CS6250 Computer Networks Exam 1
Comprehensive Review with Solved Questions and
Accurate Answers
What are advantages and disadvantages of a layered architecture?
Each protocol layer offers different services. Some advantages are scalability,
flexibility, and ease of adding / removing components making it easier for cost-
effective implementations. Disadvantages include: some layers functionality
depends on the information from the other layer and violates the goal of layer
separation; one layer may duplicate lower layer functionalities; overhead both in
computation and in message headers caused by abstraction barriers between
layers.
What are the differences and similarities of the OSI model and five-layered
Internet model?
The OSI model and the 5-layered Internet Model have many of the same layers,
with the difference being three of the layers are combined in the 5-layered model.
Specifically the five-layer model combines the application, presentation, and
session layers from the OSI model into a single application layer.
What are sockets?
A network socket is a software structure within a network node of a computer
network that serves as an endpoint for sending and receiving data across the
network. The structure and properties of a socket are defined by an application
,programming interface (API) for the networking architecture. Sockets are created
only during the lifetime of a process of an application running in the
node.https://en.wikipedia.org/wiki/Network_socket."A process sends messages
into, and receives messages from, the network through a software interface called
a socket. Let's consider an analogy to help us understand processes and sockets. A
process is analogous to a house and its socket is analogous to its door....a socket is
the interface between the application layer and the transport layer within a host."
- Kurose and Ross, 2.1
Describe each layer of the OSI model.
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 connected through a physical link. Ex: Ethernet
(twisted-pair copper, coax, fiber-optics).
Provide examples of popular protocols at each layer of the five-layered Internet
model.
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?
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?
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?
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?
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.
Comprehensive Review with Solved Questions and
Accurate Answers
What are advantages and disadvantages of a layered architecture?
Each protocol layer offers different services. Some advantages are scalability,
flexibility, and ease of adding / removing components making it easier for cost-
effective implementations. Disadvantages include: some layers functionality
depends on the information from the other layer and violates the goal of layer
separation; one layer may duplicate lower layer functionalities; overhead both in
computation and in message headers caused by abstraction barriers between
layers.
What are the differences and similarities of the OSI model and five-layered
Internet model?
The OSI model and the 5-layered Internet Model have many of the same layers,
with the difference being three of the layers are combined in the 5-layered model.
Specifically the five-layer model combines the application, presentation, and
session layers from the OSI model into a single application layer.
What are sockets?
A network socket is a software structure within a network node of a computer
network that serves as an endpoint for sending and receiving data across the
network. The structure and properties of a socket are defined by an application
,programming interface (API) for the networking architecture. Sockets are created
only during the lifetime of a process of an application running in the
node.https://en.wikipedia.org/wiki/Network_socket."A process sends messages
into, and receives messages from, the network through a software interface called
a socket. Let's consider an analogy to help us understand processes and sockets. A
process is analogous to a house and its socket is analogous to its door....a socket is
the interface between the application layer and the transport layer within a host."
- Kurose and Ross, 2.1
Describe each layer of the OSI model.
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 connected through a physical link. Ex: Ethernet
(twisted-pair copper, coax, fiber-optics).
Provide examples of popular protocols at each layer of the five-layered Internet
model.
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?
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?
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?
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?
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.
