CS6250 Computer Networks Exam 1 |
Questions and Verified Answers |
GRADED A+ | Latest Update 2026
What are advantages and disadvantages of a layered architecture? -
CORRECTANSWER Each protocol layer offers different services. Some advantages
are scalability, flexibility, 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 five-layered Internet
model? -CORRECTANSWER 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? -CORRECTANSWER 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. -CORRECTANSWER 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. -
CORRECTANSWER 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? -CORRECTANSWER
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? -CORRECTANSWER 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? -CORRECTANSWER 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? -CORRECTANSWER 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. -CORRECTANSWER EvoArch is a discrete-time
model that is executed over rounds. At each round, we perform the following steps: A)
Questions and Verified Answers |
GRADED A+ | Latest Update 2026
What are advantages and disadvantages of a layered architecture? -
CORRECTANSWER Each protocol layer offers different services. Some advantages
are scalability, flexibility, 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 five-layered Internet
model? -CORRECTANSWER 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? -CORRECTANSWER 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. -CORRECTANSWER 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. -
CORRECTANSWER 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? -CORRECTANSWER
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? -CORRECTANSWER 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? -CORRECTANSWER 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? -CORRECTANSWER 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. -CORRECTANSWER EvoArch is a discrete-time
model that is executed over rounds. At each round, we perform the following steps: A)
