mirror of
https://github.com/jackyzha0/quartz.git
synced 2025-12-27 14:54:05 -06:00
114 lines
3.2 KiB
Markdown
114 lines
3.2 KiB
Markdown
---
|
|
title: "18-transport-layer"
|
|
aliases:
|
|
tags:
|
|
- cosc203
|
|
- lecture
|
|
---
|
|
chapter 3
|
|
# service provided by transport layer
|
|
services
|
|
- process to process communication
|
|
- logical communication between application processes
|
|
- multi and demulti plexing
|
|
- communication for multiple applications of the same host
|
|
- flow control
|
|
- ensure production reate <= consuption rate
|
|
- congestion control
|
|
- too many sender, sending too fast
|
|
|
|
protocols
|
|
- TCP transmission control protocol
|
|
- UDP user datagram protocol
|
|
|
|
## actions and sender
|
|
- is passed an app layer lessage
|
|
- determines segment header fields values
|
|
- creates segment
|
|
- passes segement to IP
|
|
|
|
## actions at reciever
|
|
- recieves segment from IP
|
|
- checks header values
|
|
- extract app layer message
|
|
- de multiplexes message up to application via socket
|
|
|
|
# multiplexing and demultiplexing
|
|
sender: handle data from multiple sockets, add transport header
|
|
reciever: user header info to deliver segments to correct socket
|
|
|
|
|
|
|
|
## how it works
|
|
port number
|
|
- 16 bit integer (0, 66635)
|
|
- segment has a source and a port number
|
|
- host uses IP and port to direct segment to appropriate socket
|
|
|
|
IANA (internet assign number authority) has divded port number into three ranges
|
|
- 0-1023 well known
|
|
- 1024-49151 registered
|
|
- 49152-65535 dynamic
|
|
|
|
## principle of reliable data transfer
|
|
|
|
|
|
- compexity of reliable data transfer protocol depends on character istics of unreliable channel
|
|
- sender and reciever do not know the 'state' of each other. they need to communicate via a message - ACKknowledgement
|
|
|
|
# TCP
|
|
- point to point communicate
|
|
- one sender, one reciever
|
|
- reliable, in-order byte stream
|
|
- no message boundaries
|
|
- each byte has a position in the stream
|
|
- full duplex data
|
|
- bi directional data flow in the same connection
|
|
- MSS: maximum segment size
|
|
- cumulative ACKs
|
|
- one ack message confirms multiple segments
|
|
- connection-oriented
|
|
- handshaking (exchange of control messages) initializes sender, reciever state before data exchange
|
|
- flow controlled
|
|
- sender will not overwhelm reciever
|
|
- congestion controlled
|
|
- dynamically adjust congestion window size
|
|
|
|
Structure
|
|
- sequence number - numbe assigned to the first byte of data in this segment
|
|
- ACK # - the seq # of the next expected byte; flagged as a single bit
|
|
- internet checksum - used to check for corruption
|
|
- TCP options (variable length)
|
|
- length (of TCP header)
|
|
- application data
|
|
- RST, SYN, FIN - connection management
|
|
- recieve window - flow control # of bytes reciever willing to accept
|
|
- protect against buffer overflow
|
|
- C, E: congestion notification
|
|
|
|
|
|
|
|
seq number
|
|
- byte stream
|
|
- "number" of first byte in segments data
|
|
- sliding window 
|
|
|
|
ack
|
|
- seq # of next bytes expected from other side
|
|
- cumulative ACK
|
|
|
|
|
|
|
|
lost and duplicated segments
|
|
- lost
|
|
- host does not recieve data, ack is not send,
|
|
- timeout + retransmission
|
|
- 
|
|
- sender sets the retransmittion timer when sending a segment
|
|
- sender retransmits the segment iin ACK is not recieved when timer fires
|
|
- duplicated
|
|
- host recieved data, ack is send and lost
|
|
- data is resent, and a duplicat
|
|
|
|
|
|
# UDP |