Transport Layer

Question 1

Implications of best effort

Answer 1

drop messages, out of order messages, duplicates, finite message size, delays

Question 2

End to end services

Answer 2

guarantee message delivery, in order, at most 1 copy, large messages, synchonization, receive flow control sender, multiple application processes on hosts

Question 3

How can processes on different systems get the right messages?

Answer 3

Ports

Question 4

Ports

Answer 4

numeric locators which enable messages to be demultiplexed to proper process

Question 5

Ports are typically implemented as

Answer 5

messages queues

Question 6

Simplest function of the transport layer

Answer 6

multiplexing/demultiplexing of messages

Question 7

transport layer functions

Answer 7

connection control, error detection, in order delivery, flow control, congestion control

Question 8

What is UDP?

Answer 8

user datagram protocol

unreliable unordered datagram service

Question 9

Does UDP have flow or congestion control?

Answer 9

No

Question 10

Does UDP have reliability?

Answer 10

optional checksum

Question 11

What does UDP do?

Answer 11

adds multiplexing/demultiplexing

Question 12

How are end points identified in the transport layer?

Answer 12

Ports

Question 13

What does the UDP demultiplexer do?

Answer 13

extends host-to-host delivery service of the underlying network into a process-to-process communication service

Question 14

UDP Checksum computer over?

Answer 14

UDP header + body + pseudoheader

Question 15

What does the UDP psuedoheader consist of?

Answer 15

Protocol number (UDP or TCP), IP src, IP dst, UDP length

Question 16

What is TCP?

Answer 16

2 way, reliable, byte stream oriented end-to-end protocol

Question 17

TCP Features:

Answer 17

Connection oriented, full duplex, flow control, congestion control, byte stream, reliable data transfer

Question 18

what is in the acknowledgement field?

Answer 18

next expected bye in reverse direction

Question 19

advertised winow

Answer 19

amount of room to receive data

Question 20

Each connection identified with a 4-tuple

Answer 20

SrcPort, SrcIpAddr, DsrPort, DestIPAddr

Question 21

Sequence numbers

Answer 21

each packet has a sequence number, wrap around supported, initial number selected at connection time

Question 22

ACK indicates what?

Answer 22

next bye expected

Question 23

TCP’s sliding window serves what purposes?

Answer 23

1) guarantees reliable delivery of data
2) ensures in order delivery
3) enforces flow control between sender and receiver

Question 24

window

Answer 24

upper bound on unACKed frames

Question 25

Why does sender need buffer data?

Answer 25

if data is lost, it can be resent

Question 26

Why does receiver need buffer data?

Answer 26

if data is received out of order, it can be helld until all packets are received

Question 27

How to prevent sender from overflowing receiver’s buffer?

Answer 27

receiver tells sender its buffer size during connection setup

Question 28

Go-Back-N

Answer 28

Send all N unACKed packets when a loss is signaled

Question 29

Selective repeat

Answer 29

Only send specifically unACKed packets

Question 30

MaxReceivingBuffer >=

Answer 30

lastByteReceived - LastByeRead

Question 31

Receiver Advertised Window

Answer 31

MaxReceiverBuffer - (NextByteExpected - 1) - LastByeRead)

Question 32

Sending Side Advertised window

Answer 32

lastByteSent - lastByteAcked

Question 33

Sending effective window

Answer 33

advertisedWindow - (LastByteSent - lastByteAcked)