chapter 3 - transport layer Flashcards
(36 cards)
What is the main job of the transport layer?
Provide logical communication between application processes on different hosts
What does the sender transport layer do?
Breaks messages into segments and passes them to the network layer
What is multiplexing?
combining multiple data streams into one connection
What does the receiver transport layer do?
Reassembles segments and passes the message to the application
What does RDT 2.0 add?
Handles bit errors using checksums, ACKs and NAKs
What is demultiplexing?
taking a combined stream of data and separating it back into the original parts
Using header info to deliver segments to correct socket at the receiver
What does RDT 1.0 assume?
A perfectly reliable channel (no errors or losses)
What does RDT stand for?
Reliable Data Transfer
What info is used in TCP demultiplexing?
4-tuple:
* source IP
* source port
* destination IP
* destination port
Problem with RDT 2.0?
lost ACK/NAK
What is the solution in RDT 2.1?
adds sequence numbers (0,1) to avoid delivering duplicate data
if ack/nack is lost, it can send duplicates -> seq nr checks for this
What does RDT 2.2 do differently?
Uses only ACKs (no NAKs)
if receiver gets dup packet -> send ack again (i have already received this packet)
What does RDT 3.0 add?
timer
if sender not have received ACK innen en tid, resend packet
What is pipelining?
Sending multiple packets before waiting for ACKs
What is the key idea of Selective Repeat?
Only lost packets are resent
sender retransmit packets who did not receive ACK
What is the key idea of Go-Back-N?
sender sens multiple packts -> if one is lost -> send all packets after the lost one again
sends 1 pckt @ time
s -1234, lost:2, kaster 3og4, og sender 2,3,4 igjen
Is TCP point-to-point or multicast?
Point-to-point (1 sender, 1 receiver)
What does TCP use for reliability?
Sequence numbers and ACKs
What is Maximum Segment Size
(MSS) in TCP?
max size data (payload) TCP can send in one packet, without splitting
How does TCP handle out-of-order segments?
waits for all segment to arrive before delivering in right order
sender:1234 -> receiver: 1,3,4 -> venter på 2 og setter den inn 1,2,3,4
Why is timeout value important in TCP?
Too short = unnecessary retransmissions
too long = slow recovery
How is Estimated RTT calculated?
EstimatedRTT = (1 − α) × EstimatedRTT + α × SampleRTT
What is the timeout interval formula?
Timeout = EstimatedRTT + 4 × DevRTT
What is the goal of TCP flow control?
Prevent sender from overwhelming receiver’s buffer
