CS6250 COMPUTER NETWORK EXAM 1
QUESTIONS WITH VERIFIED ANSWERS
2026 | Study Guide | A+
• What are the differences and similarities of the OSI model and five-layered Internet
model? -✓✓The OSI model and the 5-layered Internet Model have many of the same
layers, with the difference being three of the layers are combined in the 5-layered
model. Specifically the five-layer model combines the application, presentation, and
session layers from the OSI model into a single application layer.
• What are sockets? -✓✓A network socket is a software structure within a network node
of a computer network that serves as an endpoint for sending and receiving data across
the network. The structure and properties of a socket are defined by an application
programming interface (API) for the networking architecture. Sockets are created only
during the lifetime of a process of an application running in the
node.https://en.wikipedia.org/wiki/Network_socket."A process sends messages into,
and receives messages from, the network through a software interface called a socket.
Let's consider an analogy to help us understand processes and sockets. A process is
analogous to a house and its socket is analogous to its door....a socket is the interface
between the application layer and the transport layer within a host." - Kurose and Ross,
2.1
• Describe each layer of the OSI model. -✓✓Application layer: Service, Interface,
Protocol. Ex: Turn on your smartphone and look at the list of apps. (HTTP, SMTP, FTP,
DNS)
Presentation layer: Plays intermediate role of formatting the information received from
the layer below and delivering it to the application layer. Ex: converting big endian to
little endian.
Session layer: Responsible for the mechanism that manages the different transport
streams that belong to the same session between end-user and application process.
Ex: teleconference app, it is responsible for tying together audio and video streaming.
Transport layer: Responsible for the end-to-end communication between end hosts. 2
transport protocols, TCP and UDP. TCP includes a connection-oriented service to the
applications that are running on the layer above, guaranteed delivery of the application-
layer messages, flow control, and congestion control mechanism. UDP provides a
connectionless, best-effort service to the applications that are running in the layer above
without reliability, flow, or congestion control. In this layer the packet is called a
segment.
Network layer: This layer is responsible for moving the packet of information, called a
datagram, from one host to another. The network layer is responsible for delivering the
datagram to the Transport layer on the destination host. In this layer there are the IP
Protocol and the routing tables.
,Data Link layer: Packets are referred to as frames. Examples include: ethernet, ppp,
wifi. Responsible for moving the frames from one node (host or router) to the next node.
Services offered by the data link layer protocol include reliable delivery (transmission of
the data from one transmitting node, across one link, to the receiving node.
Physical layer: This layer is the actual hardware responsible to transfer bits within a
frame between two nodes c
• Provide examples of popular protocols at each layer of the five-layered Internet model.
-✓✓Application: NFS, DNS, SNMP, ftp, rcp, telnet, HTTP
Transport: TCP, UDP
Internet: IP, ARP, ICMP
Data Link: PPP, IEEE 802.2, Ethernet
Physical Network: Token Ring, RS-232
• What is encapsulation, and how is it used in a layered model? -✓✓Encapsulation is
when data (called a header) is appended to the packet through each layer to signify its
on the correct path to the destination host.
• What is the end-to-end (e2e) principle? -✓✓A design choice that shaped the current
internet architecture. It states the network core should be simple and minimal, while the
end systems should carry the intelligence. Network functions should be simple and
essential commonly used functions so any host can utilize the service and higher form
functions should be built into the application itself. Lower level layers should be
independent and free to perform only their designed function and the higher-level layers
deal with the more intricate functions that deal with the specific application.
• What are the examples of a violation of e2e principle? -✓✓Violations include firewalls
and traffic filters. Firewalls violate because they are intermediate devices that are
operated between two end hosts and they can drop the end host communications.
Network Address Translation (NAT) boxes are also a violation because it uses the
single public IP address and distributes a new IP scheme to the hosts connected to it to
route data through re-writing the header info to route to the correct destination host.
NAT boxes are a violation because they are not globally addressable or routable.
• What is the EvoArch model? -✓✓An hourglass shaped model of the Internet where
the outer bands are more frequently modified or replaced and the further in you go the
harder it is for that layer to be altered or modified.
• Explain a round in the EvoArch model. -✓✓EvoArch is a discrete-time model that is
executed over rounds. At each round, we perform the following steps: A) We introduce
new nodes, and we place them randomly at layers. B) We examine all layers, from the
top to the bottom, and we perform the following tasks: 1) We connect the new nodes
that we may have just introduced to that layer, by choosing substrates based on the
generality probabilities of the layer below s(l−1), and by choosing products for them
based on the generality probability of the current layer s(l). 2) We update the value of
each node at each layer l, given that we may have new nodes added to the same layer
, l. 3) We examine all nodes, in order of decreasing value in that layer, and remove the
nodes that should die. C) Finally, we stop the execution of the model when the network
reaches a given number of nodes.
