week 3 - More transport Layer

Question 1

Acknowledgement message does not mean you should free buffer

BUFFER ONLY FREED/ PROCESSED WHEN DATA PASSED TO APPLICATION LAYER

Answer 1

Really important

ACK (message) != freeing buffer

Question 2

What is Flow Control

Answer 2

“Flow control is a specific end-to-end mechanism between sender and receiver where the receiver advertises its available buffer space (using rwnd) to prevent the sender from transmitting more data than the receiver can process. This mechanism is implemented through the sliding window protocol.”

Question 3

what is congestion control

Answer 3

“Congestion control is a sender-side mechanism in TCP that prevents network congestion by dynamically adjusting the transmission rate based on network conditions. It uses the congestion window (cwnd) and various algorithms to detect and respond to network congestion, ensuring optimal network utilization without overwhelming network resources.”
Congestion Window (cwnd) Mechanism:
“The congestion window is a dynamic, sender-maintained limit on the amount of unacknowledged data that can be in transit. It starts small (typically 1 MSS) and adjusts using algorithms:

. slow start
.

Question 4

How does persist time help(take example where window size is 0 )

Answer 4

When Window Size = 0:

.Sender stops sending (receiver buffer full)
.Persist timer activates to prevent deadlock
.Timer expires → Small packet called “window probe” is sent
.Receiver must respond with current window size
.If still 0: Timer doubles, repeat probe (5s → 10s → 20s → max 60s)
.If non-zero: Normal transmission resumes

Question 5

throughput

Answer 5

rate at which data is processed

Fast throughput -> data processed quickly and buffer empties faster so data can be sent quicker

Question 6

bandwidth

Answer 6

capacity at which a network can transmit data

Question 7

How does TCP Congestion control work?
basic definiton

Answer 7

Increase the sending rate until packet loss is observed , at which point sending rate is decreased

Question 8

What is TCP Congestion control method called AIMD

Answer 8

AIMD

Question 9

Explain TCP Congestion control now in detail

Answer 9

Additive Increase:
Increase sending rate by 1 MSS (Maximum Segment Size) per RTT (Round trip time) until a loss is detected

AT WHICH POINT

|
Multiplacitve decrease occurs:
Sending rate is cut in half at each loss event

Question 10

Multiplacitve decrease in detail

Answer 10

.When 3 duplicate acknowledements are received sending rate is cut in half

. When timeout occurs sending rate cut to one MSS ( severe)

Question 11

RTT

Answer 11

Time for:
segment to go from segment to receiver AND acknowledgement from receiver to sender

Question 12

congestion window

Answer 12

sender side flow control that changes based on network conditions

Question 13

What is the web

Answer 13

A network of resources

Question 14

Are all resources network retrievable? Explain your answer

Answer 14

No not all resoures are network tetrievalbe

humans - can represent as a resource but cant download a human

same with company

abstract things - friendsship relationships , mathematical operations etc

Question 15

URI , URL , URN

Answer 15

URI - Parent ( can be URL or URN or other type

URI (parent category)
├── URL (tells how to access/where it is)
└── URN (just names/identifies something)

URL - (Uniform Resource Locator):
- shows how to access and where to find it
- START WITH HTTP
- https://www.google.com
- ftp://ftp.example.com/downloads/file.txt
- http://localhost:8080/index.html

URN- REMAINS PERMANENET
urn:isbn:0-486-27557-4

This ISBN will always identify the same book