CS6250 COMPUTER
NETWORKS EXAM 1 200
QUESTIONS AND VERIFIED
ANSWERS RATED A+
QUESTIONDescribe each layer of the OSI model. - answer-
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
What are advantages and disadvantages of a layered
architecture? - answer-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.
QUESTIONWhat are the differences and similarities of the OSI
model and five-layered Internet model? - answer-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.
QUESTIONWhat 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.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
QUESTIONProvide 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
QUESTIONWhat 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.
QUESTIONWhat 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.
, QUESTIONWhat 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.
QUESTIONWhat 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.
QUESTIONExplain 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 nodes that should die. C) Finally, we
stop the execution of the model when the network reaches a
given number of nodes.
QUESTIONWhat are the ramifications of the hourglass shape of
the internet? - answer-A. Many technologies that were not
originally designed for the internet have been modified so that
NETWORKS EXAM 1 200
QUESTIONS AND VERIFIED
ANSWERS RATED A+
QUESTIONDescribe each layer of the OSI model. - answer-
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
What are advantages and disadvantages of a layered
architecture? - answer-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.
QUESTIONWhat are the differences and similarities of the OSI
model and five-layered Internet model? - answer-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.
QUESTIONWhat 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.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
QUESTIONProvide 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
QUESTIONWhat 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.
QUESTIONWhat 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.
, QUESTIONWhat 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.
QUESTIONWhat 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.
QUESTIONExplain 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 nodes that should die. C) Finally, we
stop the execution of the model when the network reaches a
given number of nodes.
QUESTIONWhat are the ramifications of the hourglass shape of
the internet? - answer-A. Many technologies that were not
originally designed for the internet have been modified so that
