Which,
if any, can send multiple packets across the fabric in parallel? - correct answer ✔✔Switching via memory:
Fabric switching with the use of Crossbar, and Switching with use of Bus.
Suppose Host A sends Host B a TCP segment encapsulated in an IP datagram. When Host B receives the
datagram, how does the network layer in Host B know it should pass the segment (that is, the payload of
the datagram) to TCP rather than to UDP or to some other upper-layer protocol - correct answer ✔✔The
8-bit protocol field in the IP datagram contains information about which transport layer protocol the
destination host should pass the segment to.
Do routers have IP addresses? If so, how many? - correct answer ✔✔Yes, one per router interface.
What is the 32-bit binary equivalent of the IP address 223.1.3.27? - correct answer ✔✔Each decimal
number represents a byte (8 bits).11011111 00000001 00000011 00011011
Suppose there are three routers between a source host and a destination host. Ignoring fragmentation,
an IP datagram sent from the source host to the destination host will travel over how many interfaces?
How many forwarding tables will be indexed to move the datagram from the source to the destination? -
correct answer ✔✔An IP datagram sent from a source host to a destination host will travel through 8
interfaces. 3 forwarding tables will be indexed to move the datagram from source to destination.
What is a private network address? Should a datagram with a private network address ever be present in
the larger public Internet? Explain. - correct answer ✔✔A network address only meant to be used by
devices in the same network. Never should be present in public internet because it can cause overlap
with devices assigned to the same address.
Name three header fields in an IP datagram that can be "matched" in OpenFlow 1.0 generalized
forwarding. What are three IP datagram header fields that cannot be "matched" in OpenFlow? - correct
answer ✔✔IP source address, TCP source port, and source MAC address. TTL field, datagram length
field, and header checksum can't be matched.
