The Transport Layer Flashcards

Question

What is FSM? (Finite State Machine)

Answer 1

A Finite State Machine (FSM) is used in network protocols to manage communication between devices. Example: TCP Connection (Three-Way Handshake) 🌍 When two computers connect using TCP, they follow steps (states): 1️⃣ CLOSED – No connection yet. 2️⃣ SYN SENT – Client sends a request to connect. 3️⃣ SYN-RECEIVED – Server receives the request and responds. 4️⃣ ESTABLISHED – Connection is complete, and data can be sent. 5️⃣ CLOSED – Connection ends after communication is done. Each step changes the state based on rules (like receiving a message).

Answer 2

- Defines how a network protocol reacts to different events. Finite State Machine (FSM)

Answer 3

- In TCP, FSM tracks whether a connection is established, sending data, or closed.

Answer 4

- A simple data transfer protocol where the sender waits for an ACK before sending the next packet. - It ensures reliable delivery by checking if each packet was received correctly. - If no ACK is received, the sender resends the packet.

Answer 5

- Ensures data is delivered without loss. -Makes sure data arrives in order. -Prevents overloading the receiver.

Answer 6

-When sending a photo via Bluetooth, it sends one chunk at a time, waiting for confirmation. - In email, servers use stop-and-wait to ensure complete delivery.

Answer 7

- Packet loss happens when data does not reach its destination. - It can occur due to network congestion, poor signal, or hardware issues. - Lost packets cause delays, lag, and missing information in communication. - TCP handles packet loss by resending lost packets, while UDP does not.

Answer 8

- Causes delays in video calls and streaming. - Can disrupt file downloads and require retransmission.

Answer 9

- In a video call, freezing or lagging happens due to lost packets. - A web page loads slowly if packets are lost and need to be resent.

Answer 10

Sender Utilization measures how much time a sender spends actually transmitting data versus waiting. Higher utilization = Sender is sending data most of the time. Lower utilization = Sender spends more time waiting.

Answer 11

- Helps determine if a network is efficient or slow. - Shows how much time is wasted waiting for acknowledgments.

Answer 12

- A network with high delays has low utilization because the sender is always waiting. - Pipelining increases utilization by sending multiple packets at once.

Answer 13

- Pipelining is a method that allows multiple packets to be sent before waiting for an acknowledgment (ACK). - It improves network efficiency by keeping the sender busy. - Unlike stop-and-wait, where the sender waits for each ACK, pipelining sends multiple packets in a row. - Used in TCP and other protocols to speed up communication

Answer 14

- Reduces the waiting time between packets. - Increases network throughput (how much data can be sent at once).

Answer 15

- When watching Netflix, pipelining allows several seconds of video to load ahead.

Answer 16

Go-Back-N (GBN) is a reliable data transfer protocol that sends multiple packets at once but retransmits from the last unacknowledged packet if an error occurs. How It Works: The sender sends multiple packets (up to a window size 🎯). The receiver acknowledges (ACK) received packets. If a packet is lost or corrupted, the sender retransmits that packet and all after it.

Answer 17

- Allows a sender to keep sending packets without waiting for each ACK. - If an error happens, all packets after the lost one must be resent. - Improves performance in networks with low error rates. - Helps avoid long waiting times in high-speed networks.

Answer 18

- When downloading a file, if packet 3 is lost, packets 3, 4, and 5 are all resent.

Answer 19

- The receiver in GBN only accepts packets in order. - If a packet is missing, the receiver ignores all later packets until the lost one is received. - It sends cumulative ACKs, meaning it only acknowledges the last correctly received packet. - This avoids processing out-of-order packets.

Answer 20

-Ensures data is received in the correct order. - If a packet is lost, the receiver keeps waiting until the sender resends it

Answer 21

If a student misses question 3 in a quiz, they must redo questions 3, 4, and 5. - When watching YouTube, if part of a video is missing, the rest won't load until it is resent.

Answer 22

- Packets that arrive in the wrong order due to network delays or routing changes. - This happens because packets can take different paths through the network. - The receiver must reorder them before delivering data to an application. - Some protocols, like UDP, do not fix out-of-order packets, while TCP does.

Answer 23

- Can cause video glitches, scrambled messages, or delays. - TCP fixes this by using sequence numbers to reorder packets.

Answer 24

- If a text message arrives with mixed-up words, the phone must reorder them. - Watching Netflix, if some video frames arrive out of order, they must be fixed before playing

Answer 25

- The number of packets a sender can send before needing an ACK. - A larger window size allows faster communication because the sender doesn't stop often. - It is used in pipelined protocols like TCP, Go-Back-N, and Selective Repeat. - If the window is too small, the sender waits too much; if too big, it may overload the receiver.

Answer 26

- Controls how much data can be sent at once. - Helps balance speed vs. network reliability. - Larger window = higher efficiency in fast networks.

Answer 27

- A large window lets Netflix preload more video so it plays smoothly.

