Page 1 of 42
CS 6250 COMPUTER NETWORKS STUDY
QUESTIONS - EXAM 2 LESSON 7 -
12|UPDATED QUESTIONS AND WELL
ELLABORATED ANSWERS|ALREADY
GRADED A+
What are advantages and disadvantages of a layered architecture? -
CORRECT-ANSWER-Separation of concerns among logical layers
promotes flexibility, scalibility, and maintainability. Multiple
applications can reuse the components. It enables teams to work on
different parts with minimal dependencies on other teams
What are the similarities of the OSI model and five-layered Internet
model? - CORRECT-ANSWER-They are both based on layered
architecture.
The are comparable to each other - see image 1
Both are networking standards
, Page 2 of 42
What are the differences of the OSI model and five-layered Internet
model? - CORRECT-ANSWER-OSI is a generic model based on the
functions of each layer. TCP is a protocol oriented standard.
OSI uses 3 upper layers (application, presentation, and session) while
TCP just uses application.
Likewise, OSI uses 2 Lower layers (Physical and DataLink) while TCP just
uses Link
Physical Layer - CORRECT-ANSWER-The lowest, or first, layer of the OSI
model. Protocols in this layer generate and detect signals so as to
transmit and receive data over a network medium. These protocols also
set the data transmission rate and monitor data error rates, but do not
provide error correction.
The lowest layer of the OSI Model is concerned with electrically or
optically transmitting raw unstructured data bits across the network
from the physical layer of the sending device to the physical layer of the
receiving device. It can include specifications such as voltages, pin
layout, cabling, and radio frequencies. At the physical layer, one might
, Page 3 of 42
find "physical" resources such as network hubs, cabling, repeaters,
network adapters or modems.
Distance Vector Routing Count to Infinity - CORRECT-ANSWER-If the
link between B and C is disconnected, then B will know that it can no
longer get to C via that link and will remove it from it's table. Before it
can send any updates it's possible that it will receive an update from A
which will be advertising that it can get to C at a cost of 2. B can get to
A at a cost of 1, so it will update a route to C via A at a cost of 3. A will
then receive updates from B later and update its cost to 4. They will
then go on feeding each other bad information toward infinity which is
called as Count to Infinity problem.
Solution to Count to Infinity DV Issue (Route Poisoning - Poison Reverse
- CORRECT-ANSWER-When a route fails, distance vector protocols
spread the bad news about a route failure by poisoning the route.
Route poisoning refers to the practice of advertising a route, but with a
special metric value called Infinity. Routers consider routes advertised
with an infinite metric to have failed. Each distance vector routing
protocol uses the concept of an actual metric value that represents
infinity. RIP defines infinity as 16. The main disadvantage of poison
reverse is that it can significantly increase the size of routing
announcements in certain fairly common network topologies.
, Page 4 of 42
Routing Information Protocol (RIP) - CORRECT-ANSWER-The Routing
Information Protocol (RIP) is one of the oldest distance-vector routing
protocols which employ the hop count as a routing metric. RIP prevents
routing loops by implementing a limit on the number of hops allowed in
a path from source to destination. The largest number of hops allowed
for RIP is 15, which limits the size of networks that RIP can support.
Open Shortest Path First Protocol - CORRECT-ANSWER-Link-state
routing protocol that is used to find the best path between the source
and the destination router using its own Shortest Path First
OSPF uses a shorted path first algorithm in order to build and calculate
the shortest path to all known destinations.The shortest path is
calculated with the use of the Dijkstra algorithm. The algorithm by itself
is quite complicated. This is a very high level, simplified way of looking
at the various steps of the algorithm:
Upon initialization or due to any change in routing information, a router
generates a link-state advertisement. This advertisement represents
the collection of all link-states on that router.
CS 6250 COMPUTER NETWORKS STUDY
QUESTIONS - EXAM 2 LESSON 7 -
12|UPDATED QUESTIONS AND WELL
ELLABORATED ANSWERS|ALREADY
GRADED A+
What are advantages and disadvantages of a layered architecture? -
CORRECT-ANSWER-Separation of concerns among logical layers
promotes flexibility, scalibility, and maintainability. Multiple
applications can reuse the components. It enables teams to work on
different parts with minimal dependencies on other teams
What are the similarities of the OSI model and five-layered Internet
model? - CORRECT-ANSWER-They are both based on layered
architecture.
The are comparable to each other - see image 1
Both are networking standards
, Page 2 of 42
What are the differences of the OSI model and five-layered Internet
model? - CORRECT-ANSWER-OSI is a generic model based on the
functions of each layer. TCP is a protocol oriented standard.
OSI uses 3 upper layers (application, presentation, and session) while
TCP just uses application.
Likewise, OSI uses 2 Lower layers (Physical and DataLink) while TCP just
uses Link
Physical Layer - CORRECT-ANSWER-The lowest, or first, layer of the OSI
model. Protocols in this layer generate and detect signals so as to
transmit and receive data over a network medium. These protocols also
set the data transmission rate and monitor data error rates, but do not
provide error correction.
The lowest layer of the OSI Model is concerned with electrically or
optically transmitting raw unstructured data bits across the network
from the physical layer of the sending device to the physical layer of the
receiving device. It can include specifications such as voltages, pin
layout, cabling, and radio frequencies. At the physical layer, one might
, Page 3 of 42
find "physical" resources such as network hubs, cabling, repeaters,
network adapters or modems.
Distance Vector Routing Count to Infinity - CORRECT-ANSWER-If the
link between B and C is disconnected, then B will know that it can no
longer get to C via that link and will remove it from it's table. Before it
can send any updates it's possible that it will receive an update from A
which will be advertising that it can get to C at a cost of 2. B can get to
A at a cost of 1, so it will update a route to C via A at a cost of 3. A will
then receive updates from B later and update its cost to 4. They will
then go on feeding each other bad information toward infinity which is
called as Count to Infinity problem.
Solution to Count to Infinity DV Issue (Route Poisoning - Poison Reverse
- CORRECT-ANSWER-When a route fails, distance vector protocols
spread the bad news about a route failure by poisoning the route.
Route poisoning refers to the practice of advertising a route, but with a
special metric value called Infinity. Routers consider routes advertised
with an infinite metric to have failed. Each distance vector routing
protocol uses the concept of an actual metric value that represents
infinity. RIP defines infinity as 16. The main disadvantage of poison
reverse is that it can significantly increase the size of routing
announcements in certain fairly common network topologies.
, Page 4 of 42
Routing Information Protocol (RIP) - CORRECT-ANSWER-The Routing
Information Protocol (RIP) is one of the oldest distance-vector routing
protocols which employ the hop count as a routing metric. RIP prevents
routing loops by implementing a limit on the number of hops allowed in
a path from source to destination. The largest number of hops allowed
for RIP is 15, which limits the size of networks that RIP can support.
Open Shortest Path First Protocol - CORRECT-ANSWER-Link-state
routing protocol that is used to find the best path between the source
and the destination router using its own Shortest Path First
OSPF uses a shorted path first algorithm in order to build and calculate
the shortest path to all known destinations.The shortest path is
calculated with the use of the Dijkstra algorithm. The algorithm by itself
is quite complicated. This is a very high level, simplified way of looking
at the various steps of the algorithm:
Upon initialization or due to any change in routing information, a router
generates a link-state advertisement. This advertisement represents
the collection of all link-states on that router.
