Module 12 Vocab Flashcards
Denial of Service Attacks
bad attackers try to overwhelm a web server by making requests at the same time, using up all the resources on the web server; it can often be difficult to distinguish the fake traffic from legitimate network traffic
OSI Model
a formal, standard representation of networking that splits the network functionality into seven layers.
Event Driven Programming
rather than using blocking system calls, event-driven programming allows higher performance and resource utilization by allowing functionality to continue or sleeping until the desired event occurs
Data Link Layer
determines how the raw bytes should be transferred over the physical links. In particular, the link layer puts raw bytes into messages, performs error detection and correction in transferred data, includes functions for reliable delivery, and determines where and when to send the data over the links.
Physical Layer
includes the actual wires and wireless links that move bits between two physical systems
Internet Model
an informal representation of networking that splits the network functionality into five layers. This model groups the “application, presentation, and session” layers of the OSI model together.
Network Layer
includes IP and message routing within the network
Transport Layer
includes the TCP and UDP protocols; creates network communication channels between different processes on the same or on different machines through the use of sockets
Application Layer
includes all the user level processes that require network communication. OSI model splits this into three layers: session, presentation, and application.
Interface
accepted form of representing and accessing data such that the user can decode the information
Protocol
rules and formats that govern communication between two entities over the network or network boxes
Data Frame
grouping of raw data bits; the recipient can identify the frames by the particular sequences of bits that represent the start and end
MAC Address
unique address that identifies your network card; 48-bit address space
Packet
a method of wrapping data with its control information (e.g. its error detection codes, destination, etc.)
Router
a networking device that is connected to multiple network links and determines where to send a packet based on its
Switch
within a given network, switches forward messages between devices
Encapsulation
each layer can only see the service provided by the layer immediately below it
What are the main steps a web server performs when handling a request?
A: Accept connection → Read request → Look up file → Send response (headers + data)
What does it mean when a system call is “blocking”?
A: The program pauses and waits until the operation (like read() or accept()) is complete.
Why are single-threaded servers inefficient?
A: They can only handle one client at a time and become unresponsive under load or DoS attacks.
How does multi-threading improve a web server’s performance?
A: By creating a new thread for each client, it allows concurrent request handling and better CPU utilization.
What are the risks of using too many threads?
A: High overhead from context switching, system resource exhaustion, and concurrency issues like race conditions.
How can race conditions be avoided in multi-threading?
A: Use synchronization tools like mutexes, semaphores, or locks.
What is event-driven asynchronous programming?
A: A non-blocking model where a single-threaded event loop responds to events using registered callbacks.
What are callbacks?
A: Functions that are triggered when a specific event occurs (e.g., data becomes available on a socket).
What’s a key programming challenge in event-driven programming?
A: Explicit state management — tracking where you are across multiple callbacks.
Why are event handlers expected to be short-lived?
A: There’s no preemption—long handlers block the event loop and delay other events.
What does select() do?
A: Waits for one or more file descriptors (sockets) to become ready for read/write/error or timeout.
How does the program know which socket is ready after select() returns?
A: By checking with FD_ISSET() on each file descriptor.
How does select() help avoid busy waiting?
A: It puts the program to sleep until a socket is ready, conserving CPU resources.
What are the benefits of event-driven I/O?
A: Lightweight, scalable, avoids blocking, good for I/O-bound tasks like servers and GUIs.
What are the limitations of event-driven systems?
A: No true concurrency (single-threaded), difficult state management, and long handlers can freeze the app.
What is the purpose of layering in network architecture?
A: Modularizes functionality, promotes reuse, isolates logic, and allows protocols to evolve independently.
What are the 3 key properties of a network layer?
A: Service, Interface, and Protocol
What is encapsulation?
A: Each layer adds its own header to the data as it moves down the stack and strips it on the way up.
What does peer-layer communication mean?
A: Each layer on one host communicates with the same layer on the remote host.
What is the role of the Physical Layer?
A: Transmits bits across physical media (e.g., cables, fiber). Protocols define voltage or signal levels.
What does the Data Link Layer do?
A: Delivers frames across a physical link with error detection. Uses MAC addresses.
What is the main job of the Network Layer?
A: Delivers packets between hosts using IP addresses and routing protocols.
What does the Transport Layer ensure?
A: Reliable or fast delivery between processes (TCP/UDP), with flow and error control.
What is the purpose of the Session Layer?
A: Manages logical sessions (e.g., combining audio and video streams).
What is the Presentation Layer for?
A: Formats, encodes, compresses, and encrypts data (e.g., TLS, JPEG).
What happens in the Application Layer?
A: User-facing services like web, email, DNS operate here via high-level protocols.
What is the Hourglass Model in networking?
A: IP is the narrow waist of the Internet stack — everything above and below must support IP.
What’s the advantage of the Hourglass Model?
A: Allows old and new technologies to work together, as long as they speak IP.
Which layers are implemented on all network devices?
A: Physical, Data Link, Network