Answer 28

- A transport protocol where only lost packets are resent, unlike Go-Back-N. - The receiver stores out-of-order packets and waits for missing ones. - This prevents unnecessary retransmissions. - Requires buffering to hold packets until all are received.

Answer 29

- Fixes packet loss more efficiently than Go-Back-N. - Ensures packets arrive in order without wasting bandwidth. - Uses individual ACKs for each packet instead of cumulative ACKs.

Answer 30

- When downloading a file, if one part is lost, only that part is resent.

Answer 31

- RTT is the time for a packet to travel to its destination and back. - TCP calculates RTT to decide when to retransmit lost packets. - A timeout happens if an ACK takes too long to arrive. - If the timeout is too short, TCP resends packets too early; if too long, it delays retransmission. 🔄 RTT (Round-Trip Time) = Time it takes for a packet to go to the receiver and back. ⏳ If RTT is high, the network is slow. If RTT is low, the network is fast. ⏰ Timeout = How long TCP waits for an acknowledgment (ACK) before resending a packet. If RTT is too high, TCP waits longer before resending. If RTT is low, TCP resends faster when no response is received. Example: You send a message 📩 → RTT measures how long it takes to get a reply. If no reply comes in time ⏳ → TCP resends after timeout.

Answer 32

1️⃣ Webpage Loading Slow 🌍 What it means: If a website takes a long time to load, it means RTT is high (the request & response are taking too long). Example: You click on a website, but it loads slowly because the data takes too long to travel back and forth. 2️⃣ Netflix Adjusts Video Quality 📺 What it means: If RTT is high, Netflix lowers video quality so it doesn’t keep buffering. Example: Your internet is slow → Netflix switches to lower quality to avoid interruptions. 3️⃣ Online Gaming Needs Low RTT 🎮 What it means: Low RTT = Faster response time in multiplayer games. Example: In Fortnite, if RTT is high, your character reacts slowly. If RTT is low, actions happen instantly. 4️⃣ TCP Timeout & Resending Data ⏳ What it means: If a response doesn’t arrive in time, TCP resends the data to avoid lag. Example: If a message doesn’t get delivered in time, TCP sends it again to make sure it arrives. The Main Idea: High RTT = Slow connection, delays. Low RTT = Fast response, smooth performance. TCP Timeout = If a response is too slow, it resends the data.

Answer 33

- A mechanism in TCP that resends lost packets quickly, without waiting for a timeout. - Instead of waiting for a long timeout, TCP retransmits a packet if it receives multiple duplicate ACKs. - This improves speed and avoids unnecessary delays in data transfer. - Helps prevent slow performance in networks with occasional packet loss. - If your Netflix stream suddenly buffers, TCP fast retransmit ensures missing data is resent quickly.

Answer 34

- A method that prevents the sender from overwhelming the receiver with too much data. - Uses a receive window to control how much data can be sent before waiting for an ACK. -Helps maintain smooth and efficient communication. - Used in TCP to avoid buffer overflow at the receiver.

Answer 35

A Sequence Number is a unique number assigned to each packet in a network to keep data in order. Why It’s Needed? ✅ Ensures packets arrive in the correct order. ✅ Helps reassemble messages properly. ✅ Detects missing or duplicate packets.

Answer 36

TCP Connection Management controls how a connection starts, stays open, and ends between two devices. 3 Main Phases: 1️⃣ Connection Establishment (Three-Way Handshake) 🤝 Client sends SYN (Hello, I want to connect). Server replies SYN-ACK (Okay, let's connect). Client sends ACK (Confirmed, connection open). 2️⃣ Data Transfer 📦 Data is sent and received between the devices. Uses sequence numbers to keep data in order.

Answer 37

- The process used to establish a TCP connection between two devices. - Uses three steps: SYN → SYN-ACK → ACK. - Ensures both sender and receiver agree to start communication. - Helps prevent errors and unauthorized connections.

Answer 38

- Confirms that both devices are ready to send and receive data. - Helps prevent connection issues and unauthorized access. - Ensures a stable network session before sending data. - Used in secure communication protocols like HTTPS.

Answer 39

- A method to prevent network overload when too much data is being sent. -Adjusts the amount of data sent based on network conditions. -Helps prevent packet loss, slow speeds, and crashes. -Used in TCP to manage traffic on the internet.

Answer 40

- Reduces data transmission when the network is too busy. - Prevents delays and dropped connections. - Ensures all devices get a fair share of bandwidth. - Adjusts the window size dynamically to avoid congestion.

Answer 41

- Transport Layer Security - A security protocol that encrypts data between users and websites. - Protects against hackers and keeps online communication private. -Replaces older security methods like SSL (Secure Sockets Layer). - Used in banking, emails, and secure messaging.

Answer 42

- Encrypts data to prevent hacking and eavesdropping. - Ensures safe online transactions and logins. -Protects passwords, credit card info, and personal messages. -Used in HTTPS websites to secure data transfers.

