CS 6250 Computer Networks Exam 1 Questions and
Answers Latest Guide Solved 100%;Georgia Institute
Of Technology
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 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.
What 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 they have versions that can communicate over the internet (such
as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage
of public IPv4 addresses.
Repeaters, hubs, bridges, routers operate on which layers? - ANSWER -Repeaters
and Hubs work over L1 (Physical Layer)
Bridges and Layer 2-Switches work over L2 (Data link layer)
Routers and Layer 3-Switches work over L3 (Network layer)
What is a bridge, and how does it "learn"? - ANSWER -A bridge is a device with
multiple inputs/outputs. A bridge transfers frames from an input to one (or
multiple) outputs. Though it doesn't need to forward all the frames it receives.
A learning bridge learns, populates and maintains a forwarding table. The bridge
consults that table so that it only forwards frames on specific ports, rather than over
all ports. So how does the bridge learn? When the bridge receives any frame this is
a "learning opportunity" to know which hosts are reachable through which ports.
This is because the bridge can view the port over which a frame arrives and the
source host.
Answers Latest Guide Solved 100%;Georgia Institute
Of Technology
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 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.
What 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 they have versions that can communicate over the internet (such
as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage
of public IPv4 addresses.
Repeaters, hubs, bridges, routers operate on which layers? - ANSWER -Repeaters
and Hubs work over L1 (Physical Layer)
Bridges and Layer 2-Switches work over L2 (Data link layer)
Routers and Layer 3-Switches work over L3 (Network layer)
What is a bridge, and how does it "learn"? - ANSWER -A bridge is a device with
multiple inputs/outputs. A bridge transfers frames from an input to one (or
multiple) outputs. Though it doesn't need to forward all the frames it receives.
A learning bridge learns, populates and maintains a forwarding table. The bridge
consults that table so that it only forwards frames on specific ports, rather than over
all ports. So how does the bridge learn? When the bridge receives any frame this is
a "learning opportunity" to know which hosts are reachable through which ports.
This is because the bridge can view the port over which a frame arrives and the
source host.
