CS6250 - Computer Networks Practice Questions and Answers Graded A+
What are advantages and disadvantages of a layered architecture? - Answers 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? - Answers They are both
based on layered architecture.
The are comparable to each other - see image 1
Both are networking standards
What are the differences of the OSI model and five-layered Internet model? - Answers 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
What is a socket? - Answers A socket is one endpoint of a two-way communication link between two
programs running on the network.
A socket is bound to a port number so that the TCP layer can identify the application that data is
destined to be sent to.
Physical Layer - Answers 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 find "physical" resources such as network hubs, cabling,
repeaters, network adapters or modems.
OSI Data Link Layer - Answers At the data link layer, directly connected nodes are used to perform node-
to-node data transfer where data is packaged into frames. The data link layer also corrects errors that
may have occurred at the physical layer.
,The data link layer encompasses two sub-layers of its own. The first, media access control (MAC),
provides flow control and multiplexing for device transmissions over a network. The second, the logical
link control (LLC), provides flow and error control over the physical medium as well as identifies line
protocols.
OSI Network Layer - Answers The network layer is responsible for receiving frames from the data link
layer, and delivering them to their intended destinations among based on the addresses contained
inside the frame. The network layer finds the destination by using logical addresses, such as IP (internet
protocol). At this layer, routers are a crucial component used to quite literally route information where it
needs to go between networks.
OSI Transport Layer - Answers The transport layer manages the delivery and error checking of data
packets. It regulates the size, sequencing, and ultimately the transfer of data between systems and
hosts. One of the most common examples of the transport layer is TCP or the Transmission Control
Protocol.
OSI Session Layer - Answers The session layer controls the conversations between different computers.
A session or connection between machines is set up, managed, and termined at layer 5. Session layer
services also include authentication and reconnections.
OSI Presentation Layer - Answers The presentation layer formats or translates data for the application
layer based on the syntax or semantics that the application accepts. Because of this, it at times also
called the syntax layer. This layer can also handle the encryption and decryption required by the
application layer.
OSI Application Layer - Answers At this layer, both the end user and the application layer interact
directly with the software application. This layer sees network services provided to end-user applications
such as a web browser or Office 365. The application layer identifies communication partners, resource
availability, and synchronizes communication.
5 Layer Internet Model - Application Layer - Answers As you might have guessed, the Application layer is
where applications requiring network communications live. Examples of these applications include email
clients and web browsers. These applications use the Transport Layer to send requests to connect to
remote hosts.
5 Layer Internet Model - Transport Layer - Answers The Transport layer establishes the connection
between applications running on different hosts. It uses TCP for reliable connections and UDP for fast
connections. It keeps track of the processes running in the applications above it by assigning port
numbers to them and uses the Network layer to access the TCP/IP network.
5 Layer Internet Model - Network Layer - Answers The Network layer is responsible for creating the
packets that move across the network. It uses IP addresses to identify the packet's source and
destination.
, 5 Layer Internet Model - Data Link Layer - Answers The Data Link layer is responsible for creating the
frames that move across the network. These frames encapsulate the packets and use MAC addresses to
identify the source and destination.
5 Layer Internet Model - Physical Layer - Answers The Physical layer encodes and decodes the bits found
in a frame and includes the transceiver that drives and receives the signals on the network.
What is encapsulation, and how is it used in a layered model? - Answers In networking model, the terms
encapsulation and de-encapsulation refer to a process in which protocol information is added to the
data and removed from the data when it passes through the layers.
Protocol information can be added before and after the data. If information is added before the data, it
is known as header. If information is added after the data, it is known as trailer.
What is the end-to-end (e2e) principle? - Answers When a function has to be supported in a networked
system, the designer often asks if it should be implemented at the end systems; or should it be
implemented within the communication subsystem that interconnects all the end systems. The end-to-
end argument or principle states that it's proper to implement the function in the end systems. The
communication system itself may provide a partial implementation but only as a performance
enhancement.
The architecture and growth of the Internet was shaped by the end-to-end principle. It allowed us to
keep the Internet simple and add features quickly to end systems. The principle enabled innovation.
End to End Principle Example - Answers An example of the end-to-end principle is that of an arbitrarily
reliable file transfer between two endpoints in a distributed network of a varying, nontrivial size:[3] The
only way two endpoints can obtain a completely reliable transfer is by transmitting and acknowledging a
checksum for the entire data stream; in such a setting, lesser checksum and acknowledgment
(ACK/NACK) protocols are justified only for the purpose of optimizing performance - they are useful to
the vast majority of clients, but are not enough to fulfill the reliability requirement of this particular
application. A thorough checksum is hence best done at the endpoints, and the network maintains a
relatively low level of complexity and reasonable performance for all clients
What is the EvoArch model? - Answers an hourglass model that consists of six protocol and application
layers that originate from a single bubble - IPv4
What are the ramifications of the hourglass shape of the internet - Answers
Repeater - Answers Physical Layer - A repeater operates at the physical layer. Its job is to regenerate the
signal over the same network before the signal becomes too weak or corrupted so as to extend the
length to which the signal can be transmitted over the same network. An important point to be noted
about repeaters is that they do not amplify the signal. When the signal becomes weak, they copy the
signal bit by bit and regenerate it at the original strength. It is a 2 port device.
