CS 6250 COMPUTER NETWORKS EXAM 1 QUESTIONS ANSWERED CORRECTLY LATEST UPDATE 2026
What are advantages and disadvantages of a layered architecture? - Answers Each protocol layer
offers different services.
Layered Architecture - Answers Each protocol layer offers different services.
Layered Architecture Advantages - Answers - Scalability,
- Flexibility
- Ease of adding / removing components making it easier for cost-effective implementations.
Layered Architecture Disadvantages - Answers - 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
- Overhead in message headers caused by abstraction barriers between layers.
OSI and Five-Layered Internet model Similarities - Answers Many of the layers are the same
OSI and Five-Layered Internet model Differences - Answers - Three of the layers are combined in the
5-layered model.
- Specifically the five-layer model combines the
- Application
- Presentation
- Session layers
from the OSI model into a single Application layer.
What are sockets? - Answers - 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.
- ."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. - Answers - Application layer: Service, Interface, Protocol.
- Presentation layer: Plays intermediate role of formatting the information received from the layer
below and delivering it to the application layer.
- Session layer: Responsible for the mechanism that manages the different transport streams that
belong to the same session between end-user and application process.
- Transport layer: Responsible for the end-to-end communication between end hosts.
Network layer: This layer is responsible for moving the packet of information, called a datagram, from
one host to another.
- Data Link layer: Responsible for moving the frames from one node (host or router) to the next node.
- Physical layer: This layer is the actual hardware responsible to transfer bits within a frame between
two nodes c
OSI Model Application Layer - Answers - Service, Interface, Protocol.
Ex: Turn on your smartphone and look at the list of apps. (HTTP, SMTP, FTP, DNS)
OSI Model Presentation Layer - Answers - 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.
OSI Model Session Layer - Answers - 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.
OSI Model Network Layer - Answers - This layer is responsible for moving the packet of information,
called a datagram, from one host to another.
- 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.
OSI Model Transport Layer - Answers - Responsible for the end-to-end communication between end
hosts.
- 2 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.
OSI Model Data Link Layer - Answers - 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 ___________ layer protocol include reliable delivery (transmission of the
data from one transmitting node, across one link, to the receiving node.
OSI Model Physical Layer - Answers This layer is the actual hardware responsible to transfer bits
within a frame between two nodes c
Provide examples of popular protocols at each layer of the five-layered Internet model. - Answers
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
5-Layer Model - Transport Layer Protocols - Answers - TCP- UDP
5-Layer Model - Application Layer Protocols - Answers - NFS
- DNS
- SNMP
- FTP
- RCP
- Telnet
- HTTP
5-Layer Model - Internet Layer Protocols - Answers - IP
- ARP
- ICMP
5-Layer Model - Data Link Layer Protocols - Answers - PPP
- IEEE 802.2
, - Ethernet
5-Layer Model - Physical Network Layer Protocols - Answers - Token Ring
- RS-232
What is encapsulation, and how is it used in a layered model? - Answers 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? - Answers 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? - Answers 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? - Answers 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. - Answers EvoArch is a discrete-time model that is executed
over rounds.
At each round, we perform the following steps:
A) We introduce new nodes, and we place them randomly at layers.
B) We examine all layers, from the top to the bottom, and we perform the following tasks:
1) We connect the new nodes that we may have just introduced to that layer, by choosing substrates
based on the generality probabilities of the layer below s(l−1), and by choosing products for them
based on the generality probability of the current layer s(l).
2) We update the value of each node at each layer l, given that we may have new nodes added to the
same layer l.
3) We examine all nodes, in order of decreasing value in that layer, and remove the nodes that
should die.
C) Finally, we stop the execution of the model when the network reaches a given number of nodes.
What are the ramifications of the hourglass shape of the internet? - Answers A. Many technologies
that were not originally designed for the internet have been modified so that they have versions that
can communicate over the internet (such as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage of public IPv4
addresses.
