CS6250 COMPUTER NETWORKS EXAM 1
REVIEW SHEET TESTED QUESTIONS AND
CORRECT ANSWERS ALREADY PASSED
⩥ What 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.
⩥ 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.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.
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
⩥ 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
⩥ 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
REVIEW SHEET TESTED QUESTIONS AND
CORRECT ANSWERS ALREADY PASSED
⩥ What 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.
⩥ 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.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.
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
⩥ 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
⩥ 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
