lecture6PSI

Question 1

What is WS?

Answer 1

WS - window size in sliding window algorithm

Question 2

What are the data delivery problems?

Answer 2

Packet loss, Acknowledgment loss (Duplicate packet), Late acknowledgement(Duplicate packet)

Question 3

Waht is CWL?

Answer 3

CWL - congestion window length, the maximum number of packets that the transmitter can send at one time to
avoid congesting the link

Question 4

What do you know about Sliding window algorithm?

Answer 4

It is more complex, but more effective than Stop&Wait, it has more possible implementations, it allows flow control by adjusting window size, the adjustment of the window size is optimized by various mechanisms based on the
transmission parameters (delay, RTT, packet loss)

Question 5

Two armie’s problem

Answer 5

The red army (A) wins only when A1 and A2 attack the
blue army (B) at the same time. The problem is to
agree while communicating by sending a messenger over
an enemy territory (unreliable link)

Question 6

TCP connection is always duplex Y/N?

Answer 6

Yes

Question 7

What do you know about unreliable transfer layer protocols?

Answer 7

1. It is connectionless - connections are not established
2. Simplier, easier to implement, comparing to reliable transport protosols

Question 8

What are the 2 types of transport division protocols?

Answer 8

Reliable, unreliable

Question 9

What is a port?

Answer 9

16-bit identifier that is used as the next level of addressing

Question 10

Name the most known reliable transport layer protocol

Answer 10

TCP

Question 12

WHat is the best known and most used unreliable transport layer protocol?

Answer 12

UDP

Question 13

What data transfer parameters do you know?

Answer 13

Packet loss[%], delay[ms], Round Trip Time(RTT)[ms], Instability, variable delay(jitter)

Question 14

Receiver congestion vs link congestion

Answer 14

Receiver congestion: By setting the size of the window, the receiver controls the amount of data sent (transmission control) by the
transmitter according to its capabilities (easy). All TCP variants have the same algorithm.
Link congestion: The transmitter has to regulate the amount of data sent due to the possible congestion of the link on the way (more
complicated). The algorithm used differs depending on the specific version of the TCP protocol.

Question 15

What do you know about Stop&Wait algorithm?

Answer 15

It is simple, but very little effective, it delivers data exactly in the order in which they are sent

Question 16

What do you know about reliable data transfer?

Answer 16

1.Connection-oriented, a virtual connection is established and maintained.
2.Design and implementation is more complex than unreliable protocols.
3.It must include error detection and correction mechanisms.
4.They can control the flow, prevent congestion

Question 17

Is the TCP encrypted?

Answer 17

No

Question 18

UDP

Answer 18

User Datagram protocol, it is transmitted in the data item of the IP protocol packet, used for simple data exchange, it has better throughput than TCP, is commonly used in voice or video transmission, it is unsecured

Question 19

How is TCP flow controlled?

Answer 19

Trough the flags in the packet header

Question 20

What is the difference between TCP Reno and TCP Tahoe?

Answer 20

TCP Reno and TCP Tahoe have the same way of setting CWL until an acknowledgment dropout occurs (8). Tahoe sets
CWL to 1. Reno, which is more optimistic, sets CWL to half the value before the blackout. Reno reduces ssthresh by
25%, Tahoe cuts it in half.

Question 21

Algorithms of flow control

Answer 21

Stop & Wait, Sliding Window