What are advantages and disadvantages of a layered architecture? - Answers Each protocol layer
offers different services.
Layered Architecture - Answers Each protocol layer offers different services.
Layered Architecture Advantages - Answers - Scalability,
- Flexibility
- Ease of adding / removing components making it easier for cost-effective implementations.
Layered Architecture Disadvantages - Answers - 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
- Overhead in message headers caused by abstraction barriers between layers.
OSI and Five-Layered Internet model Similarities - Answers Many of the layers are the same
OSI and Five-Layered Internet model Differences - Answers - Three of the layers are combined in the
5-layered model.
- Specifically the five-layer model combines the
- Application
- Presentation
- Session layers
from the OSI model into a single Application layer.
What are sockets? - Answers - 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.
- ."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. - Answers - Application layer: Service, Interface, Protocol.
- Presentation layer: Plays intermediate role of formatting the information received from the layer
below and delivering it to the application layer.
- Session layer: Responsible for the mechanism that manages the different transport streams that
belong to the same session between end-user and application process.
- Transport layer: Responsible for the end-to-end communication between end hosts.
Network layer: This layer is responsible for moving the packet of information, called a datagram, from
one host to another.
- Data Link layer: Responsible for moving the frames from one node (host or router) to the next node.
- Physical layer: This layer is the actual hardware responsible to transfer bits within a frame between
two nodes c
OSI Model Application Layer - Answers - Service, Interface, Protocol.
Ex: Turn on your smartphone and look at the list of apps. (HTTP, SMTP, FTP, DNS)
OSI Model Presentation Layer - Answers - 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.
OSI Model Session Layer - Answers - 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.
OSI Model Network Layer - Answers - This layer is responsible for moving the packet of information,
called a datagram, from one host to another.
- 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.
OSI Model Transport Layer - Answers - Responsible for the end-to-end communication between end
hosts.
- 2 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.
OSI Model Data Link Layer - Answers - 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 ___________ layer protocol include reliable delivery (transmission of the
data from one transmitting node, across one link, to the receiving node.
OSI Model Physical Layer - Answers This layer is the actual hardware responsible to transfer bits
within a frame between two nodes c
Provide examples of popular protocols at each layer of the five-layered Internet model. - Answers
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
5-Layer Model - Transport Layer Protocols - Answers - TCP- UDP
5-Layer Model - Application Layer Protocols - Answers - NFS
- DNS
- SNMP
- FTP
- RCP
- Telnet
- HTTP
5-Layer Model - Internet Layer Protocols - Answers - IP
- ARP
- ICMP
5-Layer Model - Data Link Layer Protocols - Answers - PPP
- IEEE 802.2
, - Ethernet
5-Layer Model - Physical Network Layer Protocols - Answers - Token Ring
- RS-232
What is encapsulation, and how is it used in a layered model? - Answers 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? - Answers 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? - Answers 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? - Answers 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. - Answers EvoArch is a discrete-time model that is executed
over rounds.
At each round, we perform the following steps:
A) We introduce new nodes, and we place them randomly at layers.
B) We examine all layers, from the top to the bottom, and we perform the following tasks:
1) We connect the new nodes that we may have just introduced to that layer, by choosing substrates
based on the generality probabilities of the layer below s(l−1), and by choosing products for them
based on the generality probability of the current layer s(l).
2) We update the value of each node at each layer l, given that we may have new nodes added to the
same layer l.
3) We examine all nodes, in order of decreasing value in that layer, and remove the nodes that
should die.
C) Finally, we stop the execution of the model when the network reaches a given number of nodes.
What are the ramifications of the hourglass shape of the internet? - Answers A. Many technologies
that were not originally designed for the internet have been modified so that they have versions that
can communicate over the internet (such as Radio over IP).
B. It has been a difficult and slow process to transition to IPv6, despite the shortage of public IPv4
addresses.