• What are the ramifications of the hourglass shape of the internet? -✓✓A. Many
technologies that were not originally designed for the internet have been modified so
that they have versions that can communicate over the internet (such as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage of
public IPv4 addresses.
• Repeaters, hubs, bridges, routers operate on which layers? -✓✓Repeaters and Hubs
work over L1 (Physical Layer)
Bridges and Layer 2-Switches work over L2 (Data link layer)
Routers and Layer 3-Switches work over L3 (Network layer)
• What is a bridge, and how does it "learn"? -✓✓A bridge is a device with multiple
inputs/outputs. A bridge transfers frames from an input to one (or multiple) outputs.
Though it doesn't need to forward all the frames it receives.
A learning bridge learns, populates and maintains a forwarding table. The bridge
consults that table so that it only forwards frames on specific ports, rather than over all
ports. So how does the bridge learn? When the bridge receives any frame this is a
"learning opportunity" to know which hosts are reachable through which ports. This is
because the bridge can view the port over which a frame arrives and the source host.
• What is a distributed algorithm? -✓✓A distributed algorithm is an algorithm designed
to run on computer hardware constructed from interconnected processors. Distributed
algorithms are used in many varied application areas of distributed computing, such as
telecommunications, scientific computing, distributed information processing, and real-
time process control.
https://en.wikipedia.org/wiki/Distributed_algorithm
• Explain the Spanning Tree Algorithm. -✓✓The algorithm runs in "rounds" and at every
round each node sends to each neighbor node a configuration message with three
fields: a) the sending node's ID, b) the ID of the roots as perceived by the sending node,
and c) the number of hops between that (perceived) root and the sending node.
At every round, each node keeps track of the best configuration message that it has
received so far, and it compares that against the configuration messages it receives
from neighboring nodes at that round.
At the very first round of the algorithm, every node thinks that it is the root.
• What is the purpose of the Spanning Tree Algorithm? -✓✓The purpose of the
Spanning Tree Algorithm is to prevent broadcast storm through the network and cause
stalls or heavy congestion.
QUESTIONS WITH VERIFIED ANSWERS
2026 | Study Guide | A+
• What are the differences and similarities of the OSI model and five-layered Internet
model? -✓✓The OSI model and the 5-layered Internet Model have many of the same
layers, with the difference being three of the layers are combined in the 5-layered
model. Specifically the five-layer model combines the application, presentation, and
session layers from the OSI model into a single application layer.
• What are sockets? -✓✓A network socket is a software structure within a network node
of a computer network that serves as an endpoint for sending and receiving data across
the network. The structure and properties of a socket are defined by an application
programming interface (API) for the networking architecture. Sockets are created only
during the lifetime of a process of an application running in the
node.https://en.wikipedia.org/wiki/Network_socket."A process sends messages into,
and receives messages from, the network through a software interface called a socket.
Let's consider an analogy to help us understand processes and sockets. A process is
analogous to a house and its socket is analogous to its door....a socket is the interface
between the application layer and the transport layer within a host." - Kurose and Ross,
2.1
• Describe each layer of the OSI model. -✓✓Application layer: Service, Interface,
Protocol. Ex: Turn on your smartphone and look at the list of apps. (HTTP, SMTP, FTP,
DNS)
Presentation layer: Plays intermediate role of formatting the information received from
the layer below and delivering it to the application layer. Ex: converting big endian to
little endian.
Session layer: Responsible for the mechanism that manages the different transport
streams that belong to the same session between end-user and application process.
Ex: teleconference app, it is responsible for tying together audio and video streaming.
Transport layer: Responsible for the end-to-end communication between end hosts. 2
transport protocols, TCP and UDP. TCP includes a connection-oriented service to the
applications that are running on the layer above, guaranteed delivery of the application-
layer messages, flow control, and congestion control mechanism. UDP provides a
connectionless, best-effort service to the applications that are running in the layer above
without reliability, flow, or congestion control. In this layer the packet is called a
segment.
Network layer: This layer is responsible for moving the packet of information, called a
datagram, from one host to another. The network layer is responsible for delivering the
datagram to the Transport layer on the destination host. In this layer there are the IP
Protocol and the routing tables.
,Data Link layer: Packets are referred to as frames. Examples include: ethernet, ppp,
wifi. Responsible for moving the frames from one node (host or router) to the next node.
