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CS6250 - Computer Networks Exam -88 Questions with Solutions
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CS6250 - Computer Networks Exam -88 Questions with Solutions
What are advantages and disadvantages of a layered architecture? - -
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?
- -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?
- -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? - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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 - -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? - -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? - -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 - -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
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