CS6250 COMPUTER NETWORKS
EXAM 1 WITH 280 CORRECT
ACTUAL QUESTIONS AND
CORRECTLY WELL DEFINED
ANSWERS LATEST 2026 ALREADY
GRADED A+
Architecture Disadvantages - ANSWER//- 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 - ANSWER//Many of the layers
are the same OSI and Five-Layered Internet model
Differences - ANSWER//- 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? - ANSWER//- 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. - ANSWER//-
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 OSI Model Application Layer -
ANSWER//- Service, Interface, Protocol. Ex: Turn on your
smartphone and look at the list of apps. (HTTP, SMTP,
FTP, DNS) OSI Model Presentation Layer - ANSWER//-
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.
OSI Model Session Layer - ANSWER//- 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.
OSI Model Network Layer - ANSWER//- This layer is
responsible for moving the packet of information, called a
datagram, from one host to another. - 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. OSI Model Transport Layer -
,ANSWER//- Responsible for the end-to-end
communication between end hosts. - 2 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. OSI Model Data Link Layer -
ANSWER//- 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 ___________ layer protocol
include reliable delivery (transmission of the data from one
transmitting node, across one link, to the receiving node.
OSI Model Physical Layer - ANSWER//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. -
ANSWER//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 5-Layer Model - Transport Layer Protocols -
ANSWER//- TCP- UDP 5-Layer Model - Application Layer
Protocols - ANSWER//- NFS - DNS - SNMP - FTP - RCP -
Telnet - HTTP 5-Layer Model - Internet Layer Protocols -
ANSWER//- IP - ARP - ICMP 5-Layer Model - Data Link
Layer Protocols - ANSWER//- PPP - IEEE 802.2 -
Ethernet 5-Layer Model - Physical Network Layer
Protocols - ANSWER//- Token Ring - RS-232 What is
encapsulation, and how is it used in a layered model? -
ANSWER//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? - ANSWER//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? - ANSWER//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? - ANSWER//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. -
ANSWER//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
EXAM 1 WITH 280 CORRECT
ACTUAL QUESTIONS AND
CORRECTLY WELL DEFINED
ANSWERS LATEST 2026 ALREADY
GRADED A+
Architecture Disadvantages - ANSWER//- 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 - ANSWER//Many of the layers
are the same OSI and Five-Layered Internet model
Differences - ANSWER//- 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? - ANSWER//- 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. - ANSWER//-
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 OSI Model Application Layer -
ANSWER//- Service, Interface, Protocol. Ex: Turn on your
smartphone and look at the list of apps. (HTTP, SMTP,
FTP, DNS) OSI Model Presentation Layer - ANSWER//-
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.
OSI Model Session Layer - ANSWER//- 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.
OSI Model Network Layer - ANSWER//- This layer is
responsible for moving the packet of information, called a
datagram, from one host to another. - 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. OSI Model Transport Layer -
,ANSWER//- Responsible for the end-to-end
communication between end hosts. - 2 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. OSI Model Data Link Layer -
ANSWER//- 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 ___________ layer protocol
include reliable delivery (transmission of the data from one
transmitting node, across one link, to the receiving node.
OSI Model Physical Layer - ANSWER//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. -
ANSWER//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 5-Layer Model - Transport Layer Protocols -
ANSWER//- TCP- UDP 5-Layer Model - Application Layer
Protocols - ANSWER//- NFS - DNS - SNMP - FTP - RCP -
Telnet - HTTP 5-Layer Model - Internet Layer Protocols -
ANSWER//- IP - ARP - ICMP 5-Layer Model - Data Link
Layer Protocols - ANSWER//- PPP - IEEE 802.2 -
Ethernet 5-Layer Model - Physical Network Layer
Protocols - ANSWER//- Token Ring - RS-232 What is
encapsulation, and how is it used in a layered model? -
ANSWER//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? - ANSWER//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? - ANSWER//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? - ANSWER//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. -
ANSWER//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
