CS6250 COMPUTER NETWORKS EXAM 1 QUESTIONS
WITH VERIFIED ACCURATE ANSWERS 2026
Layered Architecture - Answers -Each protocol layer offers different services.
Layered Architecture Advantages - Answers -- Scalability,
- Flexibility
- Ease of adding / removing components making it easier for cost-effective
implementations.
Layered Architecture Disadvantages - Answers -- Some layers functionality depends on
the information from the other layer and violates the goal of layer separation;
- One layer may duplicate lower layer functionalities
- Overhead both in computation
- Overhead in message headers caused by abstraction barriers between layers.
OSI and Five-Layered Internet model Similarities - Answers -Many of the layers are the
same
OSI and Five-Layered Internet model Differences - Answers -- Three of the layers are
combined in the 5-layered model.
- Specifically the five-layer model combines the
- Application
- Presentation
- Session layers
from the OSI model into a single Application layer.
What are sockets? - Answers -- 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.
- ."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. - Answers -- Application layer: Service,
Interface, Protocol.
,- Presentation layer: Plays intermediate role of formatting the information received from
the layer below and delivering it to the application layer.
- Session layer: Responsible for the mechanism that manages the different transport
streams that belong to the same session between end-user and application process.
- Transport layer: Responsible for the end-to-end communication between end hosts.
Network layer: This layer is responsible for moving the packet of information, called a
datagram, from one host to another.
- Data Link layer: Responsible for moving the frames from one node (host or router) to
the next 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. -
Answers -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? - Answers -
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? - Answers -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? - Answers -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? - Answers -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. - Answers -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? - Answers -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? - Answers -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"? - Answers -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? - Answers -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. - Answers -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.
WITH VERIFIED ACCURATE ANSWERS 2026
Layered Architecture - Answers -Each protocol layer offers different services.
Layered Architecture Advantages - Answers -- Scalability,
- Flexibility
- Ease of adding / removing components making it easier for cost-effective
implementations.
Layered Architecture Disadvantages - Answers -- Some layers functionality depends on
the information from the other layer and violates the goal of layer separation;
- One layer may duplicate lower layer functionalities
- Overhead both in computation
- Overhead in message headers caused by abstraction barriers between layers.
OSI and Five-Layered Internet model Similarities - Answers -Many of the layers are the
same
OSI and Five-Layered Internet model Differences - Answers -- Three of the layers are
combined in the 5-layered model.
- Specifically the five-layer model combines the
- Application
- Presentation
- Session layers
from the OSI model into a single Application layer.
What are sockets? - Answers -- 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.
- ."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. - Answers -- Application layer: Service,
Interface, Protocol.
,- Presentation layer: Plays intermediate role of formatting the information received from
the layer below and delivering it to the application layer.
- Session layer: Responsible for the mechanism that manages the different transport
streams that belong to the same session between end-user and application process.
- Transport layer: Responsible for the end-to-end communication between end hosts.
Network layer: This layer is responsible for moving the packet of information, called a
datagram, from one host to another.
- Data Link layer: Responsible for moving the frames from one node (host or router) to
the next 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. -
Answers -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? - Answers -
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? - Answers -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? - Answers -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? - Answers -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. - Answers -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? - Answers -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? - Answers -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"? - Answers -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? - Answers -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. - Answers -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.
