CS6250 COMPUTER NETWORKS EXAM 1
EXAM WITH CORRECT ACTUAL QUESTIONS
AND CORRECTLY WELL DEFINED ANSWERS
LATEST 2025 ALREADY GRADED A+
What is the main idea behind the distance vector routing algorithm? -
ANSWERS-The Distance Vector algorithm is based on the Bellman Ford
algorithm, which states each node exchanges their distance vectors to its
neighbors which update their own view of the network. It is an iterative that
loops until the neighbors do not have new updates to send to each other. It's
also asynchronous which means it does not require the nodes to be
synchronized with each other (not requiring the latest updates when they are
not ready, while still ensuring convergence). Finally it's distributed which means
direct nodes send information to one another, then they resend their results
back after performing the calculation locally on that node, this means that each
node has its own computing power and is not a centralized network.
Helpful hint: There are videos on Udacity from the previous classes at Georgia
Tech that explain this, and other concepts, in more detail. I found these videos
extremely helpful to further understand several concepts in the chapters
covered. Here is the video I found:
,https://classroom.udacity.com/courses/ud436/lessons/1729198657/concepts/
6490994890923[1]
Thanks, this was more helpful and added additional insight.
● Walk through an example of the distance vector algorithm. - ANSWERS-Each
node x updates its own distance vector using the Bellman Ford equation: Dx(y) =
minv{c(x,v) + Dv(y)} for each destination node y in the network. A node x,
computes the least cost to reach destination node y, by considering the options
that it has to reach y through each of its neighbor v. So node x considers the
cost to reach neighbor v, and then it adds the least cost from that neighbor v to
the final destination y. It calculates that quantity over all neighbors v and it
takes the minimum.
● When does the count-to-infinity problem occur in the distance vector
algorithm? - ANSWERS-When two or more nodes keep updating their values
and informs the neighbors of the change and they in turn update their values
causing the original root to update its value again. This continues for a long time
in a constant loop.
This happens primarily when a neighbor's advertised path includes the present
node's path as a loop.
● How does poison reverse solve the count-to-infinity problem? - ANSWERS-
Called poison reverse: since z reaches x through y, z will advertise to y that the
distance to x is infinity (Dz(x)=infinity). However z knows that this is not true
and Dz(x)=5. z tells this lie to y, as long as it knows that it can reach to x via y.
Since y assumes that z has no path to x except via y, it will never send packets to
x via z.
So z poisons the path from z to y.
, ● What is the Routing Information Protocol (RIP)? - ANSWERS-The Routing
Information Protocol (RIP) is based on the Distance Vector protocol.
The first version, released as a part of the BSD version of Unix, uses hop count
as a metric (i.e. assumes link cost as 1). The metric for choosing a path could be
shortest distance, lowest cost or a load-balanced path. In RIP, routing updates
are exchanged between neighbors periodically, using a RIP response message,
as opposed to distance vectors in the DV Protocols. These messages, called RIP
advertisements, contain information about sender's distances to destination
subnets.
Describe each layer of the OSI model. - ANSWERS-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.
EXAM WITH CORRECT ACTUAL QUESTIONS
AND CORRECTLY WELL DEFINED ANSWERS
LATEST 2025 ALREADY GRADED A+
What is the main idea behind the distance vector routing algorithm? -
ANSWERS-The Distance Vector algorithm is based on the Bellman Ford
algorithm, which states each node exchanges their distance vectors to its
neighbors which update their own view of the network. It is an iterative that
loops until the neighbors do not have new updates to send to each other. It's
also asynchronous which means it does not require the nodes to be
synchronized with each other (not requiring the latest updates when they are
not ready, while still ensuring convergence). Finally it's distributed which means
direct nodes send information to one another, then they resend their results
back after performing the calculation locally on that node, this means that each
node has its own computing power and is not a centralized network.
Helpful hint: There are videos on Udacity from the previous classes at Georgia
Tech that explain this, and other concepts, in more detail. I found these videos
extremely helpful to further understand several concepts in the chapters
covered. Here is the video I found:
,https://classroom.udacity.com/courses/ud436/lessons/1729198657/concepts/
6490994890923[1]
Thanks, this was more helpful and added additional insight.
● Walk through an example of the distance vector algorithm. - ANSWERS-Each
node x updates its own distance vector using the Bellman Ford equation: Dx(y) =
minv{c(x,v) + Dv(y)} for each destination node y in the network. A node x,
computes the least cost to reach destination node y, by considering the options
that it has to reach y through each of its neighbor v. So node x considers the
cost to reach neighbor v, and then it adds the least cost from that neighbor v to
the final destination y. It calculates that quantity over all neighbors v and it
takes the minimum.
● When does the count-to-infinity problem occur in the distance vector
algorithm? - ANSWERS-When two or more nodes keep updating their values
and informs the neighbors of the change and they in turn update their values
causing the original root to update its value again. This continues for a long time
in a constant loop.
This happens primarily when a neighbor's advertised path includes the present
node's path as a loop.
● How does poison reverse solve the count-to-infinity problem? - ANSWERS-
Called poison reverse: since z reaches x through y, z will advertise to y that the
distance to x is infinity (Dz(x)=infinity). However z knows that this is not true
and Dz(x)=5. z tells this lie to y, as long as it knows that it can reach to x via y.
Since y assumes that z has no path to x except via y, it will never send packets to
x via z.
So z poisons the path from z to y.
, ● What is the Routing Information Protocol (RIP)? - ANSWERS-The Routing
Information Protocol (RIP) is based on the Distance Vector protocol.
The first version, released as a part of the BSD version of Unix, uses hop count
as a metric (i.e. assumes link cost as 1). The metric for choosing a path could be
shortest distance, lowest cost or a load-balanced path. In RIP, routing updates
are exchanged between neighbors periodically, using a RIP response message,
as opposed to distance vectors in the DV Protocols. These messages, called RIP
advertisements, contain information about sender's distances to destination
subnets.
Describe each layer of the OSI model. - ANSWERS-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.
