3/25/26, 3:27 PM
CS6250 COMPUTER NETWORKS EXAM 1 QUESTIONS WITH COMPLETE VERIFIED
ANSWERS 2026/2027 LATEST UPDATE
What are advantages and disadvantages of a layered Each protocol layer offers different services. Some advantages are scalability, flexibility,
architecture? and ease of adding / removing components making it easier for cost-effective
implementations. Disadvantages include: 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 and in message
headers caused by abstraction barriers between layers.
What are the differences and similarities of the OSI model and The OSI model and the 5-layered Internet Model have many of the same layers, with the
five-layered Internet model? 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.
1/21
,3/25/26, 3:27 PM
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 connected through a physical link. Ex: Ethernet (twisted-pair copper,
coax, fiber-optics).
2/21
, 3/25/26, 3:27 PM
Provide examples of popular protocols at each layer of the Application: NFS, DNS, SNMP, ftp, rcp, telnet, HTTP
five-layered Internet model. 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.
3/21
CS6250 COMPUTER NETWORKS EXAM 1 QUESTIONS WITH COMPLETE VERIFIED
ANSWERS 2026/2027 LATEST UPDATE
What are advantages and disadvantages of a layered Each protocol layer offers different services. Some advantages are scalability, flexibility,
architecture? and ease of adding / removing components making it easier for cost-effective
implementations. Disadvantages include: 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 and in message
headers caused by abstraction barriers between layers.
What are the differences and similarities of the OSI model and The OSI model and the 5-layered Internet Model have many of the same layers, with the
five-layered Internet model? 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.
1/21
,3/25/26, 3:27 PM
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 connected through a physical link. Ex: Ethernet (twisted-pair copper,
coax, fiber-optics).
2/21
, 3/25/26, 3:27 PM
Provide examples of popular protocols at each layer of the Application: NFS, DNS, SNMP, ftp, rcp, telnet, HTTP
five-layered Internet model. 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.
3/21