Services offered by the data link layer protocol include reliable delivery (transmission of
the data from one transmitting node, across one link, to the receiving node.
Physical layer: This layer is the actual hardware responsible to transfer bits within a
frame between two nodes c
• Provide examples of popular protocols at each layer of the five-layered Internet model.
-✓✓Application: NFS, DNS, SNMP, ftp, rcp, telnet, HTTP
Transport: TCP, UDP
Internet: IP, ARP, ICMP
Data Link: PPP, IEEE 802.2, Ethernet
Physical Network: Token Ring, RS-232
• What is encapsulation, and how is it used in a layered model? -✓✓Encapsulation is
when data (called a header) is appended to the packet through each layer to signify its
on the correct path to the destination host.
• What is the end-to-end (e2e) principle? -✓✓A design choice that shaped the current
internet architecture. It states the network core should be simple and minimal, while the
end systems should carry the intelligence. Network functions should be simple and
essential commonly used functions so any host can utilize the service and higher form
functions should be built into the application itself. Lower level layers should be
independent and free to perform only their designed function and the higher-level layers
deal with the more intricate functions that deal with the specific application.
• What are the examples of a violation of e2e principle? -✓✓Violations include firewalls
and traffic filters. Firewalls violate because they are intermediate devices that are
operated between two end hosts and they can drop the end host communications.
Network Address Translation (NAT) boxes are also a violation because it uses the
single public IP address and distributes a new IP scheme to the hosts connected to it to
route data through re-writing the header info to route to the correct destination host.
NAT boxes are a violation because they are not globally addressable or routable.
• What is the EvoArch model? -✓✓An hourglass shaped model of the Internet where
the outer bands are more frequently modified or replaced and the further in you go the
harder it is for that layer to be altered or modified.
• Explain a round in the EvoArch model. -✓✓EvoArch is a discrete-time model that is
executed over rounds. At each round, we perform the following steps: A) We introduce
new nodes, and we place them randomly at layers. B) We examine all layers, from the
top to the bottom, and we perform the following tasks: 1) We connect the new nodes
that we may have just introduced to that layer, by choosing substrates based on the
generality probabilities of the layer below s(l−1), and by choosing products for them
based on the generality probability of the current layer s(l). 2) We update the value of
each node at each layer l, given that we may have new nodes added to the same layer
, l. 3) We examine all nodes, in order of decreasing value in that layer, and remove the
nodes that should die. C) Finally, we stop the execution of the model when the network
reaches a given number of nodes.
• What are the ramifications of the hourglass shape of the internet? -✓✓A. Many
technologies that were not originally designed for the internet have been modified so
that they have versions that can communicate over the internet (such as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage of
public IPv4 addresses.
• Repeaters, hubs, bridges, routers operate on which layers? -✓✓Repeaters and Hubs
work over L1 (Physical Layer)
Bridges and Layer 2-Switches work over L2 (Data link layer)
Routers and Layer 3-Switches work over L3 (Network layer)
• What is a bridge, and how does it "learn"? -✓✓A bridge is a device with multiple
inputs/outputs. A bridge transfers frames from an input to one (or multiple) outputs.
Though it doesn't need to forward all the frames it receives.
A learning bridge learns, populates and maintains a forwarding table. The bridge
consults that table so that it only forwards frames on specific ports, rather than over all
ports. So how does the bridge learn? When the bridge receives any frame this is a
"learning opportunity" to know which hosts are reachable through which ports. This is
because the bridge can view the port over which a frame arrives and the source host.
• What is a distributed algorithm? -✓✓A distributed algorithm is an algorithm designed
to run on computer hardware constructed from interconnected processors. Distributed
algorithms are used in many varied application areas of distributed computing, such as
telecommunications, scientific computing, distributed information processing, and real-
time process control.
https://en.wikipedia.org/wiki/Distributed_algorithm
• Explain the Spanning Tree Algorithm. -✓✓The algorithm runs in "rounds" and at every
round each node sends to each neighbor node a configuration message with three
fields: a) the sending node's ID, b) the ID of the roots as perceived by the sending node,
and c) the number of hops between that (perceived) root and the sending node.
At every round, each node keeps track of the best configuration message that it has
received so far, and it compares that against the configuration messages it receives
from neighboring nodes at that round.
At the very first round of the algorithm, every node thinks that it is the root.
• What is the purpose of the Spanning Tree Algorithm? -✓✓The purpose of the
Spanning Tree Algorithm is to prevent broadcast storm through the network and cause
stalls or heavy congestion.
