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CS6250 Midterm Exam Questions and answers
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CS6250 Midterm ExamQuestions and answers
What are the advantages and disadvantages of a layered architecture? - -
Advantages:
- scalability
- modularity
- flexibility
Disadvantages
- Some layers functionality depends on the info from other layers which
violates the goal of layer separation
- One layer may duplicate lower layer functionality
- Some additional overhead that is caused by the abstraction between layers
-What are the differences and similarities between the OSI model and the
five-layered Internet model? - -Application layer in IP model combines the
session, presentation, and application layers in the OSI model
-What are sockets? - -a software endpoint that enables communication
between two or more processes running on different devices over a network
-Describe each layer of the OSI model. - -Physical Layer: Deals with the
physical transmission of data over the network, including the electrical,
mechanical, and physical aspects.
Data Link Layer: Provides error-free transmission of data frames between
nodes on a network, ensuring reliable communication over the physical
layer.
Network Layer: Focuses on addressing, routing, and forwarding data packets
across multiple networks, enabling internetwork communication.
Transport Layer: Manages end-to-end communication, ensuring reliable and
error-free data delivery between hosts. It may also provide mechanisms for
flow control and congestion control.
Session Layer: Establishes, manages, and terminates connections between
applications on different devices, allowing for synchronized communication.
Presentation Layer: Handles data formatting, encryption, compression, and
other transformations to ensure that information from the application layer is
properly understood by the receiving application.
Application Layer: Provides a user interface and services for applications to
access network resources, allowing users to interact with network services
such as email, file transfer, and browsing.
-Provide examples of popular protocols at each layer of the five-layered
Internet model. - -Physical Layer:
,- Point-to-Point Protocol (PPP)
- Ethernet
- Asynchronous Transfer Mode (ATM)
- Frame Relay
Data Link Layer:
- Ethernet
- Wi-Fi (IEEE 802.11)
- Bluetooth
Internet Layer:
- Internet Protocol (IP)
- Internet Control Message Protocol (ICMP)
- Address Resolution Protocol (ARP)
Transport Layer:
- Transmission Control Protocol (TCP)
- User Datagram Protocol (UDP)
Application Layer:
- Hypertext Transfer Protocol (HTTP)
- File Transfer Protocol (FTP)
- Simple Mail Transfer Protocol (SMTP)
- Domain Name System (DNS)
- Secure Shell (SSH)
- Simple Network Management Protocol (SNMP)
- Post Office Protocol (POP)
- Internet Message Access Protocol (IMAP)
-What is encapsulation, and how is it used in a layered model? - -Refers to
the process of adding protocol-specific headers and trailers to the data as it
moves down the protocol stack and preparing it for transmission over the
network.
Overall, encapsulation in a layered model ensures that data is properly
formatted, organized, and prepared for transmission over the network,
enabling effective communication between devices across different layers
and protocols.
-What is the end-to-end (e2e) principle? - -design choice that characterized
and shaped the current architecture on the internet. Suggests that specific
application level functions usually cannot, and preferably should not be built
into the lower levels of the system at the core of the network.
- the network core should be simple and minimal, while the end systems
should carry the intelligence
- Original goals were to move functions and services closer to the apps that
use them, increases the flexibility and the autonomy of the app designer to
offer these services to the needs of the specific application
-What are the examples of a violation of e2e principle? - -- Firewalls and
Traffic filters - FWs operate on the periphery of the network and monitor
, traffic going through. They are intermediate devices operated between two
end hosts and can drop end hosts' communication
- NAT Boxes - Help us as a bandaid measure to deal with the shortage of
internet addresses. It translates the source and destination addresses and
ports as packets come into it and go out. The devices behind the NAT box
are not globally addressable or routable so it violates the e2e principle
-What is the EvoArch model? - -- helps study layered architectures and their
evolution in a quantative manner.
- Able to use it to explain how the hierarchical structure of the layer
architecture eventually led to the hourglass shape with IPv4, TCP, UDP in the
middle
-Explain a round in the EvoArch model. - -Discrete time model that is
executed over several rounds. At each round we introduce new nodes and
place them at random layers, and examine all layers from the top to the
bottom performing the following tasks:
1. Connect the new nodes that we may have just introduced to that layer
2. Update the value of each node at each layer I, given that we may have
new nodes added to the same layer I
3. Examine all nodes, in order of decreasing value in that layer and remove
nodes that should die
4. Stop execution when the network reaches a given number of nodes
-What are the ramifications of the hourglass shape of the internet? - -the
hourglass shape of the internet enables interoperability, flexibility,
innovation, and decentralization. However, it also introduces challenges
related to diversity, security, and privacy that need to be addressed for the
sustainable and secure growth of the network.
-Repeaters, hubs, bridges, and routers operate on which layers? - -
Repeaters and Hubs - operate at L1, receive and forward digital signals to
connect different Ethernet segments, provide connectivity for hsots on the
same network
- Advantage - simple and inexpensive devices
- Disadvantage - hosts that connect through these belong to the same
collision domain meaning they compete for access to the same link
Bridges and L2 Switches Operate at layer 2 and are based on MAC
addresses. Enable communication between hosts that are not directly
connected.
- Have finite bandwidth so it will forward packets to a buffer but if it gets
overfilled then it can cause packet loss
Routers and L3 Switches - operate on L3
-What is a bridge, and how does it "learn"? - -- a device with multiple inputs
and outputs. Transfers frames from an input to one or more outputs
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