Answer 43

- A newer and faster protocol that replaces TCP for web browsing. Uses UDP instead of TCP for speed but still provides reliability. Designed by Google to improve loading times for websites. Helps reduce connection delays and improve performance.

Answer 44

A bottleneck link is the slowest part of a network connection that limits overall speed. It occurs when more data is sent than the link can handle. Causes delays, packet loss, and slow network performance. When Does It Happen? 1️⃣ When sending large amounts of data (streaming, downloads, gaming). 2️⃣ When multiple users/devices share a network (Wi-Fi in a crowded place). 3️⃣ When network congestion occurs (busy hours, too much traffic). 4️⃣ When one part of the network is slower than others (old cables, weak Wi-Fi, slow ISP).

Answer 45

Instead of waiting for packet loss, it reduces speed when delay increases. Used in networks where packet loss is rare, but delay is a problem.

Answer 46

TCP Fairness means all TCP connections share network bandwidth equally so that no single connection takes up all the speed. Example: You download a file 📂 and stream a video 🎥 at the same time. TCP makes sure both get bandwidth instead of one stopping the other.

Answer 47

A cryptographic key is a special code used to lock (encrypt) or unlock (decrypt) data 🔐. Types of Keys: 1️⃣ Symmetric Key 🗝️ – Same key is used for both encryption & decryption (Fast but less secure). Example: Like a house key—whoever has it can open the door. 2️⃣ Asymmetric Keys 🔑 – Uses two keys: Public Key (to encrypt) 📤 Private Key (to decrypt) 📥 Example: Like a mailbox—anyone can put mail in (encrypt), but only the owner can open it (decrypt). Why Are Keys Important? ✅ Keep data private (encryption). ✅ Ensure messages aren’t changed (integrity). ✅ Verify identity (digital signatures).

Answer 48

A process that converts readable data into unreadable code. Protects sensitive information from hackers and unauthorized users. Used in passwords, emails, and financial transactions. Requires encryption keys to decode the data.

Answer 49

A Cipher Suite is a set of encryption rules used in TLS (Transport Layer Security) to secure internet connections 🔐. What It Includes: 1️⃣ Key Exchange Algorithm – Decides how to share encryption keys securely. 2️⃣ Encryption Algorithm – Protects data by scrambling it. 3️⃣ Message Authentication Code (MAC) – Ensures data isn’t changed. Example (TLS Cipher Suite Name 🏷️) 🔹 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 ECDHE = Key exchange RSA = Authentication AES_256_GCM = Encryption SHA384 = Integrity check

Answer 50

- A delay that happens when one slow packet blocks others behind it. - Common in network routers, TCP, and web browsing. - Slows down traffic and reduces network efficiency. Can cause buffering, delays, and lower speeds.

Answer 51

- A method for establishing a connection between two devices. Involves two steps: one device sends a SYN (synchronize) message, and the other responds with an ACK (acknowledgment). It is faster than the 3-way handshake but less secure. Mainly used in older or less secure protocols.

Answer 52

- Situations where a 2-step handshake is used instead of a 3-way handshake. Typically used in simple or internal network connections. Faster but less reliable and less secure. If one side fails, the connection might not be properly established.

Answer 53

The process of properly ending a TCP session between two devices. Uses a 4-step process with FIN (Finish) and ACK messages. Ensures that all data is sent before disconnecting safely. Prevents data loss or connection errors.

Answer 54

A method used in TCP congestion control to adjust data flow. If no congestion is detected, speed increases slowly (additively). If congestion occurs, speed is reduced sharply (multiplicatively). Helps balance network traffic and avoid congestion collapse.

Answer 55

A modern congestion control algorithm used in TCP. Designed to work better in high-speed networks. Adjusts the congestion window based on a cubic function instead of linear increases. Used in Linux, Google servers, and modern internet applications.

Answer 56

A simple data transfer protocol that assumes a perfect network. No packet loss, no corruption, and no need for retransmissions.

Answer 57

A transport layer protocol that only resends lost or corrupted packets instead of resending everything. More efficient than Go-Back-N because it does not waste bandwidth. The receiver stores out-of-order packets and waits for missing ones. Requires buffering to hold packets until they can be processed.

Answer 58

Parallelism means doing multiple tasks at the same time to make things faster and more efficient. Where It's Used? ✅ Computers – Running multiple processes at once (e.g., opening many apps). ✅ Networking – Sending multiple data packets at the same time. ✅ Cybersecurity – Scanning for threats while running other tasks..

Answer 59

An improved version of RDT 1.0, designed to handle corrupted packets. Uses error detection (checksums) to verify if packets arrive correctly. Introduces ACKs (Acknowledgments) and NAKs (Negative Acknowledgments). Ensures that only correct data is accepted and that corrupted data is resent.

Answer 60

A further improvement of RDT 2.0, designed to handle packet loss. Introduces timeouts, so if no ACK is received, the sender automatically resends the packet. Ensures all packets eventually arrive, even if the network loses some. Used in real-world networks where packets can be lost due to congestion.