Ch. 3 - Transport Layer

Question 1

Define TCP

Answer 1

Transmission Control Protocol - provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.

Question 2

UDP

Answer 2

User Datagram Protocol - Unreliable, connectionless protocol.

Question 3

Transport services & protocols

Answer 3

provide logical communication between application processes running on different hosts

Question 4

Transport vs. network layer

Answer 4

Transport: communication between processes
Network: communication between hosts

Question 5

RDT

Answer 5

Reliable Data Transfer

Question 6

What is a handshake?

Answer 6

sender/receiver agree:
* to establish connection (each knowing the other willing to establish connection)
* on connection parameters (e.g., starting seq #s)

Question 7

What is a connection closure?

Answer 7

This is a special message to securely close a connection.

Question 8

ECN

Answer 8

Explicit Congestion Notification

Question 9

QUIC

Answer 9

Quick UDP Internet Connections

Question 10

TCP Fairness goal

Answer 10

if K TCP sessions share same bottleneck link of bandwidth R, each should have average rate of R/K

Question 11

Congestion Control Mechanisms in TCP (4)

Answer 11

Slow start, AIMD/congestion avoidance, fast retransmit, fast recovery

Question 12

AIMD (Congestion Avoidance)

Answer 12

Additive Increase Multiplicative Decrease
senders can increase sending rate until packet loss (congestion) occurs, then decrease sending rate to half.

Question 13

Slow Start

Answer 13

Sender gradually increases the number of packets sent in each round trip time (RTT) until congestion is detected.

Question 14

Fast Retransmit

Answer 14

Detects packet loss and retransmits the lost packet immediately without waiting for the RTT timeout.

Question 15

Fast Recovery

Answer 15

After a fast retransmit, the sender reduces the congestion window to half its size and then increases it slowly, similar to congestion avoidance.

Question 16

Multiplexing

Answer 16

Combining multiple data streams into a single channel.

Question 17

Demultiplexing

Answer 17

Separating multiple data streams from a single channel.

Question 18

Flow control mechanisms (4)

Answer 18

Stop-and-wait protocol, pipelining protocol, Go-Back-N, Selective Repeat

Question 19

Stop-and-Wait Protocol

Answer 19

Sender sends one frame at a time and waits for acknowledgment.

Question 20

Pipelining Protocol

Answer 20

Sender can send multiple frames before receiving acknowledgments.

Question 21

Go-Back-N Protocol

Answer 21

Sender sends up to N frames before receiving ACKs. If an ACK is lost, all unacknowledged frames are retransmitted.

Question 22

Selective Repeat Protocol

Answer 22

Sender sends multiple frames, receiver acknowledges each frame individually. Only lost frames are retransmitted, improving efficiency compared to Go-Back-N.

Question 23

Checksum Algorithm

Answer 23

Add up all the data words, add the carry to the 1s place, take the one’s complement of the sum, append the checksum to the data.